Peripheral nerve injury Flashcards
What is neurapraxia ?
Compression of the myelin sheath of an axon resulting in blockage of conduction of nerve impulses. This is reversible and is temporary. Caused by compression/a blow to the area.
What is axonotmesis?
Degeneration of the axon and myelin sheath of a neurone, however the endoneurium (sheath around the myelin sheath) remains intact. This is as a result of a more serious blow/contusion e.g a bone breakage. The axon undergoes wallerian degeneration.
What is neurotmesis?
A more serious degeneration of the axon and myelin sheath of a neurone. The endoneurium also disintegrates. Full recovery is almost always impossible.
What is Wallerian Degeneration?
The distal part of the axon not connected to the cell body disintegrates. This is caused by macrophages and schwann cells. However nerve fibres start to regenerate and re-grow, re-connecting the axon together. This is irreversible in the CNS but reversible in the PNS.
What are the motor effects of PNI?
Muscle weakness, atrophy, painful cramps, decreased reflexes, muscle spasms/twitching.
What are the sensory effects of PNI?
Decreased sensation, numbness and tingling, decreased balance and coordination.
What are the autonomic effects of PNI?
Decreased bladder control, heat intolerance, inability to sweat, unable to cause the blood vessels to contract resulting in dizziness and being lightheaded.
What is the root value and course of the common peroneal nerve?
L4-S3
It divides from the sciatic nerve at the popliteal fossa. Here it moves laterally down the short head of the biceps femoris towards the lateral head of the gastrocnemius. It moves around the head of the fibula moving anteriorly. Here it divides into the deep peroneal nerve which innervates the anterior compartment of the lower leg, and the superficial peroneal nerve which innervates the lateral compartment of the lower leg.
What are the 2 main causes of PNI and what gait changes are seen?
Multiple sclerosis and Parkinson’s.
-Foot drop causes a functional leg length discrepancy so the patient has to have a high stepping gait so that the toes do not drag on the floor, causing them to trip.
- Slapping sound on the heel strike phase due to no eccentric control of the tibialis anterior. No propulsion on toe off.
- Numbness and tingling, muscle atrophy and decreased sensation of the affected side.
What is a lower motor neurone lesion?
A lesion affecting the nerve fibres travelling from the anterior horn cell of the spinal cord to the muscle(s) it innervates.
What are the 3 main differences between and upper and lower motor neurone lesion?
Reflexes -
UMN - exaggerated reflexes
LMN - absent/decreased
Muscle tone -
UMN - increased tone causing hypertonicity.
LMN - decreased tone, flaccid response.
Fasciculations (twitching) -
UMN - absent
LMN - present
