Neurophysiology

What would be the resting membrane potential of a cell that is only permeable to chloride ions?

-63 mV the equilibrium potential for Cl-

Let's say that you use a voltmeter to measure the membrane potential of a typical neural cell. You stick one electrode inside the cell and a ground electrode outside the cell. What will the reading on the voltmeter be if the cell is at rest?

-70 mV (because the inside of the cell is more negative relative to the outside)

Let's say that you repeat the procedure above, but instead of putting the ground electrode outside the cell, you stick it inside another nearby cell. What will the reading on the voltmeter be if both cells are at rest?

0 mV (there should be no difference in charge between the inside of both cells)

ECa2+=

137 mV

In the year 2173, you are the chief scientific officer on an expedition of Lazarus 5, the fourth moon of the planet Septar. You are investigating a new species of alien life and curious about its alien physiology. You dissect some of the alien tissue and place it in a dish with buffered solution. Using a voltmeter, you use an intracellular electrode to determine that the resting membrane potential is +40 mV. You immediately wonder which ions might be important for this resting membrane potential. The seas of Lazarus 5 are abundant with calcium, fluoride, potassium, lithium, and magnesium. What experiments could you perform to determine whether each of these elements contributes to the resting membrane potential?

A cell membrane potential is influenced by an ion if it is permeable to that ion. You could increase or decrease the extracellular concentration of various ions to change the Eion, then determine if the resting membrane potential is affected. For example, you could increase the ionic concentrations within a solution that the tissue is suspended in. If the elements contribute to the resting membrane potential, changing the extracellular concentration will change the membrane potential as measured by the voltmeter. If they don't change the membrane voltage, the ions do not contribute to membrane potential.

What kind of ionotropic receptor would be best at causing an IPSP that hyperpolarizes the membrane, a channel permeable for Na+, K+, Cl-, or Ca2+?

A channel permeable for K+. K+ has the most negative equilibrium potential, so making the cell membrane more permeable to K+ would bring the membrane potential closer to EK+=-90mV

How is electrical flow down an axon similar to electrical flow down the length of a wire?

A signal can be sent from one end of an axon to the other, just like a signal can be sent from one end of a wire to the other

What is the difference between an absolute versus relative refractory period?

Absolute refractory period is the time period during which you cannot generate a second action potential no matter how hard you try. Relative refractory period is the time period during which generating a second action potential is possible, but it takes a stronger stimulus than what triggered the first action potential

What would happen to an action potential waveform if a scientist added a drug that blocked voltage-gated K+ channels?

After the voltage-gated Na+ channel inactivation gates close, there would not be a rapid repolarization of the membrane. The membrane would slowly repolarize due to the ATP-dependent Na+/K+ pump.

Which kinds of cells have a membrane potential?

All cells have a membrane potential, though they are different in charge

Ionotropic GABA receptors are anion channels that are permeable to Cl-. Will the binding of Cl- cause an EPSP or IPSP?

An EPSP- but not enough to bring the membrane to threshold Will never cause an action potential (-63 mv is capacity) Prevents neuron from firing an action potential

A neuron has a resting potential of -70mV. A drug causes the opening of an ion channel that is permeable to both Na+ and K+ ions. What is the effect on the cell membrane?

Both permeabilities are changing. Cell is already highly permeable to K+ relative to Na+ (1:20). Opening a 1:1 ion channel, even though we are increasing permeability to both ions, will only increase the relative permeability of Na+ so that the cell membrane resting potential will shift to a more positive value.

What best describes what specifically causes synaptic vesicles to fuse with the plasma membrane at the end of the axon terminal?

Ca2+ ions interact with proteins on the synaptic vesicles and cause them to fuse with the membrane

In what way is the role of Ca2+ ions in neurophysiology different from the role of Na+ and K+ ions?

