Module 3: Lecture 2 Flashcards
what dictates what ion drives membrane potential?
the permeability
- the greater the permeability of the plasma membrane for a given ion, the greater is the tendency for that ion to drive the membrane potential toward the ion’s own equilibrium potential
are leak channels always open?
yes, they are passive
- ions are always passively passing through
what channels dictate the resting membrane permeability?
the leak channels
are there more potassium or sodium leak channels?
more potassium leak channels
- this is why potassium can leave the cell much more than sodium can enter
the resting membrane potential is more dictated by? why?
potassium. this is because more positive ions is leaving the cell than more positive ions is entering
why is potassium more permeable at rest?
because there is more potassium leak channels
what is the net resting membrane potential of a neuron?
usually -70mV (much closer to potassium’s membrane potential)
how much more permeable is potassium to sodium at rest?
50-75 times more permeable
the passive ion movements are responsible for how much of the resting membrane potential? what is responsible for the rest?
80%
- Na+/K+ pump is responsible for the other 20% (active transport)
what can change the membrane potential?
ions concentration across the membrane
what does a structure of a cell dictate?
its function
what goes through very transient and rapid changes in their membrane potentials?
neural and muscle cells
what can neural cells or neurons do?
- receive a signal
- initiative/elaborate a message
- transmit a message
what is polarization?
separation of charge across the membrane
- membrane potential does NOT equal 0mV
- not static - it can rapidly change
what is depolarization?
- decreasing the amount of polarization that has occurred
- less charge that is separated across the cell membrane
- the membrane is less polarized than under resting conditions
- polarization goes closer to 0mV
what is repolarization?
- the membrane returns to resting membrane potential value AFTER having been depolarized
what is hyperpolarization?
- increase in the magnitude of the negative potential –> membrane is more polarized than under resting conditions
- separated more charge across the membrane
what is generated when resting potential changes?
electrical signals
what are the two forms of electrical signals?
- the graded potentials (short-distance signals) - very localized
- the action potentials (over long distances)
what is the main difference between the two electrical signals?
the distance they occur over
what triggers an action potential?
graded potentials
what is a graded potential?
- local changes in the membrane potential
- short distance signals (small areas of a cell membrane change their potential)
- graded potentials can have various magnitudes and durations
when are mechanically gated channels going to open?
- in response to some sort of triggering event like a touch for example
when we open a gated channel, does our cells become more negative or positive? why?
more positive because sodium can now enter (can be -50mV as opposed to -70mV)
- this causes a depolarization. we are getting less charge difference between the inside and outside of the cell
what are the two types of triggering events of a gated channels?
- chemically (usually a neurotransmitter)
- mechanical (ex. touch)
when a depolarization occurs in an area due to a graded potential, what is that area called?
the active area
- a localized area so the area around it will be the inactive area
graded potentials can vary in both?
magnitude as well as duration
a graded potential is generated where?
at a specific point on the plasma membrane
what opens chemically gated ion channels?
they open in response to a neurotransmitter
what is the beginning of a current?
the active and inactive areas have opposite charge differences across the membrane
the direction of CURRENT flow is always designated by the direction in which?
the positive charges are moving
when do inactive areas become depolarized?
when there is a spread of those positive sodium ions in the cell because of the graded potential previously created
- happens after gated channel closes and no more ions are enters
what does it mean that “graded potentials are decremental”?
as it moves along the cell membrane, it decreases in magnitude. they are getting weaker. so it progressively decreases as it traverses along that cell membrane
- returning it back to polarization
- both dispersion among the large area or the cell and also physically leaving the cell
what is the reason as to why graded potential is decremental?
- the leaking of charge-carrying ions across parts of the membrane (from leak channels)
- sodium leaves from leak channels to return back to its resting polarization
what are action potentials?
changing membrane potential
- flow of ions
- brief and rapid
- large amplitude
- the membrane potential reverses: the inside becomes more positive than the outside (not simply less negative than the outside as can occur for the graded potential)
- strength is the same as when they are initiated to when they end (not decremental)
what initiates your action potentials?
a graded potential can generate an action potential if it reaches a sufficient magnitude (threshold potential)
- when the threshold potential is reached from enough depolarization
what is the threshold potential that changes a graded potential to an action potential?
-55 to -50mV
when is the threshold potential reached?
- if there is sufficient magnitude of a stimulus
- enough sodium or enough depolarizing events occur and enough sodium enters to cell to depolarize the resting membrane from -70mV to -55 or -50mV
what is needed to turn a graded potential into an action potential?
many graded potentials because they are very weak
- depolarization is slow (graded potentials) until it reaches the threshold potential of -55 to -50mV
