Neurophysiology lectures Flashcards
Routine Nerve conduction studies don’t assess EVERYTHING in the PNS - they only assess….
- LARGE-diameter myelinated fibers
NOT - small sensory autonomic fibers
What is distal latency?
Time needed for the FASTEST conducting nerve to generate a muscle fiber AP
What is amplitude?
Total number of axons activated by a SUPRAMAXIMAL stimulus
What are the three electrophysiological hallmarks of demyelination?
- Prolongation of the distal latency
- Slowing conduction velocity (D/T)
- Conduction block
What does a reduced amplitude suggest?
Loss of axons
What does slowed conduction velocity suggest?
Demyelination
Define a conduction block (demyelination BUT NO AXONAL LOSS) in terms of latency and amplitude
- Normal amplitude distal to lesion/block
- Reduced amplitude proximal
Fibers fail to conduct between wrist and elbow
WITH AXONAL Loss describe latency and amplitude
- Reduced amplitude both proximal and distal
2. Normal or mildly slowed conduction velocity
Axonal loss may look like a conduction block, decrease in amplitude proximal, normal amplitude distal (1-3 days) but what happens later?
Conduction failure will appear after 7-10 days.
What does the needle electrode examination involve?
- Assessing motor function only
- Assessing spontaneous (relaxed) activity
- Assessing motor units (voluntary)
What is seen in the Needle electrode exam with axonal injury?
Fibrillation potentials (TAKE 3-6 weeks to develop after axonal damage) suggests lesion is subacute
Whereas LARGE amplitude - long duration - chronic
What are the 3 key features of a neurogenic lesion?
- Motor units need to fire faster (REDUCED RECRUITMENT) can’t RECRUIT more
- Motor units become larger in size with reinnervation
- LARGE SCALE (large units)
What are the 2 features of a myopathic lesion?
- Less motor units - smaller
- More motor units need to be recruited even in early (low-level) contraction
EARLY/RAPID RECRUITMENT - SMALL scale (small units)