Ca2+ ions play a major role in axon terminals Na+ and K+ ions play a role in the resting membrane potential in the cell body and axon All three ions play a role in the postsynaptic response to neurotransmitters Ca2+ plays a role inside the cell by actually interacting with intracellular synaptic vesicles - Na+ and K+ don't interact with intracellular proteins or organelles and simply exist as electrically charged species

Nernst equation

Calculates the equilibrium potential for any ion dependent on the charge and the relative concentration of the ion inside and outside of the cell

What is a possible evolutionary reason that most neurons in the central nervous system employ chemical synapses versus gap junctions, even though gap junctions allow for faster communication?

Chemical synapses allow for the integration and summation of multiple inputs to the postsynaptic cell. Some presynaptic inputs are excitatory in nature and cause EPSPs; other inputs are inhibitory and cause IPSPs. Postsynaptic potentials can summate locally on the postsynaptic cell (spatial summation) or quickly over time (temporal summation) to influence the ability of the postsynaptic cell to fire an action potential. The chemical synapses allow for a high degree of info processing.

What can a chemical synapse do that an electrical synapse cannot do?

Chemical synapses can integrate info, especially integrating excitatory or inhibitory signals from presynaptic neurons

What determines whether an ionic species will exhibit net movement through a membrane?

Depending on how permeable the membrane is to the ionic species, the electrostatic gradient across the membrane (the charge of the ionic species), and the concentration gradient of the ion across the membrane.

What word describes a phenomenon in which a population of neurons in the CNS sends axons to 5 distinct brain regions to regulate a behavioral phenotype

Divergence

If the body temperature of an animal slightly increased, what would be the effect on EK+?

EK+ would become more negative

If the body temperature of an animal slightly increased, what would be the effect on ENa+?

ENa+ would become more positive

For a typical neuron at a normal mammalian body temperature of 37°C, ENa+= +60 mV, EK+= -90 mV, and ECl-= -63 mV. What would be the effect of raising the temperature on ENa, EK, and ECl?

ENa- more positive EK- more negative ECl- more negative Increasing the temperature would increase the magnitude of the Eion.

If a neurotransmitter caused the opening of a Na+ channel on the postsynaptic cell, what would you call the resulting change in membrane potential in the postsynaptic cell?

EPSP, a graded potential that slightly depolarizes the membrane

What determines the effect that a neurotransmitter will have on a postsynaptic cell?

Effect is determined by the postsynaptic receptor identity. The postsynaptic receptor dictates what kinds of ion channels open in response to a neurotransmitter.

What is an advantage of an electrical synapse over a chemical synapse?

Electrical synapses are much faster than chemical synapses - decreased time necessary to signal between cells

A neuron sits at rest at -70mV. An upstream neuron releases GABA, opening ionotropic GABA receptors (permeable to Cl- ions). What effect does this have on the neuron?

Experiences an EPSP because it is depolarized and GABA has an inhibitory effect on the ability of the neuron to fire an action potential

What is the difference between a resting membrane potential, a graded potential, and an action potential?

Graded potentials are changes in membrane potential from the resting potential that are insufficient to generate an action potential. An action potential is an all-or-none depolarization of membrane potential.

What makes a synapse excitatory?

If the neurotransmitter released by the presynaptic cell causes a receptor on the postsynaptic cell to depolarize the membrane and potentially cause the postsynaptic cell to reach threshold potential to fire an action potential.

A neuron has a resting potential of -70mV. A drug causes the opening of Cl- ion channels on the membrane. What is the effect on the cell membrane potential?

Increasing proportion of Cl- will increase the permeability of Cl- ion channels, ECl-=-63mV so the membrane potential becomes slightly more positive (approaching -63 mV)

Ionotropic acetylcholine receptors are cation channels that are permeable to both Na+ and K+. Will the binding of acetylcholine cause an EPSP or an IPSP?

Increasing sodium portion permeability An EPSP- raise the membrane potential and make it more positive

A neuron has a resting potential of -70mV. A drug causes the opening of Na+ ion channels on the membrane. What is the effect on the cell membrane potential?

