Explain how the following agents are involved in the excitation and contraction of skeletal muscle. i....

Explain how the following agents are involved in the excitation and contraction of skeletal muscle.

i. Acetylcholine (ACh)

ii. Calcium (Ca²⁺)

iii. Adenosine triphosphate (ATP)

Solutions

Expert Solution

Mechanism of muscle contraction:

•>Muscle contraction is initiated by a signal sent by the CNS via a motor neuron.The junction between a motor neurons and the sarcolemma of the muscle fibre is called the Neuromuscular junction.

•A neural signal reaching this junction releases a neurotransmitter(Acetylcholine) which generates an action potential in the sarcolemma.This spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm.Increase in Ca++ level leads to the binding of calcium with the Troponin C subunit on actin filaments and thereby remove the masking of active sites for myosin.

•Utilising the energy from the hydrolysis of ATP, the myosin head now binds to the exposed active sites on actin to form a cross bridge.

•This pulls the attached actin filaments towards towards the centre of 'A' band.The 'Z' line attached to these actins are also pulled inwards thereby causing shortening of the sarcomere, i.e., contraction.

•The myosin,releasing the ADP and Pi goes back to its relaxed state.A new ATP binds and the cross- bridge is broken.The ATP is again hydrolysed by the myosin head and the cycle of cross bridge formation and breakage is repeated.

Sydney Mullin answered 8 months ago

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