clinical neurophysiology

Question 1

what are the clinical neurophysiological tests for the following

1. peripheral nervous system
2. brain
3. sensory pathways
4. visual pathways
5. motor pathways

Answer 1

1. peripheral nervous system - nerves conduction studies (NCS) and electromyography (EMG)
2. brain - EEG
3. sensory pathways - somatosensory evoked potentials
4. visual pathways - visual evoked potentials
5. motor pathways - transcranial magnetic stimulation

Question 2

what is saltatory conduction?

Answer 2

Action potentials traveling down the axon “jump” from node to node in myelinated axons. This is calledsaltatory conduction. It mediates faster AP propagation, thus, more conduction speed

Question 3

how to carry out NCS for sensory function?

Answer 3

• electrical stimulation makes the outside of nerve -ve
• therefore, the inside is +ve comparatively - this trigger an AP which moves down the nerve
• this is recorded with surface electrodes
• the size of response and speed is measured

Question 4

how to carry out NCS for motor function?

Answer 4

• electrical stimulation induces an AP
• AP reaches the MNJ to cause Ach release
• Ach activates AchRs on the muscles to contract - a visible twitch is seen
• the size of response and speed is measured

Question 5

how to interpret the NCS measurements?

Answer 5

1. small response - axon loss

2. slow response - myelin loss (demyelination)

Question 6

name cases in which EMG is carried out?

Answer 6

• axonal neuropathy
• demyelinating neuropathy
  1. ulnar neuropathy/ focal nerve neuropathy
  2. generalised peripheral neuropathy
  3. myopathy
  4. MND

Question 7

what happens in myasthenia gravis?

Answer 7

normally, the time b/w contraction of muscles fibres are same however, in MG it varies - this called jitter

Question 8

how and when is EEG its carried out?

Answer 8

• primarily one for patients with seizures
• electrodes placed ins specific locations on the scalp
• patients asked to various things during the recording e.g. closed eyes, hyperventilate, under photo stimulation

Question 9

what are the uses of somatosensory evoked potentials?

Answer 9

1. MS - demyelination slows impulses so response recorded from scalp is delayed
2. intra-operative monitoring e.g. spinal cord surgery
   - if cord is compromised, response gets smaller and then is lost

Question 10

what are the uses of visual evoked potentials?

Answer 10

MS - demyelination of optic nerve

Question 11

how does the TMS work?

Answer 11

• Place magnetic over motor cortex and record from a contralateral muscle
• A brief magnetic pulse induces an electric current that excites cells in the motor cortex
• These fire down the motor pathway – can record a response from a
  limb muscle: the motor evoked potential

Question 12

what are the uses of TMS?

Answer 12

• looks at the integrity of motor cortex and target muscle
• used in MND, MS
• also used as therapeutic tp treat severe depression