Final answer:
Lower motor neurons release acetylcholine, which binds to nicotinic acetylcholine receptors at the neuromuscular junction of jaw muscles, leading to depolarization, action potential generation, and muscle contraction.
Step-by-step explanation:
The lower motor neurons drive the jaw by releasing a neurotransmitter known as acetylcholine (ACh). This occurs during processes such as chewing, speaking, and other movements involving the jaw. When an action potential reaches the axon terminal of a motor neuron, it induces the opening of voltage-gated calcium channels. The influx of calcium ions triggers the fusion of synaptic vesicles with the presynaptic membrane and subsequent release of acetylcholine into the synaptic cleft.
Once acetylcholine is released into the synaptic cleft of the neuromuscular junction, it binds to nicotinic acetylcholine receptors on the postsynaptic membrane of the muscle fiber. This action opens ion channels, allowing positive ions (Na+) to enter the muscle cell, leading to depolarization and the generation of an action potential within the muscle fiber. This electrical event triggers muscular contraction and thereby enables movement of the jaw.