Action Potential Flashcards
What is the resting membrane potential
-70mV
At the cell membrane, are the ICF and ECF positive or negative
ICF is negative
ECF is positive
What concentrations of Na, K and Cl are found in the ECF
Na - 145mM
K - 4mM
Cl - 110mM
What concentrations of Na, K and Cl are found in the ICF
Na - 15mM
K - 150mM
Cl - 10mM
Describe the diffusion potential of a cell at resting membrane potential
Impermeable to Na
Very permeable to K
Describe the diffusion gradients of a cell
Na diffuses into the cell
K diffuses out of the cell
What creates the resting membrane potential
Diffusion of K gives an excess negative charge inside of the cell membrane and an excess positive charge outside of the cell
What happens to small amounts of Na which leak into the cell at resting membrane potential
It is expelled by the Na/K pump
How does the N/K pump contribute to the resting membrane potential
It exchanges unequal numbers of Na and K ions
It moves 3Na outwards and 2K inwards
What causes an action potential to form
A stimulus
What is the threshold in an action potential
The voltage at which the voltage gated sodium channels open, allowing sodium influx
-55mV
What causes the falling phase in an action potential
Voltage gated K channels open allowing K efflux
What are the different types of ion channels
Ligand gated - activated by a ligand binding to a receptor
Voltage gated - when the RMP is moved to a threshold voltage which opens the channel
Describe a voltage gated sodium channel at resting membrane potential
M-gate is closed and h-gate is open so sodium cannot pass through
Describe voltage gated sodium channels when the threshold is reached
Both the m-gate and the h-gate are open so sodium can pass through
Describe a voltage gated sodium channel during the refractory stage
M-gate is open but the h-gate is closed so sodium cannot pass through
Describe a voltage gated potassium channel
Can either be open or closed
Potassium leaves the ICF when open
Describe an action potential when the threshold potential is met
Na channels start opening causing sodium influx which promotes depolarisation and sodium channels keep opening
Potassium channels remain closed
What happens after depolarisation
When MP reaches 35mV the Na channels shut as the h-gate closes
K channels open and K efflux begins, creating a recovery to the RMP
What is the refractory period
The period of inexcitability of an action potential due to the inactivation of voltage gated sodium channels
The h-gates are shut so NA can’t diffuse into the neurone
What are the effects of the refractory period
Limits maximum firing frequency of APs in axons
Ensures unidirectional propagation of APs
Prevents summation of APs
Prevents summation of contractions in the cardiac muscle - AP lasts as long as ventricular contraction
Describe action potential propagation
An AP sets up longitudinal current flow
This depolarises adjacent resting parts of the axon
The AP is regenerated further along the axon
More current flows and the next region of axon is activated
APS travel along the axon as waves of depolarisation
What increases the speed of action potential propagation
Increasing axon diameter
Myelin sheaths
What is a myelin sheath
Many layers of cell membranes wrapped around the axon
