Excitable Cells Flashcards
Intracellular vs extra cellular recording techniques
Extra cellular- electrode outside the cell Intracellular - electrode inside of cell Patch clamping: pinched cell membrane to allow single pump to be measured
Resting potential
More negative charged inside the cells 3Na our 2K in
Events of action potential
- Wave of depolarisation arrives and activates sodium and potassium gated channels. Potassium open slowly.
- Sodium flows in and membrane potential rises
- When it gets to +40 (close to sodium equilibrium potential), sodium channels innactivate, and potassium flows out of the cell, driving potential back down.
- Potential falls almost to potassium potential (-90) before the potassium channels close and Na/K pumps restore the resting potential.
Equilibrium potential
When Force of conc gradient pushing K out = electrical force pulling k+ back into the cell
Osmotic force = electrical force
Driving force:
The electrochemical force generated by the ion causing to go down its electrochemical gradient
What property is capacitors
The ability of the membrane to hold electrical charges on both sides
Voltage
The work or energy needed to separate the charges across the membrane
Nerst equation EZF = RT ln(concentration gradient)
Electrical work = osmotic work R,T,F are constants so with temperature and concentration gradient’ you can figure out what the equilibrium potential is. If you assume temp is 25 degrees, eaution can be simplified to E=58*log(concentration gradient) Concentration gradient = conc in over conc out
Concentrations of N’a and K at rest
Outside: K 4mM. Na 140mM Inside: K 140mM Na 10mM
Driving force
Membrane potential - equilibrium potential of an ion For sodium: -70Mv - (+50mV) = -120mV, so the driving force of -120 mV trying to get sodium into cell For potassium, +20 mV trying to get it out of the cell BUT easier to get potassium out so balances differences in driving force
Properties of action potentials
Triggered by depolarization Threshold of depolarization must be reached At peak, Vm approaches Equilibrium Na Membrane is an excitable during refractory period
Depolarization
Opening of Na channels, Na flows in Membrane voltage driven to Na equilibrium
Repolarization
Opening of K channels, causing K to flow out. Membrane voltage driven to K equilibrium
Absolute refractory period vs relative refractory period
Absolute refractory is during repolarization Relative is during hyperpolarization Because sodium gated channels are inactivated during repolarization
Effect of thin axon, myelination on conduction velocity and why these effects.
Thin axon: conducts slower because axoplasmic (longitudinal) resistance to current in the axon decreases as axon gets wider.
Myelination: conducts faster because it reduces Rm, since there are less channels for the ions to flow out of.
Events in synaptic transmission
Presynaptic action potential
Depolarization of synaptic terminal
Opening of voltage gated calcium channels
Fusion of ACh vesicles with membranes
Release of neurotransmitter (followed by reuptake of degradation)
ACh receptor-activated action channels open, causing activation of Na and K channels
Miniature end plate potentials
Small depolarization of the postsynaptic terminals caused by the random release of a single vesicles of ACh. Sumation of these can cause action potentials.
Excitatory and inhibitory post synaptic potentials
Excitatory: small potential that increases the chances of an action potential occurring in the post synaptic nerve
Inhibitory: small negative potential that causes slight hyperpolarisation and therefore makes it harder for an action potential to occur
Spatial summation
when excitatory potentials from many different pre-synaptic neurons cause the post-synaptic neuron to reach its threshold and fire
Temporal summation
when repeated excitatory potentials from a single neuron pre-synaptic neurons cause the post-synaptic neuron to reach its threshold and fire
Explain how conductance along a channel is altered and how this related to permeabilty
Conductance is the a amount of current that flows through a membrane. Increasing permeability of a membrane to an ion (by opening channels) increases the conductance. Vise versa.
Difference in Na and K conductance during an action potential
K channels open and close slower than Na channels do.
Goldman Hodgking Katz equation (adapted Nerst) what extra factor does it consider?
It takes into account the relative permeability of the membrane to each ion, allowing for a more accurate membrane potential.
Why is there a threshold?
At rest, the membrane is much more permeable to K than Na. Therefore an influx of Na can be counteracted by an outflux of k until a certain point (-50mv).
Explain Rm and Rl
Rl: longitudinal resistance (along the axon)
Rm: resistance across the membrane (vertically through the channels)
What channels help propagate the action potential in the muscle
acetylcholine gated receptors initiate the depolarisation at the neuromuscular junction, then it spreads via sodium and potassium voltage gated channels throughout the muscle.
3 molecules than can cause reduced axonal vesicle release
Low calcium
high magnesium
curare
