NETTER - Neuroscience Flash Cards

Conduction Velocity
1. Node (site of action potential reinitiation)
2. Nodes of Ranvier
3. Myelin sheath
4. Axolemma
5. Axoplasm
Comment: An action potential is triggered in a neuronal cell
membrane when sufficient depolarization has occurred to allow
the influx of sodium ions to overwhelm the capacity of the efflux of
potassium ions to counter the influx of positive charge. This results in
an explosive depolarization that moves the neuronal cell membrane
toward its sodium equilibrium potential (approximately +55 mV). An
action potential at one node exerts enough local influence on the
adjacent node (and perhaps several distant nodes) to bring those
sites to a depolarized state sufficient to trigger an action potential.
This process reinitiates the action potential at each node. If a local
anesthetic is used to block the excitability (capacity to depolarize)
at several successive nodes, then a conduction block will occur
and propagation of the action potential will cease. The conduction
velocity of an axon depends upon the axonal diameter, also a
reflection of the extent of myelination.
Overview of the Nervous System See book 1.15