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Old 07-14-2011, 02:18 PM
Wrangler Wrangler is offline
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Join Date: Dec 2010
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Default Question about events at the neuromuscular junction?

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?

A) Acetylcholine is degraded by acetylcholinesterase.
B) Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis.
C) Acetylcholine diffuses away from the cleft.
D) Acetylcholine is transported back into the axon terminal by a reuptake mechanism.


The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?

A) Acetylcholine is released by axon terminals of the motor neuron.
B) Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein.
C) Acetylcholine is released and moves across the synaptic cleft bound to a transport protein.
D) When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal.


Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons :

A) extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber
B) extend from the brain to the sarcolemma of a skeletal muscle fiber
C) extend from the spinal cord to the sarcolemma of a skeletal muscle fiber
D) arise in the epimysium of a skeletal muscle and extend to individual skeletal muscle fibers

Calcium entry into the axon terminal triggers which of the following events?

A) Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.
B) Cation channels open and sodium ions enter the axon terminal while potassium ions exit the axon terminal.
C) Acetylcholine binds to its receptor.
D) Acetylcholine is released into the cleft by active transporters in the plasma membrane of the axon terminal.


Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

A) the opening of voltage-gated calcium channels
B) the opening of ligand-gated anion channels
C) the opening of calcium-release channels
D) the opening of ligand-gated cation channels


Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

A) The outside surface of the sarcolemma is negatively charged compared to the inside surface. Sodium ions diffuse outward along favorable chemical and electrical gradients.

B) The outside surface of the sarcolemma is negatively charged compared to the inside surface. Potassium ions diffuse outward along favorable chemical and electrical gradients.

C) The inside surface of the sarcolemma is negatively charged compared to the outside surface. Potassium ions diffuse inward along favorable chemical and electrical gradients.

D) The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.
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