Chapter 6 and 7: membrane potential and Action Potential Flashcards
resting potential
- resting charge of athe neuron (relative difference in voltage btwn inside and outside of cell)
- (-)70 mV
how measured
voltage amplifier and oscilloscope
major players in resting potential
-K+ NA+ Cl- Ca++ Proteins (A-)
which are inside and outside
K+ inside NA+ outside Cl- outside Ca++ outside A- inside
equilibrium potential
- balance between diffusion and electrostatic pressure of ions
- ex K=
- diffusion=out
- electrostatic pressure=in
Nernst equation
used to determine an ions equilibrium potential
equilibrium potentials of ions
K+ = -75 Na+ = +55 Cl- = -60
neurons at rest are permeable to several types of ions
- K+, many open channels
- Na+, only a few open channels
- Na+ influx pulls resting potential closer to 0
- leaky membrane
how is equilibrium maintained with leaky channels?
- pumps
- NA+/K+
- also several Ca++
- pumps are slower, require energy, different structure than ion channel. binding site, not pore
what happens when permeability changes?
-dendrite vs axon
- wont see AP at dendrites
- only see graded potentials at dendrites and cell body
- depolarizing axon will see AP at certain level
graded potential
-initial stimulus, needs to reach axon to create action potential
4 properties of AP
- threshold: graded potentials to certain voltage, than AP happens. Once depolarization gets over threshold, AP happens (all or none)
- All or none-same every time once you get over threshold
- does not diminish (self regenerative)
- followed by refractory period (period of time where you cant get another AP)
two critical voltage gated channels
- Na+
- K+
change in potential opens gate
two key differences - Na+ channels open faster
- Na+ channels become inactivated
what does K+ want to do gradient wise
wants to diffuse out, but is attracted to inside of cell because of electrical gradient
what does Na+ want to do
diffuse in, electrical gradient is also pulling it in
-remember that resting potential is +55 for Na+
what does Cl- want to do
diffuse in, charge pushes out
what makes resting potential charge -70
-4 factors of cl-, na+, K+ and A- at rest create charge of -70
how ap works
- stimulus applied to neuron
- na+ channels open, because fastest, allow Na+ into cell
- K+ channels will open, but slower. when they do open, potassium leaves the cell
- at peak, Na+ channels inactivate, K+ continues to exit
- exiting K+ brings cell back to negative potential, K+ channels clise
- remainging K+ ions outside cell (+ charge) make the inside of the cell negative (relative to outside) so cell is briefly hyperpolarized
- Na+ de-inactive (ready to be opened again)
- K+ ions diffuse away outside cell and cell returns to rest (Na+/K+ pump at work to reestablish equilibrium)
absolute refractory period
-period of time following an AP during which no stimulus can initiate another ap - mediated by the inactivated Na+ channels (peak of stimulus)
relative refractory period
-period of time follow and ap during which an ap can be initiated only by a stronger than normal stimulus. occurs at point that the na+ channels are de-inactivated, but membrane is still hyperpolarized (K+ hasnt diffused away yet)
where are voltage gated Na+ channels located
axon hillock, not dendrites
saltatory conduction
in myelinated axons
- ap jumping down axon bc myelin sheath
- unmyelinated is more like wave
demyelinated axon (ex ms)
-ap cannot reach terminal butoun. not the same as normal unmyelinated ap, this neuron is made to be myelinated but the myelin is gone, and there is too much distance between the concentrations of Na+ channels at the nodes of ranvier for them to diffuse across too. ap peters out
