At the neuromuscular junction, what event leads to the generation of an end plate potential?

At the neuromuscular junction, what event leads to the generation of an end plate potential?

• A. Acetylcholine binding to its receptor and opening Na+/K+ channels
• B. Release of calcium from the SR
• C. ATP hydrolysis by myosin
• D. Depolarization of the T‑tubules

Answer: (A)

The end plate potential starts when acetylcholine released from the motor neuron binds to nicotinic receptors on the motor end plate. These receptors are ligand-gated ion channels that open to let Na+ (and some K+) flow across the membrane, producing a net inward current. This depolarizes the end plate region, creating the local end plate potential. If this depolarization is large enough, it triggers an action potential in the muscle fiber. Other steps—calcium release from the sarcoplasmic reticulum, ATP hydrolysis by myosin, or depolarization of the T-tubules—occur later in excitation-contraction coupling and are not what generates the end plate potential itself.

The end plate potential starts when acetylcholine released from the motor neuron binds to nicotinic receptors on the motor end plate. These receptors are ligand-gated ion channels that open to let Na+ (and some K+) flow across the membrane, producing a net inward current. This depolarizes the end plate region, creating the local end plate potential. If this depolarization is large enough, it triggers an action potential in the muscle fiber. Other steps—calcium release from the sarcoplasmic reticulum, ATP hydrolysis by myosin, or depolarization of the T-tubules—occur later in excitation-contraction coupling and are not what generates the end plate potential itself.