Exam 1 Physio Chapter 5

neurotransmitters

-released at end of nerve terminal -concentration of this changes with frequency of action pot.

Inside the cell because excess negatively charged chloride ions diffuse to the inside, while leaving the nondiffusible positive ions on the outside.

A chloride ion gradient from the outside to the inside causes electronegativity where and why?

Inside the membrane

A positive ion concentration gradient from inside the membrane to the outside causes electronegativity where?

saltatory; Electrical current flows through the surrounding extracellular fluid outside the myelin sheath, as well as through the axoplasm inside the axon from node to node, exciting successive nodes one after another.

Action potentials are conducted node to node by _____ conduction. how?

Goldman equation

Gives the calculated membrane potential on the inside of the membrane when two univalent positive ions, sodium (Na+) and potassium (K+), and one univalent negative ion, chloride (Cl−), are involved.

The ratio of the concentrations of that specific ion on the two sides of the membrane. The greater this ratio, the greater the tendency for the ion to diffuse in one direction, and therefore the greater the Nernst potential required to prevent additional net diffusion.

How is the Nernst potential determined?

0.3milliseconds -Changes in membrane permeability are very rapid

How long does the nerve action potential last?

This resting membrane potential allows this nerve cell to create an action potential at the cells body of the nerve and have it travel down the axon into the nerve terminal to release chemical substances called neurotransmitters.

This resting membrane potential allows this nerve cell to create an ___ ___ at the cells ___ of the nerve and have it travel down the axon into the nerve ___ to release chemical substances called ___.

This resting membrane potential is mainly produced by sodium and potassium diffusion potentials.

This resting membrane potential is mainly produced by ___ and ___ diffusion potentials.

Action potential

Transmits nerve signals along the nerve fiber membrane

Sodium would diffuse into the cell carrying positive charge with it. The inside of the cell would become positive with respect to the outside cell. The membrane potential increases high enough within milliseconds to block further net diffusion of sodium ions to the inside

What would happen if a nerve cell membrane was permeable to only sodium?

The concentration gradient would decrease and less positive charges would diffuse out of the cell, making the resting membrane potential more positive. -Makes the cell easier to fire -screws up volatge gated ion channels

What would happen if plasma potassium concentration increased?

This would make the resting MP more negative, making the cell harder to fire because it would become further from threshold

What would happen if the membrane became more permeable to Cl-?

Resting membrane potential would be more negative and it would be harder for the cell to fire

What would happen if the membrane became permeable to Cl-?

Potassium would diffuse outside of the cell down its concentration gradient -Membrane potential would be more negative since positive charges leave the cell -Resting membrane potential would be -94mV (when net diffusion stops)

What would happen if there were potassium leak channels on the membrane of a large nerve cell?

Sodium would diffuse into the cell down its concentration gradient causing the membrane potential to be more positive from the positive charges entering the cell. -Resting membrane potential is +61mV (when net diffusion stops)

What would happen if there were sodium leak channels on the membrane of a large nerve cell?

When the membrane is out of the refractory stage -Allows for one nerve to have several action potentials following each other down the axon

When can a new action potential be generated?

When the membrane potential returns near the original RMP of -90mV

When does the inactivation gate of the VGSC return to resting (open) position?

The permeability of potassium is 100 times greater than that of sodium

Why is the resting membrane potential of a nerve cell closer to that of potassium than sodium?

electrogenic pump

a pump that creates a net charge across the membrane (ex: Na/K pump)

3 Na out of the cell, 2 K into the cell (think: uses energy so ions can go AGAINST concentration gradient)

Na/K pump pumps ___ Na ___ of the cell, and ___ K ___ of the cell

FALSE; the resting membrane potential of a neuron is more closely associated with the equilibrium potential of potassium because the membrane is way more permeable to potassium than to sodium (think: leak channels)

T/F - The membrane potential is more closely associated with the equilibrium potential of sodium

FALSE; an ion with zero permeability cannot enter or exit the cell and therefore, there is no way it can contribute to the membrane potential

T/F - an ion that has zero permeability does contribute to the membrane potential

True; heart rates always increases due to increase in AP frequencies

T/F - increase in the frequency of firing causes heart rate to increase, rather than the strength of firing

True; think: insulation allows AP to travel faster and more efficiently, just like insulation allows the heat to stay in your home efficiently

T/F - myelinated nerves can travel APs much faster than unmyelinated nerves

true; think refractory period

T/F - once depolarization has happened, the sodium channel cannot reopen the inactivation gates

False; the nerve trunk contains twice as many UNMYELINATED fibers than myelinated fibers

T/F - the average nerve trunk contains about twice as many myelinated fibers as unmyelinated fibers

False; the greater the Nernst potential, the higher probability of the ion to diffuse

T/F - the greater the Nernst potential, the less likely for an ion to diffuse

Positivity on the inside from sodium diffusing into the cell

The concentration gradient for sodium is from outside to inside results in positivity where?

