Question

The movement of sodium ions through the chemically regulated ion channel initiates depolarization of the motor end plate. What happens after this depolarization is generated?

A. The motor end plate repolarizes.
B. The T-tubules contract.
C. An action potential is propagated along the sarcolemma and the T-tubules.
D. Acetylcholine is reabsorbed by the synaptic vesicles.

Answer 1

Following the depolarization at the motor end plate, an action potential spreads along the sarcolemma and down the T-tubules, leading to the release of Ca2+ from the sarcoplasmic reticulum and initiating muscle contraction.

Step-by-step explanation:

After the depolarization of the motor end plate is generated, the action potential that has begun at the motor end plate continues its journey. As positively charged sodium ions (Na+) enter, they trigger an action potential that rapidly spreads along the entire membrane of the muscle fiber, including the T-tubules. This series of events can be summarized as follows:

• Acetylcholine (ACh), a neurotransmitter, is released from the axon terminal of the motor neuron and binds to receptors on the sarcolemma.
• The binding of ACh to its receptors triggers the opening of sodium ion channels, resulting in rapid depolarization.
• The action potential, once initiated, travels down the sarcolemma and down the T-tubules.
• The spreading action potential causes Ca2+ to be released from the sarcoplasmic reticulum (SR) into the sarcoplasm.
• The released calcium ions then initiate muscle contraction.

Therefore, the correct answer to the question is C. An action potential is propagated along the sarcolemma and the T-tubules.