Final answer:
The correct answer is a) Sodium flows in, and potassium flows out through the nicotinic receptor at the NMJ. Sodium's inward flow depolarizes the cell, potentially leading to an action potential and muscle contraction. Potassium's outward flow helps to reset the resting potential.
Step-by-step explanation:
The ions that pass through the nicotinic receptor at the neuromuscular junction (NMJ) are primarily sodium (Na+) and potassium (K+). The correct answer to the question, "What ions pass through the nicotinic receptor at the NMJ? What flows in and what flows out?" is a) Sodium flows in, and potassium flows out. When the neurotransmitter acetylcholine binds to the nicotinic receptor, it causes the receptor to open, which allows the rapid diffusion of Na+ ions into the cell. This creates an action potential which leads to muscle contraction. Following this, K+ ions flow out to reset the resting potential of the cell.
The flow of these ions changes the relative charge inside the neuron. Normally, the resting membrane potential is negative. The influx of Na+ ions disrupts this potential by making the inside of the cell less negative (depolarization). If depolarization is significant, it can lead to an action potential, a reversal of the normal membrane polarity, which travels along the neuronal or muscle cell membrane to trigger a physiological response, such as further neurotransmission or muscle contraction.
In the context of calcium ions (Ca2+), they are involved in the release of neurotransmitters at the synaptic cleft. Ca2+ ions do not pass through the nicotinic receptor, but they are actively transported into the sarcoplasmic reticulum and can diffuse out of the sarcoplasmic reticulum during muscle contraction and relaxation, respectively.