College of Massage Therapists of British Columbia (CMTBC) Practice Exam

Which neurotransmitter is responsible for initiating an action potential at the neuromuscular junction?

1. Dopamine

2. Acetylcholine

3. Norepinephrine

4. Serotonin

The correct answer is: Acetylcholine

At the neuromuscular junction, acetylcholine plays a crucial role in initiating an action potential in muscle fibers. When a motor neuron releases acetylcholine into the synaptic cleft, it binds to specific receptors on the muscle cell membrane, leading to depolarization of the muscle fiber. This depolarization is what triggers an action potential, allowing for muscle contraction to occur. Acetylcholine is essential for this process because it is the primary neurotransmitter involved in communication between motor neurons and skeletal muscle. The binding of acetylcholine to its receptors opens ion channels, allowing sodium ions to flow into the muscle cell, thereby generating an action potential that eventually results in muscle contraction. The other neurotransmitters listed, such as dopamine, norepinephrine, and serotonin, have different roles and functions in the nervous system but are not directly implicated in initiating action potentials at the neuromuscular junction. Dopamine is primarily associated with reward and pleasure mechanisms, norepinephrine plays a role in arousal and the fight-or-flight response, and serotonin is involved in mood regulation. Therefore, acetylcholine is the correct neurotransmitter for this specific function at the neuromuscular junction.