Principles of electrophysiology

Question 1

What are the 3 layers of connective tissue that surround axon bunches?

Answer 1

Endoneurium
Perineurium
Epineurium

Question 2

What is the physiology of nerve conduction?

Answer 2

Myelinated axons conduct faster than unmyelinated axons
In myelinated fibres there is a linear relationship between fibre diameter and conduction velocity
Myelin acts as an insulator forcing current to travel longitudinally down axon to node of Ranvier
Action potential jumps down nodes increasing speed
Resting membrane potential -90mV
Sodium-potassium pump
- 3 sodium ions pumped out in exchange for 2 potassium ions
- Chloride ions also involve
- Relative concentrations of ions and the charge they carry
Depolarisation of membrane potential to critical level from -90 to -65/75
Sodium channels open and sodium ions flood into cell
Membrane potential reverses to become positive +29/30
This reversal of membrane potential moves in a wave-like manner down the cell
All or none phenomenon

Question 3

What affect does temperature have on NCS?

Answer 3

Increase in amplitude and duration of responses and slowing of conduction velocity

Question 4

What affect does age and height have on action potentials?

Answer 4

Myelination not complete at birth but rapidly completed by age 4-5
Velocity and amplitudes progressively decline above 60
Taller individuals have slower velocities as nerves taper distally
Proximal segments have faster velocities

Question 5

What is neuropraxia?

Answer 5

Failure of nerve conduction with preserved axonal continuity AKA conduction block

Question 6

What happens in neuropraxia?

Answer 6

Focal demyelination
Motor fibres more affected
Good prognosis

Question 7

What is axonotmesis?

Answer 7

Varying degree of axonal function

Question 8

What happens in axonotmesis?

Answer 8

Epineurium unaffected
Resultant Wallerian degeneration
Low amplitude responses
Prognosis variable

Question 9

What is neurotmesis?

Answer 9

Total disruption of nerve and supporting connective tissue with Wallerian degeneration

Question 10

What happens in neurotmesis?

Answer 10

No responses recordable
Poor prognosis
Mixed pattern very common

Question 11

Name a generalised axonal neuropathy

Answer 11

Diabetes

Alcohol

Question 12

Name a demyelinating acute neuropathy

Answer 12

GBS

Question 13

Name a demyelinating chronic neuropathy

Answer 13

Chronic inflammatory demyelination polyneuropathy

Question 14

Name a hereditary motor sensory neuropathy

Answer 14

Charcot Marie Tooth syndrome

Question 15

Name the demyelinating type of GBS

Answer 15

Acute inflammatory demyelination polyneuropathy

Question 16

Name the 3 axonal types of GBS

Answer 16

Acute motor neuropathy
Acute motor sensory neuropathy
Acute sensory ataxia neuropathy

Question 17

What are the main patterns of diabetic neuropathy?

Answer 17

Generalised sensorimotor axonal neuropathy
Glove and stocking sensory loss
Proximal diabetic neuropathy
Autonomic neuropathy
Mononeuritis multiplex
Small fibre neuropathy

Question 18

How does proximal diabetic neuropathy present?

Answer 18

Diabetic amyotrophy - often occurs around switch over to insulin due to poor glycaemic control, often associated with weight loss
Pain the weakness
Femoral nerve most common
Usually unilateral but may spread to other side

Question 19

How does autonomic diabetic neuropathy present?

Answer 19

Dizziness
B/B dysfunction
Sexual dysfunction
Loss of hypoawareness

Question 20

How does small fibre diabetic neuropathy present?

Answer 20

Burning sensation in hands/feet

Often worse at night

Question 21

What are focal but not compressive neuropathies?

Answer 21

Multiple nerves affected but not at typical entrapment sites
Axonal loss
Causes - vasculitis, DM