Parts/structure and terminology of PNS

P. 225

what does the PNS consist of?

12 cranial and 31 spinal nerves

ganglia and sensory receptors

where does sensory nerves originate?

dorsal root ganglion

where do motor nerves originate?

anterior horn of spinal cord

what two nerves are the autonomic neurons divided into?

sympathetic

parasympathetic

where do sympathetic nerves originate?

lateral horn of thoracic spinal cord

where do parasympathetic nerves originate?

lateral grey horn of sacral level of sc and brain

what are the cutaneous end-organ receptors in the PNS?

thermoreceptors

nociceptors

mechanoreceptors

chemoreceptors

photoreceptors

Axon

conducts impulses

dendrite

receives signals

motor unit

a single motor neuron and all muscle fibers that innervates it

myelin

sheath of proteins and lipids that inc conduction of nerve impulses

nerve conduction velocity

measures nerve of speed impulses along axon

neurons

nerve cells that receive and send signals to other cells

dendrites, axon, cell body

nodes of Ranvier

brief gaps in myelination of an axon

facilitates rapid conduction of nerve impulses via jumping gap node → gap node

saltatory conduction

action potential moving along axon by jumping from node to node

dec use of sodium - potassium pumps and inc speed of conduction

Schwann cells

cover nerve fibers w/in PNS

form myelin sheath

A fibers

large

myelinated

high conduction rate

alpha, beta, gamma, delta subsets

B fibers

medium fibers

myelinated

reasonably fast conducting

preganglionic fibers of autonomic system

C fibers

small fibers

poorly myelinated or unmyelinated

slow conduction rate

postganglionic fibers of sympathetic system

exteroceptors for pain, temp, touch