Traffic - Week 3 (ch. 4) Flashcards
excitable tissues
capable of producing electrical signals (temporary, rapid changes in membrane potential), nerve and muscle
resting membrane potential
the membrane potential that exists when no net changes in potential are occurring
graded potentials
local changes in membrane potential that vary in magnitude (flow of ions)
action potentials (reverse action)
brief, rapid reversals in membrane potential, which can spread throughout the membrane (flow of ions). inside positive.
voltage-gated channels (action)
Only with AP*** membrane channels that open or close in response to changes in potential
a membrane that has potential is…
polarized
depolarization (deemed for good)
a decrease in membrane potential (inside becomes more positive)
triggering event
event that initiates a depolarization (stimulus like light or touch, chemical messenger)
hyperpolarization
an increase in membrane potential (inside becomes more negative)
repolarization (action potentials) (return)
return to resting potential after a depolarization
Graded Potentials - stronger the trigger….
- stronger trigger➝greater magnitude of change in potential
current flow (graded potential)
when a graded potential occurs, a piece of the membrane (called the active area) has a different potential than the rest of the membrane (which is at resting potential, called the inactive area)
a. current flows between active area and the inactive areas (opposite charges attract)
b. previously inactive areas become active and more current flow occurs
spread of graded potential decreases…
a. as it moves along the membrane because current leaks into ECF
b. function as signals over short distances
spread of graded potential usually not an actual reversal of charges (potential)
just a reduction in potential (inside becomes less negative than before, small depolarization). graded potential important for nerve and muscle cells (e.g., postsynaptic potentials)
Action Potentials (AP) (distance)
can be transmitted over long distances without losing strength
Depolarization for AP
triggering event causes a slow depolarization until threshold is reached (about -50 to -55 mV). once threshold is reached, membrane quickly depolarizes to +30 mV
when triggering event begins depolarization (shooting salt)
some voltage-gated Na+ channels open, Na+ flows into cell (proteins that make up the channel have charged portions, shape change when charges interact with charges surrounding the membrane)
triggering events…
this further depolarizes the membrane, causing even more Na+ channels to open
at threshold
all the Na+ channels are open and there is an explosive increase in Na+ permeability (P Na+)
at peak depolarization (action potential) (goat)
the Na+ channels close (the channel is constructed so that the same depolarization that opens them also closes them)
Repolarization begins (action potential)
as Na+channels close, K+channels open (PK+ increases) due to delayed voltage-gated response to the depolarization, K+ flows out of cell
2. this restores internal negativity
as repolarization progresses…(last step)
a. Na+channels go back to closed, but can open. b. newly opened K+ channels close
(1) hyperpolarization occurs before channels close (membrane even more negative than at resting potential)
(2) resting potential restored
AP lasts…
about 1 millisecond. Ion gradient restored.
Na+-K+ pump restores ion gradients (after repolarization) (action potential) (maintenance man)
a. important for long term maintenance of gradient
b. not necessary between action potentials (AP)
(1) ion shifts during AP are not so great that they wipe out concentration gradients, so many APs can occur