membrane potential

Question 1

what is the resting membrane potential?

Answer 1

charge separation between the inside and outside of cells in the absence of any other stimuli or inputs
membrane acts as a capacitor where the charge separation gives the cell the ability to do work
in neuron or muscle fiber usually about -40 to -90 mV

Question 2

how long of a distance can a neuron transmit a signal?

Answer 2

up to a meter or so

Question 3

how fast can a neuron transmit a signal?

Answer 3

very rapid: can be greater than 200 meters per second

Question 4

what is the difference between depolarization and hyperpolarization?

Answer 4

depolarization means a reduction in charge separation (eg -70 to -30)
hyperpolarization means increase in charge separation (eg -70 to -100)
the inside of the cell is hyperpolarized with respect to the outside of the cell

Question 5

what is ohm’s law?

Answer 5

V=IR

I=GV

Question 6

what ions usually create the charge in cells?

Answer 6

small ions such as K, Na, Cl, Ca

charged so can’t pass the membrane - makes voltage across the membrane

Question 7

what are ion channels?

Answer 7

integral membrane proteins
selectively permeable (only let specific ions go through)
conduct ions much faster than pumps/transporters

Question 8

what are the energy requirements of ion channels?

Answer 8

passive! so no energy is required

Question 9

what are the classes of ion channels? (list)

Answer 9

leak channels
voltage-gated channels
ligand-gated channels
mechanosensory channels

Question 10

when are leak channels open and what do they help generate?

Answer 10

have high probability of being open in the absence of any stimulus
critical for generation of Vrest
tend to be selective for K ions
open at rest

Question 11

when are VG channels open and what do they help generate?

Answer 11

opened by a change in the membrane potential
critical for generation of act. pot. allow Ca influx into presyn. terminals (for NT release)
shape synaptic events as they traverse dendrites and integrate

Question 12

which channel is the fundamental mechanism for synaptic transmission?

Answer 12

ligand-gated channels

Question 13

where do mechanosensory channels get their signals, where are they found, and what are they sensitive to?

Answer 13

give rise to signals from pacinian corpuscles
in nerve endings in skin
responsible for sensitivity to pain and pressure

Question 14

how does patch clamping work?

Answer 14

creates high resistance mechanical and electrical seal between the walls of a glass pipette and the plasma membrane
allows you to measure flow of ions through a single protein (ideally - basically you pick up a tiny piece of membrane and hope that you only have one channel in that piece of membrane - but each additional channel will add an equivalent amount of charge change, so if you do this enough, you can determine the intervals that the charge is changing and that will tell you how much charge is flowing through that channel)

Question 15

what are the two key concepts that allow for the generation of resting membrane potential? (summary)

Answer 15

membrane is selectively permeable and there is an uneven distribution of individual ions

Question 16

what does it mean for something to be selectively permeable?

Answer 16

at rest it will allow some ions to cross more readily than others

Question 17

how are individual ion species distributed across cell membranes?

Answer 17

there’s an uneven distribution on the inside versus the outside

Question 18

what are the typical concentrations of ions inside and outside the cell?- na- k- cl- anions

Answer 18

• Na:
  
  • out = 117
  • in = 30
• K:
  
  • out = 3
  • in = 90
• Cl:
  
  • out = 120
  • in = 4
• anions
  
  • out = 0
  • in = 116

Question 19

describe the process of establishing RMP (from a neutral situation - which obviously never happens in reality…)

Answer 19

put in K leak channels - K pushed out of cell by concentration gradient
anions can’t follow because they’re too big to fit though the leak channels
K ions can’t get that far away from the anions though, because the anions are their complementary molecules
so the anions get stuck to the inner membrane - get buildup of negative charge around the inner membrane

Question 20

what are the two factors that allow of the separation of charge across the membrane?

Answer 20

1: uneven distribution of ions
2: having channels selective for only some of those ions

Question 21

what keeps all of the K ions from leaving the cell?

Answer 21

buildup of electrical gradient pushes K back in (because gets very + outside of cell and K ions are repelled from + and attracted to -)

Question 22

what is the equilibrium potential?

Answer 22

the point at which the concentration gradient pushing an ion out of (or into) a cell is equal to the electrical gradient pushing that ion into (or out of) the cell

so for K: it’s the concentration of K inside the cell at which the concentration gradient pushing it out of the cell is exactly equal to the electrical gradient pushing K back into the cell, so the same amount leaving is also entering and there’s no net movement of K across the membrane = steady state

note that these are for specific ions (rather than for the cell overall)

Question 23

what is the nernst equation and what is it used to measure?

Answer 23

used to calculate equilibrium potential of a specific ion

know:
for cation:
Eion = 61 log ([ion]out/[ion]in) for a monovalent cation at 37 degrees
if it’s an anion, put in over out

the true equation is:
Eion - RT/ZF * log ([ion]out/[ion]in)
where T= temp in kalvins
Z = charge of ion (so for K = 1 (monovalent), for Ca = 2 (divalent))

Question 24

how does Na affect RMP?

Answer 24

there are a few Na channels that will be open so there will be some Na going into the cell
Ena = +36 (so if there were only Na channels, resting membrane potential would be +36)
this means that resting membrane potential is a little higher than -90 as it would be if only K were moving across the membrane

Question 25

what do cardiac glycosides (eg ouabain) do?

Answer 25

block the Na/K atpase
thereby activate the Na/Ca exchanger in reverse mode => increase in [Ca]in
use to increase Ca levels in cardiac myocytes => ionotropic action => greater cardiac contraction

Question 26

what are the clinical characteristics of rapid-onset dystonia-parkinsonism (RDP)?

Answer 26

involuntary spasms

sudden onset often triggered by stress (usually in young adulthood)

Question 27

what mutation causes RDP? what are the effects of this mutation?

Answer 27

mutation in alpha3 subunit of Na/K ATPase

causes aberrant cerebellar activity that leads to concomitant abnormal activity in the basal ganglia

Question 28

what mutation causes thomsen and becker myotonia congenita?

Answer 28

mutation in CLCN1 gene = Cl channel subunit
in skeletal muscle fibers - after act pot, Cl leaves cell to hyperpolarize it - makes Ca leave too and cell goes back to normal
these Cl channels aren’t open in the disorder
results in abnormally low resting Cl conductance => abnormally prolonged depolarization from K+ build-up in T-tubule extracellular space => repetitive action potentials, sustained muscle contraction