MICROANATOMY

Detailed explanation-1: -Synaptic transmission at the neuromuscular junction begins when an action potential reaches the presynaptic terminal of a motor neuron, which activates voltage-gated calcium channels to allow calcium ions to enter the neuron.

Detailed explanation-2: -Na+ channels are clustered at the neuromuscular junction (NMJ) and are responsible for generation of the muscle action potential.

Detailed explanation-3: -The Na+ entering the cell depolarizes the sarcolemma which then will cause the voltage-gated Na+ channels to open, initiating an action potential that spreads out from the neuromuscular junction. The action potential not only travels across the sarcolemma, but also down the T tubules.

Detailed explanation-4: -Upon depolarization, an action potential travels down the axon, causing voltage-gated calcium channels to open, resulting in an influx of calcium ions into the nerve terminal.

Detailed explanation-5: -Answer and Explanation: The correct answer is (b): Depolarization occurs when sodium ions enter into the muscle fiber cell causing the membrane potential to move towards +30 mV. Cholinergic receptors embedded in sarcolemma are ligand-gated sodium channels that open when they bind acetylcholine.