neurons - potentials and aspects

Question 1

neuron

Answer 1

• consists of dendrites, soma, axon, myelin sheath, axon hillock

Question 2

donnan equilibrium

Answer 2

• compromise between the electrical and chemical equilibria
• based on the electronegativity of individual ions
• cells are always trying to get to this

Question 3

sodium potassium pump

Answer 3

• pumps out sodium and pumps in potassium
• relatively large K+ permeability
• relatively small Na+ permeability

Question 4

graded potentials

Answer 4

• what happens when the stimuli do not result in enough depolarization to be an action potential

Question 5

resting membrane potential

Answer 5

• -70 mV
• any stimulus can move this amount, but depending on the stimulus it will be either excitatory (depolarization) or inhibitory (hyperpolarization)

Question 6

threshold value

Answer 6

• -55mV
• this must be reached in order for an action potential to occur

Question 7

action potential

Answer 7

• must reach -55mV to happen
• involves an all-or-nothing response that causes voltage gated channels to open (which happens at threshold value)

Question 8

Na+

Answer 8

• equilibrium at +62 mV
• gated channels are quick to open and close
• these channels will propagate the opening of more of the surrounding channels of this kind

Question 9

K+

Answer 9

• equilibrium at -101 mV
• gated channels are slow to open and close
• will gradually leak out of the cell in large quantities

Question 10

upstroke

Answer 10

• the steep climb that occurs as Na+ channels snap open
• drives Na+ into the cell
• opening one of these channels causes the opening of more channels which is why the entire thing depolarizes so fast
• potassium channels will begin opening as membrane potential becomes more positive

Question 11

downstroke

Answer 11

• sodium reached equilibrium and potassium channels will remain open while Na+ channels close
• membrane potential will dip as potassium channels begin to close
• large and positive EMF will drive potassium out of the cell

Question 12

refractory period - relative

Answer 12

• some Na+ channels can be activated again but K+ is still high so it would take a really large stimulus in order for it to happen
• large stimulus to initiate depolarization; no firing due to hyperpolarization

Question 13

refractory period - absolute

Answer 13

• Na+ channels are closed and mechanically unable to open again for a period of time
• K+ channels are still open