1.16 Evoked potentials Flashcards
Draw a labelled diagram of action potential in
a peripheral axon
cardiac ap
.
Cardiac Action potential
Describe how membrane permeability to key ions renders a cell excitable
- All mammalin cells are enclosed by a phospholipid bilayer
- the cell membrane - Phsyciochemical grdient is established
- allowing elective ion permeability - Potential responsible allowing a cell to be excitable
- Membrane relatively impermeable to most cation except K+
- Intracellular conc K (150mM)
higher than extracellular (5mM)
Mebrane permability continued
- K Leaks out the cell
down conc gradient
terminated by electric gradient that develops d/t imper of other Ions
- RMP where chem grad K out equals electrical gradient pulling K in
(usually -70 mV)
- Main extracellular anion is Cl-
Similiar equilibrium established by balancing its electrochemical gradient
- Relative impermeability of membrane to Na+ helps to maintain electrochem gradient into cell
- However - small amounts of Na + leak intrcell
- 3Na/2k/ATPase is responsible for neutralising - Active pumping of Na out allows Na gradient maintained
- Wihtout pump RMP would disappear and cells rendered unexcitable
Membrane perm continued
Similar mechanism exist for other ion
eg Ca2+ 0 maintained at low conc by membrane expulsion of ion
whilst higher conc Ca is exchanged for Na ions
Subsequently cleared via NaKATPase
Membrane potential is result of eqilibrium of multuples ions
individual charge calculated with Nernst equation
Goldmann Hodgkin Katz equation
aims combine effect multipole ions to generate overall RMO
Cell to be excitable - feature is present in membrane
which following trigger confers charge in membrane permaibility
followed by flux of cations intracellularly
Predom Na
Ion channells or intracellular messneger system usualy responsible
Prcess to restore Resting ptotentialy in palce to reset mechanice for subsequent stimuli
Ecoked potentials in Anaesthesia
Depth of Anaesthesia (AEP)
anaethetic agents decrease amplitude and latency
of early and mid cortcial aep
in dose dependent
Agent indepenednt manner
Early and late responses unaffected by anaesthetic agents
Degree of parylsis - PNS
Neurosurgery
Confirm integfrity of neural pathway during tissue dissection
spinal surgery / acoustic neuroma
Catoid endarterectomy - GA
more senstive subtle changes than EEG
response is slower
Visual evoked
integrity of visual pathway during neurosurgery and around visual pathwya and cortex
Some reasearch shown
somatosensory evoke potentials more sesnsitive
method of assessing epidural level of block
ICU
Prognostic aid in TBI w/ brainstem
poor prog a/w anoxic brain injury
absent evoked potentials
Integrity of nerve pathyways in investigating parlsyed limbs
Diagnosis of neuropathy and myopathy
Monitoring of NMB levels on infusions of muscle relaxants
