Membrane Potential, Action Potential, The synapse

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Calcium equilibrium potential

+ 107 mV

What happens without a functional Na+/K+ pump?

, the ion fluxes of the steady state would eventually accumulate, and the concentration gradients would disappear. Over time the cell would intracellular Na+ would increase, and the cell would become depolarized. With the pump disabled, the ions redistribute themselves until they are all in an equilibrium state. The negatively-charged anions trapped inside the cell attract cations in an effort to reach true equilibrium. This process eventually leads to cell swelling and lysis

what are some similarities with the action potential in different cell types?

- they all have a very rapid depolarization phase that is all or nothing it either occurs fully or not at all amplitude of action potential is independent of the amount of current that is produced (Larger stimuli does not create larger action potential

non-excitable cells have a resting membrane potential that range from

-5 mV to -15 mV

excitable cells have a resting membrane potential between

-50--85 mV

neuronal action potential importance

-Electrical component of "electrochemical" transmission in the central and peripheral nervous systems -Critical for neural integration of information coming from multiple sensory modalities -Allows for rapid and efficient signal transmission even over long distances

what are the for major ion channels present in the cell membrane that regulate membrane potential?

-ligand- gated -mechanically gated -always open(leak channels, play major role in resting membrane potential) -voltage-gated

Action potential conduction velocity can vary from __ to __ The main factors the determine this velocity are ___ and__

0.2 m/sec to 120 m/sec axon diameter and myelination wider diameter faster, more myelination faster

conductor

A device designed to transmit electricity, heat, etc.

Resistance

A material's opposition to the flow of electric current.

resting membrane potential

An electrical potential established across the plasma membrane of all cells by the Na+/K+ ATPase and the K+ leak channels. IN most cells, the resting membrane potential is approximately -70 mV with respect to the outside of the cell. describes electric potential difference of a cell at rest

the lipid bilayer acts as a

Capacitor plate, all capacitors have two electrical conductors separated by an insulator -they are able to store charge between these plates in an electric feild

Cl- equilibrium potential

Cl- would go into the cell and polarize the membrane to -83 mV

driving force

Driving Force in Cell with resting membrane potential of -60 Pottasium :-60 - -84 = 24 Sodium: -60 - 63 = -123 Chloride: -60- -83 = 23 Calcium: -60 - 107 = -167

the Nernst equation

Eion= (RT/zF) *(ln( ion outside./ion inside)) R= universal gas constant (8.381X 10-23 J/K) T= temperature (in Kelvins) oft constant assumed 293 Z= ion charge (valence) F= Faraday's constant (9.648x104 C/mol; electric charge

once the voltage-gated Na+ channels are closed,__________ within the K voltage gated channels.

repolarization occurs quickly. the slow closure of these voltage-gated potassium channels results in the hyperpolarization that occurs during the action potential

R in the cell is

resistance due tot he presence of a plasma membrane in ohms

Increasing the axons diameter affects velocity by decreasing axoplasm

resistance to ion flow easier to move things when tube is wider

While Ca2+ plays very little role in resting membrane potential due to the absence of Ca2+ leak channels, it has a critical role in, which can

role in intracellular signaling, which can then alter membrane permeability to other ions, ultimately influencing the membrane potential of the cell.

ion channels are characterized not only by how / what opens them but their

selectivity to specific ions

graded potential are changes in

shifts of current (I) amplitude- ie they are the result of a change in the flow ions across the membrane due to an alteration in conductance- such changes alter membrane potential

graded potentials are considered__ what numerical value difference is assigned?

small fluctuation any change less than 20 mV in membrane potential

___ will try to move the membrane potential toward its positive equilibrium potential, while___ will try to move the membrane potential toward its negative equilibrium potential

sodium, potassium

EK is the voltage required for diffusional and electrical forces to be equal and opposite. When not considering the influence of permeability, Eion is moderately influenced by , but considerably influenced

temperature but considerably influenced by intra- and extracellular ion concentrations.

phase 3 an of action potential initiation

the K+ is trying to reach its Ek+, and the cell* is becoming more negative than the resting potential, but before it can the voltage gated pottasium channels CLOSE and The activity of leak channels and hte NA/K pump restore the resting membrane potential

Capacitance

the ability of a conductor to store energy in the form of electrically separated charges

When depolarization of the membrane at the axon hillock reaches the threshold for that neural* cell, what happens

the abundant Na+ channels at the axon hillock (and initial segment) open and an action potential is initiated

In non-myelinated axons, the action potential must

the action potential must propagate continuously along the plasma membrane

the wave of depolarization of the AP in the neuron move from the cell body toward

the axon terminal. the forward regions the axolemma (axonal membrane) depolarize due the opening of Na channels

how is a voltage gated Na+ channel closed?

