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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