Stages of muscle contraction

What happens during the Excitation phase of muscle contraction?

A somatic motor neuron releases acetylcholine (ACh), which generates an end plate potential and leads to the initiation of an action potential in the muscle fiber.

What occurs during Excitation-Contraction Coupling?

The action potential travels down the T-tubules, triggering the release of calcium ions (Ca2+) from the sarcoplasmic reticulum (SR). Ca2+ binds to troponin, moving tropomyosin to expose actin's active sites, initiating muscle contraction.

What happens during the Contraction phase of muscle contraction?

Myosin heads form cross-bridges with actin, and power strokes pull the thin filaments (actin) toward the center of the sarcomere, using ATP to generate tension.

What happens during the Relaxation phase of muscle contraction?

The nerve signal stops, calcium is actively transported back into the sarcoplasmic reticulum (SR), and antagonistic muscles help return the muscle to its resting length.

What is the first step in the sequence of muscle contraction?

A nerve impulse arrives at the axon terminal of the motor neuron and triggers the release of acetylcholine (ACh).

What happens after acetylcholine (ACh) is released into the synaptic cleft?

ACh binds to receptors on the motor end plate, causing a muscle action potential (AP) to be generated.

What role does acetylcholinesterase play in muscle contraction?

Acetylcholinesterase breaks down ACh in the synaptic cleft, preventing the continuous stimulation of the muscle unless more ACh is released from the motor neuron.

What happens when the muscle action potential travels down the transverse tubules?

It opens calcium release channels in the sarcoplasmic reticulum (SR), causing calcium ions to flood into the sarcoplasm and activate muscle contraction.

How does calcium (Ca2+) contribute to muscle contraction?

Calcium binds to troponin on the thin filament, which causes tropomyosin to move, exposing the binding sites on actin for myosin.

What occurs during the contraction phase in detail?

Myosin heads bind to actin, form cross-bridges, rotate (power stroke), and release ADP and inorganic phosphate (Pi), pulling the thin filaments toward the center of the sarcomere.

What happens when the muscle contraction ends?

Calcium release channels in the sarcoplasmic reticulum close, and calcium pumps use ATP to restore low calcium levels in the sarcoplasm.

How does muscle relaxation occur after contraction?

The troponin-tropomyosin complex moves back into position, blocking the myosin-binding sites on actin, and the muscle relaxes.