graded potentials and action potentials (lec 4) Flashcards
excitability
- ability to produce an electrical signal that can transmit information between different regions of the membrane
- their membrane is called excitable membrane
polarized
resting membrane potential : -70mV
depolarization
-cell is getting more positive following resting state
overshoot
inside cell is more positive because K+ channels have not begun to open yet (slow)
repolarization
- coming back to -70 mV
- K+ channels are finally open
hyperpolarized
potassium channels slow to close so cell becomes more negative than normal polarized cell
graded potentials
- a small, local change in membrane potential
- can occur in depolarizing or hyperpolarizing direction
- are graded
- are decremental
- can be summed
- have no threshold
action potentials
- can be sustained nerve signaling over longer distances
- are large alterations in membrane potential
- are rapid and have a high frequency
- need voltage gated channels to occur
- 1-2ms duration
- all-or-none
- cannot be summed
- has refractory period
na+ and K+ voltage gated channels
- activated by a change in electrical membrane potential
- important for action potentials
- both channels open at -55 mV
- K has only activation gate, Na has activation and inactivation gates
ligand gated channels
- open in response to the binding of a chemical messenger
- important for graded potentials
mechanically gated channels
- open in response to physical deformation
- important for graded potentials
action potential 3 phases
action potentials occur at action hillock
-rising (depolarization)
stimulus occurs to get to -55mV
voltage-gated Na+ channels open at ciritcal threshold -55mV
-falling (repolarization)
Na channels closed
voltage gated k+ channels triggered open at -55 but very slowly
-after-hyperpolarization
K+ channels slow to close = hyperpolarized
true or false : action potentials are all-or-none phenomenon
true
-once it hits -55mV action potential happens automatically
Na+ channels : resting state
- activation gate is closed
- inactivation gate is open
see lect 4 for specific openings and closing of channels
DRAW IT OUT
lidocaine and tetrodotoxin
- prevents action potentials by blocking voltage-gated Na+ channels
- poison produced by puffer fish that blocks Na+ voltage gated channels
threshold stimulus
- just strong enough to depolarize the membrane to this level
- usually 15 mV less negative than resting membrane potential
absolute refractory period
- second action potential cannot be triggered
- AP will not fire
- sodium channels already open during rising and during falling there is an inactivation gate inhibiting from firing
relative refractory period
larger than normal stimulus is required to trigger another action potential
-AP can fire
AP
- 1 sec ~ 10 million ions can diffuse through 1 ion channel
- 50 million ions to change membrane potential by 100 mV
- one AP WILL NOT AFFECT concentration gradients
DO graded or action potentials lose strength with distance
- graded potentials lose strength with distance
- AP do not
why doesnt action potential propagate backward?
-refractory period prevents firing of another AP
saltatory conduction
- action potentials jump from node to node as they propogate along a myelinated fiber
- dont actually jump, are generated at each node
- at nodes of ranvier
what do myelin on axons help with?
- sends info faster than an axon without myelin
- faster and with minimal leak
- greater myelination and diameter = faster conduction
