Electrochemical gradients

Question 1

how do transporters and channels have fundamentally different properties

Answer 1

a cells phospholipid bilayer limits the passage of charged molecules across the cell membrane (lipid part of the cell membrane has high electrical resistance)
gap junctions, membrane transporters and ion channels provide routes for charged molecules to cross the cell membrane

Question 2

what do ion channel characteristics contain

Answer 2

selectivity
gating

Question 3

how can channels be gated

Answer 3

mechanically
ligand and/or voltage-gated

Question 4

what do all cells have

Answer 4

a membrane potential

Question 5

what does Ohm’s law define

Answer 5

the relationship among membrane potential (voltage)
current
conductance (inverse of resistance)
I=CV

Question 6

live cells resting membrane potential

Answer 6

Vm or RMP
is negative with respect to the extracellular fluid

Question 7

electrically excitable cells resting membrane potential

Answer 7

neurons and myocytes
-30 to -70 mV RMP
they have a larger number of K+ channels open at rest

Question 8

primary function of Na+/K+ ATPase

Answer 8

establishment of the concentration gradients for Na+ and K+
needed to generate resting, graded and action potentials
only mildly electrogenic
nt result of the actions of Na+/K+ ATPase is Vm of -5 to -12mV

Question 9

ion reversal potential

Answer 9

also known as the equilibrium potential
membrane potential where the net flow through any open channel is 0
Erev the chemical and electrical forces are in balance

Question 10

what equation do you use to calculate the Erev

Answer 10

the Nerst equation
R= gas constant
T= temperature in K
z= ion charge
F=Fraday’s constant

Question 11

sodium ion equilibrium potential

Answer 11

+60mV

Question 12

potassium ion equilibrium potential

Answer 12

-88mV

Question 13

in order to calculate RMP what must you account for

Answer 13

the relative contribution of each channel type
expressed in terms of permeability P
resting membrane potential will be close in value to the reverse potential for the ion that carries the majority of the resting current

Question 14

what can easily pass through the phospholipid bilayer

Answer 14

gases
some neurotransmitters
small amphiphilic compounds (most general anaesthetics)

Question 15

what does the bilayer have high resistance to

Answer 15

the passage of current

Question 16

3 types of membrane proteins that enable charged molecules to cross the membrane

Answer 16

gap junctions
electrical synapses
membrane transporters

Question 17

what are gap junctions

Answer 17

large pores that form between 2 adjacent cells and can pass ions and small molecules
includes ATP
electrical synapses are a specialised form of gap junctions

Question 18

what are membrane transporters

Answer 18

also known as pumps
integral membrane proteins that mediate facilitated diffusion or active transport of ions and other small molecules across the membrane

Question 19

facilitated diffusion

Answer 19

occurs via specific transport proteins, permeases
only allow specific ions/molecules to pass through the membrane

Question 20

three types of transporters

Answer 20

uniports
symports
antiports

Question 21

uniports

Answer 21

move a single molecule

Question 22

symports

Answer 22

move multiple molecules in the same direction

Question 23

antiports

Answer 23

move multiple molecules in opposing directions

Question 24

what do channels do

Answer 24

allow water or ions to flow rapidly through a water-filled pore

Question 25

channels information

Answer 25

direct connection between the intracellular and extracellular spaces move small molecules always move charged molecules down their concentration gradients, passive process dissipate concentration gradients extremely high speed 10x10^6 molecules per second

Question 26

pumps information

Answer 26

never any connection between the intracellular and extracellular spaces can move larger molecules using ATP, some pumps (anti ports) can move molecules against their concentration gradients, active build up concentration gradients slower 1 x 10^3 molecules per second

Question 27

typical membrane potential

Answer 27

+40mV to -70mV

Question 28

Vm

Answer 28

potential difference relative measure movement of one positive ion from the outside to the inside results in a +2 change in Vm

Question 29

depolarisation

Answer 29

movement to a more positive membrane potential

Question 30

hyperpolarisation

Answer 30

movement to a more negative membrane potential

Question 31

principle intracellular cation

Answer 31

potassium

Question 32

principle extracellular cation

Answer 32

sodium

Question 33

principle anion

Answer 33

chloride mainly extracellular

Question 34

environment outside the cell compared to inside

Answer 34

inside is more negative than outside more negative ions inside the cell resting membrane potential as there is no active stimulus

Question 35

how do you measure membrane potential

Answer 35

micro electrode

Question 36

mammalian neuron at 37 degrees Nerst equation

Answer 36

K+ is -90 Na is +61 Cl- is -52

Question 37

what is used to maintain the resting potential

Answer 37

sodium-potassium pump

Question 38

action potential

Answer 38

generated in the presence of a stimulus nerve endings are stimulated sodium channels open membrane is depolarised membrane potential changes from -70 to +40 reaches the threshold potential all sodium channels open more sodium ions move into the cell

Question 39

threshold/ all or nothing principle

Answer 39

when the membrane potential reaches +40mV the threshold is reached and all the sodium ion channels will open to allow influx of sodium ions into the cell

Question 40

repolarisation

Answer 40

once the membrane is depolarised sodium channels will close and the potassium channels will open membrane is repolarised as the membrane potential becomes more negative may fall into a temporary overshoot known as hyper polarisation new action potential can't be generated, known as the refractory period sodium potassium pump maintains the potential

Question 41

what occurs if there is an electrolyte imbalance

Answer 41

the equilibrium potential and membrane potential will change

Question 42

hypokalaemia

Answer 42

more potassium ions leak out of the cell during the resting state changes the membrane potential to a more negative value of -90

Question 43

hyperkalaemia

Answer 43

fewer potassium ions move out of the cell through leaky potassium channels resting potential becomes less negative elevated plasma (extracellular fluid) K+ concentration

Question 44

effect of current on membrane potential

Answer 44

direction of current alters the membrane potential efflux of positive ions cell will become hyper polarised influx of positive ions the cell may become depolarised and generate an action potential

Question 45

what can cause a change in potassium ion concentrations

Answer 45

increased intake decreased renal elimination renal failure adrenal disease medications that alter kidney function angiotensin-converting enzyme inhibitors angiotensin II receptor blockers potassium-sparing diuretics non-steroidal anti-inflammatory drugs increased release from intracellular stores due to tissue damage

Question 46

effects of high potassium on the body

Answer 46

irregular heartbeat changes in mood chest pain shortness of breath weakening pulse heart palpitations kidney conditions nausea, vomiting or diarrhoea numbness or tingling muscle weakness

Question 47

most life threatening consequence of hyperkalemia

Answer 47

arrhythmia cardiac arrest due to depolarisation of the resting potential of cardia myocytes