Question

In the neuromuscular junction, acetylcholine receptor binding sites are found on the ________.

1) α-subunits
2) β-subunits
3) δ-subunits
4) ε-subunits

Answer 1

Acetylcholine receptor binding sites at the neuromuscular junction are found on the α-subunits of the nicotinic acetylcholine receptors in the muscle fiber's sarcolemma, initiating muscle contraction upon ACh binding.

Step-by-step explanation:

In the neuromuscular junction (NMJ), acetylcholine receptor binding sites are predominantly found on the α-subunits of the nicotinic acetylcholine receptor. These receptors are located on the motor endplate, specifically within the sarcolemma of the muscle fiber. When acetylcholine (ACh) is released from the presynaptic neuron, it crosses the synaptic cleft and binds to these receptors, thereby initiating a sequence of events that leads to muscle contraction.

The binding of ACh to the α-subunits is critical for the activation of the receptor and subsequent opening of its associated ion channel, which allows Na+ ions to enter the muscle cell and trigger depolarization. This depolarization is known as the end-plate potential, which then leads to the generation of an action potential that propagates along the muscle fiber, causing it to contract.