Disorders of the PNS Flashcards
What happens if there is a lesion in the dorsal root?
Loss of sensation in the dermatome supplied by the corresponding spinal nerve
What happens if there is a lesion in a somatic sensory nerve?
loss of sensation in the area of disribution of that peripheral nerve
Why is loss of sensation at dermatomes sometimes not detected?
There may some overlap in dermatome innervation
What happens if there is a lesion in the ventral root?
Muscle weakness, as the spinal nerve that innervates the muscle has been shut off
Why is paralysis of muscles not always seen?
More limb muscles are innervated by more than one nerve so paralysis is unlikely
What happens if there is damage directly to the motor neurone?
Paralysis of the muscle as the impulse cannot reach the muscle
What happens if there is damage to the mixed spinal nerve?
Loss of sensation in dermatome and muscle weakness
What common medical scenarios result in such lesions
- Strain injuries to spine eg prolapsed or herniated intervertebral disc
- Peripheral neuropathy
- Brachial plexus affected by trauma to shoulder join
Why are there 30 dermatomes but 31 spinal nerves?
C1 does not have a sensory root so dermatomes begin with C2
What is lumbar spinal radiculopathy commonly known as?
Sciatica, caused by compression of the sciatic nerve
What is a slipped disc?
When the soft cushion of tissue between bones pushes out and presses on nerve
What are the symptoms of sciatica
Pain that radiates from the lower back through the hips and buttocks and down each leg
What structures are involved to produce the symptoms of sciatica
The dermatomes of dorsal and ventral roots of lumbar and sacral nerves cover the areas that pain is felt
What happens to the intervertebral foramine when there is a slipped disc?
It narrows
What can be used to confirm diagnosis of sciatica?
The straight leg raise - stretches sciatic nerve and recreates the pain felt by the patient
