The point of contact between a motor neuron and a skeletal muscle cell is the ...

• A. Muscle fiber
• B. Nucleus
• C. Neuromuscular junction
• D. Dendrites

Answer: (C)

At the contact point where a nerve signal is translated into a muscle response, the key structure is the neuromuscular junction. Here, the motor neuron releases acetylcholine into the synaptic cleft. This neurotransmitter binds to receptors on the muscle cell’s motor end plate, opening ion channels and depolarizing the sarcolemma to create an end-plate potential. The depolarization then propagates along the muscle fiber, triggering calcium release from the sarcoplasmic reticulum, which enables the actin-myosin interactions that cause contraction. The other options aren’t contact points between a neuron and muscle: a muscle fiber is the muscle cell itself, a nucleus is a cell’s genetic control center, and dendrites are neuronal input structures.