Biology (Mader), 10th Edition

Chapter 39: Locomotion and Support Systems

Function of the Neuromuscular Junction

How are nerves and muscles connected? Nerves and muscles are connected through synapses in the same way that different neurons are connected to one another. Acetylcholine is the neurotransmitter used by the motor neurons to stimulate action potentials in the muscle cells. When an action potential reaches the end of a neuron, the acetylcholine is released and a new action potential begins in the muscle tissue. Nerves connecting to muscles are called motor neurons. Each neuromuscular junction is connected to a bundle of muscle fibers. A motor neuron may branch several times and connect to several bundles. All of these bundles will contract together upon getting a signal from the motor neuron.

View the animation below, then complete the quiz to test your knowledge of the concept.



1.

An action potential arriving at the presynaptic terminal causes...
A)voltage-gated sodium ion channels to open, and sodium ions to diffuse into the cell.
B)voltage-gated sodium ion channels to open, and sodium ions to diffuse out of the cell.
C)voltage-gated calcium ion channels to open, and calcium ions to diffuse into the cell.
D)acetylcholine to diffuse into the cell.
E)ligand-gated sodium channels to open, and sodium ions to diffuse out of the cell.
2.

In the neuromuscular junction, acetylcholine...
A)diffuses across the synaptic cleft and binds to acetylcholine receptors on the postsynaptic muscle fiber.
B)is actively transported across the synaptic cleft and binds to acetylcholine receptors on the postsynaptic muscle fiber.
C)diffuses across the synaptic cleft and causes calcium ions to diffuse into the postsynaptic muscle fiber.
D)diffuses across the synaptic cleft and causes sodium ions to diffuse out of the postsynaptic muscle fiber.
E)is actively transported across the synaptic cleft and causes calcium ions to diffuse into the postsynaptic muscle fiber.
3.

The neurotransmitter in the neuromuscular junction...
A)causes ligand gated calcium channels in the muscle fiber to increase their permeability to calcium, which depolarizes the postsynaptic membrane.
B)causes ligand gated sodium channels in the muscle fiber to increase their permeability to sodium, which depolarizes the postsynaptic membrane.
C)increases the calcium ion permeability of the presynaptic membrane.
D)increases the sodium ion permeability of the presynaptic membrane.
E)depolarizes the presynaptic membrane by increasing the permeability of sodium ions.
4.

Acetylcholine is broken down into acetic acid and cholinesterase by choline.
A)True
B)False
5.

Once threshold is reached on the postsynaptic membrane, an action potential is generated and propagated over the muscle cell membrane.
A)True
B)False
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