ANATOMY

Detailed explanation-1: -As a neurotransmitter binds, these ion channels open, and Na+ ions cross the membrane into the muscle cell. This reduces the voltage difference between the inside and outside of the cell, which is called depolarization.

Detailed explanation-2: -Activation of the nAChR leads to an influx of cations (sodium and calcium) that causes depolarization of the muscle cell membrane. This depolarization in turn activates a high density of voltage-gated sodium channels on the muscle membrane, eliciting an action potential.

Detailed explanation-3: -In muscle: Release of acetylcholine from the nerve terminal. The channels are opened by depolarization (an increase in membrane potential) of the nerve terminal membrane and selectively allow the passage of calcium ions. In muscle: The frequency of contraction.

Detailed explanation-4: -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.

Detailed explanation-5: -Cell membrane depolarization is stimulated by nerve impulses arriving at the neuromuscular junction. Following the generation of a sufficient motor endplate potential, depolarization occurs along the sarcolemmal membrane.