Membrane Potentials Flashcards
what is the assigned voltage for outside the membrane ?
0 mV
what is the value for the resting membrane potential ?
- 70 mV
varies between -5 to -100 depending on the cell type
where is the membrane potential situated ?
within close proximity of the plasma membrane meaning that the rest of the intracellular/extracellular fluid remains a neutral charge
the magnitude of resting membrane potential depends on what 2 parameters ?
- the differences in specific ion concentrations
2. the differences in membrane permeability for the different ions
what are the 3 parts that make up the resting membrane potential ?
- sodium potassium pump
- voltage gated sodium ion channels
- potassium ion channels
explain the role that the ‘sodium potassium pump’ plays in the maintenance of resting potential (3 points)
- active transport (uses ATP)
- pumps 3 Na+ out
- pumps 2 K+ in
explain the role that the ‘voltage gated sodium ion channels’ play in the maintenance of resting potential (2 points)
- CLOSED (blocked by an inactivation gate)
2. membrane is impermeable to Na+
explain the role that the ‘potassium ion channels’ play in the maintenance of resting potential (3 points)
- OPEN
- K+ diffuses down electrochemical gradient
- doesn’t reach equilibrium due to electrical repulsion of more positive charge outside the membrane
state what it is meant by the key term - graded potentials
graded potentials are potential changes of variable amplitude and duration that are conducted decremental; it has no threshold or refractory period
explain how a ‘graded potential’ works (6 points)
- GP occurs + charge flows between origin + adjacent areas
- small region of PM becomes depolarised
- ion channels briefly open + become more negative than adjacent areas
- simultaneously, outside cell, positive regions flow to more negative regions
- depolarisation spreads to adjacent areas of PM
- local current moves P charges to depolarisation on outside and away from depolarised site on inside
depending on the initiating event, a graded potential can be what ?
depolarising or hyper polarising
can graded potentials be summated ?
yes
state what it is meant by the key term - action potentials
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
charge varies from what in an AP ?
changes from - 70 to + 30 mV and then repolarizes age membrane
how do AP’s travel ?
action potential propagation over long distances (GP’s travel short distances)
state what it is meant by the key term - potential
the voltage difference between two points
state what it is meant by the key term - membrane potential
the voltage difference between the inside and the outside of the membrane
state what it is meant by the key term - equilibrium potential
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
state what it is meant by the key term - resting potential
the steady transmembrane potential of a cell that is not producing an electrical signal
state what it is meant by the key term - synaptic potential
a graded potential change produced in the post-synaptic knob in response to the release of a neurotransmitter by a pre-synaptic knob
state an additional fact about ‘synaptic potentials’
may be depolarising (EPSP) or inhibitory (IPSP)
state what it is meant by the key term - receptor potential
a graded potential produced at the peripheral endings of afferent neurones (or in separate receptor cells) in response to a stimulus
state what it is meant by the key term - pacemaker potential
a spontaneously occurring graded potential change that occurs in certain specialised cells
state what it is meant by the key term - threshold potential
the membrane potential at which an action potential is initiated
state the 6 steps, in order, of the action potential mechanism
- resting potential
- generator potential
- threshold potential
- depolarisation
- repolarisation
- hyper-polarisation
explain the following step of the action potential mechanism:
step 1 - resting potential (4 points)
- sodium potassium pump maintains resting potential
- active transport (used ATP)
- 3 Na+ out, 2 K+ in
- some K+ diffuses back out
explain the following step of the action potential mechanism:
step 2 - generator potential (5 points)
- weak stimulus
- some Na+ channels open
- some Na+ diffuses in
- doesn’t reach AP threshold
- sodium potassium pump re-establishes resting potential
explain the following step of the action potential mechanism:
step 3 - threshold potential (4 points)
- generator potential reaches AP threshold
- many voltage gated Na+ channels open (inactivation gate is removed)
- Na+ diffuses into the axon
- positive feedback mechanism
explain the following step of the action potential mechanism:
step 4 - depolarisation (2 points)
- Na+ channels are open
2. Na+ diffuses into the axon
explain the following step of the action potential mechanism:
step 5 - repolarisation (3 points)
- voltage gates K+ channels are open
- K+ diffuses out of the axon
- Na+ channels close
explain the following step of the action potential mechanism:
step 6 - hyperpolarisation (2 points)
- K+ channels are slow to close
2. membrane potential becomes more negative (compared to resting potential)
what are the two benefits of resting potentials ?
- ensures action potentials are discrete (don’t overlap)
2. ensures action potentials are unilateral
what are the two types of refractory periods ?
- absolute refractory period
2. relative refractory period
what are ‘absolute refractory periods’ ? (3 points)
- during the AP, a second AP can’t be generated, no-matter how strong the stimulus
- occurs when Na+ channels are open/opening
- the inactivation gate must be removed by repolarizing the membrane and closing the channels before they can re-open to a second stimulus
what are ‘relative refractory periods’ ? (3 points)
- a second AP can be generated if stimulus is greater than usual
- some Na+ channels have returned to resting states, and some K+ channels are still open
- possible to depolarise the membrane again
how much longer are relative refractory periods to absolute refractory periods ?
1 - 15 ms longer
