Question

question 24 (1 point)
which of the following correctly lists the sequence of structures that action potentials must move through to excite skeletal muscle contraction?
sarcolemma,axon of neuron,t tubules
myofibrils,myofilaments,mitochondria
axon of neuron,sarcolemma,t tubules
t tubules,sarcolemma,myofilament

Explanation:

• When a nerve impulse (action potential) reaches the axon terminal of a motor neuron, it triggers the release of neurotransmitters.
• These neurotransmitters bind to receptors on the sarcolemma (muscle cell membrane), causing depolarization of the sarcolemma.
• The depolarization then spreads along the sarcolemma and into the T - tubules (invaginations of the sarcolemma). The T - tubules carry the action potential deep into the muscle fiber, which is crucial for the subsequent steps of muscle contraction (such as the release of calcium from the sarcoplasmic reticulum).
• Let's analyze each option:
• Option 1: The action potential starts in the axon of the neuron, not in the sarcolemma first. So, "Sarcolemma, axon of neuron, T tubules" is incorrect.
• Option 2: Myofibrils and myofilaments are involved in the contraction mechanism (e.g., sliding - filament theory), but the action potential does not move through myofibrils, myofilaments, and mitochondria in the sequence of excitation. Mitochondria are for energy production (ATP synthesis) for muscle contraction, not part of the action - potential - conduction sequence for excitation.
• Option 3: The action potential travels down the axon of the neuron, then depolarizes the sarcolemma, and then travels down the T - tubules. This is the correct sequence.
• Option 4: The action potential first depolarizes the sarcolemma and then moves into the T - tubules. So, "T tubules, sarcolemma, myofilament" is incorrect.

Answer:

C. Axon of neuron, sarcolemma, T tubules