Neurophysiology: Conduction Velocity (axon diameter)

Chapter 11.6

Speed of AP movement down the axon is determined by…

Axon Diameter: larger the diameter, faster the impulse

Myelination: continuous vs saltatory conduction; degree of myelination (sheath thickness)

A Fibers

Faster (15-120 m/s)

large (5-20microm); myelinated, short ARP (absolute refractory period)

Sense Danger- do something about it FAST

1. motor neurons to skeletal muscles

2. sensory neurons (touch, temp, joint position)

B fibers

Slower

Smaller, light myelination, longer ARP and A’s

Visceral sensory

autonomic moto neurons

C Fibers

Slowest

Smallest; unmyelinated, longest ARP

myelination axons

myelin does not conduct electricity; it is an insulator that prevents ion movement

electrical currents only at the nodes of Ranvier

high concentration of V-G Na+ Channels at nodes

APs jump from one node to the next

Advantages of Saltatory Conduction

Less energy expended by Na+/K+ pump to resent RMP

increased conduction speed

smaller axon diameters

*allows people to have small diameter axons with rapid APs, rather than space consuming large diameter axons 

What is the purpose of generating and propagating an AP down the axon to the axon terminal branches?

Releases of chemicals stored in vesicles

• chemicals are used to transmit information from the neurons to another cell, with myelination it can be done quickly