Node of Ranvier

The juncture between each two successive Schwann cells along the axon, a small uninsulated area where ions still can flow with ease through the axon membrane between the extracellular fluid and the intracellular fluid inside the axon

VG Ca channels

The plateau phase of the cardiac cells AP is due to what type of channels

Refractory period

The time where another action potential cannot be generated -Limits the number of times a nerve can fire

Na VG channel

depolarization stage is caused by which type of channel

-K+ channel opens allowing K+ to rush out of the cell -membrane potential becomes more negative -only has activation gate

describe how repolarization occurs

The increase in sodium permeability rapidly decreased and the membrane becomes permeable to potassium. -The rapid diffusion of potassium down its electrical and concentration gradient reestablishes the normal resting membrane potential and the process can start again

describe repolarization stage

The membrane suddenly becomes permeable to sodium ions, allowing lots of positively charged sodium ions to diffuse to the interior of the axon. -Membrane potential can go as high as +35mV

describe the depolarization stage

frequency

change in what determines how strong an action potential is? (overshoot points are still the same)

closed, open

during resting membrane potential, the activation gate of sodium is ___ and the inactivation gate is ___

Na

during the depolarization phase, ___ membrane permeability increases, allowing the MP to become more positive because it rushes down its concentration gradient inside the cell

Na decreases, K increases

during the depolarization phase, permeability of ___ decreases and permeability of ___ increases, rushing down its concentration gradient outside of the cell

The entire nerve does not depolarize at once, only a small area -Opening of sodium channels generates local current circuit that depolarizes adjacent membrane, opening more sodium channels -allows many currents to travel down same axon at once

explain propagation

\During exercise, heart rate increases due to an increase in sympathetic stimulation. The way this occurs is that the nerve doesn't fire harder, it fires faster. The increase in the frequency of firing causes heart rate to increase depending on nerve frequency firing.

how can nerve produce different degrees of heart rate change?

permiability plays a big factor; it is more permiable to K+ than it is to Na+

if the equilibrium potential for potassium is -94mV and that of sodium is +61mV, why is the resting membrane potential closer to that of potassium than sodium?

calcium, sodium, potassium

most important ions involved in the development of membrane potential in muscle and nerve

Excitable

trait of Cells that make them capable of generating electrochemical impulses at the membrane

nodes of ranvier

uninsulated area of the nerve where the action potential hops to because ions can flow in and out of the cell

Inside: neg, outside: pos

what does membrane potential usually look like

The diffusion potential or voltage difference across a membrane that exactly opposes the net diffusion of a particular ion through the membrane; one ion

what does the nernst equation calculate? what does it calculate it for?

More charges are pumped to the outside than to the inside causing a negative potential inside the cell membrane. -Ex. Na+ K+ Pump

what is the Na/K pump considered an electrogenic pump

goldman is based on several ions; nernst is one ion

what is the difference between Goldman and Nernst equations?

myelinated; increases velocity

what kind of nerve fibers result in signal jumping from node to node? how does this affect the potential?

schwann cells

what type of cells is the myelin sheath made up of

the concentration gradient for potassium would decrease and less positive charges would diffuse out of the cell making resting membrane potential more positive. This would make the cell easier to fire because it would reach threshold easier for sodium

what would happen to a cell if plasma K+ concentration increased (extracellular concentration)?

make it more negative because more positive charges are flowing out of the cell, making the inside more negative

what would potassium leak channels do to the membrane potential?

It would make the membrane potential positive because positive charges would be entering the cell.

what would the membrane potential be if the membrane was only leaky to sodium?

no, cell must fully repolarize first

when activation gate of sodium voltage channel is closed and inactivation gate is open, can depolarization occur?

activation gate (inactivation gate is open)

when cell is resting, which gate of the sodium voltage channel is closed

to the inside of the cell down the conc gradient

where would sodium diffuse if the membrane was only leaky to sodium?

inactivation gate

which gate of sodium voltage channel is closed to inactivate Na+ rush into cell

Some cells also have rhythmicity of their action potential in that the cells rhythmically discharge on their own with out and external stimulus. These rhythmical discharges are responsible for the rhythmical beating of the heart, rhythmical peristalsis of the intestines, and such neuronal events as the rhythmical control of breathing.

why do some cells have rythmicity to their action potentials?

because the Na/K pump is actively restoring these concentrations from APs and the AP happens so fast that not much of the Na/K can pump into or out of the cell

why does the action potential change sodium and potassium concentrations very little?

-because signals are local -only membrane potentials (concentrations) are changed

why don't Na+ and K+ concentrations change in nerves

there are no Cl channels so it has no permiability

why is Cl not considered in the Goldman equation

Myelin sheath

Deposited around the axon by Schwann cells and is an excellent electrical insulator called....

used to calculate the diffusion potential when the membrane is permeable to SEVERAL different ions

Goldman Equation calculates what?

