Muscle contraction occurs when a motor neuron sends a signal (Ach) to the muscle cell, depolarizing it, and triggering contraction. The correct option is A. 2,4,3,1,5.
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How does muscle contraction occur?</h3>
Just before muscle contraction occurs, there is a sequence of events that involve motor neurons, neurotransmitters, and ion flow.
1) The central nervous system generates an action potential that travels to the muscle fiber activating the calcium channels.
2) Calcium triggers vesicle fusion to the presynaptic membrane releasing acetylcholine (Ach) into the synaptic space.
3) Once released, Ach moves forward to the postsynaptic membrane of the skeletal muscle fiber where it binds to its receptors causing ion channels to open.
4) Positively charged sodium ions cross the membrane to get into the muscle fiber (sarcoplasm) and potassium leaves the cell.
5) The difference in charges caused by these ion transport charges positively the muscle fiber membrane. It depolarizes.
6) The action potential enters the t-tubules depolarizing the inner portion of the muscle fiber. Contraction initiates.
The correct sequence is as follows,
2. impulse reaches axon's synaptic knob.
4. Synaptic vesicles fuse with neuron's membrane and release ACh via exocytosis.
3. Ach binds to receptors on the muscle cell membrane.
1. sodium channels open and sodium flows in.
5. If enough sodium moves in to the muscle cell, an impulse (action potential) develops.
The correct option is A. 2,4,3,1,5.
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