Increasing the proportion of Na+ (so it carries greater weight in permeability context). Na+ permeability is increasing so the relative contribution of ENa+=60mV increases as well, changing the resting potential of -70mV (more positive)

In a single sentence, what is the main difference between an ionotropic and metabotropic receptor?

Ionotropic receptor is ligand-gated ion channel whereas metabotropic receptor indirectly activates a separate ion channel

Why can't ions cross cell membranes without the assistance of transmembrane proteins?

Ions cannot cross the cell membrane without transmembrane proteins because ions are polar (hydrophilic) and the plasma membrane has hydrophobic tails (that are nonpolar) so the ions are repelled. Polar ions cannot cross the nonpolar interiors of plasma membranes.

Which ions affect the membrane potential of neurons and why?

K+, Na+, and Cl- because neuron cells are permeable to these ionic species.

Name at least 5 categories of ion channels (categorized by how they are opened/gated, not by the ions they are permeable to)

Leak channels (always open), voltage-gated ion channels, ligand-gated ion channels, mechanosensitive ion channels, temperature-sensitive ion channels, light-sensitive ion channels... in non-mammalian species there are magnetic-sensitive ion channels, electric-sensitive ion channels (sensitive to electric fields in the environment, not just in the membrane potential)

Naomium is much more concentrated on one side of a membrane than the other side. The side that is less concentrated also has a slight positive charge. Suddenly, ion channels open and allow Naomium ions to pass through. What will happen?

Like charges repel each other. The ions will still try to go down their concentration gradient, but there will be a higher concentration of Naomium on the side without the positive charge because it is positively charged.

Name at least 6 transmembrane proteins that exist in neurons

Na+ leak channel, K+ leak channel, Na+/K+ ATPase pump, voltage-gated Na+ channel, voltage-gated K+ channel, Cl- leak channel

Will ECl- be positive or negative?

Negative charge will build up inside the cell and repel Cl- ions so that they stop flowing down their concentration gradient. Equilibrium is eventually reached. ECl- = -63 mV

Will EK+ be positive or negative?

Negative charge will buildup inside the cell which will attract K+ ions so that they stop moving down their concentration gradient. Equilibrium is eventually reached. EK+ = -90 mV

What would be the effect of a drug that blocks voltage-gated Ca2+ channels on neurons?

Neurons would be able to fire action potentials that propagate down the length of the axon, but the neurons would not be able to release neurotransmitter onto downstream neurons. Neurons with electrical synapses would be unaffected.

Does magnesium contribute to the resting membrane potential of a neuron? Why or why not?

No because the cell membrane is not permeable to Mg2+ so Mg2+ does not contribute to the membrane potential of the cell

Do neurons always synapse onto other neurons?

No, some neurons synapse onto muscle fibers to contract muscles, for example.

Does an animal need a brain to survive?

No. Many animals don't have brains but instead utilize organism-wide "neural nets"

A neuron has a resting potential of -70 mV. A scientist adds concentrated KCl to the extracellular solution. What happens to the permeability of the cell for K+ and Cl- ions? What is the effect on the cell membrane potential?

Nothing about adding KCl would influence permeability., since ion channels are not opening. Nothing would change about permeability since we are increasing extracellular concentration of KCl. In normal conditions, EK+=-90mV, BUT more K+ to the outside of the cell makes EK+ less negative because the concentration gradient has less of an influence. More K+ to the outside makes EK+ more positive. In normal conditions, ECl- = -63 mV, BUT more Cl- to the outside of the cell makes ECl- more negative because we are increasing the influence of the concentration gradient. More Cl- to the outside makes ECl- more negative. Cell membrane potential will become more positive because K+ permeability matters more.

Will ENa+ be positive or negative?

Positive charge will build up inside the cell so much so that it will eventually repel future Na+ ions from entering, thus reaching equilibrium. ENa+ = +60 mV

PNS

Somatic and Automatic

A neuron sits at rest at -70 mV. If a scientist adds MgCl2 to the extracellular media, what will be the effect on the membrane potential?

