neurons

Question 1

what do neurones do?

Answer 1

during brain development, they probe their environment for guidance clues to extend axons and dendrites

Question 2

what does the function of a neuron depend on?

Answer 2

its elongated structure

Question 3

what is the fundamental task of a neuron?

Answer 3

to receive, integrate, conduct and transmit signals

Question 4

what does the axon do

Answer 4

conducts electrical signals away from the body towards its target cells

Question 5

what do dendrites do?

Answer 5

receive signals from the axons of other neurones

Question 6

what is the transport like in ion channels and why?

Answer 6

passive as they are not coupled to an energy source

Question 7

what do ion channels do?

Answer 7

accelerate passage of ions

Question 8

what do ion channels show high selectivity to?

Answer 8

charge and size of ions

Question 9

what are the types of ion channels?

Answer 9

voltage gated
ligand gated
mechanically gated

Question 10

what are voltage gated ion channels like?

Answer 10

change in voltage across the membrane

Question 11

what are channel proteins of the plasma membrane?

Answer 11

narrow, highly selective pores that can open and close rapidly

Question 12

what are channel proteins?

Answer 12

ion channels

Question 13

what do ion channels transport?

Answer 13

inorganic ions

Question 14

what are action potentials triggered by?

Answer 14

depolarisation of the membrane

Question 15

how are action potentials generated?

Answer 15

by opening and closing of voltage gated cation channels located in the cell plasma membrane

Question 16

what do action potentials do?

Answer 16

changes membrane potential from a resting value, depolarising it (make it less negative)

Question 17

how does plasma membrane potential change with time for voltage-gated ion channels due to a stimulus?

Answer 17

at resting, then increases when there is a stimulus, past threshold potential, to active potential, then back down to resting

Question 18

what values does the action potential cover?

Answer 18

all plasma membrane potentials greater than threshold potential

Question 19

what are action potentials used for?

Answer 19

allow rapid, long-range communication

Question 20

what does the membrane potential change and what does it NOT change?

Answer 20

does NOT change width of ion pore
does change probability of channel being open to ions

Question 21

how does plasma membrane potential change over time due to a stimulus without voltage-gated ion channels?

Answer 21

resting potential, then increases a small amount (stays much lower than threshold potential) at stimulus , then decreases down to resting again

Question 22

what does the electrochemical gradient depend on?

Answer 22

membrane potential and concentration gradient of ions across membrane

Question 23

what affects an ion’s transport through a membrane?

Answer 23

electrochemical gradient

Question 24

how can electrical and chemical gradients work together?

Answer 24

additively to increase driving force on ion
or against each other

Question 25

what do action potentials rely on?

Answer 25

voltage-gated ion channels

Question 26

what is the main contribution to the voltage gradient on a cell membrane?

Answer 26

negative charge on membrane (due to phospholipids) causes accumulation of positive ions in a thin layer on membrane (largely K+)

Question 27

what causes the membrane potential?

Answer 27

a thin layer of ions close to the membrane, held in place by their electrical attraction to oppositely charged ions on other side of membrane

Question 28

what is the flow of an ion through a membrane channel protein driven by?

Answer 28

electrochemical gradient for that ion

Question 29

what is equilibrium potential?

Answer 29

membrane potential at which there is no net flow of ion through channel

Question 30

when is there no net flow of an ion through a channel?

Answer 30

when voltage gradient and concentration gradient of ion across membrane is balanced so electrochemical gradient for ion is 0

Question 31

what is V in the Nernst equation?

Answer 31

equilibrium potential

Question 32

how do we derive the Nernst equation?

Answer 32

an ion in solution moves according to concentration gradient so ΔG < 0 free energy change for mole of solute moved across a plasma membrane: ΔG(conc) = -RTln(Co/Ci) if solute is an ion, there is an additional free energy change per mole of solute ΔG(volt) = zFV where V is interior voltage of plasma membrane and z = charge of ion when concentration and voltage gradients balance: ΔG(conc) + ΔG(volt) = 0 so -RTln(Co/Ci) + zFV = 0 V = RT/zF ln(Co/Ci)

Question 33

what does membrane permeability relate to?

Answer 33

number of ion channels for the ion and the probability of their opening

Question 34

which ions cross the membrane?

Answer 34

K+ Na+ Ca2+ Cl-

Question 35

what is the symbol for permeability of a membrane to a particular ion?

Answer 35

Px

Question 36

what is the symbol for resting membrane potential?

Answer 36

Vm

Question 37

what is resting membrane potential?

Answer 37

sum of contribution of all ions whilst taking into account permeability of membrane to ions

Question 38

what is the equation for resting membrane potential?

Answer 38

Vm = RT/F ln((px [x]o) + py [y]o +....)/(px [x]i + py[y]i + ...)) where x, y etc are ions crossing membrane

Question 39

what is the resting membrane potential of most neurones close to and what does this mean?

Answer 39

potential for potassium so there is high permeability of membrane to potassium, hence large number of potassium channels and high probability of them being open

Question 40

what happens during action potentials in terms of ion channels?

Answer 40

shortly after Na+ channels open, depolarisation causes opening of voltage gated K+ channels which allows K+ to flow out of axon and return membrane to resting potential

Question 41

what causes the action potential?

Answer 41

opening of Na+ channels and flow of Na+ into axon alters membrane potentials and gives rise to action potential

Question 42

which way can action potentials travel and why?

Answer 42

only forward (away from site of depolarisation) as Na+ channel inactivation after an action potential prevents advancing front of depolarisation from spreading backward

Question 43

when can a second action potential take place?

Answer 43

not until Na+ channels have returned from inactivated to closed conformation

Question 44

what does repolarisation occur due to?

Answer 44

K+ channel opening