MAP607 Physiological Basis of Behaviour(1)-converted

MASTER OF PSYCHOLOGY SEMESTER-II PHYSIOLOGICAL BASIS OF BEHAVIOUR MAP607 1 CU IDOL SELF LEARNING MATERIAL (SLM)

CHANDIGARH UNIVERSITY Institute of Distance and Online Learning Course Development Committee Prof. (Dr.) R.S.Bawa Pro Chancellor, Chandigarh University, Gharuan, Punjab Advisors Prof. (Dr.) Bharat Bhushan, Director – IGNOU Prof. (Dr.) Majulika Srivastava, Director – CIQA, IGNOU Programme Coordinators & Editing Team Master of Business Administration (MBA) Bachelor of Business Administration (BBA) Coordinator – Dr. Rupali Arora Coordinator – Dr. Simran Jewandah Master of Computer Applications (MCA) Bachelor of Computer Applications (BCA) Coordinator – Dr. Raju Kumar Coordinator – Dr. Manisha Malhotra Master of Commerce (M.Com.) Bachelor of Commerce (B.Com.) Coordinator – Dr. Aman Jindal Coordinator – Dr. Minakshi Garg Master of Arts (Psychology) Bachelor of Science (Travel &Tourism Management) Coordinator – Dr. Samerjeet Kaur Coordinator – Dr. Shikha Sharma Master of Arts (English) Bachelor of Arts (General) Coordinator – Dr. Ashita Chadha Coordinator – Ms. Neeraj Gohlan Academic and Administrative Management Prof. (Dr.) R. M. Bhagat Prof. (Dr.) S.S. Sehgal Executive Director – Sciences Registrar Prof. (Dr.) Manaswini Acharya Prof. (Dr.) Gurpreet Singh Executive Director – Liberal Arts Director – IDOL © No part of this publication should be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording and/or otherwise without the prior written permission of the authors and the publisher. SLM SPECIALLY PREPARED FOR CU IDOL STUDENTS Printed and Published by: TeamLease Edtech Limited www.teamleaseedtech.com CONTACT NO:- 01133002345 For: CHANDIGARH UNIVERSITY 2 Institute of Distance and Online Learning CU IDOL SELF LEARNING MATERIAL (SLM)

First Published in 2020 All rights reserved. No Part of this book may be reproduced or transmitted, in any form or by any means, without permission in writing from Chandigarh University. Any person who does any unauthorized act in relation to this book may be liable to criminal prosecution and civil claims for damages. This book is meant for educational and learning purpose. The authors of the book has/have taken all reasonable care to ensure that the contents of the book do not violate any existing copyright or other intellectual property rights of any person in any manner whatsoever. In the even the Authors has/ have been unable to track any source and if any copyright has been inadvertently infringed, please notify the publisher in writing for corrective action. 3 CU IDOL SELF LEARNING MATERIAL (SLM)

CONTENT Unit 1 Introduction To The Physiological Basis Of Behaviour ........................................... 5 Unit 2 Neurons And Synapse ................................................................................................ 16 Unit 3 The Nervous System................................................................................................... 36 Unit 4 The Endocrine Glands ............................................................................................... 49 Unit 5 Methods Of Study....................................................................................................... 62 Unit 6 Recording Brain Activity........................................................................................... 78 Unit 7 Physiological Basis: Senses ........................................................................................ 90 Unit 8 Sleep........................................................................................................................... 106 Unit 9 Arousal And Biological Rhythm ............................................................................. 121 Unit 10 Motivation An Emotion ......................................................................................... 132 Unit 11 Hunger Thirst ......................................................................................................... 144 4 CU IDOL SELF LEARNING MATERIAL (SLM)

UNIT 1INTRODUCTION TO THE PHYSIOLOGICAL BASIS OF BEHAVIOUR Structure Learning Objectives Introduction Meaning and definition of physiological psychology History of Physiological Psychology Theories of Physiological Psychology Theory of Evolution Scope of Physiological Psychology Relationship with other disciplines Research Methods in Physiological Psychology Summary Key Words/ Abbreviations 1.10.Learning Activity 1.11.Unit End Questions (MCQs and Descriptive) 1.12.References LEARNING OBJECTIVES After this unit, you will be able to; • Explain the concept of physiological psychology • Critically analyse the theories of physiological psychology • Outline the history of physiological psychology • Chart out the scope of physiological psychology • Describe the relationship between the physiological psychology and related fields • Identify the research methods and approaches used inphysiological psychology INTRODUCTION The mental functions form a part of the phenomena of life. Wherever we observe them, they are accompanied by the processes of nutrition and reproduction. On the other hand, the general phenomena of life may be manifested in cases where we have no reason for supposing the presence of a mind. Biological psychologists are interested in measuring biological, physiological, or genetic variables in an attempt to relate them to psychological or behavioural variables. Because all behaviour is controlled by the central nervous system, biological psychologists seek to understand how the brain functions in order to understand behaviour. Key areas of focus include sensation and perception; motivated behaviour (such as hunger, thirst, and sex); control of movement; learning and memory; sleep and biological rhythms; 5 CU IDOL SELF LEARNING MATERIAL (SLM)

and emotion. As technical sophistication leads to advancements in research methods, more advanced topics such as language, reasoning, decision making, and consciousness are now being studied. MEANING AND DEFINITION OF PHYSIOLOGICAL PSYCHOLOGY Psychology is the science of behaviour and mind including the conscious and unconscious phenomenon and thought. Psychologists attempt to understand the role of metal functions in individual and social behaviour. Psychology is the scientific study of behaviour. The word ‘psychology’ comes from two Greek words, psukhe, meaning ‘breath’ or ‘soul’, and logos, meaning ‘word’ or ‘reason’. The modern meaning of psycho- is ‘mind’ and the modern meaning of -logy is ‘science’; thus, the word ‘psychology’ literally means ‘the science of the mind’. Physiological Psychology is the branch of psychology that is involved with the relation between the nervous system and behaviour. Physiological Psychology is the study of the physiological basis of how we think by connecting the physical operations of the brain. In other words, it attempts to relate the physiology of our thoughts, emotions and behaviour. According to the physiological psychologists the mind is a function performed by the brain. Physiological psychology studies brain cells, its structure and components, and the chemical interactions involved in the process. Physiological psychological is concerned with sensation, sleep, emotion, motivation, memory, learning, nerve cells, brain structure and its components. HISTORY OF PHYSIOLOIGCAL PSYCHOLOGY Biological psychology has its roots in early structuralist and functionalist psychological studies, and as with all of the major perspectives, it has relevance today. The early structural and functional psychologists believed that the study of conscious thoughts would be the key to understanding the mind. Their approaches to the study of the mind were based on systematic and rigorous observation, laying the foundation for modern psychological experimentation. In terms of research focus, Wundt and Titchener explored topics such as attention span, reaction time, vision, emotion, and time perception, all of which are still studied today. Wundt’s primary method of research was introspection, which involves training people to concentrate and report on their conscious experiences as they react to stimuli. This approach is still used today in modern neuroscience research; however, many scientists criticize the use of introspection for its lack of empirical approach and objectivity. Structuralism was also criticized because its subject of interest – the conscious experience – was not easily studied with controlled experimentation. Structuralism’s reliance on introspection, despite Titchener’s rigid guidelines, was criticized for its lack of reliability. Critics argued that self-analysis is not feasible, and that introspection 6 CU IDOL SELF LEARNING MATERIAL (SLM)

can yield different results depending on the subject. Critics were also concerned about the possibility of retrospection, or the memory of sensation rather than the sensation itself. Today, researchers argue for introspective methods as crucial for understanding certain experiences and contexts.Two Minnesota researchers (Jones & Schmid, 2000) used auto- ethnography, a narrative approach to introspective analysis (Ellis, 1999), to study the phenomenological experience of the prison world and the consequent adaptations and transformations that it evokes. Jones, serving a year-and-a-day sentence in a maximum security prison, relied on his personal documentation of his experience to later study the psychological impacts of his experience. The study of physiology and biological processes has played a significant role in psychology since its earliest beginnings. It was Charles Darwin who first introduced the idea that evolution and genetics play a role in human behaviour. Natural selection influences whether certain behaviour patterns are passed down to future generations. Behaviours that aid in survival are more likely to be passed down while those that prove dangerous are less likely to be inherited. The early structural and functional psychologists believed that the study of conscious thoughts would be the key to understanding the mind. Their approaches to the study of the mind were based on systematic and rigorous observation, laying the foundation for modern psychological experimentation. In terms of research focus, Wundt and Titchener explored topics such as attention span, reaction time, vision, emotion, and time perception, all of which are still studied today. Wundt’s primary method of research was introspection, which involves training people to concentrate and report on their conscious experiences as they react to stimuli. This approach is still used today in modern neuroscience research; however, many scientists criticize the use of introspection for its lack of empirical approach and objectivity. Structuralism was also criticized because its subject of interest – the conscious experience – was not easily studied with controlled experimentation. Structuralism’s reliance on introspection, despite Titchener’s rigid guidelines, was criticized for its lack of reliability. Critics argued that self- analysis is not feasible, and that introspection can yield different results depending on the subject. Critics were also concerned about the possibility of retrospection, or the memory of sensation rather than the sensation itself. Today, researchers argue for introspective methods as crucial for understanding certain experiences and contexts. Two Minnesota researchers (Jones & Schmid, 2000) used auto- ethnography, a narrative approach to introspective analysis (Ellis, 1999), to study the phenomenological experience of the prison world and the consequent adaptations and transformations that it evokes. Jones, serving a year-and-a-day sentence in a maximum- security prison, relied on his personal documentation of his experience to later study the psychological impacts of his experience. 7 CU IDOL SELF LEARNING MATERIAL (SLM)

