Question

When acetylcholine binds to and opens the acetylcholine receptor-channel, both Na+ and K+ can potentialy move through the now-open channel. However, one of these two ions ( K+ or Na+ ) is far more permeable when the channel opens. Answer the folfowing questions: 1. Which ion can more easily diffuse across the membrane as soon as the channel opens 2. Justify your answer to the above question 3. What effect does opening the channel have on the membrane potential of the muscle cell?

Answer 1

Sodium ions (Na+) can more easily diffuse across the membrane when the acetylcholine receptor-channel opens, leading to a rapid depolarization and the initiation of an action potential which is key in muscle contraction.

Step-by-step explanation:

When acetylcholine binds to and opens the acetylcholine receptor-channel at the neuromuscular junction, sodium ions (Na+) can more easily diffuse across the membrane as opposed to potassium ions (K+). This is due to the electrochemical gradient that favors the influx of Na+ into the muscle cell which is relatively low inside the cell in comparison to the outside. When the channel opens, Na+ ions rush into the cell, and K+ ions move out, but the permeability to Na+ is greater, thus Na+ influx predominates.

The opening of these ligand-gated ion channels causes a rapid depolarization as the membrane potential becomes more positive. This depolarization is an electrical event known as an action potential, which is crucial for initiating a muscle contraction. As the membrane depolarizes, another set of ion channels called voltage-gated sodium channels are triggered to open, allowing even more Na+ to enter the muscle fiber and spreading the action potential along the entire membrane.