BEST MATCH
Which statement regarding the ligand-gated channel at the vertebrate neuromuscular junction is false? K+ travels through this channel when it is open. When the channel opens, ions depolarize the membrane. Two acetylcholine molecules need to bind to the intracellular side of the receptor. It binds acetylcholine.
The Correct Answer and Explanation is:
The false statement regarding the ligand-gated channel at the vertebrate neuromuscular junction is: “K+ travels through this channel when it is open.”
Explanation:
At the vertebrate neuromuscular junction, the primary receptor involved is the nicotinic acetylcholine receptor (nAChR). When acetylcholine (ACh) is released from the motor neuron and binds to the receptor, it opens the ion channel, allowing ions to flow across the membrane.
- Ions depolarize the membrane: This statement is true. When the nicotinic acetylcholine receptor opens, it allows positively charged ions, primarily Na+ (sodium ions), to flow into the muscle cell, which depolarizes the membrane. This depolarization is essential for initiating muscle contraction.
- Two acetylcholine molecules bind to the receptor: This statement is also true. For the nicotinic acetylcholine receptor to open, two molecules of acetylcholine must bind to the receptor, one to each of the two α-subunits. This binding causes a conformational change in the receptor, opening the ion channel.
- It binds acetylcholine: This is true as well. The nicotinic acetylcholine receptor specifically binds to the neurotransmitter acetylcholine, which is released from the presynaptic terminal of the motor neuron into the synaptic cleft.
- K+ travels through the channel: This is false. While potassium (K+) is present in the extracellular fluid, it is not the primary ion that travels through the nicotinic acetylcholine receptor channel. When the receptor opens, the influx of Na+ ions is much more significant than the efflux of K+ ions. This results in depolarization of the muscle cell membrane. Although some K+ ions may leave the cell, the net effect is the influx of Na+, not K+ movement.
Therefore, the false statement is: “K+ travels through this channel when it is open.” The main ion moving through the ligand-gated channel is Na+, not K+.
