Chapter 6 and 7: membrane potential and Action Potential

Question 1

resting potential

Answer 1

• resting charge of athe neuron (relative difference in voltage btwn inside and outside of cell)
• (-)70 mV

Question 2

how measured

Answer 2

voltage amplifier and oscilloscope

Question 3

major players in resting potential

Answer 3

-K+
NA+
Cl-
Ca++
Proteins (A-)

Question 4

which are inside and outside

Answer 4

K+ inside
NA+ outside
Cl- outside
Ca++ outside
A- inside

Question 5

equilibrium potential

Answer 5

• balance between diffusion and electrostatic pressure of ions
• ex K=
• diffusion=out
• electrostatic pressure=in

Question 6

Nernst equation

Answer 6

used to determine an ions equilibrium potential

Question 7

equilibrium potentials of ions

Answer 7

K+ = -75
Na+ = +55
Cl- = -60

Question 8

neurons at rest are permeable to several types of ions

Answer 8

• K+, many open channels
• Na+, only a few open channels
• Na+ influx pulls resting potential closer to 0
• leaky membrane

Question 9

how is equilibrium maintained with leaky channels?

Answer 9

• pumps
• NA+/K+
• also several Ca++
• pumps are slower, require energy, different structure than ion channel. binding site, not pore

Question 10

what happens when permeability changes?

-dendrite vs axon

Answer 10

• wont see AP at dendrites
• only see graded potentials at dendrites and cell body
• depolarizing axon will see AP at certain level

Question 11

graded potential

Answer 11

-initial stimulus, needs to reach axon to create action potential

Question 12

4 properties of AP

Answer 12

1. threshold: graded potentials to certain voltage, than AP happens. Once depolarization gets over threshold, AP happens (all or none)
2. All or none-same every time once you get over threshold
3. does not diminish (self regenerative)
4. followed by refractory period (period of time where you cant get another AP)

Question 13

two critical voltage gated channels

Answer 13

1. Na+
2. K+
   change in potential opens gate
   two key differences
3. Na+ channels open faster
4. Na+ channels become inactivated

Question 14

what does K+ want to do gradient wise

Answer 14

wants to diffuse out, but is attracted to inside of cell because of electrical gradient

Question 15

what does Na+ want to do

Answer 15

diffuse in, electrical gradient is also pulling it in

-remember that resting potential is +55 for Na+

Question 16

what does Cl- want to do

Answer 16

diffuse in, charge pushes out

Question 17

what makes resting potential charge -70

Answer 17

-4 factors of cl-, na+, K+ and A- at rest create charge of -70

Question 18

how ap works

Answer 18

• 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)

Question 19

absolute refractory period

Answer 19

-period of time following an AP during which no stimulus can initiate another ap - mediated by the inactivated Na+ channels (peak of stimulus)

Question 20

relative refractory period

Answer 20

-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)

Question 21

where are voltage gated Na+ channels located

Answer 21

axon hillock, not dendrites

Question 22

saltatory conduction

Answer 22

in myelinated axons

• ap jumping down axon bc myelin sheath
• unmyelinated is more like wave

Question 23

demyelinated axon (ex ms)

Answer 23

-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