28. Nervous fibres. Types, structural, ultrastructural, chemical and functional characteristics.

A nerve fibre consists of an axon and a __________.

myelin sheath

Type A fibres are the __________ and fastest conducting nerve fibres.

thickest

The diameter of Type A fibres ranges from __________ microns.

1.50-20.00

Type A fibres have a speed of conduction ranging from __________ m/sec.

4-120

Type B fibres are __________ in size.

medium

The diameter of Type B fibres ranges from __________ microns.

1.50-3.50

Type C fibres are the __________ and thinnest nerve fibres.

smallest

Type C fibres are __________ (myelinated/non-myelinated).

non-myelinated

The diameter of Type C fibres ranges from __________ microns.

0.1-2.0

The speed of conduction for Type C fibres is __________ m/sec.

0.5-4.0

Myelinated fibres form the bulk of the __________ nerves.

somatic

The speed of transmission in myelinated nerve fibres is increased through __________ conduction.

saltatory

Neurolemmal sheath is necessary for __________ of a damaged nerve.

regeneration

Endoneurium is a thin layer of __________ tissue that surrounds the neurolemmal sheath.

loose connective

nerve fibre

thread-like extension of nerve cell and consists of axon and myelin sheath, present in CNS and PNS, 3 main types ABC

all have a neurolemmal sheath, which are from Schwann cells in the PNS

type A

• thickest and fastest

• myelinated

• diameter of 1.5-20 um

• 4-120m/sec

• have skeletomotor fibres, fusimotor fibres and afferent fibres to skin

type B

• medium size

• myelinated

• diametre of 1.5-3.5 um

• 3-15m/sec speed conduction

• slower than type A fibres

• example : preganglionic autonomic efferents

type C

• smallest and thinnest

• non-myelinated

• diameter of 0.1-0.2 um

• 0.5-4m/s

• slowest conduction

• example : postganglionic autonomic efferent and afferent fibres to skin

what do myelinated fibres form?

bulk of somatic nerves, consist of the axoplasm and covered by axolemma

neurolemmal sheath function

for regeneration of damaged nerve fibres and support of myelinated axons.

endoneurium

loose connective tissue surrounding individual nerve fibers, providing support and protection

surround all the neurolemmal sheath by virtue, can regenerate after damage