Degeneration and Regeneration of Nerve Fibers

These flashcards cover key concepts regarding the degeneration and regeneration of nerve fibers, including degrees of injury, pathological changes, and criteria for regeneration.

What are the five degrees of nerve injury as classified by Sunderland?

First degree, Second degree, Third degree, Fourth degree, Fifth degree.

What is first degree injury in nerve fibers known as?

Seddon neuropraxia.

What happens to the axon in a first degree injury?

The axon is not destroyed but experiences mild demyelination, leading to a temporary conduction block.

How long does it take for function to return in first degree injury?

Function returns within a few hours to a few weeks.

What is second degree injury of nerve fibers called?

Axonotmesis.

What occurs during second degree injury?

Prolonged severe pressure leads to Wallerian degeneration, but the endoneurium remains intact.

How long does repair and restoration take in a second degree injury?

About 18 months.

What occurs during third degree injury to a nerve fiber?

The endoneurium is interrupted, while the epineurium and perineurium remain intact.

What are the possible outcomes of third degree injury?

Recovery is slow and may be poor or incomplete.

What are the injuries termed after third degree?

Neurotmesis.

What is Wallerian degeneration?

Pathological changes that occur in the distal cut end of a nerve fiber.

When does Wallerian degeneration begin?

Within 24 hours of injury.

What happens to the myelin sheath during Wallerian degeneration?

It disintegrates into fat droplets from the 8th to the 35th day.

What happens to the axis cylinder during Wallerian degeneration?

It swells and breaks up into small pieces, appearing as debris.

What changes occur in the nerve cell body within 48 hours after nerve injury?

Nissl granules disintegrate, Golgi apparatus disintegrates, and the cell body swells and loses neurofibrils.

What is transneuronal degeneration?

Degenerative changes that occur in neurons that are synaptically connected to an injured neuron.

What are some examples of transneuronal degeneration?

Chromatolysis in lateral geniculate body cells due to optic nerve section; degeneration in dorsal horn from posterior nerve root cut.

What is necessary for nerve fiber regeneration?

Criteria must be met including gap size, presence of neurilemma, intact nucleus, and alignment of cut ends.

How long can it take for regeneration to complete after nerve injury?

About 80 days.

What initially grows from the proximal cut end during regeneration?

Pseudopodia-like extensions called fibrils or regenerative sprouts.

What do Schwann cells do during nerve regeneration?

They line up in the neurilemmal tube; guide fibrils and synthesize nerve growth factors.

How long does it generally take for myelination to be completed after regeneration?

1 year.

What is the expected recovery of diameter in a regenerated nerve fiber compared to the original?

The degenerated nerve fiber attains only about 80% of the original diameter.

What begins to appear in the nerve cell body during regeneration?

First, Nissl granules appear, followed by the Golgi apparatus.

How is functional recovery achieved after nerve regeneration?

Anatomical regeneration occurs, but functional recovery can take a long period.

What types of degenerative changes occur in a neuron after injury?

Wallerian degeneration, retrograde degeneration, and transneuronal degeneration.

What happens in retrograde degeneration?

Pathological changes occur in the nerve cell body and axon proximal to the injury.

What occurs in the axon proximal to the cut end?

Changes similar to those in the distal cut end, but limited to the first node of Ranvier.

What happens to the nucleus in a nerve cell during degenerative changes?

It may shift to the periphery or be extruded, leading to potential neuron death.

What is a fifth degree nerve injury?

Complete transaction of the nerve trunk with loss of continuity.

What is required for useful regeneration to occur in a fifth degree injury?

The cut ends must be rearranged and approximated quickly by surgery.

How are the changes in myelin sheath described during Wallerian degeneration?

It disintegrates into fat droplets.

What is the maximum gap between cut ends for regeneration to be possible?

The gap should not exceed 3 mm.

What happens during the initial stages of nerve regeneration?

Fibrils grow from the proximal end towards the distal end.

What is the function of macrophages during Wallerian degeneration?

They invade to remove debris from the axon and disintegrated myelin sheath.

What anatomical structure remains unaffected during Wallerian degeneration?

Neurilemmal sheath.

What leads to the slow and incomplete recovery in third degree injury?

Interruption of the endoneurium.

What are the general pathological changes occurring in an injured neuron collectively referred to as?

Degenerative changes.

How long does regeneration take to show effectiveness after nerve injury?

Effective regeneration begins after 30 days.

What is the significance of neurofibrils in nerve cells?

Their disappearance is a sign of degenerative changes in the neuron.

What does chromatolysis refer to?

The disintegration of Nissl granules in the nerve cell.

How do Schwann cells contribute to the guidance of regenerating axons?

They provide a pathway and growth factors to attract the regenerative sprouts.

What cellular structure can be extruded from the cell body leading to a loss of potential regeneration?

The nucleus.

What does the term ‘conduction block’ refer to in first degree nerve injury?

Temporary loss of function due to mild demyelination.

What is the timeline for changes in the nerve cell body to commence after an injury?

Changes begin within 48 hours.

What is the condition of the axon after a second degree injury?

Wallerian degeneration occurs, but with the endoneurium intact.

How is the recovery during a third degree injury characterized?

It is often slow and may result in incomplete functional recovery.

What does the presence of a neurilemma indicate for any potential to regenerate?

Regeneration may occur outside the CNS, but not within it.

What does the axon do as part of the regeneration process within the neurilemmal tube?

It forms an axis cylinder.

After an injury, which cell type plays a critical role in cleaning up the debris?

Macrophages.

What is the primary focus in addressing a fifth degree nerve injury?

Surgical intervention to rearrange and approximate cut ends.

What developmental feature of nerve fibers typically decreases in regenerated fibers compared to original fibers?

The length of newly formed internodes.

What clinical significance does understanding nerve injury and regeneration have?

It informs treatment strategies for nerve repairs and recovery.