Biological Systems MCAT Practice Exam

Which neurotransmitter is primarily involved in the neuromuscular junction?

1. Dopamine

2. Serotonin

3. Acetylcholine

4. Norepinephrine

The correct answer is: Acetylcholine

Acetylcholine is the neurotransmitter that plays a pivotal role at the neuromuscular junction, which is the synapse between a motor neuron and a muscle fiber. When an action potential travels down a motor neuron, it triggers the release of acetylcholine from the neuron’s synaptic vesicles into the synaptic cleft. Once in the synaptic cleft, acetylcholine binds to nicotinic acetylcholine receptors on the muscle membrane (sarcolemma), leading to the influx of sodium ions into the muscle cell and the generation of an action potential in the muscle fiber. This action potential ultimately results in muscle contraction. This specific mechanism highlights the critical function of acetylcholine in enabling communication between the nervous system and muscular system, facilitating voluntary movements. Other neurotransmitters like dopamine, serotonin, and norepinephrine play significant roles in other aspects of nervous system function, such as mood regulation, emotion, and the autonomic nervous system, but they are not primarily involved in the communication at the neuromuscular junction.