Question

describe the neuroglia of the PNS. explain how an injured neuron may regenerate

Answer 1

Answer:

Neuroglial cells in the PNS are schwann cells and satellite cells.

Schwann cells : It provide myelination to peripheral neurons.

- They also perform phagocytic functions and clear cellular debris, allowing for the regrowth of PNS neurons.

- Functionally, the schwann cells are similar to oligodendrocytes of the CNS.

Satellite cells: They perform a similar function to astrocytes.

- They surround neurons in sensory, sympathetic, and parasympathetic ganglia, helping to regulate the external chemical environment.

- They are highly sensitive to injury and inflammation, and appear to contribute to pathological states, such as chronic pain.

Nerve regeneration:

- Injury to the peripheral nervous system elicits the migration of phagocytes, Schwann cells, and macrophages to the lesion site in order to clear away debris such as damaged tissue which is inhibitory to regeneration.

- When a nerve axon is severed, the end still attached to the cell body is labeled the proximal segment, while the other end is called the distal segment.

- After injury, the proximal end swells and experiences some retrograde degeneration, but once the debris is cleared, it begins to sprout axons and the presence of growth cones can be detected. The proximal axons are able to regrow as long as the cell body is intact, and they have made contact with the Schwann cells in the endoneurium (also known as the endoneurial tube or channel).

- The distal segment, however, experiences Wallerian degeneration within hours of the injury; the axons and myelin degenerate, but the endoneurium remains.

- In the later stages of regeneration the remaining endoneurial tube directs axon growth back to the correct targets.

- During Wallerian degeneration, Schwann cells grow in ordered columns along the endoneurial tube, creating a band of Büngner cells that protects and preserves the endoneurial channel. Also, macrophages and Schwann cells release neurotrophic factors that enhance re-growth.