Regeneration of Nerve Fibers

Nerve fibers of the PNS are vulnerable to cuts, crushing injuries, and other trauma. A damaged peripheral nerve fiber can regenerate, however, if its soma is intact and at least some neurilemma remains. Within the first few weeks after injury, the severed distal end of an axon and its myelin sheath degenerate and macrophages remove the debris (fig. 12.8). A regeneration tube, formed by the neurilemma and endoneurium, is necessary for regeneration. The axon stump puts out several sprouts until one of them finds its way into the tube. This sprout begins to grow rapidly (about 3-5 mm/day), possibly under the influence of chemicals secreted by the tube (see insight 12.3), while the other sprouts are reabsorbed. The regeneration tube guides the growing axon back to its original destination until the neuron reestablishes a connection with the cells that it originally innervated. Skeletal muscle fibers atrophy

Saladin: Anatomy & I 12. Nervous Tissue I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

454 Part Three Integration and Control

Muscle Fiber Growth And Regeneration

Figure 12.8 Regeneration of a Damaged Nerve Fiber. (a) Normal nerve fiber. (b) Injured fiber with macrophages cleaning up tissue debris at the point of injury, and with early degeneration of the nerve fiber, myelin sheath, and axon terminals distal to that. (c) Early regeneration; the soma is swollen, the Nissl bodies have dispersed, and the axon stump has begun producing multiple growth processes, while the severed distal part of the nerve fiber shows further degeneration. In the case of somatic motor neurons, muscle fibers atrophy for lack of innervation. (d) Continued regeneration; the Schwann cells, basal lamina, and neurilemma form a regeneration tube, one growth process grows into the tube, and the other growth processes are reabsorbed. (e) Continued regeneration; the growth processes have almost reestablished contact with the muscle fibers. (f) Regeneration complete; the muscle fibers are reinnervated and have regrown, and the soma of the neuron has returned to its original appearance.

Figure 12.8 Regeneration of a Damaged Nerve Fiber. (a) Normal nerve fiber. (b) Injured fiber with macrophages cleaning up tissue debris at the point of injury, and with early degeneration of the nerve fiber, myelin sheath, and axon terminals distal to that. (c) Early regeneration; the soma is swollen, the Nissl bodies have dispersed, and the axon stump has begun producing multiple growth processes, while the severed distal part of the nerve fiber shows further degeneration. In the case of somatic motor neurons, muscle fibers atrophy for lack of innervation. (d) Continued regeneration; the Schwann cells, basal lamina, and neurilemma form a regeneration tube, one growth process grows into the tube, and the other growth processes are reabsorbed. (e) Continued regeneration; the growth processes have almost reestablished contact with the muscle fibers. (f) Regeneration complete; the muscle fibers are reinnervated and have regrown, and the soma of the neuron has returned to its original appearance.

Saladin: Anatomy & 12. Nervous Tissue Text © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 12 Nervous Tissue 455

when their nerve fiber is severed (denervation atrophy), but regrow after the connection is reestablished. Damaged neurons in the CNS cannot regenerate, but since the CNS is enclosed in bone, it suffers less trauma than the PNS.

Insight 12.3 Clinical Application

Was this article helpful?

0 0
Peripheral Neuropathy Natural Treatment Options

Peripheral Neuropathy Natural Treatment Options

This guide will help millions of people understand this condition so that they can take control of their lives and make informed decisions. The ebook covers information on a vast number of different types of neuropathy. In addition, it will be a useful resource for their families, caregivers, and health care providers.

Get My Free Ebook


Responses

Post a comment