The Peripheral Nervous System

peripheral nervous system

all neural structures distal to the spinal cord consisting of parallel bundles of axons

endoneurium

connective tissue sheath of peripheral nervous system; individual axons

perineurium

connective tissue sheath of peripheral nervous system; bundles of axons

epineurium

connective tissue sheath of peripheral nervous system; entire nerve trunk

7-130 m/sec (typically 90-120)

conduction speed of large myelinated axons

A-alpha

efferent axon group for large myelinated axons

extrafusal muscle fibers

large myelinated efferent axons innervate

Ia, IIb, II

afferent axon group for large myelinated axons

spindles, Golgi tendon organs, touch and pressure receptors

large myelinated afferent axons innervate (4)

2-10 m/sec

medium myelinated axons conduction speed

A-gamma

medium myelinated efferent axons group

intrafusal muscle fibers

medium myelinated efferent axon groups

12-45 m/s, 4-25 m/sec

small myelinated axons conduction speed

B

small myelinated efferent axon group

presynaptic autonomic

small myelinated efferent axons innervate

A-beta

small myelinated afferent axon group

pain, temperature, visceral receptors

small myelinated afferent axons innervate

0.2-2.0 m/s

unmyelinated axons conduction speed

C

unmyelinated efferent axon group

postsynaptic autonomic

unmyelinated efferent axons innervate

C

unmyelinated afferent axon group

pain, temperature, visceral receptors

unmyelinated afferent axons innervate

mononeuropathy

peripheral nerve disorder affecting a single nerve; example: carpal tunnel

multiple mononeuropathy

peripheral nerve disorder affecting many single nerves; examples: diabetes, inflammation of blood vessels

radiculopathy

peripheral nerve disorder; damage to spinal nerve; example: disc herniation, foraminal stenosis

polyneuropathy

peripheral nerve disorder affecting many nerves; example: diabetes (more common), Guillain-Barre

I

Sunderland Classification

Pathoanatomy: disruption of axonal myelin

Prognosis: complete recovery occurs over a period of days to 3 months

neurapraxia

Seldon Classification

Pathoanatomy: disruption of axonal myelin

Prognosis: complete recovery occurs over a period of days to 3 months

II

Sunderland Classification

Pathoanatomy: disruption of myelin and axon but endoneurium intact

Prognosis: complete recovery occurs, in anatomic order, and time to recovery is a function of the rate of axonal regeneration

III

Sunderland Classification

Pathoanatomy: disruption of myelin, axon, and endoneurium but perineurium intact

Prognosis: incomplete recovery occurs because of disruption of endoneurium allow some regenerating axons to become misrouted; the rate of recovery occurs at the same rate as a class II injury

IV

Sunderland Classification

Pathoanatomy: disruption of myelin, axon, endoneurium, and perineurium, but epineurium intact

Prognosis: recovery does not occur unless surgical repair is undertaken

axonotmesis

Seddon Classification

Consists of Sunderland classifications II-IV

V

Sunderland Classification

Pathoanatomy: complete nerve transection

Prognosis: recovery does not occur unless surgical repair is undertaken

VI

Sunderland Classification

Pathoanatomy: a mixed nerve lesion in which a combination of degrees of nerve injury are present in the same segment of nerve

Prognosis: recovery of each part is dependent on the degree of injury as described above

neurotmesis

Seddon Classification

Consists of Sunderland classifications V-VI