Cellular excitability Flashcards
electrical signals can be split into…
action potentials and graded potentials.
what are action potentials (basic)?
a fixed rise in membrane potential, an all-or-nothing signal that propagates along the axon.
what are graded potentials (basic)?
they have a variable size, are local signals so do not propagate over long distances.
what is resting potential?
at rest, the outside of the axon membrane is positively charged compared to the inside - because there are more positive ions on the outside than there are on the inside.
how is resting potential achieved?
a sodium potassium pump moves 3 Na+ out for 2 K+ in - is a process that requires ATP.
there are more K+ leak channel proteins than Na+ leak channel proteins, more K+ diffuse back to the outside of the membrane.
ionic gradients influence membrane potential by determining equilibrium potential.
what is equilibrium potential?
it is the membrane potential that would be achieved in a neuron if the membrane was selectively permeable to an ion.
what is the Nernst equation used for?
it is used to calculate equilibrium potential for an ion.
how do we calculate the resting potential when the membrane is permeable for a large no. of channels?
the Goldman equation.
what is threshold in action potentials?
sufficient voltage-gated Na+ channels open so that permeability to Na+ is greater than K+.
what is rising phase in action potentials?
rising depolarisation caused by large force drives Na+ into the neuron.
what is falling phase in the action potential?
voltage-gated Na+ channels inactivate, voltage-gated K+ channels open, large force drives K+ out of the neuron.
what is undershoot in action potential?
voltage-gated K+ channels add to resting K+ membrane permeability and reduced Na+ permeability, so electrical force = diffusional force.
what are two factors that influence conduction velocity?
diameter and myelination.
