What term describes the electrical signal that rapidly depolarizes and repolarizes the muscle cell membrane and propagates along the sarcolemma and into T-tubules?

What term describes the electrical signal that rapidly depolarizes and repolarizes the muscle cell membrane and propagates along the sarcolemma and into T-tubules?

• A. Action potential
• B. End-plate potential
• C. Depolarization
• D. Graded potential

Answer: (A)

The signal described is the action potential. It is an electrical impulse that rapidly depolarizes and then repolarizes the muscle cell membrane and travels across the sarcolemma, continuing into the T-tubules so the interior of the muscle fiber is reached. This propagation is an all-or-none event driven by voltage-gated ion channels: sodium channels open to depolarize, then potassium channels help repolarize, allowing the impulse to travel along the entire membrane and into the T-tubule system to trigger calcium release and contraction. This differs from an end-plate potential, which is a local, not-to-be-confined depolarization at the neuromuscular junction caused by acetylcholine binding. It can initiate an action potential but it itself does not propagate along the membrane into the T-tubules. Depolarization describes the process of membrane potential becoming less negative, which is part of the action potential but does not capture the traveling, all-or-none nature. Graded potentials are variable, decremental signals that occur locally and do not reliably propagate to induce the full muscle fiber response.

The signal described is the action potential. It is an electrical impulse that rapidly depolarizes and then repolarizes the muscle cell membrane and travels across the sarcolemma, continuing into the T-tubules so the interior of the muscle fiber is reached. This propagation is an all-or-none event driven by voltage-gated ion channels: sodium channels open to depolarize, then potassium channels help repolarize, allowing the impulse to travel along the entire membrane and into the T-tubule system to trigger calcium release and contraction.

This differs from an end-plate potential, which is a local, not-to-be-confined depolarization at the neuromuscular junction caused by acetylcholine binding. It can initiate an action potential but it itself does not propagate along the membrane into the T-tubules. Depolarization describes the process of membrane potential becoming less negative, which is part of the action potential but does not capture the traveling, all-or-none nature. Graded potentials are variable, decremental signals that occur locally and do not reliably propagate to induce the full muscle fiber response.