Chapter 55 - Peripheral Nerve Injuries Flashcards
What does the peripheral nervous system (PNS) connect?
It connects the periphery of the body with the central nervous system (CNS).
How many pairs of spinal nerves originate from the spinal cord?
There are 42 to 43 pairs of spinal nerves.
What are the two types of roots that attach spinal nerves to the spinal cord?
Afferent dorsal roots and efferent ventral roots.
What structures do spinal nerves exit through?
Lateral vertebral foramina or intervertebral foramina.
What is formed when the ventral rami of neighboring spinal nerves connect?
Nerve plexuses such as the cervical, brachial, and lumbosacral plexus.
Which cervical nerves form the phrenic nerve?
Cervical nerves 5, 6, and 7.
What is the primary function of the phrenic nerve?
Motor innervation of the diaphragm and sensory supply to thoracic structures.
Where is the brachial plexus located?
Immediately cranial to the first rib, between the two parts of the scalenus muscle.
What spinal nerves contribute to the brachial plexus?
Spinal nerves C6 to T2.
Which spinal nerves form the lumbosacral plexus?
Spinal nerves L4 to S2.
What major nerves arise from the lumbosacral plexus?
The femoral, obturator, sciatic, tibial, and peroneal nerves.
What components make up a nerve?
Numerous nerve fibers and their supporting soft tissues.
What does the term “nerve fiber” refer to?
The axon and its enveloping Schwann cells, myelin sheath, and surrounding endoneurium.
What is the role of the endoneurium?
It is the connective tissue layer surrounding individual nerve fibers.
What structure envelopes a bundle of nerve fibers?
The perineurium.
What surrounds fascicles of nerve fibers?
The interfascicular epineurium.
How does the epineurium function in a nerve?
It encircles the entire nerve, providing structural support.
What is neurapraxia?
A temporary conduction block due to blunt trauma without axonal damage.
Define axonotmesis.
An injury where the axon is damaged but the connective tissue layers remain largely intact.
What is the expected recovery time for neurapraxia?
Complete recovery can take up to 3 months.
What happens during third-degree axonotmesis injuries?
Disruption of endoneurial sheaths leads to disorganized axonal regrowth.
What occurs in fourth-degree peripheral nerve injuries?
Complete disruption of internal nerve structure, with scar tissue blocking regenerating axons.
What characterizes a second-degree axonotmesis injury?
The connective tissue is intact, allowing for optimal axonal regrowth.
What is the prognosis for recovery from a third-degree injury?
Rarely more than 60% to 80% of normal function is regained.