11/5 Graded Potentials

Question 1

The basic outline of nyelinated neuron signal transduction:

Answer 1

signal in the dendrites, computed from many different inputs then output through the cell body, to the axon hillock (where if there is a great enough net signal then…) down the axon, to the next neuron where a synapse releases neurotransmitters, that conduct the signal (which may be stored long term and or inform many other cells) to the dendrites of the next cell.

Question 2

what is ion pore selectivity

Answer 2

the central pore will only allow a specific type of ion to flow through.

Question 3

what are gating properties of ion channels

Answer 3

they open and close in respone to things such aas membrane potential, ions, hormones, etc.

Question 4

channesl that open and close due to changes in membrane potential

Answer 4

voltage gated channels

Question 5

compare the rate of movement in transporters and channels

Answer 5

they channels are fast and the transporters are complex and slow

Question 6

what is the action of the Na-K pump?

Answer 6

the movement of 2 potassium ions into the cell and three sodium ions out of the cell.

Question 7

what are the two passive driving forces to move ions?

Answer 7

they are the electrical gradient and the concentration gradient (electrochemical gradient)

Question 8

why would a normal resting cell tend to pull sodium into itself and expel chlorine ions?

Answer 8

Cations tend to have a force vector into the cell and anions tend to have a force vector out of the cell. (intracellular about -85mv)

Question 9

what sets the resting potential of a cell?

Answer 9

the Potasium concentrations with a little adjustment by the sodium leak

Question 10

how to calculate the Vk for a cell?

Answer 10

Vk= 60 log ([Kout]/[Kin])

Question 11

conceptual interpretation of Vk?

Answer 11

the volatage that must exist across the cell inorder for that concentration difference of K to exist.

Question 12

why would the action potential go positive when the Na ion channels are opened?

Answer 12

The cell is permiable to K usually and so sets the potential with its equilibrium value, and then when AP is triggered then permeable to Na and so resets the membrane potential to Na equilibrium value (positive value).

Question 13

What if the cell did not have any open K+ channels – and then I changed the external potasium concentration by half?

Answer 13

it wouldn’t change the resting Vm!

Question 14

Oh, no I have a membrane that is permeable to multiple ions at the same time, ho do lI find the resting potential?

Answer 14

use the relative membrane permeabilities: and the nernst equation would be modified with the out/in conc. of each ion that is permiable with each conc. multiplied by the ions permiablility!

Question 15

hmmm,my membrane just became much more permeable to sodium, how will this change my membrane potential?

Answer 15

it will swing the potential towards sodium! this is how we get a action and/or graded potential.

Question 16

contrast Action potentials moving through a system and graded potentials moving through a system.

Answer 16

Action potentials have a voltage threshold, refractory period and conduct without decrement. Graded potentials have no threshold ror refractory period, have variable amplitude and duration and conduct decrementally, they are depolarizing or hyperpolarizing

Question 17

contrast the purpose of action potentials and graded potentials:

Answer 17

action potentials relay a signal, such as in the heart or in a nerve axon, graded potentials relay a stimulus that may or may not cause a reaction!

Question 18

a graded mpotential that leas to action potential are?

Answer 18

synaptic potentials (post-synaptic neurons); Generator potentials/receptor potentials (sensory cells); end plate potentials (skeletal muscle cells)

Question 19

how did this graded potential originate in my cell?!

Answer 19

external stimuli and neurotransmitters activate ion channels!!

Question 20

what are some external sitmulus that can cause a graded potential?

Answer 20

pain, light, stretch, temperature, sound etc.

Question 21

what are some neurotransmitters that can cause a graded potential?

Answer 21

ACh, NE, dopamine, serotonin, glutmate, GABA, glycine, etc.

Question 22

wait….how can a graded potential be either a depolarizing or a hyperpolarizing stimulus?

Answer 22

let either positive (Na+) or negative (Cl-) ion channels open

Question 23

great, a graded potential has been created from multiple stimuli and depolarized my cell, how do I know if it will cause an AP?

Answer 23

the AP and the number of AP will depend onthe graded potential causing the cell to depolarize Vm to the AP threshold and the magnitude above the threshold will coorilate to the number of APs!

Question 24

hmm…graded potential stimuli can be either depolarizing or hyperpolarizing, so what?!

Answer 24

depolarizing stimuli cause Excitatiory postsynaptic potentials, and hyperpolarizing stimuli cuase inhibitory postsynaptic potentials – EPSPs bring the membrane potential closer to threshold and to firing an action potential. IPSPs bring the membrane farther from it!

