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
Potassium vs Sodium gates dissimilarities
potassium gates open later than sodium gates.
delayed rectifier
Potassium conductance (g(K)) serves to rectify/ reset membrane potential
Voltage-gated potassium channels
four separate polypeptide subunits join to form a pore
relative refractory period
the period after an action potential by which it takes more to depolarize and reach the threshold to create another action potential
Orthodromic
action potential travels in one direction: down the acon terminal
Antidromic
backwards propagation
conduction velocity (typical)/length of action potential
10m/s
2ms
factors influencing concudction velocity in an action potential
- spread of action potential along membrane (dependent upon axon structure)
- Path of +ve charge (inside of the axon=faster, across the axonal membrane=slower)
- Axonal excitability (axonal diameter: bigger=faster, number of voltage-gated channels)
- Myelin (layers of myelin sheath facilitate current flow)
saltatory conduction
at nodes of ranvier (in myelinating cells), voltage gated sodium channels are concentrated at the nodes and travel to another node quicker
spike initiation zone
membrane with high density of voltage-gated sodium channels, either at sensory nerve endings or the axon hillock
Neuronal signal transmits
as the generation and regeneration of action potentials
