graded potentials Flashcards
why are graded potentials needed?
- depolarise cell towards -55mV
- allow action potential to be fired
what are the different types of potentials and where are they found?
generator -> sensory receptors
postsynaptic -> synapses
end plate -> neuromuscular junction
pacemaker -> pacemaker tissue
what are the properties of graded potentials?
- graded (small/big stimulus -> small/big response)
- decremental
- can be hyperbolising or depolarising
- can summate to generate bigger potential which is more likely to
why are graded potentials decremental?
Become smaller as they travel along membrane because they decay (positive ions leaking out of cell membrane)
So only useful over short distances
what to do to depolarise cell?
sodium channels open to depolarise cell
Potassium channels closed so k+ doesn’t leave via concentration gradient, but it is actively pumped into cell → Depolarised
what to do to hyperbolise cell?
Chloride channels open, negatively charged ions flow into cell and make it more negatively charged → hyperbolise it
Potassium channels open so positively charged ions flow out, cell more negatively charged → hyperbolized
describe fast inhibitory postsynaptic potential
- ionotropic receptor
- Neurotransmitter binds to a receptor containing an integral chloride channel causing it to open.
- Chloride flows into the cell.
describe slow inhibitory postsynaptic potential
Metabotropic receptor
Receptor uses G protein which finds potassium channels and opens them to allow flow of potassium out the cell
describe fast excitatory postsynaptic potential
-excitatory neurotransmitter binds to ionotropic receptor to open its integral ion channel
-Ion channels allows flow of anything that has a charge of 1+ known as non-specific cation channel
-May allow some K+ to flow out fo cell (not significant)
-Lots of Na+ will flow into cell via its large electrochemical and concentration gradient
describe slow excitatory postsynaptic potential
-Excitatory neurotransmitter binds to metabotropic receptor, its G protein will close leaky potassium channels
-Potassium will not leak out of cell continuously, but will continue being bumped into cell by Na+/K+ pump
T-his slowly depolarizes the cell
GABA is the principle inhibitory neurotransmitter in the central nervous system. Would you expect it to depolarise or hyperpolarise neurons?
hyperpolarizes neurons, making them less likely to fire.
GABA inhibits neurons by acting on two different types of receptors,gating two different types of channels. Which two types of ion channels do you think these would be?
ionotropic receptors open chloride channels, leading to hyperpolarization by letting chloride ions into the neuron.
metabotropic receptors can open potassium channels, also causing hyperpolarization by allowing potassium ions to leave the neuron.
GABA evokes fast IPSPs and slow IPSPs in neurons. What makes fast IPSPs fast and slow IPSPs slow?
the influx of chloride ions happens rapidly, leading to a speedy hyperpolarization
slow response is due to G-protein coupling, initiating a cascade of events, contrasting GABA-A’s direct and rapid ion flow
Glutamate excites neurons by acting on at least two different types of receptor, gating two different types of channels. Which two types of ion channel do you think these would be?
ionotropic receptors opening
sodium channels and calcium channels
temporal summation
involves a single presynaptic neuron rapid-firing signals to a postsynaptic neuron.
spatial summation
involves simultaneous signals coming from multiple presynaptic neurons being received by a single postsynaptic neuron
properties of action potentials
Have threshold
All or nothing principle
Self-propagating
Refractory period
Travel slowly
Only encoded stimulus intensity in firing, not amplitude
All mediated by voltage-gated channels (as opposed to the ligand-gated channels that generate postsynaptic potentials)
what is an action potential
the depolarisation of the cell membrane so that the inside is more +ive than the outside
membrane potential difference about +40mV
describe action potential
- resting potential +70mV
- stimulus detected so Na Chanel opens and Na+ move down electrochemical gradient
- if stimulus big enough, threshold of -55mV is reached. voltage gated Na channels open and membrane depolarises
- at +40mV, Na channels close. K voltage gates chanels open
- membrane repolarises as K+ leaves cell and Na+ stay
- refractory period - hyperbolization at -90mV
- sodium-potassium pump transports Na+ out of cell and K+ into cell to depolarise it
sodium-potassium pump ratio?
NA: k is 3:2
what are the different membrane potentials and why are they needed?
Action potentials
- transmit signals over long distances
Graded potentials
Decide when an action potential should be fired
Resting membrane potentials
Keep cells ready to respond
how does sodium-potassium pump contribute to the ionic basis of the resting membrane potential?
Contributes about 5mV
Protein that actively transports
3 NA+ OUT
how does Selective permeability of the membrane contribute to its ionic basis?
allows certain ions to pass through.
At rest, potassium ions have greater permeability than sodium ions due to more open potassium channels
what is equilibrium potential?
the voltage at which ion diffusion = electrostatic force
so no net movement of ions across membrane
how does the equilibrium potential contribute to the ionic basis of the membrane potential?
Under resting conditions, the concentration gradient tends to drive potassium out of the cell because there are more potassium ions inside the cell.
However, the negative interior of the cell (due to the leaky potassium channels and the sodium-potassium pump actively transporting sodium out) attracts potassium ions back into the cell.
The resting membrane potential is closest to the equilibrium potential for potassium,
how do the sodium leak channels contribute to the ionic basis of the membrane potential?
These channels are always open, allowing potassium ions to move down their concentration gradient. Since there are more potassium ions inside the cell (due to the sodium-potassium pump actively transporting them in), they tend to leak out through these channels
As potassium ions move out through the leaky channels, they carry a positive charge with them. This results in a net loss of positive charges from the inside of the cell, creating a negative charge inside relative to the
outside