THEORIES OF PHYSIOLOGICAL PSYCHOLOGY 1.4.1. Theory of Evolution Theory of evolution claims that all forms of life hold relationships through ancestral sharing. For instance, the similarities in the skeletal makeup and human genes of chimpanzees, apes, and humans lead researchers to believe the three-share ancestry with other larger historical primates. Charles Darwin’s idea of homology explained the more anatomical and genetic similarities between species implies closer relationships. The philosophical theory of evolution paved the foundation of evolutionary psychology. The evolutionary perspective “was built on Darwin’s principle of natural selection” and argues that the basis of current human behaviour rests in ancestral behaviour. It argues that understanding ancestry is vital to understanding the relationship of human mental processes and behaviour. The theoretical approach aims to understand the design of the human mind by explaining useful psychological and mental traits such as perception, memory, and language as products of natural selection. The proposition of evolutionary psychology suggests the human brain comprises cognitive mechanisms which evolved through the process of natural selection. The idea stands that evolution resembles branching in that the genomes that survive in a certain environment last long enough to replicate genetic material and adapt to survive changing environments. Darwin faced his theory off four ideologies: 1. Generational individuals reproduce in increasing numbers that can survive evolving environments. 2. Compensation for evolving environments gives credit to heritable variations in genetics. 3. Individuals with genetically evolved heritable traits adapt to changing environments easier. 4. New species of the same ancestry of a pre-existing species evolve from species that can no longer breed successfully with the same species. As of late, the evolutionary perspective has been used in studies trying to prove behaviour is a genetic adaptation received from parents and ancestors. His evolutionary perspective provides an explanation of the diversity of species contained within the world and why so many variations of those species exist. According to Donovan, research stakes claim that 98% of human genes are bacteria necessary for environmental survival. Biopsychology claims that humans are biological creatures that evolve from genetics, cause us to eat for survival, and behave because of the neuronal firings that throughout our brain. These theories, just like dispositional theories seek to identify consistencies in individual differences. However, biological theories tend to delve into the biological aspects of personality such as genetics and evolutionary origins. Bio psychologists claim that personality develops through genetics derived from evolutionary history and impacted by 8 CU IDOL SELF LEARNING MATERIAL (SLM)

hormones and neurotransmitters. Biological psychology created a bridge between psychology and biology as it seeks to explain how the brain contributes to behaviour. Biological theories stem from Darwin’s theory of evolution and theory of natural selection (McLeod, 2015). Harlow’s research of Phineas Gauge led Bio psychologists to the idea of localization (McLeod, 2015). The tamping iron tore through only the frontal lobes of the brain. The fact that Gage was able to remain in a “normal,” conscious stature after the accident implied that motor and muscular functioning, as well as life support functions, were unaffected by the accident. Additionally, the records of severe behaviour and personality changes post-accident led researchers to make the assumptions of localization (McLeod, 2015). SCOPE OF PHYSIOLOIGCAL PSYCHOLOGY Psychologists study a wide variety of phenomena, including physiological processes within the nervous system, genetics, environmental events, personality characteristics, human development, mental abilities, health, and social interactions. A psychologist may provide treatment that focuses on behavioural adaptations. Psychologists explore behaviour and mental processes, which include perception, cognition, attention, emotion, intelligence, motivation, functioning of the brain and personality. Psychologists engage in research, teaching, counselling and psychotherapy; they advise industry and government about personnel matters, the design of products, advertising, marketing and legislation; they devise and administer tests of personality, achievement and ability. The biological approach to the study of human and animal behaviour is known as biopsychology. The bio psychologists try to investigate scientifically how biological processes interact with cognition, emotions and other psychological processes. We can trace a long history of the study of biology of behaviour. But biopsychology as a separate discipline of neuroscience, emerged in the 20th century. D. O. Hebbs' (Canadian psychologist) seminal publication, The Organization of Behaviour in 1949, in the field of psychology and neuroscience, paved the way for future investigation of neural foundations of behaviour. Biopsychology, thus, draws information from neurosciences and uses the information to study human and animal behaviour. It may be better understood as that neuroscience is a team effort and bio-psychologist is a part of this team. A bio-psychologist may draw information from other disciplines of neuroscience and apply it to the study of behaviour. Biopsychology also aims to understand aspects like, the evolution of brain and its influence on behaviour, the development of the nervous system across the life span, which areas of the brain are involved in sensation, perception, memory, movement, the role of brain in emotional expression and regulation, language and cognition, and how the behavioural change occurs after brain damage or trauma. It also seeks to understand the role of genetics and endocrine system in maintenance of homeostasis, and enhancing health and wellbeing of people suffering from various neurological disorders. 9 CU IDOL SELF LEARNING MATERIAL (SLM)

Biological psychologists are interested in measuring biological, physiological, or genetic variables to relate them to psychological or behavioural variables. Because all behaviour is controlled by the central nervous system, biological psychologists seek to understand how the brain functions to understand behaviour. Key areas of focus include sensation and perception; motivated behaviour (such as hunger, thirst, and sex); control of movement; learning and memory; sleep and biological rhythms; and emotion. As technical sophistication leads to advancements in research methods, more advanced topics such as language, reasoning, decision making, and consciousness are now being studied. The current scope of biological psychology includes the following themes: Evolution of brain and behaviour; development of the nervous system and behaviour over the life span; psychopharmacology; sensory and perceptual processes; control and coordination of movement and actions; control of behavioural states (motivation), including sex and reproductive behaviour, and regulation of internal states; biological rhythms and sleep; emotions and mental disorders; neural mechanisms of learning and memory, language and cognition; and recovery of function after damage to the nervous system. Developing from biological psychology and overlapping with parts of it are such fields as behaviour genetics as well as hormones and behaviour. Through all these methods, biological psychology is a hopeful domain, one that has much to offer in terms of improving the quality of life of the healthy as well as those suffering from disorders. The biological perspective is essentially a way of looking at human problems and actions. Consider an issue like aggression, for example. Someone using the psychoanalytic perspective might view aggression as the result of childhood experiences and unconscious urges. Another person might take a behavioural perspective and consider how the behaviour was shaped by association, reinforcement, and punishment. A psychologist with a social perspective might look at the group dynamics and pressures that contribute to such behaviour. The Biological Perspective seeks to determine the psychological aspects of human behaviour looking at evidence from genetic and neurological studies as well as studies of the immune system. Also known as biopsychology, it has played a significant role in psychology from the beginning. The biological viewpoint, on the other hand, would involve looking at the biological roots that lie behind aggressive behaviours. Someone who takes the biological perspective might consider how certain types of brain injury might lead to aggressive actions. Or they might consider genetic factors that can contribute to such displays of behaviour. RELATIONSHIP WITH OTHER DISCIPLINES Neuroscience is a team effort, and physiological psychologists are important members of the team (). Biopsychology can be further defined by its relation to other neuroscientific disciplines. Physiological psychologists are neuroscientists who bring to their research a knowledge of behaviour and of the methods of behavioural research. It is their behavioural orientation and expertise that make their contribution to neuroscience unique (see Cacioppo 10 CU IDOL SELF LEARNING MATERIAL (SLM)

& Decety, 2009). You will be able to better appreciate the importance of this contribution if you consider that the ultimate purpose of the nervous system is to produce and control behaviour (see Grillner & Dickinson, 2002). Biopsychology is an integrative discipline. Physiological psychologists draw together knowledge from the other neuroscientific disciplines and apply it to the study of behaviour. The following are a few of the disciplines of neuroscience that are particularly relevant to biopsychology: Neuroanatomy The study of the structure of the nervous system Neurochemistry The study of the chemical bases of neural activity Neuroendocrinology The study of interactions between the nervous system and the endocrine system Neuropathology The study of nervous system disorders Neuropharmacology The study of the effects of drugs on neural activity Neurophysiology The study of the functions and activities of the nervous system RESEARCH METHODS IN PHYSIOLOGICAL PSYCHOLOGY When you're conducting research, you generally take one of two directions, generalization or reductionism. Physiological psychologists must use both. Generalization means that you take the various behaviours that you observe and then hypothesize, proposing laws that apparently govern those behaviours. Then you do more tests to find out if you're right. What you're hoping for, in the end, is statistical certainty. In other words, if things work the same way enough times, you can say that for all practical purposes you're right about the laws behind them. This is the approach taken by most psychologists. They watch behaviour, looking for consistencies. They introduce new environments, and then observe the results. They might carefully introduce certain chemicals to try to help people deal with their problems, and then observe how behaviour changes. They're looking at the big picture. Physiological psychologists take a different path. They are psychologists, so they are interested in the generalized approach. How does the patient (or subject) behave? What is the 11 CU IDOL SELF LEARNING MATERIAL (SLM)

