Peripheral nerve lesions Flashcards
Describe the consequences of damage to the dorsal root
Damage to dorsal root leads to loss of sensation in dermatome supplied by the corresponding spinal nerve. (Probably difficult to detect if only one root affected as there is some overlap of dermatome innervation by adjacent spinal nerves)
Describe consequences of damage to the ventral root
Damage to ventral root leads to weakness of muscles supplied by the corresponding spinal nerve. (Most limb muscles are innervated by 2 or more spinal nerves therefore paralysis is unlikely unless all spinal roots are damaged)
Describe the consequences of damage to the spinal nerve distal to the junction of the ventral and dorsal root
Damage to a spinal nerve distal to the junction of the dorsal and ventral root leads to combined effects of damage to the dorsal and ventral roots
Describe the consequences of damage to the sensory nerve close to its target organ
Damage to a sensory nerve close to its target organ (eg. in the skin) leads to loss of sensation in the area of distribution of that peripheral nerve
Describe the consequences of damage to the motor neurone close to its target organ
Damage to a motor nerve close to its target muscle leads to paralysis of that muscle.
Describe the consequences of nerve lesions close to its target organ
In this diagram lesions Y and Z are shown affecting nerve branches close to their targets and would therefore have a purely sensory or motor effect. More proximal lesions to peripheral nerves would probably affect both motor and sensory function.
Describe the importance of the plexus
Contrasting the effects of V/W v Y/Z demonstrates the effect of the plexus which redistributes the axons from spinal nerves into the peripheral nerves
Describe the insults that can produce such damage
Spinal root and spinal nerve damage is most often a consequence of strain injuries to the spine, eg. prolapsed disc.
“Shingles” is a syndrome in which a single dermatome becomes blistered and painful because of the reactivation of the chickenpox virus in a dorsal root.
Peripheral nerves may be affected by trauma or disease (peripheral neuropathy)
The brachial plexus may be affected by trauma to the shoulder joint. The lumbosacral plexus is much better protected and therefore less likely to be injured.
How may pathology of the nerve appear
This nerve was crushed 3 days earlier. It shows degenerating myelin that is paler staining and ‘ovoid’ in shape.
An alternative explanation would be demyelinating neuropathy but this is less likely as you would expect a less uniform appearance at such an early stage.
When would you expect the best recovery of function: after nerve crush or nerve section?
Better recovery would be expected after nerve crush because the nerve sheath (endoneurium) remains intact and helps to guide regeneration.
Summarise nerve regeneration
After nerve section the distal part of the axon degenerates and Schwann cells proliferate.
Sprouts grow out from the proximal stump of the axon, guided by Schwann cells
The first sprout to connect with the target organ becomes myelinated; the other sprouts regress.
The regenerated axon, usually with slightly shorter internodes.
