Final answer:
Acetylcholine must bind to receptors on the muscle cell's sarcolemma, triggering an action potential that causes the release of calcium ions for muscle contraction.
Step-by-step explanation:
In order to excite a muscle cell, acetylcholine must bind to receptors on the muscle cell membrane, initiating a series of events leading to muscle contraction. When acetylcholine (ACh) is released from the motor neuron, it crosses the synaptic cleft and attaches to ACh receptors on the sarcolemma of the muscle fiber.
This binding opens ion channels, allowing Na+ ions to influx and cause depolarization, leading to an action potential along the sarcolemma. This action potential triggers the release of calcium ions (Ca2+) from the sarcoplasmic reticulum, which then interact with actin to facilitate actin-myosin cross-bridging and muscle contraction as per the sliding filament theory.