Question

explain different steps of mechanism of muscle contraction?
IN POINTS PLZZZZ

Answer 1

ANSWER⤵⤵⤵

During skeletal muscle contraction, the thick filament slides over the thin filament by a repeated binding and releases of myosin head along the filament. This whole process occurs in a sequential manner.

✔Step 1:

Muscle contraction is initiated by signals that travel along the axon and reach the neuromuscular junction or motor end plate. Neuromuscular
junction is a junction between a neuron and the sarcolemma of the muscle
fibre. As a result, Acetylcholine (a neurotransmitter) is released into the synaptic cleft by generating an action potential in sarcolemma.

✔Step 2:

The generation of this action potential releases calcium ions from the sarcoplasmic reticulum in the sarcoplasm.

✔Step 3:

The increased calcium ions in the sarcoplasm leads to the activation
of actin sites. Calcium ions bind to the troponin on actin filaments and
remove the tropomyosin, wrapped around actin filaments. Hence, active
actin sites are exposed and this allows myosin heads to attach to this site.

✔Step 4:

In this stage, the myosin head attaches to the exposed site of actin
and forms cross bridges by utilizing energy from ATP hydrolysis. The
actin filaments are pulled. As a result, the H-zone reduces. It is at this stage that the contraction of the muscle occurs.

✔Step 5:

After muscle contraction, the myosin head pulls the actin filament and releases ADP along with inorganic phosphate. ATP molecules bind and detach myosin and the cross bridges are broken.

✔Step 6:

This process of formation and breaking down of cross bridges continues until there is a drop in the stimulus.As a result, the
concentration of calcium ions decreases, thereby masking the actin filaments and leading to muscle relaxation.

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Answer 2

Different steps of mechanism of ‘muscle contraction’:

i)   Depolarisation:

  a. ‘Nerve impulse’ travels to neuromuscular junction.

  b. Acetylcholine (Ach) is released from axons and binds to receptors on sarcolemma.

  c. Ach binding to sarcolemma causes ion channels on muscle to open and Na+ ions to enter which depolarise the muscle fibres.

ii)   Generation of action potential and Ca2+ ion release:

   a. Depolarisation causes generation of action potential that travels to T-tubules and causes Ca2+ ion release from sarcoplasmic reticulum.

iii)   Actin-myosin ‘cross-bridge’ formation:

Ca2+ ions bind to troponin and removes blocking ‘action of tropomyosin’ on actin binding sites for cross-bridge formation with myosin.

iv)   Contraction:

   a. Myosin binds to ATP, hydrolysed protein it and gets activated to its high-energy position.

    b. Actin and myosin forms cross-bridge.

   c. The actin slides along myosin therefore shortening the sarcomere and causing muscle contraction.