Chapter 4 Flashcards
The action potential
Cytosol relative to extracellular space
(-ve) charge
Generating an action potential (cause)
caused by depolarization of membrane beyond threshold (-40mV)
Chain reaction example
puncture foot-stretch membrane of nerve fibers-opens Na+permeable channels-Na+ influx-depolarized membrane-reaches threshold-Action potential
Generation of multiple action potentials
Firing frequency reflects the magnitude of the depolarizing current
Depolarization
influx of Na+
repolarization
efflux of K+
Membrane current
the net movement of K+ across membrane
Potassium channel number
proportional to electrical conductances
membrane potassium current
flow and driving force
Rising phase
influx of Na+ (inward sodium current)
transient increase in g(Na)
falling phase
efflux of K+ (outward potassium current)
transient increase in g(K)
hodgekin and Huxley
Voltage clamp creators: clamped the membrane at a chosen potential value.
discovered existence of sodium “gates) in the axonal membrane
Voltage-gated sodium channel
transmembrane, 6 subunits, one pore loop, a selectivity filter, voltage sensor and gate. selective to size of partially hydrated Na+ ion, as K+ is too big to fit. Opens at -40mV
patch clamp method
(erwin Neher) for sodium gated channels
functional properties of Voltage-gated sodium channel
- open with little delay
- Stay open for about 1ms
- Cannot be opened again by depolarization
Absolute refractory period
Channels are inactivated
generalized epilepsy with febrile seizures
a channelopathic genetic disease
tetrodotoxin
clogs Na+ permeable pore
red tide (saxitoxin)
is a Na+ channel-blocking toxin
Batrachotoxin
(frog) blocks inactivation so channels remain open
Veratridine
(lillies) inactivates channels
Aconitine
(buttercups) inactivates channels
clues about 3D structure of channels
due to differential toxin binding sites and result it has on the Voltage-gated sodium channels
Potassium vs Sodium gates similarities
both are open in response to depolarization