electrophysiology Flashcards
RMP
resting membrane potential
charge of cytoplasm of typical cells
-70mV
potassium leak
○ Membrane is 50-75x more permeable to K+ that to Na+
§ K+ leak
Gibbs-donnan effect
§ Macromolecules assembled inside cells
§ Small building blocks diffuse in, and combine to produce larger molecules (proeteins, RNA) that can diffuse out
§ Most proteins ionise as anions (-ve) plus small ion H+ that can leave the cell
§ Traps negatively charged macromolecules in cytoplasm
§ Significant contribution to RMP
leak channels
always open
ligand-gated channels
open or shut when bound boy a specific ligand
voltage gated channels
open at a specific membrane potential, close at a specific membrane potential
influx of Na causes
depolarisation
makes the inside of the cell more positive
efflux of K causes
hyperpolarisation
makes the inside of the cell less positive
need for positive feedback
- Passive local potentials diminish over distance so are no good for transmitting messages
- Depolarising stimuli wont transmit long distances without positive feedback
action potential
□ 'all or nothing response' □ Always the same size (amplitude) □ Positive feedback after threshold value is exceeded □ Des not diminish over distance □ Open voltage gated sodium channels
ligand gated Na channels
open when bound by specific ligands
provide initial stimulus
voltage gated sodium channels
○ Open when membrane potential voltage exceeds threshold
○ Close a few ms later
○ Inactivated for a few ms afterwards (cant be activated again)
- Voltage gated channels K+
○ Open due to membrane potential voltage exceeding threshold
○ Slower to open that Na channels (open later)
○ Close a few ms later
○ K channels don’t lock
positive feedback in AP depolarisation
- Sub-threshold stimuli cause some Na+ channels to open, some Na+ enters the cell causing further depolarisation
- Once the threshold membrane potential is exceeded all voltage gated Na channels open
- Na floods into cell down its electrochemical gradient, causing rapid rise in membrane potential
what causes initial stimulus of depolarisation
ligand gated sodium channel
depolarisation
- At peak membrane potential, the cell is highly positively charges compared to ECF
- Once the cell membrane potential peaks, voltage gates Na+ channels close and voltage gated K channels open
- K+ floods out of the cell down electrochemical gradient causing repolarisation
Hyperpolarisation
- After repolarisation, low K+ in cell and Na is being pumped out
- K+ channels are slower to close so K+ leaks back out of the cell
- Causes ICF to be more negative than at rest (until all the K+ channels close)
Absolute refractory period
Neurone cannot be made to reach AP
intraceullar calcium
maintained at low levels
- Relative refractory period
○ Neurone can generate AP, but requires greater stimulus
○ Some Na+ cannels are reactivated
After AP, neurones need to recover
○ Re-establish polarisation
○ Na+/K+ - ATPase pumps Na out of the cell and K in
3 reasons to have a negative RMP
- Asymmetric ion distribution maintained by active transport
- Membrane is 50-75x more permeable to K+ than Na+ causing K+ leak
- Gibbs donnan effect
a greater stimulus generates
- Greater stimulus does not generate more intense Aps, just more APs
action potential propogation
- When an AP is achieved, it is only achieved in a small part of the membrane (not the whole cell)
- Each AP generates electrical current, which generates a field, which changes the membrane potential next to the part that has generated an AP
- The electrical field depolarises the neighbouring part of the membrane
- Phenomenon spreads along the plasma membrane
action potentials are spread along
membrane microdomains
action potential starts at the
trigger zone - high density of voltage gated sodium channels
why can’t an action potential propagate backwards
the backward areas have locked channels due to refractory periods
AP propagation velocity
2m/s
schwaan cells secrete
myelin
what does myelin do
fat that insulates and prevents action potentials from occurring
myelin secreted by
glial cells
schwaan cells in PNS
oligodendrocytes in CNS
gaps between myeline isolation
nodes of ranvier
the process of jumping between nodes of ranvier is called
saltatory conduction