the conformational change induced by depolarization also closes the inactivation gate but this process is delayed (very brief delay~ .1ms) so it is said to be time dependent now far less permeable to Na+ membrane potential begins to return to resting potential. the inactivation gate will not open again until the membrane returns to resting potential even if there is a depolarizing event, no Na+ can enter the cell until the inactivation gate opens- This is what results in the absolute refractory period

conductance (G)

the ease with which ions flow through a channel G = 1/R it is simply the reciprocal of resistance for our purposes it is how easily an ion can move through an ION channel in a membrane

a cells resting membrane potential is based on

the equilibrium potential of multiple ions as well as on membrane permeability

I in the cell is

the flow of charged particles through "conductors" in the membrane ( in amperes)

the amplitude of the graded potential is dependent on

the intensity of the stimulus

The distance between nodes and the number of voltage-gated Na+ channels at the node influence

the speed of conductance

if there is a LARGE difference between equilibrium potential and resting membrane potential then

there is a large electrochemical gradient ( driving force) for that ion

on myelinated axons, as the depolarization wave moves down the axon it activates what

these voltage-gated Na+ channel in the nodes of Ranvier and propagates (or re-amplifies) the signal

what is the role of pumps and active transport in membrane potential

they are needed to offset the continuous leakage of ions across membrane important for working against both concentration gradients and electrical forces

the presence of inhibitory potentials in neurons result in what

they hyperpolarize the membrane, which also serve to diminish membrane depolarization

the repolarization from the K channels in the axolemma of a neuron is important because

this repolarization prevents the action potential from moving backwards (back propagation). For this reason we say that the movement of the action potential is unidirectional

the myelin sheath is composed of __ which provide

tightly wrapped lipid bilayers and specialized proteins insulation which decreases the decay of the depolarizing wave and support to axons

what closes the voltage-gated potassium channel?

until the Na+ channel closes both gated Na and K channels are open •Remember that Na+ has a stronger driving force, so with increased permeability it is winning the tug of war

when an excitatory potential depolarizes a neurons membrane this depolarization

will travel towards the axon hillock (which possesses a much higher density of voltage-gated Na+ channels then the cell body) diminishing exponentially with TIME and DISTANCE

Goldman-Hodgkin-Katz equation

•Includes the intra- and extracellular concentration of the three major ions influencing resting membrane potential •Includes permeability of the membrane to individual ions (both the number of ion channels and their permeability) •Also includes the other "constant" values discussed in the Nernst equation.

One critical function of myelin is to

•to increase the speed of electrical transmission (i.e. conduction velocity); the more myelin, the faster the conduction

it is the _______ that is correlated with the intensity of a stimulus and transmit variation in the information being transmitted

FREQUENCY of action potential

Nodes of Ranvier

Gaps in the myelin sheath to which voltage-gated sodium channels are cluster in the unmyelinated axolemma

initiation of an action potential in NEURONS

Incoming stimuli produces local changes membrane potentials (graded potentials). these Graded potentials can either be excitatory or inhibitory

sodium equilibrium potential

Na+: positive equilibrium -Driven inside by concentration, but once interior is too positive, positively-charged ions are repelled -Balanced at +63mV E =ion 58 mV/ 1 ( log (120/10)

How do we calculate the equilibrium potential?

Nernst equation

what different events are initiated from an action potential that differs between cell types?

Neuron-cellular communication via chemical transmission muscle cell-contraction endocrine cell-secretion

Graded potentials are

Short-lived, localized changes in membrane potential modulation of the membrane potential away from the resting membrane potential of that cell-

Na+/K+ pump (-ATPase):

The low concentration of intracellular Na+ must be actively maintained since Na+ has a strong driving force (i.e both diffusion and electrical potential are driving it into the cell). The pump works against both these concentration and electrical forces. This requires lots of energy to maintain •Consumes 10-40% of available ATP depending on cell type •Single most energy requiring process in the body 3 Na+ pumped out while 2 K+ ions are pumped in

Ohm's law equation

V=IR can be rearranged etc V= potential in volts I = current ( Amps) R = resistance in Ohms states that current between 2 points is equal to the voltage difference between those same two points divided by the resistance

when the cell membrane depolarizes what happens to the voltage-gated potassium channels?

a conformational change occurs and the gates open, these gates open slightly slower than the Na+ channel

capacitance is greater when there is

a narrower separation between conductors. and when the conductors have a larger surface area

What is an action potential?

a rapid, substantial but transient increase in membrane potential ( depolarization) that is propagated (spreading activation)

_________ occurs immediately after the initiation of the action potential. DURING THIS TIME ANOTHER ACTION POTENTIAL CANNOT BE GENERATED

absolute refractory period

__________ immediately follows absolute refractory period and _______

absolute refractory period. lasts for a longer time, DURING THIS TIME A SECOND ACTION POTENTIAL CAN BE GENERATED but only if a stronger stimulus is used

salutatory conduction

action potential jumps from node to node, which speeds up the impulse.

what are the TWO Na+ gates that are involved in the generation of an action potential? where are they located?

activation gate-extracellular side of a membrane- CLOSED at rest inactivation gate-intracellular side of membrane- OPENED at rest

___________ of the voltage changes of membranes tends to be roughly the same across excitable cells

amplitudes

What are some therapeutic effects of modulating voltage-gated K+ channels on Action Potential Frequency?

