Resting and Action Potentials Flashcards
Explain why the resting membrane potential of most cells is around -70 mV.
The equilibrium potential of potassium is around -80 mV and the membrane is very permeable to potassium so the resting membrane potential is around the same as the equilibrium potential of potassium.
What does the Nernst equation show?
It allows you to calculate the equilibrium potential of a particular ion (dependent on temperature and charge)
What does the Goldman-Hodkin-Katz equation show?
Takes into account the permeability of the membrane to different ions so you can figure out the resting membrane potential.
What is electrochemical equilibrium?
The point at which the concentration gradient balances the electrical gradient.
What is equilibrium potential?
The potential that prevents diffusion of ions down its concentration gradient.
What is the difference between graded potentials and action potentials?
Action potentials are an all-or-nothing event - they have the same amplitude every time
Graded potentials can vary in amplitude and the amplitude is affected by the strength of the stimulus. Graded potentials can be positive or negative and they decrease in altitude as they travel away from the point of origin.
Where do graded potentials occur?
Synapses and sensory receptors
What is the role of graded potentials?
Generate or prevent action potentials
What are the two gates in voltage gated ion channels?
Activation gate - opened by conformational changes
Inactivation gate - ball and chain
What happens during depolarisation?
Depolarisation makes the voltage gated sodium channels open so there is a large increase in the permeability to sodium. The membrane potential drives towards the equilibrium potential of sodium. The voltage gated potassium channels are much slower to activate.
What happens during the start of repolarisation? What makes this the absolute refractory period?
The inactivation gate of the VGSCs close meaning that regardless of the stimulus strength, another action potential cannot be generated - absolute refractory period
What is the relative refractory period?
The activation gate closes and the inactivation gate opens so an action potential can be generated but only with a stimulus of greater than normal strength.
How long does a normal action potential last?
2 ms
What factors affect conduction velocity?
Myelination and diameter (greater diameter = faster)
