Membrane Potential Flashcards
What are excitable cells?
Cells capable of generating action potentials on stimulation including neurons and muscles
Give the definition of an action potential
A short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls
What is membrane potential?
The difference in voltage between the interior and exterior of a cell
what is electrochemical equilibrium?
A combination of the voltage gradient and the concentration gradient of an ion
What drives the flow of any ion through a membrane channel protein?
The electrochemical gradient for that ion
What is equilibrium potential?
The membrane potential at which there is no net flow of the ion, can be calculated by the Nerst equation
What determines the resting membrane potential?
Potassium, because resting channels in animal cells are selective for potassium only
Define depolarization
Making the membrane potential less negative, the cell interior becomes less negative
What is depolarization dependent on?
Inward current of positive charges
Define hyperpolarization
Makes the membrane potential more negative, the cell interior becomes more negative
What is hyperpolarization dependent on?
The outward current of positive charges
What are some properties of action potentials?
Stereotypical size and shape, propagating, all or nothing
Describe upstroke of an action potential
Upon stimulation, inward current depolarizes the membrane to threshold causing rapid opening of Na+ channels but does not reach the Na+ equilibrium potential (65mV)
Describe repolarization of an action potential
Repolarization is the combined effect of Na+ channels closing and K+ channels opening
What is undershoot/hyperpolarization?
The K+ channel conductance remains higher than at rest a while making it approach the K+ equilibrium potential
What is the absolute refractory period?
A period in which another action potential cannot be elected no matter how large the stimulus because the Na+ channels are closed when the membrane potential is depolarized and will remain closed until repolarization
What is the relative refractory period?
An action potential can be elected only if a larger than usual inward stimulus is provided because the membrane potential is closer to the K+ equilibrium and further from the threshold
How long does the relative refractory period last?
Brings at the end of the absolute refractory period and contained until the membrane potential returns to resting levels
What is the accommodation refractory period?
Occurs when the cell membrane is held at a depolarized level such that the threshold potential is passed without firing an action potential because the Na+ channels close and remain closed
How can an action potential be propagated?
By the spread of local currents to adjacent areas of the membrane which are depolarized to threshold
How can conductance velocity while propagating an action potential be increased?
Increasing fiber size to decrease the internal resistance, myelination
Where are action potentials generated on an axon?
Only at nodes of ranvier which increases conductance
Define saltatory conductance
When the action potential jumps from one node to the next
What do inhibitory neurotransmitters do to a post synaptic membrane?
Hyperpolarize the membrane
What do excitatory neurotransmitters do to the postsynaptic membrane?
Depolarize the membrane
