Degeneration & Regeneration of Nervous Tissue

Vocabulary practice flashcards covering the cellular mechanisms, stages, and characteristics of axonal degeneration and neural regeneration in both the peripheral and central nervous systems.

Degeneration

The structural and functional changes occurring in a neuron (nerve cell body and its processes) as a result of an axonal injury caused by a knife, trauma, or infection.

Anterograde (Wallerian) Degeneration

Degeneration of an axon occurring distal to the site of injury in the peripheral portion of the nerve fiber.

Retrograde (Traumatic) Degeneration

Changes occurring proximal to the site of injury in the cell body of a neuron, initiated by retrograde signaling that alters gene expression and reorganizes the perinuclear cytoplasm.

Initial Axonal Response to Injury (Wallerian Degeneration)

Axonal swelling followed by disintegration occurring $8\text{ to }24\text{ hours}$ after damage, resulting in the breakdown of the axonal cytoskeleton (microtubules, neurofilaments) and axonal fragmentation.

PNS Schwann Cell Response in Degeneration

Dedifferentiation of Schwann cells and breakdown of the myelin sheath enclosing the axon following the loss of axonal contact.

CNS Oligodendrocyte Response to Axonal Injury

Initiation of apoptotic programmed cell death when contact with axons is lost, because oligodendrocyte survival depends directly on axonal signals.

Chromatolysis

The dispersion, reduction in size, and eventual disappearance of Nissl granules (Nissl substance), accompanied by swelling of the neuronal cell body.

Perikaryon Morphological Changes in Retrograde Degeneration

The nerve cell body swells, loses its dendrites, and takes on a globular shape.

Nuclear Changes in Retrograde Degeneration

The nucleus migrates to an eccentric (peripheral) position and becomes small and pyknotic.

Organelle Alterations in Retrograde Degeneration

Fragmentation and disappearance of mitochondria, the Golgi apparatus, and neurofibrils, along with an increase in lysosomes.

Neural Regeneration

The process of healing in a neuron and its processes following axonal injury caused by trauma, a knife cut, or infection.

Prerequisites for Nerve Regeneration

Presence of an intact neurolemma sheath, a partially cut nerve fiber, absence of infection at the injury site, and a short distance between the two cut ends.

Primary Reason for Failure of CNS Regeneration

The absence of Schwann cells and the failure of oligodendrocytes to behave like Schwann cells.

Interleukin-1 (IL-1)

A substance secreted by macrophages during nerve regeneration that stimulates Schwann cells to release factors promoting nerve growth.

Bands of von Bünger

Compact cellular cords formed by proliferating Schwann cells that are penetrated and followed by regrowing axonal sprouts.

Rate of Axonal Growth

A regeneration rate of $0.5\text{ to }3\text{ mm/day}$ guided along the column formed by proliferating Schwann cells.

Barriers to Axonal Regeneration in the CNS

Inefficient clearance of myelin debris due to limited macrophage access, inadequate phagocytosis by microglia, and the formation of an astrocyte-derived scar.

Multiple Sclerosis Plaques

Pathological lesions in the central nervous system (brain and spinal cord) caused by the selective autoimmune loss of myelin.