overall effect? What conclusions can we draw? However, they're also physiologists (people who study the physical body), so they apply a reductionist approach to most of their research, looking at complex things happening in the body and then breaking them down into individual functions, effects, chemical reactions, etc. They study the most complex events by analysing their simplest pieces. Early biological psychologists or behavioural neuroscientists focused their research on the relationships between mental processes and behaviours amongst different nonhuman animals. The areas that have been studied include sensation and perception, emotion, learning and memory, movement and control, motivation, language, sleep, reasoning and consciousness. Biological psychology has had a thorough list of contributions in the comprehensive study of various medical disorders. The most notable ones include Alzheimer’s disease (progressive cognitive deterioration and behavioural changes), Parkinson’s disease (central nervous system disorder) and Huntington’s disease (neurogenetic disorder). Schizophrenia, clinical depression, mania, anxiety disorders, autism and drug abuse are also hot areas of study in behavioural neuroscience today. SUMMARY 1. The physiological approach to the study of human and animal behaviour is known as physiological psychology. 2. The physiological psychologists try to investigate scientifically how physiological processes interact with cognition, emotions and other psychological processes. 3. Physiological psychology deals with how emotional responses, memory, mental illness, states of consciousness and sensory perception are affected by physiology, genetics and biology. 4. The definition of physiological psychology is the study of the human neurological functions as they relate to behaviour and perception. 5. Some sub-disciplines of neuroscience are of particular relevance for physiological psychology. 6. List of these sub-disciplines include neuroanatomy, neurochemistry, neuropathology, neuroendocrinology, neuropharmacology and, neurophysiology. 7. Research in physiological psychology is done with the aim is to understand the basis of behaviour and if there is any damage to the nervous system, and how it produces a corresponding change in behavioural functions. 8. Studies are conducted on animal subjects as well as human subjects through the use of modern techniques such as magnetic and functional magnetic resonance imaging. 9. By either manipulating the brain in controlled experiments or studying damage caused by natural means scientists can being to understand the neural correlates that affect emotions, memory and behaviour. 10. An example of this would be the function of cells or the brain in regard to psychopharmacology. It is very useful to gain information that is from the biological underpinnings of pathology as both a tool to teach and as a way of understanding in actual treatment settings. 12 CU IDOL SELF LEARNING MATERIAL (SLM)

11. Various methods to record and understand brain-behaviour relationship are ablation, psycho-physiological recordings, electrical and chemical stimulation, stereotaxic lesion, neuroimaging, and neuropsychological assessments. 12. There are various ethical issues that need to be taken care of while doing research in biopsychology KEY WORDS/ ABBREVIATIONS • Biopsychology-The science that studies the areas of overlap between biology and psychology and the interactions of mind and body. • biopsychosocial model- A view of development as a complex interaction of biological, psychological, and social processes. • Physiological psychology- Physiological psychology is the study of human behaviour through physiological impact. LEARNING ACTIVITY 1. Try to fast for at least 12 hours. Note the thoughts you have during those 12 hours. 2. Set an alarm for 3 am. Try to solve a complex mathematical problem. Now solve a similar problem during anytime in the day. Note the difference in the speed, accuracy, concentration while solving the problem. UNIT END QUESTIONS (MCQS AND DESCRIPTIVE) A. Descriptive Questions 1. Describe the following: Physiological psychology studies the relation between human physiology and human psychology. 2. Physiological psychology assumes biological aspect of a human being influences our personality and cognitive process. What are the other areas that physiological psychology studies? 3. Physiological psychology is an established field with history full of significant events. Chart out the history of physiological psychology. 4. Physiological psychology is inter-connected with quite a few of fields related to biology and psychology. Elaborate on some of those fields. 13 CU IDOL SELF LEARNING MATERIAL (SLM)

5. Identify the influence of Darwin’s theory of evolution on physiologicalpsychology? B. Multiple Choice Questions 1. The role of brain, body chemical, central nervous system, neural mechanism, etc., are considered the branch of psychology. [a] Cognitive psychology [b] Positive psychology [c] General Psychology [d] Physiological Psychology 2. is the science of behaviour and mind including the conscious and unconscious phenomenon and thought. [a] Cognitive psychology [b] Biological psychology [c] Psychology [d] Physiological Psychology 3. has its roots in early structuralist and functionalist psychological studies. [a] Cognitive psychology [b] Biological psychology [c] Psychology [d] Physiological Psychology 4. The theory proposed by Charles Darwin is called 14 [a] Theory of Cognition [b] None of the above [c] Theory of Psychology [d] Theory of Evolution CU IDOL SELF LEARNING MATERIAL (SLM)

5. was the primary method of research of Wilhelm Wundt. [a] Introspection [b] Experiment [c]Observation [d]All of the above Answer 1 [d]2 [c]3 [b]4 [d]5 [a] REFERENCES • Martin, N. (2010). Psychology, (4th ed). Pearson Education Limited • Mangal, S.K. (1995). An Introduction to Psychology. Sterling Publishers Private Limited • Eynenck, M. (2014). Fundamentals of Psychology. Taylor & Francis. • Woodworth, R. S. & Marquis, D. G. (2015). Psychology a study ofmental life. Taylor & Francis. • Bernstein D. (2018) Essentials of Psychology. Cengage Learning. • Feldman, R. S. (2012) Understanding Psychology (11th ed). McGraw-Hill Education – Europe • Pinel, J.P.J. (2007). Biopsychology. New Delhi: Pearson • Rosenzweig, M. R., Leiman, A. L. & Breedlove, S. M. (1996). Biological Psychology. Sunderland, Mass: Sinauer Associates. • Green, S. (1995). Principles of biopsychology. UK: Lawrence Erlbaum Associates Ltd. • Pinel, J. P. J. (2004). Biopsychology. Boston, MA: Allyn & Bacon. • Annett, M. (1984). Left, right, hand and brain: The right shift theory. London: Lawrence Erlbaum Associates Ltd. • Bannett, T.L. (1977). Brain and Behaviour. California: Brooks/ Cole. • Leukel, F. (1985). Introduction to Physiological Psychology. New Delhi: CBS Publishers 15 CU IDOL SELF LEARNING MATERIAL (SLM)

UNIT 2NEURONS AND SYNAPSE Structure Learning Objectives Introduction Structure of a Neuron Function of a Neuron Types of Neurons Stages of Neural Impulses Synapse The Electrical Synapse The Chemical Synapse Differences between Electrical and Chemical Synapses Neurotransmitters Types of Neurotransmitters Neural Networks The Function of Neural Networks The Capacity of Neural Networks Summary Key Words/ Abbreviations Learning Activity Unit End Questions (MCQs and Descriptive) References LEARNING OBJECTIVES After this unit you will be able to, • Explain the structure, role and functions of neurons • Chart out types of neurons • Outline the stages of neural impulse • Describe the types and functions of neurotransmitters • Describe the types and functions of neural networks INTRODUCTION To understand how the entire nervous system processes information, we need to examine the structure and function of the cells that constitute the nervous system. Individual neural cells, called neurons, transmit electrical signals from one location to another in the nervous system (Carlson, 2006; Shepherd, 2004). The greatest concentration of neurons is in the neocortex of the brain. The neocortex is the part of the brain associated with complex cognition. This tissue can contain as many as 100,000 neurons per cubic millimetre (Churchland & Sejnowski, 2004). The neurons tend to be arranged in the form of networks, which provide 16 CU IDOL SELF LEARNING MATERIAL (SLM)

information and feedback to each other within various kinds of information processing (Vogels, Rajan, & Abbott, 2005). Neurons are specialized cells that transmit chemical and electrical signals to facilitate communication between the brain and the body. The neuron is the basic building block of the brain and central nervous system. Neurons are specialized cells that transmit chemical and electrical signals. The brain is made up entirely of neurons and glial cells, which are non-neuronal cells that provide structure and support for the neurons. Nearly 86 billion neurons work together within the nervous system to communicate with the rest of the body. They are responsible for everything from consciousness and thought to pain and hunger. There are three primary types of neuron: sensory neurons, motor neurons, and interneurons. STRUCTURES OF A NEURON In addition to having all the normal components of a cell (nucleus, organelles, etc.) neurons also contain unique structures for receiving and sending the electrical signals that make neuronal communication possible. Figure2.1: Structure of a neuron Dendrite Dendrites are branch-like structures extending away from the cell body, and their job is to receive messages from other neurons and allow those messages to travel to the cell body. Although some neurons do not have any dendrites, other types of neurons have multiple dendrites. Dendrites can have small protrusions called dendritic spines, which further increase surface area for possible connections with other neurons. Cell Body 17 CU IDOL SELF LEARNING MATERIAL (SLM)

