Denervation Flashcards
Denervation
Damage to peripheral nerves
Denervation of Lower and upper Motor neurons
Upper- spasticity (stiff), normal peripheral nerves
Lower- flaccid, Loss of axons or peripheral nerve cell body
Sensory function damage
Discriminative touch- feel for surfaces, shapes, objects etc
Provided by large myelenatedc fives
Pain and Temperature- thin unmylenated fibers
Effect Of Denervation
Loss of function in root distribution
Loss of function in distribution of named nerve
Peripheral nerve structures
Individual fascicles within nerve
Epineurium surrounds the nerve
Perineurium surrounds the fascicles
Axons within myelin sheath
Endoneurium- within fascicles, any connective tissue
Myelin formed by Schwann cells
Nodes Of ranvier
Things that can do wrong in a nerve
Damage to myelin
Damage to Axon
Loss of motor/ sensory function in the distributor Of The nerve affected—— caused by axon damage (Primary or secondary)
Causes of damage to nerves
Trauma:
Compression
Transaction
Stretching
Disease:
Peripheral neuropathy;
Diabetes, B12 deficiency
Inflammation
Autoimmune
Infections- HIV, leprosy
Drugs and toxins
Inherent
Peripheral neuropathy
Length dependent- loss of function affects distal parts of body, works it’s way up
Non length dependent-patchy process affecting short and long nerves
Mono neuropathy- named nerve that is damaged
Radiculopathy- nerve damage at the level of the root
Axon loss
Trauma:
– Axonotmesis
● can recover but slow and may be incomplete
-Neurotmesis
● recovery requires grafting transected ends
– recovery requires axon regrowth
● 1mm/day
Medical cause:
Peripheral neuropathy
Myelin damage
Neuropraxia
Demyelination
-slow conduction
-conduction block
Can recover in 8-12 week after removal of cause
Wallerian degeneration
Disintegration/removal/degeneration Of axons divided from their cell bodies
Transecting an axon
Expose proteins such as cal pain which interacts with calcium
Will still conduct when artificially stimulated
Distal portion starts to degenerate and over the coming days, macrophages will get rid of the distal part
The axon still attached you cell body will then start to regenerate and reinnovation starts
Reinnovation very inefficient (esp in adults)
Denervation effects
Sensory nerve
– altered sensation: numbness, pain, paraesthesia
motor nerve
– atrophy
– weakness
– paralysis
Effects of Denervation on muscles
Atrophy
Spontaneous motor activity
– fibrillations and fasciculations
– cramps
muscles remain viable for up to 2 years without a nerve supply after which they fibrose and cannot return to normal function
Denervation conclusion
Axons
● axon loss results in loss of function
Myelin
– slow nerves: generally does not cause symptoms
– secondary axon loss does
KNOW ANATOMY OF PNS
