Question

starting from the arrival of an action potential at the neuromuscular junction what are the sequence of events that lead to the release of ca2+ from the terminal cisternae?

Answer 1

At the motor end plate, the action potential causes the release of packets or quanta of acetylcholine into the synaptic clefts on the surface of the muscle fiber.

Acetylcholine causes the electrical resting potential under the motor end plate to change, and this then initiates an action potential which passes in both directions along the surface of the muscle fiber.

At the opening of each transverse tubule onto the muscle fiber surface, the action potential spreads inside the muscle fiber.

At each point where a transverse tubule touches part of the sarcoplasmic reticulum, it causes the sarcoplasmic reticulum to release Ca++ ions.

The calcium ions result in movement of troponin and tropomyosin on their thin filaments, and this enables the myosin molecule heads to “grab and swivel” their way along the thin filament. This is the driving force of muscle contraction.