Like other cells, each neuron has a cell body (or soma) that contains a nucleus, smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria, and other cellular components. Axon An axon, at its most basic, is a tube-like structure that carries an electrical impulse from the cell body (or from another cell’s dendrites) to the structures at opposite end of the neuron— axon terminals, which can then pass the impulse to another neuron. The cell body contains a specialized structure, the axon hillock, which serves as a junction between the cell body and the axon. Synapse The synapse is the chemical junction between the axon terminals of one neuron and the dendrites of the next. It is a gap where specialized chemical interactions can occur, rather than an actual structure. FUNCTION OF A NEURON The specialized structure and organization of neurons allows them to transmit signals in the form of electric impulses from the brain to the body and back. Individually, neurons can pass a signal all the way from their own dendrites to their own axon terminals; but at a higher level neurons are organized in long chains, allowing them to pass signals very quickly from one to the other. One neuron’s axon will connect chemically to another neuron’s dendrite at the synapse between them. Electrically charged chemicals flow from the first neuron’s axon to the second neuron’s dendrite, and that signal will then flow from the second neuron’s dendrite, down its axon, across a synapse, into a third neuron’s dendrites, and so on. This is the basic chain of neural signal transmission, which is how the brain sends signals to the muscles to make them move, and how sensory organs send signals to the brain. It is important that these signals can happen quickly, and they do. Think of how fast you drop a hot potato—before you even realize it is hot. This is because the sense organ (in this case, the skin) sends the signal “This is hot!” to neurons with very long axons that travel up the spine to the brain. If this didn’t happen quickly, people would burn themselves. Other Structures Dendrites, cell bodies, axons, and synapses are the basic parts of a neuron, but other important structures and materials surround neurons to make them more efficient. Myelin Sheath Some axons are covered with myelin, a fatty material that wraps around the axon to form the myelin sheath. This external coating functions as insulation to minimize dissipation of the electrical signal as it travels down the axon. Myelin’s presence on the axon greatly increases the speed of conduction of the electrical signal, because the fat prevents any electricity from leaking out. This insulation is important, as the axon from a human motor neuron can be as 18 CU IDOL SELF LEARNING MATERIAL (SLM)

long as a meter—from the base of the spine to the toes. Periodic gaps in the myelin sheath are called nodes of Ranvier. At these nodes, the signal is “recharged” as it travels along the axon. Glial Cells The myelin sheath is not actually part of the neuron. Myelin is produced by glial cells (or simply glia, or “glue” in Greek), which are non-neuronal cells that provide support for the nervous system. Glia function to hold neurons in place (hence their Greek name), supply them with nutrients, provide insulation, and remove pathogens and dead neurons. In the central nervous system, the glial cells that form the myelin sheath are called oligodendrocytes; in the peripheral nervous system, they are called Schwann cells. Figure 2.2.: Neuron in the central nervous system 2.4 TYPES OF NEURONS There are three major types of neurons: sensory neurons, motor neurons, and interneurons. All three have different functions, but the brain needs all of them to communicate effectively with the rest of the body (and vice versa). Sensory Neurons Sensory neurons are neurons responsible for converting external stimuli from the environment into corresponding internal stimuli. They are activated by sensory input, and send projections to other elements of the nervous system, ultimately conveying sensory 19 CU IDOL SELF LEARNING MATERIAL (SLM)

information to the brain or spinal cord. Unlike the motor neurons of the central nervous system (CNS), whose inputs come from other neurons, sensory neurons are activated by physical modalities (such as visible light, sound, heat, physical contact, etc.) or by chemical signals (such as smell and taste). Most sensory neurons are pseudo unipolar, meaning they have an axon that branches into two extensions—one connected to dendrites that receive sensory information and another that transmits this information to the spinal cord. Figure 2.3.: Multipolar and pseudo unipolar neurons: This diagram shows the difference between: 1) a unipolar neuron; 2) a bipolar neuron; 3) a multipolar neuron; 4) a pseudo unipolar neuron. Motor Neurons 20 CU IDOL SELF LEARNING MATERIAL (SLM)

Motor neurons are neurons located in the central nervous system, and they project their axons outside of the CNS to directly or Interneurons Interneurons are neither sensory nor motor; rather, they act as the “middle men” that form connections between the other two types. Located in the CNS, they operate locally, meaning their axons connect only with nearby sensory or motor neurons. Interneurons can save time and therefore prevent injury by sending messages to the spinal cord and back instead of all the way to the brain. Like motor neurons, they are multipolar in structure. Stages of the Action Potential Neural impulses occur when a stimulus depolarizes a cell membrane, prompting an action potential which sends an “all or nothing” signal. Neural Impulses in the Nervous System The central nervous system (CNS) goes through a three-step process when it functions: sensory input, neural processing, and motor output. The sensory input stage is when the neurons (or excitable nerve cells) of the sensory organs are excited electrically. Neural impulses from sensory receptors are sent to the brain and spinal cord for processing. After the brain has processed the information, neural impulses are then conducted from the brain and spinal cord to muscles and glands, which is the resulting motor output. A neuron affects other neurons by releasing a neurotransmitter that binds to chemical receptors. The effect upon the postsynaptic (receiving) neuron is determined not by the presynaptic (sending) neuron or by the neurotransmitter itself, but by the type of receptor that is activated. A neurotransmitter can be thought of as a key, and a receptor as a lock: the key unlocks a certain response in the postsynaptic neuron, communicating a particular signal. However, in order for a presynaptic neuron to release a neurotransmitter to the next neuron in the chain, it must go through a series of changes in electric potential. 2.5. STAGES OF NEURAL IMPULSES ” Resting potential” is the name for the electrical state when a neuron is not actively being signalled. A neuron at resting potential has a membrane with established amounts of sodium (Na+) and potassium (K+) ions on either side, leaving the inside of the neuron negatively charged relative to the outside. The action potential is a rapid change in polarity that moves along the nerve fibre from neuron to neuron. In order for a neuron to move from resting potential to action potential—a short-term electrical change that allows an electrical signal to be passed from one neuron to another—the neuron must be stimulated by pressure, electricity, chemicals, or another form of stimuli. The level of stimulation that a neuron must receive to reach action potential is known as the threshold of excitation, and until it reaches that threshold, nothing will happen. Different neurons are sensitive to different stimuli, although most can register pain. 21 CU IDOL SELF LEARNING MATERIAL (SLM)

The action potential has several stages. Depolarization: A stimulus starts the depolarization of the membrane. Depolarization, also referred to as the “upswing,” is caused when positively charged sodium ions rush into a nerve cell. As these positive ions rush in, the membrane of the stimulated cell reverses its polarity so that the outside of the membrane is negative relative to the inside. Repolarization. Once the electric gradient has reached the threshold of excitement, the “downswing” of repolarization begins. The channels that let the positive sodium ion channels through close up, while channels that allow positive potassium ions open, resulting in the release of positively charged potassium ions from the neuron. This expulsion acts to restore the localized negative membrane potential of the cell, bringing it back to its normal voltage. Refractory Phase. The refractory phase takes place over a short period of time after the depolarization stage. Shortly after the sodium gates open, they close and go into an inactive conformation. The sodium gates cannot be opened again until the membrane is repolarized to its normal resting potential. The sodium-potassium pump returns sodium ions to the outside and potassium ions to the inside. During the refractory phase this particular area of the nerve cell membrane cannot be depolarized. Therefore, the neuron cannot reach action potential during this “rest period.” Figure 2.4.: Action potentials: A neuron must reach a certain threshold in order to begin the depolarization step of reaching the action potential. This process of depolarization, repolarization, and recovery moves along a nerve fibre from neuron to neuron like a very fast wave. While an action potential is in progress, another cannot be generated under the same conditions. In unmyelinated axons (axons that are not 22 CU IDOL SELF LEARNING MATERIAL (SLM)

covered by a myelin sheath), this happens in a continuous fashion because there are voltage- gated channels throughout the membrane. In myelinated axons (axons covered by a myelin sheath), this process is described as saltatory because voltage-gated channels are only found at the nodes of Ranvier, and the electrical events seem to “jump” from one node to the next. Saltatory conduction is faster than continuous conduction. The diameter of the axon also makes a difference, as ions diffusing within the cell have less resistance in a wider space. Damage to the myelin sheath from disease can cause severe impairment of nerve-cell function. In addition, some poisons and drugs interfere with nerve impulses by blocking sodium channels in nerves. All-or-none Signals The amplitude of an action potential is independent of the amount of current that produced it. In other words, larger currents do not create larger action potentials. Therefore, action potentials are said to be all-or-none signals, since either they occur fully or they do not occur at all. The frequency of action potentials is correlated with the intensity of a stimulus. This is in contrast to receptor potentials, whose amplitudes are dependent on the intensity of a stimulus. Reuptake Reuptake refers to the reabsorption of a neurotransmitter by a presynaptic (sending) neuron after it has performed its function of transmitting a neural impulse. Reuptake is necessary for normal synaptic physiology because it allows for the recycling of neurotransmitters and regulates the neurotransmitter level in the synapse, thereby controlling how long a signal resulting from neurotransmitter release lasts. Mechanics of the Action Potential The synapse is the site at which a chemical or electrical exchange occurs between the presynaptic and postsynaptic cells. SYNAPSES The synapse is the junction where neurons trade information. It is not a physical component of a cell but rather a name for the gap between two cells: the presynaptic cell (giving the signal) and the postsynaptic cell (receiving the signal). There are two types of possible reactions at the synapse—chemical or electrical. During a chemical reaction, a chemical called a neurotransmitter is released from one cell into another. In an electrical reaction, the electrical charge of one cell is influenced by the charge an adjacent cell. 23 CU IDOL SELF LEARNING MATERIAL (SLM)

image Figure 2.5.: The electrical response of a neuron to multiple synaptic inputs: Synaptic responses summate in order to bring the postsynaptic neuron to the threshold of excitation, so it can fire an action potential (represented by the peak on the chart). All synapses have a few common characteristics: • Presynaptic cell: a specialized area within the axon of the giving cell that transmits information to the dendrite of the receiving cell. • Synaptic cleft: the small space at the synapse that receives neurotransmitters. • G-protein coupled receptors: receptors that sense molecules outside the cell and thereby activate signals within it. • Ligand-gated ion channels: receptors that are opened or closed in response to the binding of a chemical messenger. • Postsynaptic cell: a specialized area within the dendrite of the receiving cell that contains receptors designed to process neurotransmitters. THE ELECTRICAL SYNAPSE The stages of an electrical reaction at a synapse are as follows: 1. Resting potential. The membrane of a neuron is normally at rest with established concentrations of sodium ions (Na+) and potassium ions (K+) on either side. The membrane potential (or, voltage across the membrane) at this state is -70 mV, with the inside being negative relative to the outside. 2. Depolarization. A stimulus begins the depolarization of the membrane. Depolarization, also referred to as the “upswing,” occurs when positively charged sodium ions (Na+) suddenly rush through open sodium gates into a nerve cell. If the membrane potential reaches -55 mV, it has reached the threshold of excitation. 24 CU IDOL SELF LEARNING MATERIAL (SLM)

