what 3 things did hodgkin and huxleys voltage clamp experiement predict?
1. sepearete na and k channels
2. voltage sensors in channels
3. high conductance of channels to specific ions
what happens once the patch clampvoltage reaches + 52 mv
early inward Na current is missing
what happens once the patch clampvoltage reaches + 65+ mv
early inward Na reverses to outward instead of inward
outward K current increases in magnitudie as the the voltage becomes more
patch clamp technieque records
microscopic currents (current flowing through a single membrane channel due to depolarization)
what are macroscopic currents due to?
current flow through may channels
what did patch clamp recording show?
provided evidence for single channels
in channels, there is a fast switch between
open and close states
In response to depolarizing effect from the pipette, single channels open and close in a ____ fashion
all or none fashion that is random or stochastic in nature
what does the probability of opening a channel depend on?
depolarization increases the proability a channel will be opened
what is gating? what does it involve?
gating is the transition between open and closed states
involves a temporary conformational change in the channels structure
what does macroscropic current arise from?
the aggregate effects of THOUSANDS of microscopic currents
there is a close correlation of the____ of macroscopic and the sum of many trials of microscopic currents
what is different about K channel and Na channel properties?
K channels have longer latency time and longer duration
also obviously different dierection
(Na on left, K on right)
on average the K+ channels tend to be an ____ state while the membrane is depolarized
open state (this results in a more sustained response)
most cns neurons ahve multiple ___ channels with different characteristics
charactersitics that vary with K channels
1. low voltage vs. high voltage activation (voltage dependence)
2. how fast the population reaches maximum conductance (rate of activation)
3. how fast they inactivate (some dont even inactivate)
what is important about the varying rates of K channel inactivation
produce a diversity of spike waveforms and spike patterns for different cells
Fast AHP ____ action potential
FAST AHP involves ___ repolarization
when does fast AHP affect the early spike frequency
at very high frequencies
what does medium AHP control
controls early interspike interval
what does medium AHP control
1. early spike frequency adaption (slowly activating by Ca entry)
2. late spike frequency adaption
BK K+ channels have ___ inactivation
___ and ___ are nonainactivating K channels
IK and SK
what do slow AHP do?
limits firing frequency by an unkwnon channels
order of channel activation
what is the order of K channel activation
1. Ka and Kdr channels first open
2. Kbk channels open
3/ other known and unknown K channels open
large number of ion channel genes create neurons with diverse ___
fast AHP occurs in ___ seconds