Lecture 11.2 main points

Question 1

describe excitable cells in their resting state. What are ions, what do opposite charges do? what do some charges do?

Answer 1

excitable cells in their resting state have a negative charge on the inside of the membrane (-70mV is the average for neurons) compared to the outside (0mV)
Ions are charged atoms, or molecules, that have lost or gained electrons
opposite charges attract
like charges repel

Question 2

define electric potential

Answer 2

separated electrical charges of opposite sign have the potential to do work if they are allowed to come together

Question 3

define membrane potential

Answer 3

voltage of the intracellular region of the membrane compared to the extracellular

Question 4

what does it mean for the membrane voltage to increase/ decrease membrane potential

Answer 4

increasing the membrane potential - excite the call - makes it more positive
decrease the membrane potential - inhibit the cell - make it more negative

Question 5

define potential difference

Answer 5

the difference in potential (charge) between the outside of the cell and the inside

Question 6

what does it mean for the membrane voltage to increase/ decrease potential difference

Answer 6

increasing the potential difference of a resting membrane voltage - make it more negative
decrease the potential difference - make it more positive

Question 7

define conductance? what is the shorthand?

Answer 7

the permeability of the membrane to an ion
represented by the lowercase g
gK= conductance of potassium

Question 8

can charge/polar chemicals pass easily directly through the membrane

Answer 8

the plasma membrane is relatively impermeable to charge atoms and molecules

Question 9

how is the membrane conductance for charged or polar chemicals altered?

Answer 9

ions must travel through transmembrane protein, when more are open, the greater the conductance for that ion

Question 10

define current? what is the shorthand representation?

Answer 10

current is the actual movement (flow) of ions through membrane channels
represented by a capital I
INa= current for sodium
IK= current for potassium

Question 11

what does it mean to increase/ decrease current

Answer 11

increase current means high flow of ions across the membrane

Question 12

what does it mean to have positive/negative current

Answer 12

positive current means ions flowing out of the cell
negative current means ions flowing into the cell

Question 13

sodium concentration inside v outside

Answer 13

cation, higher outside the cell

Question 14

chloride concentration inside v outside

Answer 14

an anion, higher concentration outside

Question 15

calcium concentration inside v outside

Answer 15

cation, higher outside

Question 16

potassium concentration inside v outside

Answer 16

cation, higher concentration inside the cell

Question 17

phosphate concentration inside v outside

Answer 17

polyatomic ion, higher inside the cell
majority of phosphate bound to proteins and ATO

Question 18

shorthand representation for concentration of intracellular/ extracellular potassium, sodium?

Answer 18

[K]o or [K]e for extracellular
[K]I for intracellular

Question 19

describe concentration differences intra vs extracellular K and Na

Answer 19

intracellular K > intracellular Na
extracellular Na > extracellular K

Question 20

define diffusion

Answer 20

movement of an atom or molecule from a region of high concentration to a region of low concentration

Question 21

where does sodium want to go? inside or outside the cell? does it flow up or down its concentration gradient

Answer 21

sodium wants to flow into the cell, down its concentration gradient

Question 22

describe the charge of the extracellular region by the membrane vs intracellular region by the membrane

Answer 22

extracellular region is more positive than intracellular region

Question 23

why would sodium want to flow into the cell at typical neuronal resting membrane potential

Answer 23

sodium wants to flow from the positive extracellular into the negative intracellular at resting membrane voltage

Question 24

when sodium flows from a positive region to a more negative one, it is said to flow up or down its concentration gradient

Answer 24

down its concentration gradient

Question 25

define the equilibrium potential (Nernst value)

Answer 25

the voltage at which the electrical gradient cancels the chemical gradient
specific for each ion based on intracellular and extracellular concentration

Question 26

with respect to a particular chemical, what does it mean for the chemical and electrical forces when the Vm is at the Nernst value

Answer 26

there is no net movement (current) of ions across the membrane
the electrical repulsion force cancels out the diffusion force (they oppose each other with equal force)

Question 27

if intracellular v extracellular concentration for a particular ion changes, is the nersnt affected? why?

Answer 27

Yes, because there will be a net movement of ions up or down the concentration gradient

Question 28

what is the value for ENa listed in the powerpoints? describe the effect on sodium’s want to flow into the cell if the Vm is at the sodium Nernst?

Answer 28

roughly +55mV
this means that the intracellular membrane voltage is so positive that it will repel the positive sodium on the outside and keeps it from entering the cell despite Na wanting to flow into the cell down its concentration gradient

Question 29

what is the value of EK listed in the powerpoints? Describe the effect on potassium’s want to flow out of the cell if the Vm is at the potassium Nernst

Answer 29

roughly -78mV
means that inside of the cell is so negative that the potassium is repelled from wanting to leave the cell
despite wanting to flow out of the cell down its concentration gradient

Question 30

specifically describe driving force

Answer 30

how much, or how badly, something wants to go across the membrane
for ions - depends on concentration and electrical gradients

Question 31

how does concentration affect driving force

Answer 31

greater concentration difference across the membrane, greater the driving force of that ion

Question 32

how do charges and magnitude affect driving force

Answer 32

greater the electrical gradient across the membrane, the greater the driving force for that ion

Question 33

what is the shorthand representation for resting membrane potential

Answer 33

RMP or Vrm

Question 34

how is resting membrane potential created by cells? how does lipid bilayer play an important role in this?

Answer 34

created using ion gradients and variety of ion channels that open or close in response to specific stimuli
because the lipid bilayer of the plasma membrane is a good insulator, ions must flow through these channels

Question 35

where can ion channels be found in the body ? where are they especially prominent?

Answer 35

present in the plasma membrane of all cells in the body
especially prominent component of the nervous system

Question 36

ligande - gated channels

Answer 36

respond to specific chemical stimulus and are mainly concentrated at the synapse
neurotransmitters, hormones, and some ions can open or close these channels
-nicotinic ACh recepotors are an example

Question 37

voltage gated channels

Answer 37

respond to changes in the transmembrane electrical potential and are mainly located along the neuronal axon
participate in the generation and conduction of AP
-voltage gated Ca channels are an example

Question 38

mechanically - gated channels

Answer 38

respond to mechanical deformation (ex. applying pressure to, or stretching, a receptor)
-ryanodine receptors are an example

Question 39

leakage channels

Answer 39

randomly alternate between open and closed states
allow ions to “leak” across the membrane

Question 40

when is a neurons RMP measured

Answer 40

at rest, not conducting a nerve impulse

Question 41

how is the difference in concentrations created and maintained in the RMP

Answer 41

by transport proteins in the cell’s plasma membrane

Question 42

is the buildup of charge only close to the membrane, or is it found throughout the entire cell?

Answer 42

only very close to the membrane, the cytosol everywhere else in the cell is electrically neutral