Additional sodium rushes in, and the membrane of the stimulated cell actually reverses its polarity so that the outside of the membrane is negative relative to the inside. The change in voltage stimulates the opening of additional sodium channels (called a voltage-gated ion channel), providing what is known as a positive feedback loop. Eventually, the cell potential reaches +40 mV, or the action potential. 3. Repolarization. The “downswing” of repolarization is caused by the closing of sodium ion channels and the opening of potassium ion channels, resulting in the release of positively charged potassium ions (K+) from the nerve cell. This expulsion acts to restore the localized negative membrane potential of the cell. 4. Refractory Phase. The refractory phase is a short period of time after the repolarization stage. Shortly after the sodium gates open, they close and go into an inactive conformation where the cell’s membrane potential is actually even lower than its baseline -70 mV. The sodium gates cannot be opened again until the membrane has completely repolarized to its normal resting potential, -70 mV. The sodium- potassium pump returns sodium ions to the outside and potassium ions to the inside. During the refractory phase this particular area of the nerve cell membrane cannot be depolarized; the cell cannot be excited. THE CHEMICAL SYNAPSE The process of a chemical reaction at the synapse has some important differences from an electrical reaction. Chemical synapses are much more complex than electrical synapses, which makes them slower, but also allows them to generate different results. Like electrical reactions, chemical reactions involve electrical modifications at the postsynaptic membrane, but chemical reactions also require chemical messengers, such as neurotransmitters, to operate. Figure 2.6.: Neuron & chemical synapse: This image shows electric impulses traveling between neurons; the inset shows a chemical reaction occurring at the synapse. A basic chemical reaction at the synapse undergoes a few additional steps: 25 CU IDOL SELF LEARNING MATERIAL (SLM)

1. The action potential (which occurs as described above) travels along the membrane of the presynaptic cell until it reaches the synapse. The electrical depolarization of the membrane at the synapse causes channels to open that are selectively permeable, meaning they specifically only allow the entry of positive sodium ions (Na+). 2. The ions flow through the presynaptic membrane, rapidly increasing their concentration in the interior. 3. The high concentration activates a set of ion-sensitive proteins attached to vesicles, which are small membrane compartments that contain a neurotransmitter chemical. 4. These proteins change shape, causing the membranes of some “docked” vesicles to fuse with the membrane of the presynaptic cell. This opens the vesicles, which releases their neurotransmitter contents into the synaptic cleft, the narrow space between the membranes of the pre- and postsynaptic cells. 5. The neurotransmitter diffuses within the cleft. Some of it escapes, but the rest of it binds to chemical receptor molecules located on the membrane of the postsynaptic cell. 6. The binding of neurotransmitter causes the receptor molecule to be activated in some way. Several types of activation are possible, depending on what kind of neurotransmitter was released. In any case, this is the key step by which the synaptic process affects the behavior of the postsynaptic cell. 7. Due to thermal shaking, neurotransmitter molecules eventually break loose from the receptors and drift away. 8. The neurotransmitter is either reabsorbed by the presynaptic cell and repackaged for future release, or else it is broken down metabolically. DIFFERENCES BETWEEN ELECTRICAL AND CHEMICAL SYNAPSES • Electrical synapses are faster than chemical synapses because the receptors do not need to recognize chemical messengers. The synaptic delay for a chemical synapse is typically about 2 milliseconds, while the synaptic delay for an electrical synapse may be about 0.2 milliseconds. • Because electrical synapses do not involve neurotransmitters, electrical neurotransmission is less modifiable than chemical neurotransmission. • The response is always the same sign as the source. For example, depolarization of the presynaptic membrane will always induce a depolarization in the postsynaptic membrane, and vice versa for hyperpolarization. 26 CU IDOL SELF LEARNING MATERIAL (SLM)

• The response in the postsynaptic neuron is generally smaller in amplitude than the source. The amount of attenuation of the signal is due to the membrane resistance of the presynaptic and postsynaptic neurons. • Long-term changes can be seen in electrical synapses. For example, changes in electrical synapses in the retina are seen during light and dark adaptations of the retina. NEUROTRANSMITTERS Neurotransmitters are chemicals that transmit signals from a neuron across a synapse to a target cell. Neurotransmitters are chemicals that transmit signals from a neuron to a target cell across a synapse. When called upon to deliver messages, they are released from their synaptic vesicles on the presynaptic (giving) side of the synapse, diffuse across the synaptic cleft, and bind to receptors in the membrane on the postsynaptic (receiving) side. An action potential is necessary for neurotransmitters to be released, which means that neurons must reach a certain threshold of electric stimulation in order to complete the reaction. A neuron has a negative charge inside the cell membrane relative to the outside of the cell membrane; when stimulation occurs and the neuron reaches the threshold of excitement this polarity is reversed. This allows the signal to pass through the neuron. When the chemical message reaches the axon terminal, channels in the postsynaptic cell membrane open up to receive neurotransmitters from vesicles in the presynaptic cell. Inhibitory neurotransmitters cause hyperpolarization of the postsynaptic cell (that is, decreasing the voltage gradient of the cell, thus bringing it further away from an action potential), while excitatory neurotransmitters cause depolarization (bringing it closer to an action potential). Neurotransmitters match up with receptors like a key in a lock. A neurotransmitter binds to its receptor and will not bind to receptors for other neurotransmitters, making the binding a specific chemical event. There are several systems of neurotransmitters found at various synapses in the nervous system. The following groups refer to the specific chemicals, and within the groups are specific systems, some of which block other chemicals from entering the cell and some of which permit the entrance of chemicals that were blocked before. These neurotransmitters are chemical messengers for transmission of information across the synaptic gap to the receiving dendrites of the next neuron (von Bohlen und Halbach & Dermietzel, 2006). Although scientists have identified more than 100 transmitter substances, it seems likely that more remain to be discovered. Medical and psychological researchers are working to discover and understand neurotransmitters. In particular, they wish to understand how the neurotransmitters interact with drugs, moods, abilities, and perceptions. We know much about the mechanics of impulse transmission in nerves. But we know relatively little about how the nervous system’s chemical activity relates to psychological 27 CU IDOL SELF LEARNING MATERIAL (SLM)

states. Despite the limits on present knowledge, we have gained some insight into how several of these substances affect our psychological functioning. TYPES OF NEUROTRANSMITTERS At present, it appears that three types of chemical substances are involved in neurotransmission: • monoamine neurotransmitters are synthesized by the nervous system through enzymatic actions on one of the amino acids (constituents of proteins, such as choline, tyrosine, and tryptophan) in our diet (e.g., acetylcholine, dopamine, and serotonin); • amino-acid neurotransmitters are obtained directly from the amino acids in our diet without further synthesis (e.g., gamma-aminobutyric acid, or GABA); • neuropeptides are peptide chains (molecules made from the parts of two or more amino acids). Acetylcholine is associated with memory functions, and the loss of acetylcholine through Alzheimer’s disease has been linked to impaired memory functioning in Alzheimer’s patients (Hasselmo, 2006). Acetylcholine also plays an important role in sleep and arousal. When someone awakens, there is an increase in the activity of so-called cholinergic neurons in the basal forebrain and the brainstem (Rockland, 2000). Dopamine is associated with attention, learning, and movement coordination. Dopamine also is involved in motivational processes, such as reward and reinforcement. Schizophrenics show very high levels of dopamine. This fact has led to the “dopamine theory of schizophrenia” which suggests that high levels of dopamine may be partially responsible for schizophrenic conditions. Drugs used to combat schizophrenia often inhibit dopamine activity (von Bohlen und Halbach & Dermietzel, 2006). In contrast, patients with Parkinson’s disease show very low dopamine levels, which leads to the typical trembling and movement problems associated with Parkinson’s. When patients receive medication that increases their dopamine level, they (as well as healthy people who receive dopamine) sometimes show an increase in pathological gambling. Gambling is a compulsive disorder that results from impaired impulse control. When dopamine treatment is suspended, these patients no longer exhibit this behaviour (Drapier et al., 2006; Voon et al., 2007; Abler et al., 2009). These findings support the role of dopamine in motivational processes and impulse control. Serotonin plays an important role in eating behaviour and body-weight regulation. High serotonin levels play a role in some types of anorexia. Specifically, serotonin seems to play a role in the types of anorexia resulting from illness or treatment of illness. For example, patients suffering from cancer or undergoing dialysis often experience a severe loss of appetite (Agulera et al., 2000; Davis et al., 2004). This loss of appetite is related, in both cases, to high serotonin levels. Serotonin is also involved in aggression and regulation of impulsivity (Rockland, 2000). Drugs that block serotonin tend to result in an increase in aggressive behaviour. 28 CU IDOL SELF LEARNING MATERIAL (SLM)