Question 25

what are some Excitatory Postsynaptic portetials (EPSP signals)?

Answer 25

ACh, norepinephrine, epinephrine, dopamine, glutamate, and serotonin.

Question 26

what are some inhibitory postsynaptic potential (IPSP) signals

Answer 26

Gama-aminobutric acid (GABA) and glycine.

Question 27

what channels cause a Excitatory ostsynaptic potential?

Answer 27

open Na+ and K+ channels (postive to depolarize and drive potential to about zero, or half between the Na and K nernst potentials)

Question 28

what channels cause an Inhibitory postsynaptic potential?

Answer 28

Cl- that will drive the potential towards the Vcl of -90mV!

Question 29

how can graded potentials act as a little computational center in the neuon cell body?

Answer 29

the cell wil recieve multiple IPSP and EPSP that will be graded over space and time through local circuit currents etc. in the cell and sum together to give a net post-synaptic potential (PSP) in the initial segment that can reach a INa threshold to trigger an action potential(s) that will be large, constant and fast with a refractory period etc. as it travels down the axon.

Question 30

contrast spatial summation and temporal summation in a nerve cell

Answer 30

spatial summation is the summation of multiple pre-synaptic axons giving a signal to the cell. Temporal is the same axon giving a signal in rapid succession; either can lead to a larger graded potential and therefore can cause the PSP to reach the threshold and cause action potential(s)

Question 31

Action potentials are some uniform, how can they ever cary as much information as the graded potential originally did?

Answer 31

they will vary (and code info) by the average rate of firing, the total number of potentials, and the temporal pattern. (or a combination of signals)

Question 32

In summary how do we depolarize and repolarize a cell in an action potential?

Answer 32

threshold is reached Na channel opens, sodium postive ion flow in depolarizes the cell, the channel blocks and refractory period, K channels allow K positive ion flow out that will repolarize the cell. the Na channels reset! in sum: outward ionic currents repolarize Vm and inward ionic urrnets depolarize Vm.

Question 33

How could I slow the rate of rise of the cation potential…hypothetically speaking of course!

Answer 33

by having sodium channel blockers partially inhibit the sodium current.

Question 34

how could I prolong the duration of an action potential (just sayin’)

Answer 34

could slow the sodium channel innactivation!

Question 35

what if I don’t like sodium…what other ion could I use to depolarize and action potential (looking at you cardiac muscle)

Answer 35

Calcium!

Question 36

what if I just have a little potasium channel blocker thrown in on those cells…?

Answer 36

then it will prolong the action potential by preventing the rapid repolarization of the cell!

Question 37

how is the cardiac action potential so different (heart alwasy has to be special!0

Answer 37

it is much longer and relies on a calcium current to creat that duration! the refractory period will also be longer (refractory periods are about as long as the AP)

Question 38

What is the one spot(s) along an axon where the AP can be continued by the presence of a sodium current due to sodium channels (i.e. where are the sodium channels)

Answer 38

at the nodes of Ranvier!

Question 39

How can I prevent my local circuit currents from excaping from my axon and diminishing before it can cause the next AP down the axon?

Answer 39

by myelinating the axon!!

Question 40

The horrible disease that attacks the myelination of neruons

Answer 40

Multiple sclerosis.

Question 41

man, it is a good thing that the nodes of ranvier are space where they are…why?

Answer 41

the local circuit currents can only propigate a depolarization of the cell so far, even with mylination and so the nodes need to be somewhat close, but the signal is fast!

Question 42

the hopping of action potential form node of ranvier to node of ranvier

Answer 42

saltatory conduction.

Question 43

What is the primary cause of the change in membrane potential during an action potential (inital depolarization)

Answer 43

the movement of Na out of the cell due to the opening of Na+ channels.

Question 44

what is primary responsible for the nerve AP repolarization?

Answer 44

the opening of K+ channels and the influx of potasium into the cell.

Question 45

What type of ion signal would be an inhibitory post synaptic potential?

Answer 45

opeing of ligand gated chloride channels and omvement of clorid ionsinto the clel leads to hyperpolariztion of the membrane!

Question 46

how are signals transmitted from the dendrite to the soma of a neouron

Answer 46

electronic conduction

Question 47

how can we describe the mechanorecptive receptor potentials?

Answer 47

increase in stimulus energy results in and increawe in receptor potential; when receptor potential rises above a certain threshold action potentials will appear in the neruon attached to the receptor. number of action potentials generated in the neuron attached to the recpdtro is proportional to receptor potential