When is neurophysiology useful?
In diagnosing and locating nervous disorders and monitoring the brain during surgery
What and how does an Electromyograph test?
Electrode placed in a muscle
- > Measures amplitude and frequncy of potentials at rest
- > Then get the patient to contract
Can also do single fibre Electromyograms e.g. for Myasthenia Gravis
What studies are involved in clinical neurophysiology?
Nerve conduction studies Electromyogram Sensory Studies Electroencephalogram Evoked Potentials (potentials evoked in the brain in response to somatosensory stimulation
What would a sensory study tell us?
Involvement of sensory nerves
Stimulate a sensory nerve fibre in the fingers for instance and measuring the activity of the nerve
In terms of clinical neurophysiology what would appear if you damaged the peripheral nerve, or both dorsal & ventral root above the DRG (Radiculopathy)?
- Peripheral Neuropathy
Slowing of Motor conduction somewhere along the nerve
Motor changes on EMG
No sensory changes on sensory study because the 1st order sensory fibres are undamaged its just they dont connect to the spinal cord so you cant feel them
What is myaesthenia gravis?
Fatigable Weakness with Normal Sensation due to antibodies binding to Ach receptors at the NMJ
How can neurophysiology help with detecting Myaesthenia Gravis?
Single Fibre Electromyography
allows us to compare how long the EPSPs of different adjacent motor fibres take to elicit an AP.
Normally they will be almost identical, in Myasthenia Gravis you get a “jitter” where there’s a slight discrepancy in when the AP is fired in different fibers. This can actually be picked up before the patient experiences any symptoms
Weakness only arises when it gets so bad that the EPSP never reaches potential and APs aren’t elicited at all.
Whats the use of an encephalogram?
Use it to record electrical activity of cortical neurons at multiple points on the scalp.
In order to diagnose epilepsy, assess sleep stages and diagnose braindeath
What are the types of epilepsy?
- Presents in childhood
- Acquired due to brain damage
How is an EEG useful in epilepsy?
- Allows you to diagnose generalised vs focal and locate the specific area
- Helps in planning treatment
- Distinguishes true epilepsy from people with psychogenic attacks
How does a Nerve Conduction study work?
1) Conduction velocity along a nerve
- by asking the patient to move a muscle
- > measuring the response at two seperate points along the nerve
- > Measuring the time difference in the two responses
- > V=S/T
2) Amplitude of the nerves response to stimulation. You move the electrode along until you find an area where the amplitude drops off, this is where the conduction block/demyelination is