The preceding description drastically oversimplifies the intricacies of constant neuronal communication. Such complexities make it difficult to understand what is happening in the normal brain when we are thinking, feeling, and interacting with our environment. Many researchers seek to understand the normal information processes of the brain by investigating what is going wrong in the brains of people affected by neurological and psychological disorders. In the case of depression, for example, in the early 1950s a drug (iproniazid, a monoamine oxidase inhibitor) intended to treat tuberculosis was found to have a mood-improving effect. This finding led to some early research on the chemical causes of depression. Perhaps if we can understand what has gone awry— what chemicals are out of balance—we can figure out how processes normally work and how to put things back into balance. One way of doing so might be by providing needed neurotransmitters or by inhibiting the effects of overabundant neurotransmitters. Table 2.1.: Neuro-transmitters and its types Neuro- Description General Function Specific Examples transmitters Monoamine Excitatory in brain and either Believed to be involved in Acetylcholine neurotransmitter excitatory (at skeletal memorybecause of high (Ach) synthesized muscles)or inhibitory (at concentration found from choline heartmuscles) elsewhere in in the hippocampus thebody Dopamine (DA) Monoamine Influences movement, Parkinson’s disease, neurotransmitter attention,and learning; mostly characterized bytremors and synthesized inhibitorybut some limb rigidity, results fromtoo from tyrosine excitatoryeffects little DA; some schizophreniasymptoms are Epinephrine Monoamine Hormones (also known as associated with too and neurotransmitter adrenaline and noradrenaline) much DA synthesized involved in regulation of Involved in diverse effects norepinephrine from tyrosine alertness on bodyrelated to fight-or- Monoamine Involved in arousal, sleep flight reactions,anger, and Serotonin neurotransmitter and dreaming, and mood; fear synthesized usually inhibitory but some Normally inhibits dreaming; GABA (gamma from tryptophan excitatory effects defects in amino butyric Amino acid General neuro-modulatory serotonin system are linked neurotransmitter effects resulting from to severedepression acid) inhibitoryinfluences on Currently believed to presynapticaxons influence certain Glutamate Amino acid General neuro-modulatory mechanisms for learning and neurotransmitter effects resulting from memory excitatory influences on Currently believed to presynaptic axons influence certain mechanisms for learning and memory 29 CU IDOL SELF LEARNING MATERIAL (SLM)

Neuropeptides Peptide chains General neuro-modulatory Endorphins play a role in serving effects resulting from pain relief. as neuro- influences on postsynaptic Neuro-modulating transmitters membranes neuropeptides sometimes are released to enhance the effects of Ach NEURAL NETWORKS Neural networks consist of a series of interconnected neurons, and serve as the interface for neurons to communicate with each other. A neural network (or neural pathway) is the interface through which neurons communicate with one another. These networks consist of a series of interconnected neurons whose activation sends a signal or impulse across the body. Figure 2.7.: Neural networks: A neural network (or neural pathway) is the complex interface through which neurons communicate with one another. THE STRUCTURE OF NEURAL NETWORKS The connections between neurons form a highly complex network. The basic kinds of connections between neurons are chemical synapses and electrical gap junctions, through which either chemical or electrical impulses are communicated between neurons. The method through which neurons interact with neighboring neurons usually consists of several axon terminals connecting through synapses to the dendrites on other neurons. If a stimulus creates a strong enough input signal in a nerve cell, the neuron sends an action potential and transmits this signal along its axon. The axon of a nerve cell is responsible for transmitting information over a relatively long distance, and so most neural pathways are made up of axons. Some axons are encased in a lipid-coated myelin sheath, making them appear a bright white; others that lack myelin sheaths (i.e., are unmyelinated) appear a darker beige color, which is generally called gray. 30 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 2.8.: The process of synaptic transmission in neurons: Neurons interact with other neurons by sending a signal, or impulse, along their axon and across a synapse to the dendrites of a neighboring neuron. Some neurons are responsible for conveying information over long distances. For example, motor neurons, which travel from the spinal cord to the muscle, can have axons up to a meter in length in humans. The longest axon in the human body is almost two meters long in tall individuals and runs from the big toe to the medulla oblongata of the brain stem. THE FUNCTION OF NEURAL NETWORKS The basic neuronal function of sending signals to other cells includes the capability for neurons to exchange signals with each other. Networks formed by interconnected groups of neurons are capable of a wide variety of functions, including feature detection, pattern generation, and timing. In fact, it is difficult to assign limits to the types of information processing that can be carried out by neural networks. Given that individual neurons can generate complex temporal patterns of activity independently, the range of capabilities possible for even small groups of neurons are beyond current understanding. However, we do know that we have neural networks to thank for much of our higher cognitive functioning. SUMMARY 1. Neurons are specialized cells that transmit chemical and electrical signals in the brain; they are the basic building blocks of the central nervous system. 2. The primary components of the neuron are the soma (cell body), the axon (a long slender projection that conducts electrical impulses away from the cell body), dendrites (tree-like 31 CU IDOL SELF LEARNING MATERIAL (SLM)

structures that receive messages from other neurons), and synapses (specialized junctions between neurons). 3. The neurons (or excitable nerve cells) of the nervous system conduct electrical impulses, or signals, that serve as communication between sensory receptors, muscles and glands, and the brain and spinal cord. 4. An action potential occurs when an electrical signal disrupts the original balance of Na+ and K+ within a cell membrane, briefly depolarizing the concentrations of each. 5. An electrical impulse travels along the axon via depolarized voltage-gated ion channels in the membrane, and can either “jump” along a myelinated area or travel continuously along an unmyelinated area. 6. While an action potential is being generated by a cell, no other action potential may be generated until the cell’s channels return to their resting state. 7. Action potentials generated by neural impulses are “all or nothing,” meaning the signal reaches the threshold for communication or it doesn’t. No signal is stronger or weaker than another. 8. Neurotransmitters dictate communication between cells by binding to specific receptors and depolarizing or hyperpolarizing the cell. 9. Inhibitory neurotransmitters cause hyperpolarization of the postsynaptic cell; excitatory neurotransmitters cause depolarization of the postsynaptic cell. 10. Too little of a neurotransmitter may cause the overaccumulation of proteins, leading to disorders like Alzheimer’s; too much of a neurotransmitter may block receptors required for proper brain function, leading to disorders like schizophrenia. 11. The three neurotransmitter systems in the brain are cholinergic, amino acids, and biogenic amines. 12. The connections between neurons form a highly complex network through which signals or impulses are communicated across the body. 13. The basic kinds of connections between neurons are chemical synapses and electrical gap junctions, through which either chemical or electrical impulses are communicated between neurons. 14. Neural networks are primarily made up of axons, which in some cases deliver information as far as two meters. 15. Networks formed by interconnected groups of neurons are capable of a wide variety of functions; in fact, the range of capabilities possible for even small groups of neurons is beyond our current understanding. KEY WORDS/ ABBREVIATIONS Nerve- A bundle of nerve cells running together in a branching path outside the central nervous system and usually encased in a myelin sheath. Nerves connect the brain with the rest of the body and may be afferent, efferent, or mixed in function. nerve cell- An individual unit in the nervous system defined by a cell wall and consisting of a cell body, an axon, and one or more dendrites. 32 CU IDOL SELF LEARNING MATERIAL (SLM)

LEARNING ACTIVITY 1. Draw the diagram of the neuron and label the different parts of the neuron. 2. With help of a flow chart demonstrate how the neuron transmits messages to one another. UNIT END QUESTIONS (MCQS AND DESCRIPTIVE) A. Descriptive Questions 1. Neurons are the basic unit of nervous system. With the help of a diagram explain the structure and function of the parts of neurons. 2. Identify the chemicals secreted from neurons and explain their types and functions. 3. There is gap between two neurons. Explain what is the purpose of this space and why is it necessary. 4. Messages from one neuron to another pass like electric current. Elaborate on the process if impulse transmission in the nervous system. 5. Neurons form a network of information in our body. Explain this network, its structure and functions. B. Multiple Choice Questions 1. In neurons, the axon are insulated by the matter called [a] Nerve fibre [b] Myelin Sheath [c] Ganglion [d] Sylvain Sheath 2. The term soma refers to [a] Synapse [b] Cell body 33 CU IDOL SELF LEARNING MATERIAL (SLM)

[c] Neuron [d] Axon 3. Who discovered the chemical basis of neuro transmission? [a] Albert Bandura [b] Charles Sherrington [c] Luigi Galvini [d] Otto Leowi 4. The two kinds of cells in the nervous system are , which receive and transmit information to other cells, and , which do not transmit information. [a] Neurons, Glia [b] Glia, Hypoglia [c] Glia, Neurons [d] Neurons, Corpuscles 5. The function of a myelin sheath is to [a] Prevent action potentials from traveling in the wrong direction. [b] Increase the velocity of transmission along an axon. [c] Increase the magnitude of an action potential. [d] Enable an action potential in one cell to influence the transmission in other cells. Answer 1 [b]2 [b]3 [d]4 [a]5 [b] REFERENCES • Martin, N. (2010). Psychology, (4th ed). Pearson Education Limited • Mangal, S.K. (1995). An Introduction to Psychology. Sterling Publishers Private Limited • Eynenck, M. (2014). Fundamentals of Psychology. Taylor & Francis. 34 CU IDOL SELF LEARNING MATERIAL (SLM)

• Woodworth, R. S. & Marquis, D. G. (2015). Psychology a study ofmental life. Taylor & Francis. • Bernstein D. (2018) Essentials of Psychology. Cengage Learning. • Feldman, R. S. (2012) Understanding Psychology (11th ed). McGraw-Hill Education - EuropePinel, J.P.J. (2007). Biopsychology. New Delhi: Pearson • Rosenzweig, M. R., Leiman, A. L. & Breedlove, S. M. (1996). Biological Psychology. Sunderland, Mass: Sinauer Associates. • Green, S. (1995). Principles of biopsychology. UK: Lawrence Erlbaum Associates Ltd. • Pinel, J. P. J. (2004). Biopsychology. Boston, MA: Allyn & Bacon. • Annett, M. (1984). Left, right, hand and brain: The right shift theory. London: Lawrence Erlbaum Associates Ltd. • Bannett, T.L. (1977). Brain and Behaviour. California: Brooks/ Cole. • Leukel, F. (1985). Introduction to Physiological Psychology. New Delhi: CBS Publishers 35 CU IDOL SELF LEARNING MATERIAL (SLM)