The Mg2+ ions will have no effect on the cell membrane potential because the cell is not permeable to Mg2+. Increasing the extracellular concentration of Cl- ions will cause ECl- to become more negative so the membrane potential of the cell will then become more negative.

In a single sentence, what does the Nernst equation tell you?

The Nernst equation tells you the equilibrium potential for an ionic species, the membrane potential at which there will be no net movement of the ion across the membrane.

What prevents a propagating action potential from going backward (from the axon back towards the cell body)?

The absolute refractory period. During this period, it is impossible to initiate a second action potential, so the propagating action potentials can only go in the "forward" direction.

E Nao+ is more concentrated on the outside of the cell than the inside. Will ENao+ be positive or negative?

The cell would eventually be more positive; at a certain point it reaches equilibrium when the cell gets more positive and therefore ENao+ is positive.

What two distinct phenomena dictate whether there will be a net movement of ions from one side of a membrane to the other side of a membrane?

The concentration gradient of the ion and the electrostatic gradient across the membrane

If the summation of EPSP's depolarized the soma of a neuron to -58 mV but did not cause an action potential, why wouldn't this graded depolarization spread down the length of the axon anyway?

The depolarization at a tiny patch of the cell membrane, if not followed by any additional EPSPs or membrane events, would quickly dissipate within the local area. The slightly higher positive charge would weakly spread to adjacent areas, but quickly repolarize.

Membrane potential

The difference in charge between the intracellular and extracellular fluid in all cells.

A hypothetical ion has a positive charge. It is more concentrated inside a cell relative to the outside of a cell. Will this ion's equilibrium potential be positive or negative and why?

The equilibrium potential will be negative. The membrane potential would need to be negative to prevent the positively charged ionic species from continuously flowing down its concentration gradient from the inside to the outside of the cell.

In mammals, the extracellular concentration of magnesium (Mg2+) is 1 mM and the intracellular concentration is 15 mM. For a typical neuron, is the equilibrium potential for Mg2+ positive or negative?

The equilibrium potential would be negative. The membrane potential must be negative to counteract the concentration gradient of the positively charged ion.

What best describes why an action potential on a patch of membrane will trigger an action potential on an adjacent patch of membrane?

The influx of Na+ ions during the first action potential will spread to a local region to the point where that region is depolarized to threshold potential

Using a fictional positively charged element, Naomium: Naomium is much more concentrated on one side of a membrane than the other side. Suddenly, Naomium ion channels open and allow Naomium ions to pass through. What will happen?

The ions will flow down the concentration gradient until the net flow is zero and equilibrium is reached between the intracellular and extracellular fluid of the cell

An action potential for a particular neuron will always have the same maximum depolarization (usually around 30 mV). What is the mechanism by which an action potential will have a consistent maximum depolarization, even if the intensity of a stimulation event increases?

The maximum peak of an action potential is reached when the voltage-gated Na+ channel inactivation gates close. At this point, the voltage-gated K+ channels also open, but the Na+ channel inactivation gates completely stop the positive increase in membrane potential voltage.

In a single sentence, what does the Goldman equation tell you?

The membrane potential of the cell based on the permeability of each ion species, as well as the charge and concentration of the ion across the membrane. The membrane potential of a cell given the concentrations, charges, and relative permeabilities of all the surrounding ions.

A scientist uses a voltmeter to record the resting membrane potential of a neuron, which sits at -70 mV. A drug that causes the opening of K+ channels. What is the effect on cell membrane potential?

The membrane potential will become more negative

A scientist uses a voltmeter to record the resting membrane potential of a neuron, which sits at -70 mV. The scientist then adds a drug that completely blocks the Cl- leak channels. What is the effect on cell membrane potential?

The membrane potential will become more negative

Why don't zinc ions contribute to the resting membrane potential of a cell even though there is zinc present in animal tissues?

The neural cell membrane is not permeable to the ionic species and so zinc cannot impact membrane potential.

What is the best reason for why a neural membrane potential quickly repolarizes from +30mV to a negative value during an action potential?

