neurophysiology Flashcards
what neurological disorders are nerve conduction studies useful in?
MND, radiculopathy, brachial neuritis, peripheral neuropathy, entrapment neuropathy, myasthenia gravis, Lambert Eaton Syndrome.
what is the latency ?
time between stimulus and potential
what are the normal conductance speeeds for an adult?
arm> 48ms leg >38ms
what happens to the action potential in demyelinating pathology?
it is delayed
what happens to the action potential in degeneration?
reduction in amplitude because there are fewer axonc contributing to the impluse.
what is a normal sensory amplitude?
> or = to 5 micro volts
what is an F wave?
conduction the opposite way up the nerve resulting in a second delayed wave
what is decrement?
when the nerve is repeatedly stimulated, the amplitude of the action potential diminishes with each impulse.
in what conditions would you find decrement?
lambert eaton, and myasthenia gravis
in which condition would you see increment and decrement?
lambert eaton myasthenic syndrome
what is increment?
initial excessive amplitude, followed by decrement.
what evoked potential tests can be done?
somatosensory EPs upper and lower limbs
VEPs/ERGs ( electroretinograms)
Auditory
MEP
what can SSEPs be used for?
test when suspected demyelination and myelopathy
IE ms
spinal cord lesions
what can VEP readings tell us
normal VEP: visual pathway intact
absent VEP: atrophy
unilateral latency: slowing of conduction ie demyelination
reduced amplitude: ischaemic disease of the eye and optic nerve
BAEPs can be used to
screen hearing in infants
evaluation of possible acoustic neuroma
evaluate peripheral and central auditory pathways in sedated and anethatised patients
