clinical neurophysiology Flashcards
what are the clinical neurophysiological tests for the following
- peripheral nervous system
- brain
- sensory pathways
- visual pathways
- motor pathways
- peripheral nervous system - nerves conduction studies (NCS) and electromyography (EMG)
- brain - EEG
- sensory pathways - somatosensory evoked potentials
- visual pathways - visual evoked potentials
- motor pathways - transcranial magnetic stimulation
what is saltatory conduction?
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
how to carry out NCS for sensory function?
- 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
how to carry out NCS for motor function?
- 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
how to interpret the NCS measurements?
- small response - axon loss
2. slow response - myelin loss (demyelination)
name cases in which EMG is carried out?
- axonal neuropathy
- demyelinating neuropathy
1. ulnar neuropathy/ focal nerve neuropathy
2. generalised peripheral neuropathy
3. myopathy
4. MND
what happens in myasthenia gravis?
normally, the time b/w contraction of muscles fibres are same however, in MG it varies - this called jitter
how and when is EEG its carried out?
- 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
what are the uses of somatosensory evoked potentials?
- MS - demyelination slows impulses so response recorded from scalp is delayed
- intra-operative monitoring e.g. spinal cord surgery
- if cord is compromised, response gets smaller and then is lost
what are the uses of visual evoked potentials?
MS - demyelination of optic nerve
how does the TMS work?
- 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
what are the uses of TMS?
- looks at the integrity of motor cortex and target muscle
- used in MND, MS
- also used as therapeutic tp treat severe depression