The opening of voltage-gated K+ channels activation gates

If you have just taken the MCAT and are relaxing in a chair, what division of the peripheral nervous system is probably the most active?

The parasympathetic nervous system - your heart rate, breathing rate, and attention/focus are probably reduced relative to other physiological systems such as digestion, urinary systems, etc.

What would happen to the resting membrane potential of a neuron if a neuroscientist artificially caused more sodium leak channels to be expressed on the cell membrane?

The resting membrane potential of a neuron would become less negative (more positive) and approach a value of ENa+=60 mV.

What would happen to the resting membrane potential of a neuron if the extracellular concentration of potassium ions decreased from 5 mM to 1 mM?

The resting membrane potential of a neuron would become more negative. The concentration gradient for K+ would increase and EK+ would decrease from -90mV to a lower value. Therefore, the resting membrane potential would move closer in value to the new EK+ by becoming more negative.

Pretend that you could eliminate all sodium and chloride leak channels and sodium/potassium pumps from a neuron so that only potassium leak channels remain. What would be the resting membrane potential of the cell?

The resting membrane potential would be -90mV because the equilibrium potential of K+ is -90mV.

What would happen to a neuron's resting membrane potential if a scientist added a drug that blocked sodium leak channels?

The resting membrane potential would become more negative because less positively charged Na+ ions would flow through the membrane. The membrane would be impermeable to Na+ ions, so the equilibrium potential would shift towards K= and Cl- which are much more negative.

A neuron's resting potential is -70mV. What would happen to the resting membrane potential if a drug caused the opening of more K+ channels?

The resting membrane potential would become more negative. Opening more K+ channels would increase the permeability for K+. Therefore, the cell membrane potential would approach EK+=-90mV and become more negative.

If you are just about to take a big test, what division of the PNS is probably most active?

The sympathetic nervous system - your heart rate, breathing rate, and attention/focus are probably maximized at the expense of digestion, urinary systems, etc.

What transmembrane proteins are necessary for the propagation of an action potential?

The voltage-gated Na+ and voltage-gated K+ channels (necessary for generating an action potential in the first place) leak channels and Na+/K+ pump are also necessary for normal membrane functions and the establishment/maintenance of the resting membrane potential, but these transmembrane proteins do not actively participate in action potential propagation

What is the best reason for why a neuron cannot exhibit a second action potential during the repolarization phase?

The voltage-gated Na+ channel inactivation gates are closed

TTX is a chemical that blocks Na+ ions rom flowing through voltage gated sodium channels. What would be the effect of adding TTX to the interstitial fluid around neurons?

There is no rapid depolarization of the membrane when the cell reaches threshold potential, and no action potential occurs.

If an ion is relatively more concentrated outside of a cell than inside of a cell, why might that ion NOT diffuse down its concentration gradient to the inside of the cell?

There may be a strong electrostatic gradient that repels the ion from entering the cell

Using a fictional positively charged element, Naomium: Naomium is much more concentrated on one side of a membrane than the other side. The side that is less concentrated also has a high negative charge. Suddenly, Naomium ion channels open and allow Naomium ions to pass through. What will happen?

There will be a net flow of ions across the membrane to the negatively charged side. When equilibrium is reached, there will be unequal distribution caused by the negative charge on that side. There will be an influx of Naomium ions on the negatively charged side because opposites attract. The concentration gradient also applies, going in the same direction.

What causes EPSPs and IPSPs within neuronal membranes?

Ultimately the opening of ion channels on the cell membrane Other presynaptic neurons releasing neurotransmitter; Hormones secreted from other cells in the body bind to receptors on the neural membrane; Transduction of environmental stimuli via gated ion channels (mechanically-gated, thermally-gated, chemical-gated)

An unmyelinated axon has a much greater requirement for ATP than a myelinated axon of the same diameter and length. Why might this be the case?

Unmyelinated axons have more exposed membranes and therefore more leak channels. To maintain a resting potential, more ATP-dependent Na+/K+ pumps would be needed. In contrast, a myelinated axon expresses far fewer channels on the exposed nodes of Ranvier so less Na+/K+ pumps are necessary.

