Post on 22-Jan-2018
WALLERIAN DEGENERATION
AND REGENERATION
PRESENTED BY:
DR. LAKSHMI PAVANI P. (PT)
CONTENTS
INTRODUCTION
CLASSIFICATION OF NERVE INJURIES
INJURY OF THE NERVE CELL BODY
INJURY OF THE NERVE CELL PROCESS
CHANGES IN THE DISTAL SEGMENT OF THE AXON
CHANGES IN THE PROXIMAL SEGMENT OF THE AXON
CHANGES IN THE NERVE CELL BODY
RECOVERY OF THE NEURONS FOLLOWING INJURY
REGENERATION OF AXONS IN THE PERIPHERAL NERVES
REGENERATION OF AXONS IN THE CNS
WALLERIAN
DEGENERATION
REGENERATION
INTRODUCTION
Neuron is the basic functional unit of the nervous system.
In the mature human, if it is destroyed, it is not replaced.
It may be injured due to various reasons(cutting, crushing, pull & pressure).
These injuries may damage a nerve variously & the injury is classified according to the
extent of the damage.
SEDDON’S CLASSIFICATION OF NERVE
INJURY
Seddon (1944) described 3 clinical types of nerve injury:
Neurapraxia (class I)
The term applied to a transient block
Paralysis is incomplete, recovery is rapid & complete, & there is no nerve degeneration
Pressure is the most common cause
Axonotmesis (class II)
The term applied to a nerve lesion in which the axons are damaged but the surrounding
connective tissue sheaths remain intact
Wallerian degeneration occurs peripherally
Functional recovery is more rapid & more complete than after complete section of the
nerve trunk
Crush injuries, traction, & compression are the most common causes
Neurotmesis (class III)
The term applied to complete section of the nerve trunk
Occur on severe contusion, stretch, laceration
Surgical repair is required.
SUNDERLAND’S CLASSIFICATION
Sunderland (1951) expanded seddon’s classification to 5 degrees:
First-degree (class I) : seddon’s neurapraxia & first-degree are the same
Second-degree (class II) : seddon’s axonotmesis & second-degree are the same
Third-degree (class II):
Nerve fiber interruption
There is a lesion of the endoneurium, but the epineurium & perineurium remain intact
Recovery from a third-degree injury is possible, but surgical intervention may be required
Fourth-degree (class II):
Only the epineurium remain intact
Surgical repair is required
Fifth-degree (class III):
seddon’s neurotmesis
Lesion of complete transection of the nerve
Recovery is not possible without an appropriate surgical treatment
INJURY OF THE NERVE CELL BODY
Severe damage of the nerve cell body may result in degeneration of the entire neuron.
In the CNS, the tissue macrophages (microglial cells) remove the debris, & the
neighboring astrocytes replace the neuron with scar tissue
In the PNS, the tissue macrophages remove the debris, & the local fibroblasts replace the
neuron with scar tissue
INJURY OF THE NERVE CELL PROCESS
If the axon of the nerve cell is divided, degenerative changes will take place in
1. Distal segment of the axon
2. A portion of the axon proximal to the injury
3. The cell body from which the axon arises
CHANGES IN THE DISTAL SEGMENT OF
THE AXON
Wallerian degeneration is the changes that occur distally to the site of damage on an axon
Axon becomes swollen & irregular; the axon is broken into fragments, & the debris is
digested by surrounding schwann cells & tissue macrophages
Entire axon is destroyed within a week
Myelin sheath is converted into lipid droplets
The droplets are extruded from the schwann cell & subsequently are phagocytosed by
tissue macrophages
Schwann cells now begin to proliferate rapidly & axonal sprouts grow from the proximal
stump, enter the distal stump, & grow toward the nerve's end-organs
If regeneration does not occur, the axon & the Schwann cells are replaced by fibrous
tissue produced by local fibroblasts
CHANGES IN THE PROXIMAL SEGMENT
OF THE AXON
The changes in the proximal segment of the axon are similar to those that take place in the
distal segment but extend only proximally above the lesion as far as the first node of
ranvier
CHANGES IN THE NERVE CELL BODY
The changes that occur in the cell body following injury to its axon are referred to as
retrograde degeneration
The nissil material becomes fine, granular, & dispersed throughout the cytoplasm
(chromatolysis)
The nucleus moves toward the periphery of the cell, & the cell body swells & becomes
rounded
Synaptic terminals are replaced by schwann cells in the PNS & microglial cells or
astrocytes in the CNS
RECOVERY OF NEURONS FOLLOWING
INJURY
The recovery of the nerve cell body & regeneration of its processes may take several
months.
RNA & protein synthesis is accelerated
A reconstitution of the original nissil structure
A decrease in the swelling of the cell body
A return of nucleus to its characteristic central position
REGENERATION OF AXONS IN
PERIPHERAL NERVES
Depend on endoneurial tubes & possessed by schwann cells
The following mechanisms are involved:
1. The axons are attracted by chemotropic factors secreted by the schwann cells in the distal
stump.
2. Growth-stimulating factors exist within the distal stump, &
3. Inhibitory factors are present in the perineurium to inhibit the axons from leaving the
nerve
REGENERATION OF AXONS IN THE CNS
Central axons may not be as good at regeneration as peripheral axons
The regeneration process is aborted by:
1. Failure of oligodendrocytes to serve in the same manner as schwann cells
2. Laying down of scar tissue by the active astrocytes
3. Absence of nerve growth factors in the CNS
4. Neuroglial cells may produce nerve growth-inhibiting factors
REFERENCES
Clinical neuroanatomy, 7/E snell
Essentials of medical physiology, 3/E mahapatra
Principles of neural science, 5/E kandel ER, schwartz JH, jessell TM (editors)
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