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The Muscular System

Published by Roy Augustine, 2021-06-27 10:04:13

Description: The Muscular System


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Action potential  Motor neuron- releases acetylcholine at neuromuscular junction ◦ ACh depolarizes the postsynaptic muscle cell creating the action potential ◦ The action potential spreads to the T (transverse) tubule ◦ T tubule is connected to the sarcoplasmic reticulum ◦ Efflux of calcium ions is caused by a change in the permeability of sarcoplasmic reticulum due to the action potential

Overview of muscle contraction  Synaptic terminal of motor neuron releases Ach  ACh depolarizes postsynaptic muscle cell  Action potential is generated in the muscle cell  Action potential spreads through T tubules  Sarcoplasmic reticulum becomes permeable to calcium ions  Calcium ions bind to troponin  Troponin releases the active site of actin by moving the tropomyosin

Overview of muscle contraction  Myosin head with attached ATP is under low energy state  ATP is hydrolyzed creating a high energy state myosin head  Cross-bridge is formed  Release of energy relaxes the myosin molecule  Another ATP molecule detaches the myosin from actin  Contraction occurs as the myosin head walks on the thin filament

End of contraction • End of contraction occurs if calcium ion concentration in the cytosol falls leading to the blockage of the active site of actin

The all-or-none response  At the cellular level, contraction is an all- or-none response  Frequency of action potential creates the graded contraction  Summation of action potential occurs  Tetanus- a smooth and sustained contraction

Muscle tone • Muscular contractions do not always cause actual movement. • A small fraction of the total number of fibers in most muscles are usually contracting. • This serves to maintain the posture of a limb and enables the limb to resist passive elongation or stretch. • This slight continuous contraction is called muscle tone.

Muscle fatigue • ATP -energy • Oxygen - respiration • Anaerobic respiration- absence oxygen • Lactic acid accumulation - fatigue • Muscle recovery – removal of lactic acid and conversion to pyruvic acid

Action of skeletal muscle • Antagonistic • Isotonic contraction- uniform contraction with movement of body • Isometric contraction- contraction of muscle without shortening of muscle

Answer the Questions 1. Describe the three types of muscles. Draw labeled diagrams. 5 marks 2. Explain Sliding filament theory of muscle contraction. 5 marks Write notes on :- a) Neuromuscular junction b) Muscle tone c) Muscle fatigue

• d) Action of skeletal muscles • e) Muscle origin and insertion

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