Goldman equation gives the calculated membrane potential on the inside of the membrane when two univalent positive ions, sodium (Na+) and potassium (K+), and one univalent negative ion, chloride (Cl−), are involved.

Goldman equation gives the calculated membrane potential on the inside of the membrane when two univalent positive ions, __ and __, and one univalent negative ion, ___, are involved.

increase potassium permeability

How can the membrane potential become more negative?

Increase sodium permeability ie add more sodium channels

How can the membrane potential become more positive?

Act directly on the activation gates of the sodium channels, making it much more difficult for these gates to open, thereby reducing membrane excitability. When excitability has been reduced so low, nerve impulses fail to pass along the anesthetized nerves and pain impulses are not sent to the brain.

How do most local anesthetics work?

release of AcH into synapse which binds to nicotinic receptor to release Na into the cell, allowing it to reach threshold and opening the voltage gated Na channels reaching depolarization

How does action potentials reach threshold in the very beginning?

Increase sympathetic stimulation resulting in the frequency of firing to increase

How does heart rate increase during exercise?

The same threshold voltage that opened the VGSC opens the potassium channel but it is delayed. As the sodium channel is inactivated the potassium channel opens.

How does the VG potassium channel open?

The ion will not contribute to membrane potential

If a membrane has zero permeability for a specific ion, how will that ion contribute to membrane potential?

down the concentration gradient, out of the cell

If the membrane was only leaky to potassium, which direction would the potassium diffuse?

Diffusion potential

Potential difference between the inside and outside of a cell

What usually causes the cell to fire is that something must happen to cause sodium and therefore positive charges to enter the cell. This can be opening of ligand gated sodium channels or electrical stimulation. If some sodium and corresponding positive charges enters the cell and the membrane potential does not reach threshold as in A and B in the graph, the cell will not fire. Enough positive charges must enter the cell for the membrane to reach threshold for an action potential to start. -Ex. Ach Nicitinic receptor

What causes RMP to rise to threshold?

Voltage gated calcium channel -Allows heart muscle to contract for as long as the action potential, doesnt twitch -Some action potential display a plateau phase in that the membrane potential remains positive for a while before the cell repolarizes.

What causes prolonged action potentials in cardiac cells? what does this allow?

Closes the channel and stops the diffusion of sodium into the cell. The cell has to repolarize and re-establish the resting membrane potential

What does closing the VGSC inactivation gate do?

blocks pathways of pain signals along nerve by stopping sodium from entering at the site of pain by blocking the activation gates of the sodium channels(inhibits reaching threshold and therefore an AP)

What does lidocaine, procaine and tetra cause do?

Causes potassium to rush out of the cell down its electrical and concentration gradient. As the positive charge leaves the cell, the resting membrane potential is restored to -90mV and the potassium channel closes and is in the resting state.

What does opening of the VG potassium channel cause?

Continually transports sodium to the outside of the cell and potassium to the inside -Causes large concentration gradients for sodium (outside) and potassium (inside) across the resting nerve membrane -keep intracellular sodium low and potassium high

What does the Na+ K+ pump do?

The activation gate opens and inactivation gate closes -Sodium rapidly diffuses down its electrical and concentration gradient into the cell bringing positive charges which cause the cell to depolarize -Increases membrane permeability of sodium 500-5000 fold

What happens when the voltage gated sodium channel reaches its threshold voltage?

closed

What is the position of the VG potassium channel at RMP of -90mV?

Activation gate: closed Inactivation gate: open -No diffusion of ions through channel

What is the position of the VG sodium channel at RMP of -90mV?

Varries 0.25 m/sec in small unmyelinated fibers to as great as 100 m/sec (more than the length of a football field in 1 second) in large myelinated fibers.

What is the velocity of action potential conduction in nerve fibers?

Sodium potassium ATPase pump -Cellular sodium and potassium concentrations are tightly regulated by the sodium-potassium pump and the sodium that enters the cell in the areas of the membrane during an action potential is immediately pump out by this mechanism.

What keeps the concentration of sodium and potassium relatively constant after being affected by action potentials?

Potassium would tend to diffuse out of the cell and carry positive charges with it. Because negative anions that remain behind and do not diffuse outward with the potassium, the inside of the cell would become negative with response to he outside of the cell. Within a millisecond or so, the potential difference between the inside and outside becomes great enough to block further net potassium diffusion to the exterior, despite the high potassium ion concentration gradient.

What would happen if a nerve cell membrane was permeable to only potassium?

K voltage gated channel

repolarization stage is caused by which type of channel

1.) Resting stage 2.) Depolarization stage 3.) Repolarization stage

stages of action potential

Ions involved and charge Permeability of membrane to ion Concentration gradient and direction

the three factors that determines whether an ion participates in the membrane potential.

1

the voltage gated potassium channel have ___ gates

2 gates, activation, inactivation

the voltage gated sodium channels have ___ gates, one called the ___ gate and the other called the ___ gate