Question

The neuromuscular junction is equipped with a so-called safety factor that ensures that every nerve impulse that travels to the terminal of a motor neuron results in an action potential in the sarcolemma. Given a normal, healthy muscle, contraction is also ensured. The voltage sensitivity of the Ca++ channels in the presynaptic membrane and the high concentration of extracellular Ca++ ensure an influx of Ca++ sufficient to stimulate the fusion of synaptic vesicles to the presynaptic membrane and the release of acetylcholine. The overabundance of acetylcholine released guarantees a depolarization of the postsynaptic membrane and the firing of an action potential. What ensures that every nerve impulse that travels to the terminal of a motor neuron results in an action potential in the sarcolemma?

1) Safety factor
2) Voltage sensitivity of Ca++ channels
3) High concentration of extracellular Ca++
4) Fusion of synaptic vesicles
5) Overabundance of acetylcholine

Answer 1

The safety factor at the neuromuscular junction ensures that every nerve impulse results in an action potential in the muscle fiber's sarcolemma via mechanisms such as voltage-gated Ca++ channels and the release of acetylcholine.

Step-by-step explanation:

The neuromuscular junction is a critical site where the nervous system communicates with muscles, ensuring that every nerve impulse results in muscle contraction. The safety factor at the neuromuscular junction is essential, as it guarantees that an action potential in the motor neuron will reliably trigger an action potential in the muscle fiber's sarcolemma. This is achieved through the interplay of several components, including the voltage sensitivity of the Ca++ channels in the presynaptic membrane, the high concentration of extracellular Ca++ that drives a robust influx of calcium ions, and the subsequent release of an overabundance of acetylcholine into the synaptic cleft. The excess acetylcholine ensures that the postsynaptic membrane depolarizes sufficiently to trigger an action potential, leading to muscle contraction.