AP and voltage-gated ion channels Flashcards
What is depolarisation
Reduction in the difference of electrical potential across membrane nerve/ muscle cell. Excitatory signal. Potential becomes more positive inside cell
What is hyperpolarisation
Increase in difference of electrical potential across membrane nerve/ muscle cell. Inhibitory signal. Potential becomes more negative inside cell
Space constant
V=Voe^-x/lambda. V decays to 37% of Vo
Solution to overcoming space constant
Myelin and APs
What is an AP?
Same signal repeated very quickly on millisecond timescale (depol-hyperpol)
What is myelin?
Formed by glial cells and increases resistance and decreases capacitance. Space constant increases. Velocity of AP increases by 20x
What increases the frequency of APs?
The intensity of the stimulus
All or none law
Small depolarising currents produce passive membrane response but larger current generates AP. Once AP generated, always full size
Frequency code
Refractory period + threshold
What is the absolute refractory period
When sodium channels are inactivated
What is the relative refractory period
When potassium channels open
Activation
Opening following depolarisation
Inactivation
Closing independent of voltage
Deactivation
Closing following hyperphosphorylation
What does the speed of the AP depend on
How far the passive depolarisation spreads
Why are membrane channels needed
Membrane acts as energy barrier for ion crossing
Multiple Sclerosis
Episodic autoimmune destruction of myelin surrounding CNS (poor nerve conduction)
Patch clamping
Glass electrode with very fine tip placed over individual channel. Systematically change voltage using amplifier
How many coding genes code for ion channel subunits
10%
How do channels open?
Mechanical force, temperature, change in voltage, ligand binding
Voltage-gated sodium channel
Single proteins spreads through membrane 4 times. Re-enterent pore loop. TM4 = voltage sensor. Tetramer. K+ too big to pit into channel.
K+ conduction rate
10^7-10^78 ions per second
K+ leak channel
Open. Tetramer. Potassium ions interact with carbonyl groups of TVGYG sequence of selectivity pore
Saltatory conduction
Myelin and nodes of ranvier. Space constant increases
