Question

Where does the acetylcholine that stimulates muscle contraction bind?

A. Receptors in the motor end plate
B. Receptors in the sarcoplasmic reticulum
C. Receptors in the axon terminal
D. Receptors in troponin

Answer 1

Acetylcholine, which initiates muscle contraction, binds to receptors on the muscle fiber sarcolemma at the motor end-plate of the neuromuscular junction.

Step-by-step explanation:

The acetylcholine (ACh) that stimulates muscle contraction binds to receptors located on the muscle fiber sarcolemma at the motor end-plate. This is part of the neuromuscular junction (NMJ), a specialized synaptic structure where motor neuron axons connect to the muscle fibers. When ACh is released from the axon terminals, it crosses the synaptic cleft and binds to these receptors on the sarcolemma.

This binding triggers the opening of ligand-gated ion channels, allowing cations to flow across the membrane and causing depolarization. Such depolarization initiates an action potential which ultimately leads to muscle contraction.

Answer 2

Acetylcholine binds to receptors in the motor end plate at the neuromuscular junction, causing depolarization of the sarcolemma and initiating muscle contraction. A is the correct option.

Step-by-step explanation:

The acetylcholine (ACh) that stimulates muscle contraction binds to receptors in the motor end plate. This area is part of the sarcolemma of the muscle fiber at the neuromuscular junction (NMJ).

The motor end plate contains ACh-receptors that, upon binding with acetylcholine, initiate a series of events leading to muscle contraction.

Specifically, the binding of acetylcholine to these receptors opens ligand-gated ion channels, causing depolarization of the sarcolemma and initiating an action potential, which is critical for muscle contraction.