UNIT 3THE NERVOUS SYSTEM Structure Learning Objectives Introduction Classification of Nervous System Central Nervous System (CNS) The Peripheral Nervous System (PNS) Summary Key Words/ Abbreviations Learning Activity Unit End Questions (MCQs and Descriptive) References LEARNING OBJECTIVES After this unit, you will be able to; • Understand the nervous system and its components • Understand the structure and function of the brain and spinal cord (central nervous system) • Understand the components and functions of peripheral nervous system INTRODUCTION The nervous system is never at rest. There is always a job for it to do. Even when you are sleeping the nervous system is busy regulating your body functions. The nervous system controls your emotions, movements, thinking, and behavior. Structurally, the nervous system is divided into two parts—the central nervous system [CNS] (the brain and the spinal cord) and the peripheral nervous system [PNS] (the smaller branches of nerves that reach the other parts of the body) (see Figure 6.1). The nerves of the peripheral system conduct information from the bodily organs to the central nervous system and take information back to the organs. These nerves branch out from the spinal column and are about as thick as a pencil. Those in the extremities, such as the fingertips, are invisibly small. All parts of the nervous system are protected in some way: the brain by the skull and several layers of sheathing, the spinal cord by the vertebrae, and the peripheral nerves by layers of sheathing. The bony protection of the spinal cord is vital. An injury to the spinal cord could prevent the transmittal of messages between the brain and the muscles, and could result in paralysis. 36 CU IDOL SELF LEARNING MATERIAL (SLM)

CLASSIFICATION OF NERVOUS SYSTEM The nervous system controls bodily function by gathering sensory input, integrating that information internally, and communicating proper motor output. Figure 3.1.: Classification of the Nervous System The nervous system allows organisms to sense, organize, and react to information in the environment. The basic unit of the nervous system is the neuron. Synapses form between the neurons, allowing them to communicate to other neurons or other systems in the body. The general flow of information is that the peripheral nervous system (PNS) takes in information through sensory neurons, then sends it to the central nervous system (CNS) to be processed. After processing, the CNS “tells” the PNS what to do—what muscles to flex, whether the lungs need more oxygen, which limbs need more blood, any number of biological processes—and the PNS makes it happen through muscle control. The neurons responsible for taking information to the CNS are known as afferent neurons, while the neurons that carry the responses from the CNS to the PNS are known as efferent neurons. 37 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 3.2.: Human Nervous System The nervous system can be divided into two major parts—the central nervous system (CNS) and the peripheral nervous system (PNS). CENTRAL NERVOUS SYSTEM (CNS) The central nervous system includes the spinal cord and the brain. The brain is the body’s main control center. The main function of the CNS is the integration and processing of sensory information. It synthesizes sensory input to compute an appropriate motor response, or output. The central nervous system is made up of the brain and spinal cord, which process sensory input and provide instructions to the body. The central nervous system (CNS) is one of the two major subdivisions of the nervous system. The CNS includes the brain and spinal cord, which together comprise the body’s main control center. Together with the peripheral nervous system (PNS), the CNS performs fundamental functions that contribute to an organism’s life and behavior. 38 CU IDOL SELF LEARNING MATERIAL (SLM)

Activity of the CNS The nervous system has three main functions: gathering sensory information from external stimuli, synthesizing that information, and responding to those stimuli. The CNS is mainly devoted to the “information synthesizing” function. During this step in the process, the brain and spinal cord decide on appropriate motor output, which is computed based on the type of sensory input. The CNS regulates everything from organ function to high-level thought to purposeful body movement. Thus, the CNS is commonly thought of as the control center of the body. Structure of the Central Nervous System The CNS is comprised of the brain, brain stem, and spinal cord. Figure 3.3.: The central nervous system: The three major components of the central nervous system: 1) the brain, 2) brain stem, and 3) spinal cord. Brain The brain is found in the cranial cavity and consists of the cerebrum and cerebellum. It houses the nerve centers responsible for coordinating sensory and motor systems in the body. The cerebrum, or the top portion for the brain, is the seat of higher-level thought. It is comprised of two hemispheres, each controlling the opposite side of the body. Each of these hemispheres is divided into four separate lobes: • the frontal lobe, which controls specialized motor control, learning, planning, and speech; • the parietal lobe, which controls somatic or voluntary sensory functions; • the occipital lobe, which controls vision; 39 CU IDOL SELF LEARNING MATERIAL (SLM)

• the temporal lobe, which controls hearing and some other speech functions. The cerebellum is located underneath the backside of the cerebrum, and governs balance and fine motor movements. Its main function is maintaining coordination throughout the body. Table 3.1.: Part of the brain and their functions: Region of the Structure in the region Function of the structure brain Fore Brain Cerebral Cortex Involved in receiving and processing sensory information, thinking, other cognitive processing, and planning and sending motor information Basal Ganglia Crucial to the function of the motor system Limbic System Involved in learning, emotions, and motivation (in particular, the hippocampus influences learning and memory, the amygdala influences anger and aggression, and the septum influences anger and fear) Thalamus Primary relay station for sensory information coming into the brain; transmits information to the correct regions of the cerebral cortex through projection fibres that extend from the thalamus to specific regions of the cortex; comprises several nuclei (groups of neurons) that receive specific kinds of sensory information and project that information to specific regions of the cerebral cortex, including four key nuclei for sensory information: (1) from the visual receptors, via optic nerves, to the visual cortex, permitting us to see; (2) from the auditory receptors, via auditory nerves, to the auditory cortex, permitting us to hear; (3) from sensory receptors in the somatic nervous system, to the primary somatosensory cortex, permitting us to sense pressure and pain; and (4) from the cerebellum (in the hindbrain) to the primary motor cortex, permitting us to sense physical balance and equilibrium 40 CU IDOL SELF LEARNING MATERIAL (SLM)

Mid Brain Hypothalamus Controls the endocrine system; controls the Hind Brain autonomic nervous system, such as internal Superior colliculi (above) temperature regulation, appetite and thirst Inferior colliculi (below) regulation, and other key functions; involved in Reticular Formation regulation of behaviour related to species survival (in particular, fighting, feeding, fleeing, and Gray matter, red nucleus, mating); plays a role in controlling consciousness substantia nigra, ventral (see reticular activating system); involved in region emotions, pleasure, pain, and stress reactions Cerebellum Pons Involved in vision (especially visual reflexes) Medulla oblongata Involved in hearing Important in controlling consciousness (sleep arousal), attention, cardiorespiratory function, and movement Important in controlling movement Essential to balance, coordination, and muscle tone Involved in consciousness (sleep and arousal); bridges neural transmissions from one part of the brain to another; involved with facial nerves Serves as juncture at which nerves cross from one side of the body to opposite side of the brain; involved in cardiorespiratory function, digestion, and swallowing Brain Stem The brain stem is connected to the underside of the brain. It consists of the midbrain, pons, and medulla. The midbrain is found in between the hindbrain and the forebrain. It regulates motor function and allows motor and sensory information to pass from the brain to the rest of the body. The pons houses the control centers for respiration and inhibitory functions. The medulla also helps regulate respiration, as well as cardiovascular and digestive functioning. Spinal Cord The spinal cord connects the brain and brain stem to all of the major nerves in the body. Spinal nerves originate from the spinal cord and control the functions of the rest of the body. Impulses are sent from receptors through the spinal cord to the brain, where they are 41 CU IDOL SELF LEARNING MATERIAL (SLM)

processed and synthesized into instructions for the rest of the body. This data is then sent back through the spinal cord to muscles and glands for motor output. THE PERIPHERAL NERVOUS SYSTEM (PNS) The peripheral nervous system connects the central nervous system to environmental stimuli to gather sensory input and create motor output. The peripheral nervous system (PNS) is one of the two major components of the body’s nervous system. In conjunction with the central nervous system (CNS), the PNS coordinates action and responses by sending signals from one part of the body to another. The CNS includes the brain, brain stem, and spinal cord, while the PNS includes all other sensory neurons, clusters of neurons called ganglia, and connector neurons that attach to the CNS and other neurons. Figure 3.4.: The nervous system: The human nervous system, including both the central nervous system (in red: brain, brain stem, and spinal cord) and the peripheral nervous system (in blue: all other neurons and receptors). 42 CU IDOL SELF LEARNING MATERIAL (SLM)

