The nerve impulse which leads to initiation of muscle contraction ?
**Core Concept**
The initiation of muscle contraction is a complex process involving the transmission of nerve impulses to muscle fibers. This process is mediated by the neuromuscular junction, where the release of neurotransmitters from the motor neuron leads to the depolarization of the muscle fiber membrane.
**Why the Correct Answer is Right**
The correct answer is related to the action potential that travels down the motor neuron and reaches the neuromuscular junction. The action potential causes the release of acetylcholine (ACh) from the motor neuron, which then binds to nicotinic acetylcholine receptors on the muscle fiber membrane. This binding leads to a rapid depolarization of the muscle fiber membrane, known as the end-plate potential. If the end-plate potential reaches threshold, it triggers an action potential in the muscle fiber, leading to muscle contraction.
**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because it does not specify the correct mechanism of muscle contraction initiation. While muscle contraction is indeed a result of action potentials in muscle fibers, the initiation of muscle contraction starts with the transmission of nerve impulses to the muscle fibers.
* **Option B:** This is incorrect because it refers to the contraction phase of muscle contraction, rather than the initiation of muscle contraction. Muscle contraction is a result of the sliding filament theory, where actin and myosin filaments slide past each other to produce muscle shortening.
* **Option C:** This is incorrect because it refers to the regulation of muscle contraction, rather than the initiation of muscle contraction. Muscle contraction can be regulated by various factors, including the neuromuscular junction, the muscle fiber membrane, and the contractile apparatus.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the initiation of muscle contraction is a result of the transmission of nerve impulses to muscle fibers, and that the neuromuscular junction plays a critical role in this process.
**Correct Answer: C. Action potential in motor neuron**