Membrane Potentials & Action Potentials Flashcards by Betsy McCoy

Electrical potential or electrical difference across (all) cell membrane

Membrane potential

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What are some types of excitable cells that can generate electrical impulses (APs) and transmit them along the cell membrane?

Nerve fibers
Skeletal muscle fibers
Cardiac muscle fibers
Smoothie muscle fibers
Cardiac electrical fibers

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Electrical difference/gradient across the cell membrane in the resting state

Resting membrane potential

RMP

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Cell membranes are polarized, meaning what about - and + charges?

Negative charges tend to accumulate on the inside of the cell membrane, positive charges tend to accumulate on the outside of the cell membrane

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ALWAYS compare the ______ of the cell to the _______ of the cell.

Always compare the INSIDE of the cell to the OUTSIDE of the cell

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Interpret a MP of -90mV

The INSIDE of the cell membrane if 90 mV more negative than the outside of the cell membrane

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The electrical difference is just inside and just outside (RIGHT ON) the cell membrane. TRUE/FALSE

TRUE

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Intracellular and extracellular fluids are electrically charged. TRUE/FALSE

FALSE

Intracellular/extracellular fluids are ELECTRICALLY NEUTRAL!

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What are the 4 main contributors to the cell membrane in order from greatest–>least impact.

Potassium leak channels
Sodium leak channels
Sodium - potassium pump
Accumulation of negatively charges proteins along the inside of the cell membrane

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What is the main contributor to membrane potential?

Potassium leak channels

Positive charges constantly moving out of the cell

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If cell only had K+ leak channels active, what would RMP be?

-94mV

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If only had K+ and Na+ leak channels, what would RMP be?

What is the change in mV from adding Na+ leak channels?

-86mV

8mV change

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When K+ leak channels, Na+ leak channels, and Na-K pump are all present, what is the RMP?
What is the change in mV of RMP when adding pump to leak channels?

-90mV

4mV change

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Transmission of electrical impulses along membranes of excitable cells is ?

Action Potential

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What are the 4 main components of an action potential?

RMP
Threshold potential
Depolarization
Repolarization

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An initial stimulus to a skeletal/muscle or nerve fiber does what to the cell and the MP?

Inward movement of sodium into the cell, raises the RMP in a less negative fashion

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If RMP reaches TP, what type of channels are opened?

What happens to the MP?

Opening of voltage gated Na channels

Lots of + charges into cell bc FAST, MP increases quickly

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What ends depolarization? This happens at ____ amplitude or overshoot.

Closure of voltage gates sodium channels

Peak amplitude

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What happens at about the same time that voltage gated sodium channels close, and begins repolarization?

Voltage gated potassium channels are opened– + charges leaving the cell, brings RMP back down to -90mV

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Action potentials are VERY FAST in skeletal muscle fibers and Nerve fibers. TRUE/FALSE?

TRUE

Occurs in ~0.3 milliseconds!

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This allows for return to RMP and recovery of the cell membrane before another AP can occur

Refractory periods

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What are the 3 refractory periods?

Absolute
Relative
Supernormal/vulnerable

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During this period, the cell will NOT depolarize again regardless of how strong the stimulus is

Absolute refractory period

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Requires and EXTRA STRONG stimulus to depolarize the cell again

Relative refractory period

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Even a MILD stimulus may cause another depolarization during this period

Supernormal/vulnerable refractory period

This refractory period is from RMP, through depolarization, and almost through repolarization, until returns to TP.

Absolute refractory period

The Relative refractory period begins @ _______ potential (-60mV) and ends at ~______ mV.

RRP Begins @ TP Ends at -80 to -85mV

If an extra strong stimulus occurs during RRP in the heart, what will we see on the ECG?

A QRS sitting directly on top of the T wave Abnormal occurance

This refractory period is from -80-85mV to -90mV. Only a mild stimulus will initiate an AP here

Supernormal/vulnerable refractory period

What would result on our EKG if a mild stimulus occur EC in the SNP?

QRS sitting on the down stroke of the T wave | Not normal.

