Membrane Potentials

Question 1

what is the assigned voltage for outside the membrane ?

Answer 1

0 mV

Question 2

what is the value for the resting membrane potential ?

Answer 2

• 70 mV

varies between -5 to -100 depending on the cell type

Question 3

where is the membrane potential situated ?

Answer 3

within close proximity of the plasma membrane meaning that the rest of the intracellular/extracellular fluid remains a neutral charge

Question 4

the magnitude of resting membrane potential depends on what 2 parameters ?

Answer 4

1. the differences in specific ion concentrations

2. the differences in membrane permeability for the different ions

Question 5

what are the 3 parts that make up the resting membrane potential ?

Answer 5

1. sodium potassium pump
2. voltage gated sodium ion channels
3. potassium ion channels

Question 6

explain the role that the ‘sodium potassium pump’ plays in the maintenance of resting potential (3 points)

Answer 6

1. active transport (uses ATP)
2. pumps 3 Na+ out
3. pumps 2 K+ in

Question 7

explain the role that the ‘voltage gated sodium ion channels’ play in the maintenance of resting potential (2 points)

Answer 7

1. CLOSED (blocked by an inactivation gate)

2. membrane is impermeable to Na+

Question 8

explain the role that the ‘potassium ion channels’ play in the maintenance of resting potential (3 points)

Answer 8

1. OPEN
2. K+ diffuses down electrochemical gradient
3. doesn’t reach equilibrium due to electrical repulsion of more positive charge outside the membrane

Question 9

state what it is meant by the key term - graded potentials

Answer 9

graded potentials are potential changes of variable amplitude and duration that are conducted decremental; it has no threshold or refractory period

Question 10

explain how a ‘graded potential’ works (6 points)

Answer 10

1. GP occurs + charge flows between origin + adjacent areas
2. small region of PM becomes depolarised
3. ion channels briefly open + become more negative than adjacent areas
4. simultaneously, outside cell, positive regions flow to more negative regions
5. depolarisation spreads to adjacent areas of PM
6. local current moves P charges to depolarisation on outside and away from depolarised site on inside

Question 11

depending on the initiating event, a graded potential can be what ?

Answer 11

depolarising or hyper polarising

Question 12

can graded potentials be summated ?

Answer 12

yes

Question 13

state what it is meant by the key term - action potentials

Answer 13

a brief all-or-nothing depolarisation of the membrane, which reverses polarity in neurones; it has a threshold and a refractory period and is conducted without decrement

Question 14

charge varies from what in an AP ?

Answer 14

changes from - 70 to + 30 mV and then repolarizes age membrane

Question 15

how do AP’s travel ?

Answer 15

action potential propagation over long distances (GP’s travel short distances)

Question 16

state what it is meant by the key term - potential

Answer 16

the voltage difference between two points

Question 17

state what it is meant by the key term - membrane potential

Answer 17

the voltage difference between the inside and the outside of the membrane

Question 18

state what it is meant by the key term - equilibrium potential

Answer 18

the voltage difference across a membrane that produces a flux of a given ion species that is equal but opposite too the flux due to the concentration gradient of that specific ion species

Question 19

state what it is meant by the key term - resting potential

Answer 19

the steady transmembrane potential of a cell that is not producing an electrical signal

Question 20

state what it is meant by the key term - synaptic potential

Answer 20

a graded potential change produced in the post-synaptic knob in response to the release of a neurotransmitter by a pre-synaptic knob

Question 21

state an additional fact about ‘synaptic potentials’

Answer 21

may be depolarising (EPSP) or inhibitory (IPSP)

Question 22

state what it is meant by the key term - receptor potential

Answer 22

a graded potential produced at the peripheral endings of afferent neurones (or in separate receptor cells) in response to a stimulus

Question 23

state what it is meant by the key term - pacemaker potential

Answer 23

a spontaneously occurring graded potential change that occurs in certain specialised cells

Question 24

state what it is meant by the key term - threshold potential

Answer 24

the membrane potential at which an action potential is initiated

Question 25

state the 6 steps, in order, of the action potential mechanism

Answer 25

1. resting potential 2. generator potential 3. threshold potential 4. depolarisation 5. repolarisation 6. hyper-polarisation

Question 26

explain the following step of the action potential mechanism: step 1 - resting potential (4 points)

Answer 26

1. sodium potassium pump maintains resting potential 2. active transport (used ATP) 3. 3 Na+ out, 2 K+ in 4. some K+ diffuses back out

Question 27

explain the following step of the action potential mechanism: step 2 - generator potential (5 points)

Answer 27

1. weak stimulus 2. some Na+ channels open 3. some Na+ diffuses in 4. doesn't reach AP threshold 5. sodium potassium pump re-establishes resting potential

Question 28

explain the following step of the action potential mechanism: step 3 - threshold potential (4 points)

Answer 28

1. generator potential reaches AP threshold 2. many voltage gated Na+ channels open (inactivation gate is removed) 3. Na+ diffuses into the axon 4. positive feedback mechanism

Question 29

explain the following step of the action potential mechanism: step 4 - depolarisation (2 points)

Answer 29

1. Na+ channels are open | 2. Na+ diffuses into the axon

Question 30

explain the following step of the action potential mechanism: step 5 - repolarisation (3 points)

Answer 30

1. voltage gates K+ channels are open 2. K+ diffuses out of the axon 3. Na+ channels close

Question 31

explain the following step of the action potential mechanism: step 6 - hyperpolarisation (2 points)

Answer 31

1. K+ channels are slow to close | 2. membrane potential becomes more negative (compared to resting potential)

Question 32

what are the two benefits of resting potentials ?

Answer 32

1. ensures action potentials are discrete (don't overlap) | 2. ensures action potentials are unilateral

Question 33

what are the two types of refractory periods ?

Answer 33

1. absolute refractory period | 2. relative refractory period

Question 34

what are 'absolute refractory periods' ? (3 points)

Answer 34

1. during the AP, a second AP can't be generated, no-matter how strong the stimulus 2. occurs when Na+ channels are open/opening 3. the inactivation gate must be removed by repolarizing the membrane and closing the channels before they can re-open to a second stimulus

Question 35

what are 'relative refractory periods' ? (3 points)

Answer 35

1. a second AP can be generated if stimulus is greater than usual 2. some Na+ channels have returned to resting states, and some K+ channels are still open 3. possible to depolarise the membrane again

Question 36

how much longer are relative refractory periods to absolute refractory periods ?

Answer 36

1 - 15 ms longer