Final answer:
Retrograde degeneration is the correct term for the breakdown of nerve fibers proximal to an axon injury in the CNS or PNS. Anterograde degeneration occurs distally, while axon regeneration is a separate and slow process, distinct from neuronal apoptosis which is a form of programmed cell death.
Step-by-step explanation:
The degeneration that occurs proximal to a site of CNS or PNS axon injury is known as retrograde degeneration. Conversely, anterograde degeneration occurs distal to the site of injury. Retrograde degeneration involves the breakdown of the nerve fiber closest to the cell body following injury, reflecting a reverse direction of the typical axonal transport.
When nervous system injury occurs, such as through physical trauma, toxic exposure, or disease processes like diabetes and multiple sclerosis (MS), various forms of degeneration take place. These conditions can lead to symptoms like loss of feeling, tingling, burning sensations, or muscle weakness. Notably, while axon regeneration is possible in the PNS, it is a slow and imperfect process that doesn't typically occur in the CNS. Neuronal apoptosis is a process wherein neurons intentionally undergo a programmed cell death, which can also result from disease or injury.