Undershoot

VG Na+ activation - closed VG Na+ inactivation - opening Vg K+ channel - closing

Resting State

VG Na+ activation - closed VG Na+ inactivation - open Vg K+ channel - closed

Repolarization

VG Na+ activation - closing VG Na+ inactivation - closed Vg K+ channel - open

Depolarization

VG Na+ activation - open VG Na+ inactivation - open Vg K+ channel - closed

How do neurons influence other cells/tissue?

Via gap junctions with other neurons (stimulate another neuron) Stimulate by releasing neurotransmitters: onto other neurons, onto other different cell types, into the bloodstream.

Equilibrium potential

When a cell is permeable to an ionic species, that ionic species will reach equilibrium (no net movement across a cell membrane) when the membrane potential exactly opposes the concentration gradient

What is the role of Ca2+ in synaptic transmission?

When an action potential arrives at the presynaptic terminal, voltage-gated Ca2+ channels open and allow Ca2+ ions to enter the cell. These ions bind to proteins on synaptic vesicles, causing the vesicles to dock with the synaptic membrane and release their neurotransmitter contents into the synapse.

Describe the initiation of an action potential using the Goldman equation

When voltage-gated sodium channels open, the cell becomes much more permeable to Na+, and the membrane potential becomes much closer (30 mV) to the equilibrium potential for Na+ (60 mV) An action potential begins with the opening of voltage-gated sodium channels. The membrane potential quickly depolarizes and becomes positive.

Is there a fundamental difference between the mammalian central and peripheral nervous systems, besides the location of the cell bodies and axons?

Yes, for example, in the PNS, the glia that provide myelin are different

Is it possible for an ionic species to have an equilibrium potential but not affect the resting membrane potential?

Yes. This happens if there is a concentration gradient for the ion but the membrane is not permeable to the ion.

Action potentials

a brief, rapid, and large change in membrane potential a rapid depolarization triggered by events in the cell the potential reverses so that the inside of the cell becomes more positive than the outside

Metabotropic receptors

activate G-proteins which modulate ion channels indirectly through intracellular signaling

How does saltatory conduction increase the velocity of action potential propagation?

allows propagating action potential to "skip" regular intervals of myelinated axonal membrane patches and allows the action potentials to "jump" across regular intervals of the axon like skipping steps up stairs

The concentration gradient

an ionic species will diffuse from where it is more concentrated to where it is less concentrated if there are more ions on one side of the membrane, they will go down the concentration gradient until both sides are even

Action potentials propagate so quickly that

as soon as the site of the first action potential is ready to be triggered again, the action potential has already flowed so far down the axon it has no chance of triggering the first site again by the same stimulus response

Depending on what the ion channels are,

binding of neurotransmitter and the opening/closing of channels will cause a change in membrane potential in the postsynaptic cell (excitation or inhibition)

Membranes express transmembrane proteins that allow

certain ions to pass through a membrane called ion channels

Electrostatic gradient

charges of opposite valence (+ or -) attract each other while charges of the same valence (+ and + or - and -) repel each other like charges repel, opposites attract

What influences the velocity of a propagating action potential?

degree of myelination and axon diameter the more myelinated the axon and the larger the axon diameter, the faster the velocity of the propagating action potential

How are action potentials propagated down the length of an axon?

diffusion of Na+ ions. The depolarization causes an action potential in an adjacent region which, in turn, causes depolarization in a further adjacent region. a chain reaction of action potential depolarizations propagates down the length of an axon

Eion means

if ion channel opens, what does the membrane potential have to be for flow to reach equilibrium

K+ ions are much more concentrated

inside of a cell

Equilibrium potential definition

ionic species will reach equilibrium when the membrane potential exactly opposes the concentration gradient

Cell membranes, by themselves, are impermeable to

ions

Ions cannot cross a plasma membrane by themselves no matter the charge because

ions are polar (hydrophilic) and the lipid layer is nonpolar (hydrophobic tails) so ions are repelled

When a bit of Na+ spreads from one region to the next,

it causes an action potential which opens voltage-gated Na+ channels

A neurotransmitter is excitatory if

it depolarizes the cell membrane potential towards threshold potential.

