Physiology exam 1 potential membrane
Terms in this set (19)
the force with which opposite charged attract each other; measured in volts
change equilibrium potential
a shift towards a resting potential of a more positive value ; happens to membrane when ACH binds and Na+ enters the cell (open channels)
membrane returns to normal resting potential à happens when K+ leaves the cell
a shift in membrane potential past resting levels; happens when K+ channels are open and more K+ than usual leaves cell
trans membrane potential of undisturbed cell
What kinds of cells have membrane potentials? What is responsible for it?
o All cells have trans membrane potential. It is caused by differences in permeability of the membrane to various ions, as well as active transport mechanisms
o Na+ and K+ are not donnan equation because of limited membrane permeability and continued action of Na/K pump
o Protein anions—large negative ions trapped inside
What are two gating mechanisms which alter the permeability of neural and muscle membranes to specific ions?
o Chemical gates- open when they bind specific chemicals; bind ACH at neurotransmitter junction
o Resting state—gate closed à ACH arrives à gated channel opens
o Voltage gated channels- open/ close in response to membrane potential changed. Ca 2+,K+, Na+ (Na+ channels have two gates—activation and deactivation (70 mV when channel is closed, -60 when channel is open, +30 mV when channel is inactivated)
Compare the permeability of a typical cell membrane to sodium ions, to potassium ions, and to protein anions.
Impermeable to protein anions, highly permeable to K+, low permeability for Na+
o Resting potential of neurons and muscles are 70 mV
What is an action potential? How is it generated. What determines its size?
o Action potential- propagated changes in the transmembrane potential that once affected affect an entire excitable membrane
o Generated by graded depolarization, large enough to open volted gated NA2+ channels (reach threshold)
o Size is all or none—all stimuli that bring membrane to threshold generate identical action potentials
How does repolarization of a neuron occur?
o Happens when the chemical stimulus is removed as cell returns to normal resting potential à excess Na+ leaves cell
What is meant by a cell's equilibrium potential?
o The electron voltage that is able to exactly balance the concentration gradient so the net flux of ion movement is zero (calculated by Nernst equation).
. If a cell has a resting membrane potential of - 70 mV and a sodium equilibrium potential of +60 mV, why does not sodium ion simply flow into the cell in large quantities?
o Cell membrane is not freely permeable to Na+ the pump takes 3 Na+ out
9. If a cell has a resting membrane potential of - 70 mV and a potassium equilibrium potential of -90 mV, in what direction would you predict potassium ion would diffuse (net flux) if the permeability of the membrane to K+ were increased?
o If membrane was permeable to K+ if would diffuse out of cell until EQ potential was reached (-90 mV)
11.If a cell has a resting membrane potential of - 70 mV and a chloride equilibrium potential of -70 mV, what can you conclude about the distribution of chloride ion across that cell membrane?
o Electrical equation (donnan) concentration gradient = electron gradient
What are the absolute and relative refractory periods of a neuron? How does the magnitude of a threshold stimulus differ during these two states? Be able to describe the configurations of the sodium and potassium ion channels during these two refractory periods.
o Absolute refractory period- membrane cant respond to further stimulation because cell is repolarizing and Na+ is resetting
o Relative refractory period- membrane can only respond to larger than normal stimuli
o During absolute- Na+ is closed and K+ is open
o During relative- both channels are closed
.How does a threshold stimulus change as the relative refractory period progresses? What ion channel changes are responsible for the changes in threshold stimulus?
o As the relative refractory progresses, transmembrane potential is moving to normal resting potential. So as time progresses, the threshold stimulus becomes easier to reach
o Opening of NA+ channels occurs at threshold
o K+ causes change during refractory periods
14.In what portions of the neuron are voltage-gated ion channels found?
o Voltage gated ions are found in areas of excitable membranes
o Axons, rare in soma, none in dendrites (ex nodes not internodes)
15.In what portions of the neuron are transmitter-gated ion channels found?
o Transmitter- gated ion channels are found in dendrites and cell body of neurons and axons (areas where most synaptic connection occur).