Lecture 2: Graded and Action Potentials Flashcards
the membrane potential outside a cell is assumed to be ___mV and is referred to as __
zero; ground
the inside membrane potential of a cell is measured relative to what value?
ground (0mV)
what happens in the depolarization phase of a membrane potential?
na channels open and na rushes in
during depolarization, the inside of the cell becomes more __(+/-)
+
what happens in the repolarizing/hyperpolarizing phases of a membrane potential?
na channels are inactivated then closed and K channels are open and K flows out
what causes a graded potential?
stimuli that activate VG ion channels causing the cell membrane to become more permeable to certain ions
give 3 examples of stimuli that can cause a graded potential
- applied pressure
- binding of acetylcholine
- binding of glycine
graded potentials are proportional to the ___ of the stimulus
strength
why does a stronger stimulus produce a greater graded potential?
causes more ion channels to be opened
graded potentials are produced at the ___ site, they can spread __ distances
local stimulus; very short
the spread of a graded potential is caused by __
local current flow / local redistribution of charge
t/f graded potentials are good at travelling long distances
false
along with strength, graded potentials are also sensitive to the __ of stimuli
frequency
if a second stimuli is added to a graded potential before it ends, what is the effect on depolarization?
increases (piggy back)
describe the depolarization in an action potential
large and brief/fast
action potential is initiate by depolarization beyond __
threshold
what type of membrane potential is used for long-distance signalling
action potential
what must happen for a graded potential to become an action potential?
a stimuli must be great enough to result in a graded potential that depolarizes the membrane to threshold
what is the typical threshold of a nerve cell?
-50mV
what is the resting membrane potential of a nerve cell?
-70mV
t/f VG ion channels are different from background “leak” channels
true
what causes activation of VG ion channels?
changes in membrane potential (depolarization)
Na channels are ____ (fast/slow) and ___ (transient/sustained)
fast and transient
K channels are ____ (fast/slow) and ____ (transient/sustained)
slow and sustained
during an action potential, permeability to Na is __
high
describe the 4 steps of an action potential
- all channels are closed (rest)
- graded potential depolarization to threshold results in opening of Na channels which accelerates depolarization
- na channels are inactivated and K channels open, causing K to rush out, making the cell more negative (repolarization)
- after hyper polarization sodium channels are now closed and K channels remain open until resting is returned
transient increase in __ results from na channel inactivation
na conductase
do potassium channels require inactivation?
no
t/f action potential are all or none
true
why are action potentials all or none?
once threshold is met and those sodium ions rush in, all the steps must follow to restore resting potential
a bigger stimulus would generated ___ action potential
multiple
t/f a stronger stimulus results in bigger action potential
false
the absolute refractory period begins ___ and ends ___
when na channels open; when na channels recover from inactivation
the relative refractory period occurs when
na channels are closed and K channels are still open, but resting has not been returned
t/f during the absolute refractory period it is impossible to generate another action potential
true
t/f during the relative refractory period it is unlikely but possible for another action potential to be generated
true
why is it harder to start a new action potential during the relative refractory period?
b/c the baseline is lower due to hyper polarization so the depolarization needs to be larger to reach threshold
