Resting and Action potentials Flashcards
Define flux
What units are usually given to flux?
the number of molecules that cross a unit area per unit time
m^-2s^-1
What is a current and what is is due to?
movement of ions due to potential (difference)
What re the 2 main types of ion channels and which ones are responsible for the resting membrane potential?
voltage dependent - open by a change in membrane potential
voltage independent - open all the time, thereto are responsible for producing the resting membrane potential
What is electrochemical equilibrium?
when the electrical forces (charges) balance the diffusion forces
at this point, the stable membrane potential is established
What is the Nernst equation used for?
to predict the equilibrium potential for a given ion
What are the equilibrium potentials for potassium and sodium?
Why are the real membrane potentials not equal to these values?
Na+ = +73mV K+ = -92mV
depends on the permeability of the membrane to the ion - potassium is the main one that controls resting membrane potential because there are membranes are highly permeable to potassium
What is the origin of the resting membrane potential?
What is the role of the Na+-K+ pump?
movement of potassium ions from outside cells to the inside of cells
the Na+-K+ pump helps to maintain the resting membrane potential
What are the 5 stages of an action potential?
1 - RMP 2 - depolarising stimulus 3 - depolarisation/upstroke 4 - repolarisation and hyperpolarisation 5 - after-hyperpolarisation
Towards the end of the depolarisation stage, what else occurs?
voltage gated potassium channels begin to open (they open slowly)
When does the absolute refractory period occur?
during stage 4 - repolarisation
the sodium channels are inactivated and won’t become activated until the cell repolarises
Why does hyperpolarisation take place?
because the VGKCs remain open for a few seconds after repolarisation (so the membrane potential moves closer towards the equilibrium potential of K+)
What state are the VGSCs in after-hyperpolarisation?
they are closed and their inactivation gate is open
What is the relative refractory period and what happens in it?
the sodium ions channels can be opened agin, but more stimulus is needed to reach the threshold because the membrane potential is more negative then normal
the inactivation gate is the VCSCs are open
Compare the time-course for the opening of potassium and sodium ion channels
potassium ions open and close much slower than sodium channels
Other than reduced axon diameter and myelination, what else can slow the conduction velocity?
cold, anoxia, compression and drugs
