SFP: PNS tissue

Question 1

Describe the two major components of the PNS

Answer 1

Has a sensory component and a motor component. The sensory component links sensory receptors to the CNS, and the motor component connects the CNS to skeletal. Muscles and motor neurons that innervate viscera

Question 2

Describe the two major types of peripheral ganglia.

Answer 2

Sensory: the dorsal root ganglion; contains sensory neurons that bring in sensory information from the environment into the CNS

Autonomic: these are visceral motor cells. They are found in the sympathetic chain or closer to the walls of visceral organs (parasympathetic). They are multipolar and surrounded by satellite cells.

Question 3

Describe the dorsal root ganglion: composition and structure

Answer 3

They have cell bodies, satellite cells (glial), and nerve fibers. They are pseudo-unipolar cells, meaning they have a cell body with one pole that bifurcates into a peripheral component and a central component

Question 4

describe the structure of peripheral nerves

Answer 4

They contain afferent and efferent axons. The afferent are found in the dorsal root ganglia, and the efferent are in the spinal cord

Question 5

describe the characteristics of the epineurium

Answer 5

Provides a protective layer form trauma for the peripheral nerves. They have a dense outer sheath and contain blood vessels. They are contiguous with the dura mater

Question 6

describe the characteristics of the perineurium

Answer 6

It bundles axons together, forming fascicles. It is a thinner sheath with smaller blood vessels. They are contiguous with the pia/arachnoid mater

Question 7

describe the characteristics of the endoneurium

Answer 7

A connective tissue layer surrounding individual axons. It surrounds the Schwann cell and the axon.

Question 8

compare structures of myelinated and unmyelinated axons in the PNS

Answer 8

Myelinated: one internode per Schwann cell; seen as a sequence of Schwann cells along an axon with nodes of Ranvier in between.

Unmyelinated: several axons enveloped loosely by each Schwann cell.

Question 9

describe large/fast fibers

Answer 9

Involved in proprioception, mechanosensitization, and are seen in motor and skeletal muscle

Question 10

describe medium fibers

Answer 10

associated with mudcle spindles; Important for motor and muscle tone

Question 11

describe small/slow fibers

Answer 11

Involved in pain and temperature, autonomic fibers

Question 12

In electrodiagnostic, what would a decreased amplitude show? Decreased speed?

Answer 12

Axonal damage; demyelination

Question 13

Describe neurapraxia

Answer 13

1st degree aka nerve compression; axon hasn’t been disrupted but there is some demyelination. Usually no treatment is needed

Question 14

Describe axonotmesis

Answer 14

aka nerve severing

2nd degree: some axon loss, but the endoneurium, perineurium, and epineurium are intact. There is slow regeneration of the axon, resulting in regaining full function.

3rd degree: axon loss with the endoneurium disrupted, but the other two connective tissue layers are intact. Surgery may be needed.

4th degree: axon loss with the endo and perineurium disrupted, but the epineurium is intact. Surgery will be needed to remove scar tissue.

Question 15

Describe neurotmesis

Answer 15

Complete disruption of the nerve; surgical repair is needed but the patient will not regain full function

Question 16

Explain the processes involved in regeneration of peripheral nerves

Answer 16

the distal portion degenerates completely. The muscle sends out signals to direct the axon to grow back toward the muscle. In the proximal portion, the Schwann cells invade and proliferate the distal portion. The Schwann cells will remyelinate the axon. If the regeneration is unsuccessful, a neuroma forms. A neuroma results in not regaining function