8 - Degeneration & Regeneration of Peripheral Nerves Following Trauma - Vocabulary Flashcards

Vocabulary flashcards covering key terms and definitions related to degeneration and regeneration of peripheral nerves after trauma, including injury classifications, cellular players, and clinical phenomena.

Somatic Nervous System

The branch of the peripheral nervous system that controls voluntary movement of skeletal muscle.

Autonomic Nervous System

The branch of the peripheral nervous system that controls involuntary functions of smooth muscle, cardiac muscle, and glands (includes sympathetic and parasympathetic divisions).

Effector

The target organ or tissue (e.g., muscle, gland) that responds to neural signals.

Afferents (sensory fibers)

Nerve fibers that carry information from the periphery and special sense organs to the brain.

Descending pathways

Neuronal relay chains by which the brain communicates with effectors in the somatic or autonomic divisions.

CNS neurons regenerate (or not)

In the central nervous system, neurons generally do not regenerate after injury.

Pia mater

The innermost meningeal layer; marks the boundary between CNS and peripheral nervous system.

Peripheral nerve regeneration

Injured peripheral nerves have the capacity to regenerate and reinnervate their target effectors.

Epineurium

The superficial connective tissue envelope surrounding the entire nerve.

Perineurium

The connective tissue that ensheaths a nerve fascicle (bundle) of axons.

Endoneurium

The connective tissue that ensheaths an individual axon within a nerve.

Myelin sheath

The insulating layer around axons that speeds electrical conduction.

Axon

The long projection of a neuron that conducts impulses to target cells.

Neuropraxis

A mild nerve injury with temporary loss of function, typically due to myelin disturbance; full recovery expected.

Axonotmesis

Severe crush injury with axon and myelin damage but intact surrounding connective tissue; regeneration can occur along intact tubes.

Neurotmesis

Complete transection of the nerve with damage to axon and connective tissue; recovery is unlikely.

Seddon’s classification

System classifying nerve injuries by depth (epineurium, perineurium, endoneurium) and degree of insult: neuropraxia, axonotmesis, neurotmesis.

Proximal segment

The portion of a divided axon nearer to the cell body; typically survives injury.

Distal segment

The portion of a divided axon farther from the cell body; undergoes degeneration and often dies.

Wallerian degeneration

Degeneration and phagocytic digestion of the distal part of a severed axon and its myelin.

Chromatolysis

Early response of the proximal axon cell body after injury, with swelling and dispersion of the nucleus and increased protein synthesis.

Neuroma

A disorganized mass of regenerating axon endings at the proximal stump, formed during attempted reinnervation.

Axonal sprouts

Regenerating growths from the proximal axon that attempt to reinnervate targets.

Schwann cell tubes

Guiding channels formed by Schwann cells that direct regenerating axons in the peripheral nervous system.

Denervation

Loss of nerve supply to a muscle or other effector.

Reinnervation

The process of regenerating nerve fibers reestablishing connection with their target; may reinnervate a different organ.

Denervation atrophy

Muscle wasting due to prolonged loss of neural input.

Fasciculations

Involuntary muscle twitches seen in denervated muscles.

Type S motor neurons

Slow motor neurons that innervate Type S (slow-twitch) muscle fibers.

Type FF motor neurons

Fast-fatigable motor neurons that innervate Type FF muscle fibers.

Muscle fibre typing shift

After reinnervation, muscle fiber types switch to match the motor nerve supplying them.

Crocodile tears syndrome

Lacrimation triggered during eating due to miswiring of regenerating nerves.

Gastatory hyperlacrimation

Another term for crocodile tears phenomenon (lacrimation associated with tasting/chewing).

Borgorad’s phenomenon

Another name used for crocodile tears phenomenon.

Rhabdomyolysis

Breakdown of skeletal muscle that releases intracellular contents into the bloodstream, potentially causing renal failure.

Neuromuscular junction

The synapse between a motor neuron and a muscle fiber.

Fibres and nerve types (S vs FF)

Muscle fiber typing adapts to the motor nerve supplying it; switching can occur in experimental reinnervation.