Nerves

Question 1

Name 3 phases following nerve injury?

Answer 1

1. Wallerian degeneration - Macrophages degrade myelin and axoplasm
2. Schwann cells proliferate and line the endonerium basement membrane
3. Proximal budding (1month) - sprouting axons 1mm/day

Question 2

Variables that affect regeneration? 3

Answer 2

1. Contact guidance - attraction to basal lamina of Schwann cell
2. Neurotropism
3. Neutotrophic factors

Question 3

Anatomy from inside to outside? 6

Answer 3

1. Neuron cell
2. Schwann cell/myelin
3. Endoneurium
4. Fascicles
5. Perineurium
6. Epineurium

Question 4

Name 3 main parts of the microstructure of a nerve?

Answer 4

Perikaryon (body)
Axolemma (membrane)
Axoplasm

Question 5

What is the function of oligodendrocytes?

Answer 5

Schwann cells of the CNS

Question 6

What is the function of astrocytes?

Answer 6

Supportive cells - control nutrition/ NT and K+

Question 7

What do microglial cells do/

Answer 7

“macrophages of the NS”

Question 8

What allows saltatory conduction to take place?

Answer 8

Nodes of Ranvier

Question 9

Name the 3 degrees of nerve injury (Seddon) from least severe to most severe?

Answer 9

1. Neuropraxia
2. Axonotmesis
3. Neurotmesis

Question 10

Main difference between Axonetmesis and Neurotmesis injuries?

Answer 10

Axon = axon and myelin disruption
Neurotmesis = Complete disruption with disruption of endoneurium

Question 11

Functional recovery following injury in order?

Answer 11

Sympathetic
Pain
Temperature
Touch
Proprioception
Motor fx

Some Pangas Temporarily Transect Proper Muscles

Question 12

Nerve fiber types and examples?

Answer 12

A - touch
B - ANS
C - Pain

Question 13

Classification system for nerve injuries and equivalent injury?

Answer 13

Sunderland classification
Neuropraxia 1
Axonetmesis - 2 - 4
Neurotmesis 5

Question 14

Normal resting potential?

Answer 14

-70mv

Question 15

What is the threshold stimulus?

Answer 15

Minimum stimulus required to produce a action potential

Question 16

What is summation potential?

Answer 16

Repetitive subthreshold stimuli may be sufficient to create an AP

Question 17

Steps of generation of AP?

Answer 17

1. Stimulus >-55mv
2. Voltage gated Na channels open
3. Na channels shut and K channels open - start of depolarisation
4. K+ channels slow to shut
5. Na - K ATPase restore to -70

Question 18

What is the absolute refractory period?

Answer 18

Time during which another stimulus cannot generate an AP

Question 19

What is the relative refractory period?

Answer 19

Period during which a stronger than normal stimulus is required to generate an AP

Question 20

What is latency in NCS?

Answer 20

Time from external impulse to recording of amplitude

prolonged in demyelinating conditions

Question 21

Variables affecting nerve conduction speeds?

Answer 21

1. Age
2. Size
3. Myelination
4. UL>LL
5. Prox>distal
6. Decreased Temp

Question 22

NCS in neuropraxia shows?

Answer 22

Slowing/conduction block

No fibrillation potentials

Question 23

NCS in neurotmesis?

Answer 23

Fibrillations and Positive sharp waves on EMG

No voluntary MUAP

Question 24

NCS in axonetmesis?

Answer 24

Fibrillations

Increased firing rate of MUAP

Question 25

What do motor nerve conduction studies test?

Answer 25

MUAP = amplitude = no of functioning motor units

Question 26

What is a SNAP?

Answer 26

Sensory nerve action potential

Question 27

What is a CNAP?

Answer 27

Combined nerve conduction study - used for mixed nerves

Question 28

In NCS what is the F response?

Answer 28

Echo used to assess more proximal latency nerve conduction issues

Question 29

In NCS what is the H reflex equivalent to>

Answer 29

The deep tendon reflex