Which is the Primary site of propagation of action potential in a cutaneous sensory nerve?
**Core Concept**
The primary site of propagation of action potential in a cutaneous sensory nerve is the node of Ranvier, a specialized region of the myelinated nerve fiber. This concept is crucial in understanding the physiology of nerve conduction and the role of myelination in facilitating rapid transmission of signals.
**Why the Correct Answer is Right**
The node of Ranvier is a critical site where the action potential is generated and propagated. It is the site of high concentrations of sodium channels, which allow for the rapid influx of sodium ions and the generation of an action potential. The node of Ranvier is also the site where the action potential jumps from one node to the next, a process known as saltatory conduction. This mechanism allows for faster transmission of signals in myelinated nerves compared to unmyelinated nerves.
**Why Each Wrong Option is Incorrect**
**Option A:** The axon hillock is the site of integration of synaptic inputs and generation of action potential in the cell body of a neuron, not the primary site of propagation of action potential in a cutaneous sensory nerve.
**Option B:** The dendrites receive synaptic inputs from other neurons but are not the primary site of propagation of action potential in a cutaneous sensory nerve.
**Option C:** The terminal buttons or synaptic terminals are involved in the release of neurotransmitters into the synapse, but they are not the primary site of propagation of action potential in a cutaneous sensory nerve.
**Clinical Pearl / High-Yield Fact**
In clinical practice, demyelinating diseases such as multiple sclerosis can cause significant disruption to the node of Ranvier, leading to impaired nerve conduction and symptoms such as numbness, weakness, and vision loss.
**Correct Answer: C. The node of Ranvier is the primary site of propagation of action potential in a cutaneous sensory nerve.**