Nervous system: Membrane potential

Question 1

voltage of extracellular fluid

Answer 1

0

Question 2

membrane potential

Answer 2

-70mV
relative to outside

Question 3

distribution of ions across plasma membrane

Answer 3

most Na+ outside. most Cl- outside
most K+ inside
small conc of Cl- inside leads to overall negative charge inside cell

Question 4

2 factors affecting magnitude of resting potential

Answer 4

differences in specific ion concentrations
differences in membrane permeability for different ions

Question 5

why is the equilibrium potential closer to K+ for the resting potential of membrane

Answer 5

K+ has very high permeability (many potassium channels)

Question 6

graded potentials

Answer 6

signalling over short distances
changes in membrane potential that are
confined to a relatively small regionof the plasma membrane.
magnitude of the potential can vary
can depolarise or hyperpolarise
no threshold or refractory period

Question 7

action potentials

Answer 7

long distance signals
large alteration in membrane potential
all or nothing response
very rapid
excitability
amplitude is fixed

Question 8

hyperpolarisation

Answer 8

membrane more negative than resting

Question 9

how graded potentials work

Answer 9

chemical stimulus opens channels and positive ions flow in
membrane potential less negative than adjacent areas
Different stimulus intensities result in
different degrees of
depolarisation.

Question 10

why do electrical currents die out with graded potentials

Answer 10

membrane leaky/permeable to ions (decremental)
further from site of depolarisation you go, charge decreases
solved with summation

Question 11

ligand gated and mechanically gated channels

Answer 11

serve as initial stimulus for action potential

Question 12

voltage gated channels

Answer 12

allow rapid depolarisation and repolarisation

Question 13

what is responsible for the conformational change to channels when there is a change in membrane potential

Answer 13

charged amino acid residues

Question 14

why are voltage gated sodium ion channels faster to respond

Answer 14

have inactivation gates
makes it faster

Question 15

action potential mechanism

Answer 15

1. Resting membrane potential close to K+
   equilibrium as normal K+ channels are “leaky”
2. Action potential begins when a stimulus
   (e.g., a chemical neurotransmitter) binds to a
   specific ion channel, allowing Na+ to enter
3. Other Na+ channels stimulated to open by
   the depolarisation: positive feedback
4. Na+ channels become inactivated and K+
   channels now open with a delayed effect
   halting depolarisation
5. K
   + fluxes out of the cell rapidly repolarising
   the membrane
6. The return of resting membrane potential
   closes Na+ channels, but the sluggish K+
   results in hyperpolarisation
7. As K+ channels close, resting membrane
   potential returns

Question 16

threshold potential

Answer 16

15mV above resting potential

Question 17

subthreshold potentials

Answer 17

weak polarisations
caused by subthreshold stimuli

Question 18

absolute refractory period

Answer 18

during an AT, another stimulus will not cause another AT
occurs during the period when the voltage-gated Na+ channels are either already open or have proceeded to the inactivated state during the first action potential.

Question 19

relative refractory period

Answer 19

interval following absolute refractory period during which a second action potential can be produced—but only if the stimulus strength is considerably greater than usual. starts as the voltage-gated sodium (Na⁺) channels begin to reset and continues until the neuron returns to its resting membrane potential.

Question 20

refractory periods, general

Answer 20

limit the number of
action potentials an excitable
membrane can produce in a given
period of time.

Question 21

action potential propagation

Answer 21

process of AT travelling along length of neurone
there is a sequential opening and closing of voltage-gated Na+ and K+ channels along the membrane

Question 22

why dont action potentials decrease in magnitude along length like graded potentials

Answer 22

each regeneration of the action potential depends on the positive feedback cycle of a new group of Na+ channels where the action potential is occurring, the action potential arriving at the end of the membrane is virtually identical in form to the initial one