4. Physiology of muscle contraction

The sliding filament theory of muscle contraction:


 This theory was proposed by A.F Huxley and H.E Huxley in 1950s. according to this theory the muscle contraction caused due to the formation of cross-bridges in the overlap region.
 The length of the sarcomere shortened by the movement of cross-bridges which causes one filament to slide over the other.
 During muscle contraction the actin filament move inwards to bind with the myosin head. This movement utilizes the energy derived from the breakdown of ATP molecules.
Motor nerve stimulate

Nerve impulse generate and stimulate the motor nerve (voluntarily)

It will stimulate sarcoplasmic reticulum

Ca+2 is released

This Ca+2 enter into the myofiber through T-tubules

This Ca+2 removes troponin and tropomyosin

The actin myosin cross-bridge is formed

ATP is utilized and myosin head attached to actin by the influence of a powerstoke

Myosin head moving inward and the length of the sarcomere decreased. Thus muscle is contracted

As myosin head attached to the actin every time the head is moving inwards by slide with the actin filament.

Physiology of neuromuscular junction:
 It is the junction between the motor neuron and a muscle fiber in which a signal comes from brain and interact with the skeletal muscle that responsible for initiation of action potentials across the muscle’s surface, ultimately cause muscle contraction.
 The tip of the axon terminal can close to the muscle known as motor end bulb.
 The terminal membrane of the neuron is called presynaptic membrane
 The terminal membrane which face towards the neuron is called post synaptic membrane.
 The space between these two is called as synaptic cleft

Physiology of muscle contraction:
 The muscle contraction occurs due to involvement of various electrical and biochemical processes with several events.
 The axon of the motor nerve carries electrical signals from brain and reach to neuromuscular junction. It need biochemical processes that transform the electrical signal to chemical i.e., releasing of neurotransmitter (e.g., acetylcholine) for muscle contraction.
electrical signal(this happen in neuron means in axon terminal)
Chemical signal by neurotransmitter i.e., acetylcholine

After release of Ca2+ from sarcoplasmic reticulum, troponin and tropomyosin bind with it and the active site of actin getting free

Then ATP is hydrolised and energy is produced which is used to form cross-bridges with actin filament

The cross-bridges generate force to pull the myosin head inwards. This is called powerstroke.

The length of the sarcomere is decreased and muscle getting contracted

Above steps are repeated many times to move the filaments further inward and the whole contraction process is completed

After that all the energy is consumed and the myosin head comes back to its original place and the Ca2+ return to sarcoplasmic reticulum. The cross-bridges are breakdown, torponin and tropomyosin can cover the actin site and muscle getting relaxed.

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