applying a K channel inhibitor can help bring a decreased frequency of AP firing to a normal level. done for CNS depression, multiple sclerosis applying a K channel activator helps lower an increased frequency of AP firing to a normal neuron action potential firing done for CNS hyperexcitability, seizures, pain, ADHD, anxiety

potassium equilibrium potential

assumption cell membrane is only permeable to potassium aver temp of cat Eion = 62 mV/(1) * log ( 5/ 140) E ion = -84 mV

the excitatory and inhibitory potentials are summed where

at the axon hillock

in neurons action potential propagate via

axons and serve as the basis of neuronal communication

Therapeutic effect of blocking voltage-gated Na+ channels

bock fast voltage-gated SODIUM channels, preventing neuronal depolarization. This blocks the transmission of pain.

movements of ions through channels are driven by and they can

both electrical and chemical forces change the membrane potential ( tho these are small changes measured in mV)

what are the major differences between different cell types and action potential?

both the SPEED and COMPLEXITY of action potentials vary between also initial different events depending on the terminal cell

Myelination increases velocity by decreasing

capacitance and increasing membrane resistance

resting membrane varies based on

cell type, depends on cell-type membrane permeability to specific ions and intracellular concentrations of selection ion species

Depolarize the membrane

change in the cells membrane potential making it more positive ( greater than -70 mV

at resting membrane potential VOLTAGE-GATED Potassiums channels are

closed

high conductance =

decreased resistance

absolute refractory period corresponds to ___________ whereas relative refractory period corresponds to _________

depolarization and repolarization hyperpolarization

V in the cell is

difference in electrical potential energy on either side of the membrane in volts

phase 2 of an action potential initiation

drive force of NA wants to move the membrane towards E(na+) ( = + 60 mV) but before the cell is able to reach this, the increased voltage causes closure of the voltage=gated NA channels . ( sodium flowing in) this also causes the opening of K+ channels this potassium is flowing out of the cell based on its CONCENTRATION GRADIENT

resting membrane potential depends upon what

electric potential difference ion concentration gradient which both work towards equilibrium potential of K , Na and Cl - and the active transport mechanisms present

what is membrane potential in the cell?

electrical potential difference (mV) it is a measured difference between the inside and outside of the cell *FYI The electrode outside the cell is set to zero, so the membrane potential is always relative to the interior of the cell

the steeper the concentration gradient the larger the

electrical potential that balances it needs to be

graded potentials can be either ___ or____ meaning

excitatory, or inhibitory meaning it can either depolarize or hyperbolize the membrane

equilibrium or reversal potential

for an individual ion is the membrane potential (i.e. the voltage as measured inside the cell) where the net flow through any open channels is 0. This indicates that the chemical and electrical forces for that ion are in balance

Z ion charge valence =

for most but not all is 1 (K+ and Na+) or -1 (for Cl-)

the resting membrane potential will be closer to the ion type with

higher permeability

phase 1 ( initiation of an action potential)

induces by depolarization of the resting membrane potential, membrane potential changes in proportion to current amplitude via graded potentials. at some point the cell hits a voltage threshold (specific to cell type usually 15 mv above the cells resting membrane potential) this increase in volage causes voltage-gated Na ion channels to open continuing until all voltage gated Na channels are open deemed depolarization

the phospholipid bilayer is an excellent

insulator

__________ are good conductors in the cell, meaning

intra and extracellular fluid they allow for the flow of charged particles ( as ions are hydrophilic)

lots of drugs focus on changing activity of

ion channels

in neurons and skeletal muscle cells the action of potential initiation occur in

less than 5 ms

membrane potential is largely based on ___ & ___ bec

membrane permeability and electrochemical gradients charged particles are attracted to their opposites chemicals move in area of higher concentration to areas of lower

Hyperpolarization

membrane potential becomes more negative

hyperpolarized membrane

membrane potential becomes more negative than resting potential ( more negative than -70 mV)

how is a voltage gated Na+ channel opened?

membrane potential depolarization causes a Conformational change that flips the gate open. This dramatically increases membrane permeability to Na ions- RESISTANCE IS DECREASED, CONDUCTANCE IS INCREASED

when ion channels are CLOSED they act as ______ when ion channels are open they act as _____

mini resistors conductors

Most excitable membranes are more permeable to ___ due to

potassium due to a greater number of K+ leak channels

immediately after depolarization in the neuron what happens?

potassium leaves the axoplasm via potassium channels (voltage?) repolarizing the axolemma

major ions involved in SETTING and MODIFYING membrane are

potassium, sodium, chloride and calcium

electrical potential energy

potential energy associated with a charge due to its position in an electric field a test charge far away from an opposite charge is said to have high potential energy and it gets closer to the said charge it is said to have low potential energy

interior of the cell at rest is _______ due to

negative . large intracellular anions ( proteins, phosphate, sulfate) that cannot pass through the membrane

Where do action potentials occur?

occur in neuron and muscle cells ( all types skeletal, smooth and cardiac) but these different cell types have unique aspects to certain phases of action potential


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