Clinical Neurophysiology Flashcards
What are some clinical neurophysiology investigations?
- Nerve conduction studies/Electromyography (EMG)
- To investigate problems of peripheral nerve and muscle
- EEG
- Electrical activity within the brain, investigate epilepsy and states of altered consciousness
- Evoked potentials
- Visual and somatosensory, investigate problems in central pathways
What does EMG stand for?
Electromyography
What do nerve conduction studies/Electromyography (EMG) investigate?
Problems of peripheral nerve and muscle
What does EEG investigate?
- Electrical activity within the brain, investigate epilepsy and states of altered consciousness
What does evoked potentials investigate?
Visual and somatosensory, investigate problems in central pathways
What does nerve conduction studies examine?
- Conduction velocity
- Level of myelination
- Amplitude
- How many working nerves
What does the conduction velocity in nerve conduction studies indicate?
- Level of myelination
What does the amplitude in nerve condition studies indicate?
How many working nerves there are
How are nerve conduction studies performed?
Measurement of activity is taken at two different points of nerve (such as along arm) and the distance measured, this can be used to work out the conduction time and velocity
How are sensory studies performed?
Similar technique to nerve conduction studies stimulating the sensory nerve fibres in the fingers to allow for measurement of sensory and motor function separately
What is ulnar neuropathy?
disorder involving the ulnar nerve, may be caused by entrapment of the ulnar nerve
Where is the site of ulnar neuropathy normally?
- Most often at the elbow
- Occasionally at the wrist
What is the clinical presentation of ulnar neuropathy?
Ulnar distribution numbness
Wasting of small muscles, especially FDI
First thing that occurs with a trapped nerve in demyelination, which causes the action potential to decay and die away, progressing slowly (known as conduction block)
Conduction velocity should be measures in different parts of the nerve path, slow areas are where the neuropathy occurs
Amplitude of sensory fibres becomes small because has lost axons
What is seen in investigations for ulnar neuropathy?
First thing that occurs with a trapped nerve in demyelination, which causes the action potential to decay and die away, progressing slowly (known as conduction block)
Conduction velocity should be measures in different parts of the nerve path, slow areas are where the neuropathy occurs
Amplitude of sensory fibres becomes small because has lost axons
How does ulnar neuropathy impact conduction velocity?
Conduction velocity should be measures in different parts of the nerve path, slow areas are where the neuropathy occurs
Do peripheral nerve lesions lose motor or sensory fibres?
Peripheral nerve lesion loses both motor and sensory fibres:
- Motor cell body is in spinal cord, if cut the nerve at a point everything distal dies for motor, but proximal for sensory as cell body is outside of spinal cord
EMG can record two different fibres within the same motor unit, what can happen to the timing of firing in disease?
- In neuromuscular junction disease that tight relationship between the two is lost, resulting in a jitter
- This is due to basic physiology
- EPSP
- Threshold
- AP firing
- Normally more Ach is released than required to ensure threshold for firing action potential is reached, but if some end plate potentials are dropped the end plate amplitude drops and threshold is reached later on in time, causing considerable variation in time from firing the action potential
- Timing of second in relation to first jumps around, measured as jitter
How large an area does each EEG electrode record?
Each electrode records from the cortex a couple of cm in diameter beneath it:
- About 20 electrodes taped to scalp
- Takes about 20 minutes with the patient sitting quietly or doing something that alters brain function such as showing lights
- Can leave on longer to look at prolonged recordings
