Which is the Primary site of propagation of action potential in a cutaneous sensory nerve?
ANSWER: (A) Axon hillockREF: Guyton 12th Ed. Page 67, Ganong 24th Ed Pg 91GENERATION OF ACTION POTENTIAL IN POST SYNAPTIC REGION:The portion of the cell with the lowrest threshold for the production of a full-fledged action potential is the initial segment, the portion of the axon at and just beyond the axon hillock. This unmyelinated segment is depolarized or hyperpolarized electrotonically by the current sinks and sources under the excitatory and inhibitory synaptic knobs. It is the first part of the neuron to fire, and its discharge is propagated in two directions: down the axon and back into the somaThe nerve cell membrane is polarized at rest with positive charges lined up along the outside of the membrane and negative inside. During the action potential there is a reversal of the polarity for a brief period. A current sink is created which initiates depolarization and a local response and when a firing level Is reached the popagated response results.The spatial distribution of ion channels along the axon plays a key role in the initiation and regulation of the action potential. Voltage gated sodium channels are highly concentrated in the nodes of ranvier and the initial segment in the myelinated neurons. And most of the cutaneous nerve fibres are myelinated. Hence the site of propagation is the axon hillock.
Axon hillock
Dendritic spine
Axoplasm
Axon terminal
Nerve Physiology