Lecture 5 & 6 - Action Potentials Flashcards
When resting membrane potential increases, is the cell depolarising of hyper polarising? Why?
It is depolarising, since the cell was negative, so if P.D. Increases, it becomes less negative
Differentiate between sodium equilibrium potential, potassium equilibrium potential and the resting membrane potential
Na: the potential when sodium approaches equilibrium, +60 mV
K: the potential when potassium goes to equilibrium, -90 mV
Membrane resting potential: the potential across the membrane at physiological conditions, -70 mV
What is the difference between graded potentials and action potentials?
Graded potential
- Small change in voltage
- variable magnitude
Action potential
- only occur after threshold is reached
- set magnitude
Differentiate between repolarisation and hyperpolarisation
Repolarisation:
• returning from > -70mv to -70 mV
Hyperpolarisation
• membrane potential becomes less than -70 mV
Describe what is happening in a graded potential
Stimulus opens a Na channel
Na rushes in, depolarising the active region
Local current flow to neighbouring regions
How can the magnitude of the graded potential be varied?
The strength of the stimulus
Describe what happens to the magnitude of graded potentials when they spread out away from the initial area
There is loss of current and so the potential difference decreases
Describe the processes occurring during an action potential
- Stimulus adequate to trigger an AP at the hillock
- Voltage in cell increases past the threshold (-50 mV)
- Voltage gated Na channels open, sodium rushes into the cell, depolarising it
- At +30 mV, the voltage gated Ma channels close and K+ channels open.
- K rushes out of the cell, re polarising the cell
Describe the structure of the voltage gated sodium channel
Two gates:
Activation gate: closed just before threshold is reached
Inactivation gate: closed once the cell depolarises
Describe the effect that opening of sodium channels has on other sodium channels in the vicinity
Positive feedback:
• opening some channels leads to depolarisation, which leads to the opening of more channels
Trigger:
- Membrane depolarises somewhat
- Channels open - further depolarising
- More channels open
Do bigger or smaller diameter axons have reduced internal resistance, and thus conduct action potentials more quickly?
Big diameter
How are action potentials conducted down a membrane?
Due to Local Current Flow
Once one region reaches threshold and depolarises, the neighbouring region will also depolarise to threshold and fire.
This spreads down the axon.
The action potential can not flow backwards due to refractory periods
What is a more efficient way of speeding up action potentials, instead of increasing the diameter of the axon?
Myelination
When does the membrane become more permeable to Na?
Just after threshold is reached
When does the membrane become more permeable to K?
More slowly, once the cell has depolarised