Adding more K+ to the extracellular fluid makes EK+

less negative due to the concentration gradient

Ionotropic receptors

ligand-gated ion channels that combine receptor and channel function in a single protein complex

Graded potentials are

local changes in membrane potential occurring in varying degrees of magnitude or strength. minor changes in fluctuations in the membrane potential

The Goldman equation is

membrane potential of the entire cell

Calcium makes the membrane potential

more positive AND interacts directly with proteins inside the axon terminal cell binds with proteins sitting outside of the synaptic vesicles Calcium causes vesicles to fuse with the presynaptic membrane so vesicle content gets released into the synapse

Depending on the postsynaptic receptor,

neurotransmitter binding will cause an event in the postsynaptic cell to the effect of opening or closing an ion channel in the postsynaptic membrane

When the vesicle docks with the presynaptic membrane, through the process of exocytosis,

neurotransmitter is released into the synapse

Na+ and Cl- ions are much more concentrated

outside of a cell

Activity in which category is most likely to decrease heart rate

parasympathetic nerve

The expression of an ion channel on the cell membrane makes the membrane

permeable for that ion Every ion channel is very selective for specific ions

Permeability is determined by the

presence of specific channels and active transporters in the cell membrane

Action potentials are

rapid changes of membrane potential

Somatic

regulates things we are consciously aware of Sensory (touch, smell, etc.) Motor (refers to muscles)

Autonomic

regulates things we aren't aware of that we cannot really control Parasympathetic (rest and digest) Sympathetic (flight or fight)

A negative membrane potential means that the inside of the cell is negative in charge with

respect to the outside of the cell

The depolarization of the first action potential

spread to the neighboring region of the membrane, depolarizing it and initiating a second action potential

Why is an action potential considered an all-or-none event?

the amplitude is always the same, no matter the intensity of the stimulus that caused the action potential

Equilibrium potential for any ion depends on

the charge and the relative concentration of the ion inside and outside of the cell

The Nernst equation tells you

the equilibrium potential of a specific ion

At the site of the first action potential once the adjacent is triggered,

the membrane is repolarizing as K+ flows outward

A resting membrane potential is

the membrane potential of a cell that is "at rest" and not experiencing a rapid change in membrane potential

Resting membrane potential

the membrane potential of an excitable or non-excitable cell that is "at rest" and not experiencing a rapid change in membrane potential Ultimately due to the unequal distribution of ions across a membrane

Equilibrium potential of ions helps determine

the membrane potential of the cell

What causes the rapid repolarization of the cell membrane to a negative voltage following the peak of an action potential?

the opening of voltage-gated potassium channels

Why do graded potentials diminish over very short distances?

they can't be detected down the length of an axon because if Na+ activation channel opens, but not to threshold, the positively charged ions flow in and dissipate in the local area threshold potential is -55 mV Na+/K+ pump quickly restores the local membrane potential

z in the Nernst equation

valence of the ion (ex: Cl- = -1, Ca2+ = 2, Na+ = 1)

Saltatory conduction

voltage-gated Na+ channel opens, Na+ ions rush in and cause a positive charge in that area, the myelinated section of the neuron needs to be overcome and the unmyelinated areas normally have a slight negative charge so the positively charged Na+ ions are attracted and will leap the length of the myelin segment to be attracted to the negative charge, causing a second action potential

When a cell reaches threshold potential, what initiates an action potential?

voltage-gated sodium channel activation gate opening

If an action potential were somehow initiated at the axon terminal, would it be possible for an action potential to propagate back towards the cell body?

yes, the action potential propagation would travel from the terminals to the soma and the absolute refractory period would prevent reverse propagation back towards the axon terminals

By convention, the voltage outside a cell is defined as

zero