Divisions of the Peripheral Nervous System The PNS can also be divided into two separate systems: the autonomic nervous system and the somatic nervous system. Autonomic Nervous System The autonomic nervous system regulates involuntary and unconscious actions, such as internal-organ function, breathing, digestion, and heartbeat. This system consists of two complementary parts: the sympathetic and parasympathetic systems. Both divisions work without conscious effort and have similar nerve pathways, but they generally have opposite effects on target tissues. The sympathetic nervous system activates the “fight or flight” response under sudden or stressful circumstances, such as taking an exam or seeing a bear. It increases physical arousal levels, raising the heart and breathing rates and dilating the pupils, as it prepares the body to run or confront danger. These are not the only two options; “fight or flight” is perhaps better phrased as “fight or flight or freeze,” where in the third option the body stiffens and action cannot be taken. This is an autonomic response that occurs in animals and humans; it is a survival mechanism thought to be related to playing dead when attacked by a predator. Post- traumatic stress disorder (PTSD) can result when a human experiences this “fight or flight or freeze” mode with great intensity or for large amounts of time. The parasympathetic nervous system activates a “rest and digest” or “feed and breed” response after these stressful events, which conserves energy and replenishes the system. It reduces bodily arousal, slowing the heartbeat and breathing rate. Together, these two systems maintain homeostasis within the body: one priming the body for action, and the other repairing the body afterward. Somatic Nervous System The somatic nervous system keeps the body adept and coordinated, both through reflexes and voluntary action. The somatic nervous system controls systems in areas as diverse as the skin, bones, joints, and skeletal muscles. Afferent fibers, or nerves that receive information from external stimuli, carry sensory information through pathways that connect the skin and skeletal muscles to the CNS for processing. The information is then sent back via efferent nerves, or nerves that carry instructions from the CNS, back through the somatic system. These instructions go to neuromuscular junctions—the interfaces between neurons and muscles—for motor output. The somatic system also provides us with reflexes, which are automatic and do not require input or integration from the brain to perform. Reflexes can be categorized as either monosynaptic or polysynaptic based on the reflex arc used to perform the function. Monosynaptic reflex arcs, such as the knee-jerk reflex, have only a single synapse between the sensory neuron that receives the information and the motor neuron that responds. Polysynaptic reflex arcs, by contrast, have at least one interneuron between the sensory neuron and the motor neuron. An example of a polysynaptic reflex arc is seen when a person 43 CU IDOL SELF LEARNING MATERIAL (SLM)

steps on a tack—in response, their body must pull that foot up while simultaneously transferring balance to the other leg. SUMMARY 1. The nervous system is the body’s main communication system; it gathers, synthesizes, and uses data from the environment. 2. The most basic unit of the nervous system is the neuron, which serves as both a sensor and communicator of internal and external stimuli. 3. The nervous system can be broken down into two major parts—the central nervous system and the peripheral nervous system. 4. The central nervous system, the main data centre of the body, includes the brain and spinal cord. 5. The peripheral nervous system includes all of the neurons that sense and communicate data to the central nervous system. The peripheral nervous system can be further divided into the autonomic system, which regulates involuntary actions, and the somatic system, which controls voluntary actions. 6. The central nervous system (CNS) and the peripheral nervous system (PNS) comprise the entirety of the body’s nervous system, which regulates and maintains its most basic functions. 7. The CNS is the main control centre of the body—it takes in sensory information, organizes and synthesizes this input, then provides instructions for motor output to the rest of the body. The CNS is made up of the brain and spinal cord. 8. The brain is the main data centre of the body, consisting of the cerebrum (which regulates higher-level functioning such as thought) and the cerebellum (which maintains coordination). The brain stem includes the midbrain, pons, and medulla, and controls lower-level functioning such as respiration and digestion. 9. The spinal cord connects the brain and the body’s main receptors, and serves as a conduit for sensory input and motor output. 10. The peripheral nervous system (PNS) provides the connection between internal or external stimuli and the central nervous system to allow the body to respond to its environment. The PNS is made up of different kinds of neurons, or nerve cells, which communicate with each other through electric signalling and neurotransmitters. 11. The PNS can be broken down into two systems: the autonomic nervous system, which regulates involuntary actions such as breathing and digestion, and the somatic nervous system, which governs voluntary action and body reflexes. 12. The autonomic nervous system has two complementary parts: the sympathetic nervous system, which activates the “fight-or-flight-or-freeze” stress response, and the parasympathetic nervous system, which reacts with the “rest-and-digest” response after stress. 13. The somatic nervous system coordinates voluntary physical action. It is also responsible for our reflexes, which do not require brain input. 44 CU IDOL SELF LEARNING MATERIAL (SLM)

KEY WORDS/ ABBREVIATIONS • autonomic nervous system- (ANS) Literally, the system of self-knowledge. ANS is a division of the body’s neural systems which has the role of regulating involuntary activity of the glands, internal organs including the heart, and the smooth muscles of the vasculature. • hemispheric specialization- Asymmetric representation of higher-level functions in the cerebral hemispheres. • parasympathetic nervous system-The subsystem of the autonomic nervous system that typically influences activity related to the protection, nourishment, and growth of the body. • somatic nervous system- The subsystem of the peripheral nervous system that transmits information from the senses to the central nervous system and carries signals from the CNS to the muscles that move the skeleton. • sympathetic nervous system-The subsystem of the autonomic nervous system that readies the body for vigorous activity. LEARNING ACTIVITY 1. With the help of a diagram show the various components of the nervous system. 2. Write in detail about the different parts of the brain and their functions? UNIT END QUESTIONS (MCQS AND DESCRIPTIVE) A. Descriptive Questions 1. Nervous system is like a tree with several branches and sub branches. Explain the components on nervous system. 2. Elaborate on the role of different areas of the nervous system. 3. Our brain is made of several small structures with special functions. Describe in brief any six parts of the brain with their functions. 4. Identify and explain in detail the structure and the functions of the two parts of the brain that are divided into left and right hemisphere. 5. Evaluate the role of peripheral nervous system in managing and handling stress. B. Multiple Choice Questions 45 CU IDOL SELF LEARNING MATERIAL (SLM)

1. Human central nervous system is composed of [a] Somatic Nervous System [b] Brain and Spinal Cord [c] Autonomic Nervous System [d] All of these 2. The link between the nervous system and endocrine system is [a] Corpus Collosum [b] Reticular Formation [c] Cerebellum [d] Hypothalamus 3. In which lobe of the cerebral cortex, the primary olfactory cortex lies? [a] Frontal [b] Parietal [c] Temporal [d] Occipital 4. The lobe is to vision as temporal lobe is to hearing. [a] Frontal [b] Parietal [c] Temporal [d] Occipital 5. Reflexes are controlled by _ [a] Hypothalamus [b] Spinal Cord 46 CU IDOL SELF LEARNING MATERIAL (SLM)

[c] Temporal Lobe [d] Medulla 6. is a part of Peripheral Nervous system [a] Spinal Cord [b] Brain [c] Autonomic Nervous System [d] All of these Answer 1 [b]2 [d]3 [c]4 [d]5 [a]6 [c] REFERENCES • Martin, N. (2010). Psychology, (4th ed). Pearson Education Limited • Mangal, S.K. (1995). An Introduction to Psychology. Sterling Publishers Private Limited • Eynenck, M. (2014). Fundamentals of Psychology. Taylor & Francis. • Woodworth, R. S. & Marquis, D. G. (2015). Psychology a study ofmental life. Taylor & Francis. • Bernstein D. (2018) Essentials of Psychology. Cengage Learning. • Feldman, R. S. (2012) Understanding Psychology (11th ed). McGraw-Hill Education - Europe • Pinel, J.P.J. (2007). Biopsychology. New Delhi: Pearson • Rosenzweig, M. R., Leiman, A. L. & Breedlove, S. M. (1996). Biological Psychology. Sunderland, Mass: Sinauer Associates. • Green, S. (1995). Principles of biopsychology. UK: Lawrence Erlbaum Associates Ltd. • Pinel, J. P. J. (2004). Biopsychology. Boston, MA: Allyn & Bacon. • Annett, M. (1984). Left, right, hand and brain: The right shift theory. London: Lawrence Erlbaum Associates Ltd. • Bannett, T.L. (1977). Brain and Behaviour. California: Brooks/ Cole. • Leukel, F. (1985). Introduction to Physiological Psychology. New Delhi: CBS Publishers 47 CU IDOL SELF LEARNING MATERIAL (SLM)

48 CU IDOL SELF LEARNING MATERIAL (SLM)

UNIT 4 THE ENDOCRINE GLANDS Structure Learning Objectives Introduction The Endocrine System Characteristics of Endocrine Glans Types of Endocrine Glands Functions of the Endocrine Glands Summary Key Words/ Abbreviations Learning Activity Unit End Questions (MCQs and Descriptive) 4.10.References LEARNING OBJECTIVES After this unit, you will be able to; • Explain the nature and role endocrine system • Describe the different types of endocrine glands • Outline the functions of the endocrine glands • Identify the impact of endocrine gland on our behaviour INTRODUCTION Neurons are not the only cells that use chemicals to communicate with one another in ways that affect behaviour and mental processes. Another kind of cell with this ability is found in the endocrine system (pronounced “EN-doh-krin”). Operating on orders from the brain, the endocrine system regulates growth, energy consumption, and sexual behaviour, and it readies the body for action. The cells of the endocrine organs, or glands, communicate by secreting chemicals, much as neurons do. The chemicals that these glands secrete are called hormones. Hormones from endocrine organs are similar to neurotransmitters. In fact, many such chemicals, including norepinephrine and the endorphins, act both as hormones and as neurotransmitters. However, whereas neurons secrete neurotransmitters into synapses, endocrine organs put their chemicals into the bloodstream, which carries them throughout the body. In this way, endocrine glands can stimulate cells with which they have no direct connection. But not all cells receive the hormonal message. Hormones, like neurotransmitters, can influence only those cells with receptors capable of receiving them. Organs whose cells have receptors for a particular hormone are called target organs. Each hormone acts on many target organs, producing coordinated effects throughout the body. For example, when a woman’s ovaries secrete the sex hormone estrogen, it activates her 49 CU IDOL SELF LEARNING MATERIAL (SLM)