Question

Which current is NOT present in the skeletal muscle excitation, EC coupling, contraction and relaxation processes?

a. voltage gated Na+ influx into the neuron from the extracellular environment
b. voltage gated Ca2+ influx into the neuron from the extracellular environment
c. voltage gated Na+ influx into the muscle cell from the extracellular environment
d. voltage gated Ca2+ influx into the muscle cell from the extracellular environment
e. voltage gated K+ efflux out of the muscle cell from the intracellular environment

Answer 1

The correct answer is b, voltage-gated Ca2+ influx into the neuron from the extracellular environment, which is not involved in skeletal muscle's excitation-contraction coupling, contraction, or relaxation.

Step-by-step explanation:

The current not present in the skeletal muscle excitation, excitation-contraction (EC) coupling, contraction, and relaxation processes is the voltage gated Ca2+ influx into the neuron from the extracellular environment. During the EC coupling in skeletal muscles, the action potential generated in the neuron's axon triggers the release of acetylcholine at the neuromuscular junction, which then causes the sarcolemma of the muscle to depolarize. This depolarization leads to the opening of voltage-gated sodium channels in the muscle cell membrane, causing an influx of Na+ ions. Concurrently, the depolarization causes voltage-gated calcium channels in the sarcoplasmic reticulum to release Ca2+ into the muscle fiber's sarcoplasm, initiating muscle contraction. On the other hand, voltage-gated calcium channels in neurons are involved in neurotransmitter release, but not directly in the muscle fiber's EC coupling and contraction.