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Flashcards in Action Potentials Deck (17):

What is hyper polarisation

The mem pot becomes more negative


What does ionic movements across the cell mem cause

Changes in mem pot


The direction of the change in potential depends on

The direction of the movement of the ion or out of the cell
The charge carried by the ion


What does the movement of ions across the mem need

Ion channels


What is passive movement of an ion dept on

Driven by electrochem grad for that ion


Why does sodium move inward

Conc grad is inward
Electoral grad inward
Mem potential -80mv negative to equilibrium potential for sodium
Driving force for sodium influx simply vm- Ena


What are ion channels

Protein complexes that span lipid bilayer to form a central pathway that allows rapid flow of selected ions

Either open or closed

May be gated - mem voltage, chem subs, physical stimuli

Ion channels responsible for action potential in neurones
- voltage activated sodium channels depo
- voltage activated pott channels hyperporlarising


What are the properties of action potentials in neurones

APs are brief electrical signals which polarity of nerve cell mem momentarily reversed

APs propagate along nerve cell axons with constant magnitude and velocity allowing signalling over long distances

APs are gen when threshold is reached therefore are all or none


What are voltage activated sodium and pottasium channels

Both highly selective for their respectable cations
Both activated by mem depo - sodium channels rapidly, pottasium changes with a slight delay

Activation of sodium channels self reinforcing positive feedback
Activation of pott channels self limiting negative feedback


What are the refractory period and sodium inactivatin.

After sodium channels being open state they enter non conducting inactivated state

Repo required for channel to enter closed state

Inactivation contributes to the repo phase of action potentail and is responsible to refractory period


What is an absolute and relative refractory period

Absolute refractory peirod - no stimulus however strong can elicit a second action potential, all sodium channels inactivated

Relative refractory period - a stronger than normal stimulus may elicit a second action potential, mixed pop of closed and inactive channels


How do local anaesthetics work

Such as lignocaine
Are very frequently employed to prevent action potentials discharge in sensory neurones in repsonse to noxious stimuli that ultimately give rise to perception of pain by the Brian

Block pore of voltage activated sodium channels
Increase amount of time that sodium channels sends in inactivated state

Net effect is to prevent the upstroke of the AP


What does it mean the cell mem being leaky

Nerve cell mem is leaky hence passive signal do not spread far from site of origin due to current loss across mem


Passive conduction and action pot velocity

Passive conduction - is a factor in propagation of AP
The longer the length constant the greater the local current spread
Greater local current spread increases AP condition velocity


What are some strategies to increase passive current speed

Decrease ri ( by increase diameter)
Increase rm ( add insulation myelination)
Conduction in myelinated axons much faster than non myelinated


What happens at a node of ranvier

AP jumps from one node to the next


What is depolarisation

The mem pot becomes less negative