Nerves Flashcards
Name 3 phases following nerve injury?
- Wallerian degeneration - Macrophages degrade myelin and axoplasm
- Schwann cells proliferate and line the endonerium basement membrane
- Proximal budding (1month) - sprouting axons 1mm/day
Variables that affect regeneration? 3
- Contact guidance - attraction to basal lamina of Schwann cell
- Neurotropism
- Neutotrophic factors
Anatomy from inside to outside? 6
- Neuron cell
- Schwann cell/myelin
- Endoneurium
- Fascicles
- Perineurium
- Epineurium
Name 3 main parts of the microstructure of a nerve?
Perikaryon (body)
Axolemma (membrane)
Axoplasm
What is the function of oligodendrocytes?
Schwann cells of the CNS
What is the function of astrocytes?
Supportive cells - control nutrition/ NT and K+
What do microglial cells do/
“macrophages of the NS”
What allows saltatory conduction to take place?
Nodes of Ranvier
Name the 3 degrees of nerve injury (Seddon) from least severe to most severe?
- Neuropraxia
- Axonotmesis
- Neurotmesis
Main difference between Axonetmesis and Neurotmesis injuries?
Axon = axon and myelin disruption Neurotmesis = Complete disruption with disruption of endoneurium
Functional recovery following injury in order?
Sympathetic Pain Temperature Touch Proprioception Motor fx
Some Pangas Temporarily Transect Proper Muscles
Nerve fiber types and examples?
A - touch
B - ANS
C - Pain
Classification system for nerve injuries and equivalent injury?
Sunderland classification
Neuropraxia 1
Axonetmesis - 2 - 4
Neurotmesis 5
Normal resting potential?
-70mv
What is the threshold stimulus?
Minimum stimulus required to produce a action potential
What is summation potential?
Repetitive subthreshold stimuli may be sufficient to create an AP
Steps of generation of AP?
- Stimulus >-55mv
- Voltage gated Na channels open
- Na channels shut and K channels open - start of depolarisation
- K+ channels slow to shut
- Na - K ATPase restore to -70
What is the absolute refractory period?
Time during which another stimulus cannot generate an AP
What is the relative refractory period?
Period during which a stronger than normal stimulus is required to generate an AP
What is latency in NCS?
Time from external impulse to recording of amplitude
prolonged in demyelinating conditions
Variables affecting nerve conduction speeds?
- Age
- Size
- Myelination
- UL>LL
- Prox>distal
- Decreased Temp
NCS in neuropraxia shows?
Slowing/conduction block
No fibrillation potentials
NCS in neurotmesis?
Fibrillations and Positive sharp waves on EMG
No voluntary MUAP
NCS in axonetmesis?
Fibrillations
Increased firing rate of MUAP
What do motor nerve conduction studies test?
MUAP = amplitude = no of functioning motor units
What is a SNAP?
Sensory nerve action potential
What is a CNAP?
Combined nerve conduction study - used for mixed nerves
In NCS what is the F response?
Echo used to assess more proximal latency nerve conduction issues
In NCS what is the H reflex equivalent to>
The deep tendon reflex
