Lecture5: Electrophysiology II

Question 1

describe the determinants of resting membrane potential

Answer 1

permeability and concentration gradient

potassium is the ion that contributes the most

Question 2

experiment that tells us that K is important for resting membrane

Answer 2

adding extracellular K makes the inside of the cell more depolarized.
tells us
(1) membrane most permeable to K at restin
(2) more K on inside/gradient exists

Question 3

how is the gradient for resting set?

Answer 3

3na/2K atpase which pushes na out and pulls k in

…also have leaky voltage gated K channels at resting

Question 4

does flow of ions change concentration a lot?

Answer 4

no. small row of e has sufficient charge to cause large change in membrane potential. so when K leaves, the concentration isn’t changed dramatically or at all

Question 5

what is the driving force?for which ions is this greatest?

Answer 5

difference between membrane potential and equilibrium potential

at resting- this is greatest for sodium. at peak, greatest for K and Cl

Question 6

what 2 things depolarize the cell?

Answer 6

1) increase sodium (or calcium)

2) decrease defflux of potassium

Question 7

action potential phases? also combine with ion channel functions

Answer 7

0= resting
all channels closed except resting K channels

1= graded depolarizations
stimuli can be voltage, ligand, or mechanical that is causing depolarizations

2= threshold
voltage is reached for huge influx of opening of sodium channels

3= rising phase
sodium channels are open and huge influx of sodium, making cell more positive

4= peak
sodium channels inactivate( remember this is voltage independent) and K channels open. these are different than the leaky ones. the voltage falls. They stay open a wee bit longer for hyper polarization. then inactivate

0= reseting of channels

Question 8

which cells are excitable. which ones are pacemakers?

Answer 8

excitable: skeletal and some smooth, neuronal, and cardiac
pacemakers: GI, neuronal, and cardiac

Question 9

what mechanisms allow for pacemakers of cardiac?

Answer 9

(1) HCN Na or hyperpolarizing cyclic nucleotidic gated sodium channels/ funny channels.
open at hyper polarizing voltage during phase 4

(2) calcium T type cells
calcium channels that open at depolarizing voltage and contribute to AP
also seen in phase 3

(3) K-Ach channel
binding of Acetylcholine causes hyper polarization. but then when these close to help return to resting membrane

Question 10

clinical correlation:

purpose of calcium channel blockers (2)

Answer 10

hypertention:
smooth muscle cells increase calcium uptake in order to have stronger contraction to offset the restriction of vessel.

drugs will inhibit calcium so that contraction is not so intense and muscles relax

angina:
when cells take in more calcium,this uses more oxygen and hurts. By inhibiting calcium, decrease metabolic activity so less calcium use less oxygen consumption and less pain

Question 11

clinical correlation: diabetes type ___ what do drugs target?

Answer 11

II
inhibit SUR 1 of K ATP channel
why?

usually:
glucose enters the cell and makes apt which CLOSES the K AtP channel which DEPOLARIZES the cell. This depolarization allows calcium in. calcium in causes INSULIN release.

by keeping cell depolarized, get more insulin.

Question 12

what are the functions that are crucial for membrane potential

Answer 12

HIMN
hormone release
immense cell activation
Muscle contraction
neurotransmission