L12: Degeneration and Regeneration of Peripheral Nerves Following Trauma Flashcards
What are the main structural components of a nerve cell (neuron)?
The cell body and the axon.
What is the primary difference between the central and peripheral nervous systems regarding injury response?
Peripheral nerves have the capacity to regenerate under proper conditions, while central nervous system neurons generally do not regenerate after injury.
What is Wallerian degeneration?
It is the process by which the distal segment of a damaged axon degenerates and is cleared by phagocytic cells following injury.
What are the three classifications of nerve injuries according to Seddon’s classification?
Neuropraxia, axonotmesis, and neurotmesis.
What is neuropraxia?
It is the mildest form of nerve injury, often causing temporary loss of function that fully recovers once the insult is removed.
What distinguishes axonotmesis from neurotmesis?
In axonotmesis, the axon is damaged but the connective tissue structure remains intact, allowing regeneration. In neurotmesis, both the axon and connective tissue are completely disrupted, preventing regeneration.
What role do glial cells play following nerve injury?
Glial cells, such as microglia, become activated, clear debris from the injury site, and may support axonal regeneration by forming pathways.
What is chromatolysis in neurons?
It is the process of cellular swelling and displacement of the nucleus in the neuron’s cell body, typically following axonal injury.
Why is trophic support from nerves important for muscles?
It not only provides neuronal signals for muscle contraction but also influences the biochemical and structural properties of the muscle fibers.
What are fibrillations, and when do they occur?
Fibrillations are uncontrolled muscle contractions that occur in denervated muscles shortly after nerve injury.
What is crush syndrome?
A condition resulting from massive muscle damage, leading to the release of potassium and other substances into the bloodstream, potentially causing acute renal failure.
What experimental finding highlighted the specificity of motor neurons to muscle fibers?
When type S (slow contraction) motor neurons were switched to supply type F (fast contraction) muscle fibers, the contractile properties of the muscle changed to match the neuron’s characteristics.
What are the layers of connective tissue in a peripheral nerve, from innermost to outermost?
Endoneurium, perineurium, and epineurium.
What is the role of the endoneurium in nerve repair?
It forms a connective tissue tube that helps guide regenerating axons to their target.
How does nerve injury affect the action potential properties of the neuron?
Injured neurons generate ‘injury potentials,’ which are abnormal and complex electrical signals.
What happens to the distal segment of a neuron after it is cut off from the cell body?
It loses nutritional and repair support, becomes vulnerable to phagocytosis, and undergoes Wallerian degeneration.
What immediate response occurs in the proximal segment of an injured axon?
The cell body enters a phase of increased protein synthesis to support repair, leading to chromatolysis.
What is the significance of the glial cell response after nerve injury?
Glial cells, such as microglia, clear the debris from the injury site and create an environment conducive to axon regeneration.
What are growth cones, and what role do they play in nerve regeneration?
Growth cones are structures that extend from the regenerating axon, guided by chemical signals and connective tissue tubes toward their target.
What is the ‘crocodile tears syndrome’?
It is a condition where regenerating nerves misroute and innervate the lacrimal gland instead of their original target, causing tears during eating.
