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# 3-Peak Compound Action Potential

NEURO-PJXV45

When you electrically stimulate a peripheral, sensory nerve and record the compound action potential at the dorsal root ganglion of the spinal cord (the summation of all action potentials occurring across all axons in the nerve), there appear to be three different peaks as shown in the figure below.

Which of the following are potential reasons why this might occur? Select ALL that apply.

A

Myelination – Not all axons in the dorsal root are myelinated. Because myelin acts as an insulator, action potentials in myelinated axons arrive at the dorsal root ganglion earlier than the action potentials in unmyelinated axons.

B

Axon length – Not all axons in the dorsal root are the same length. Because action potentials must travel from nerve endings to the dorsal root, action potentials in longer axons that have more distant nerve endings arrive later than action potentials in shorter axons with closer nerve endings.

C

Axon diameter – Not all axons in the dorsal root are the same diameter. Because the diameter of the axon affects how quickly current can flow down the axon, action potentials in large diameter axons arrive earlier than action potentials in small diameter axons.

D

Neurotransmitter – Not all axons in the dorsal root carry the same neurotransmitters. Because some neurotransmitters have faster kinetics than others, action potentials from axons with fast synaptic transmission arrive earlier than action potentials from axons with slow synaptic transmission.