Why is it easier to to initiate another AP in the SNP than the RRP?

SNP we are closer to TP than we are at RMP The reason a lesser stimulus is needed in the SNP is because the voltage gated Na+ channels have not had time to reset themselves yet in the RRP

What are the 3 types of stimuli that can initiate APs?

Chemical Electrical Mechanical

What is an example of a chemical stimulus AP

Ach gates Na channel: binds to the Na channel, opens, influx of Na, RMP-TP; opening of v-g Na channels

What is a good example of an electrical stimulus initiating AP

The heart and conduction system

What is a good example of a mechanical stimulus initiating an AP?

Receptors in you skin that respond to pressure, touch, tickle, and itch, etc. Send AP up to the brain to interpret it.

The initial stimulus must cause enough ______ for RMP to reach TP

Sodium influx

If initial event foes not accuse RMP to reach TP then AP/depolarization will NOT occur. If initial even causes RMP to reach TP, then dep/AP WILL occur. This is described as the __________ phenomenon.

"All or none" phenomenon

If it is a suprathreshold stimulus, then it will cause a GREATER amplitude of depolarization than just a normal threshold stimulus. TRUE/FALSE?

FALSE | It will not cause a greater amplitude of depolarization, once TP is reached, the AP occurs like normal. Same every time.

The initial stimulus occurs at multiple points on the cell membrane. TRUE/FALSE?

FALSE. | Occurs at only ONE point on the cell membrane

The AP occurs along the entire length of the cell membrane from initial point of stimulus bidirectionally. TRUE/FALSE?

TRUE

Hyperkalemia causes ____polarization of the MP by doing what to the gradient?

Hyperkalemia = hypopolarization | Gradient is smaller and out flux of K is slower so MP is increased at a slower rate.

Hypokalemia causes _______polarization of the cell.

Hypokalemia = hyperpolarization

______polarization is inhibitory to APs.

Hyperpolarization

Hypopolarization of RMP moves it CLOSER/FARTHER from TP?

RMP Moves CLOSER to TP when hypopolarized

The closer RMP is to TP, the MORE voltage gated Na channels are activated. TRUE/FALSE?

FALSE. | The closer RMP to the TP , the LESS voltage gated Na channels are activated.

If less v-g Na channels are opened, causes a __________ depolarization and _________ amplitude of depolarization

Slower depolarization | Decreased amplitude

What does slow depolarization/decreased amplitude from hyperpolarization look like on the EKG?

PR interval gets longer Can lose P wave QRS will widen/flatten out Asystole or VF

In Hyperkalemia, the T wave represents repolarization, which is very _________ with _________ T waves.

Hyperkalemia; RAPED repolarization | TALL peaked T waves.

In hypokalemia depolarization is relatively normal. Repolarization is slow and prolonged. TRUE/FALSE

TRUE

Why is slow, prolonged depolarization in hypokalemia dangerous?

Ther is more opportunist for ectopic foci or electrical stimulus to cause an early depolarization

When we talk about Potassium levels, we look at changes in RMP/TP?

RMP

Extracellular concentrations of Ca regulate activity of what?

V-g Na channels

Hypocalcemia moves TP ______ to RMP and it is EASIER/HARDER to open v-g sodium channels or initiate APs.

TP closer to RMP makes is EASIER to open v-g Na channels = AP's

In hypocalcemia, cells are very _________. Signs would be what in a physical assessment?

Excitable | Chvostek/trousseau

In hypercalcemia, TP is moved CLOSER/FARTHER from RMP and it is EASIER/HARDER to open v-g Na channels.

Hypercalcemia TP FARTHER from RMP | Harder to open v-g Na channels and AP

Signs of hypocalcemia in your patient?

Sleepy, in-somnolent, comatose, death

Why are T waves peaked in hyperkalemia?

Up regulation of nicotinic receptors

Upregulation of nicotinic receptors causes opening of sodium channels and depolarization and repolarization to occur, what happens during repolarization with K+?

Outflow of K+

Succs increases K levels. What types of pts should you NOT give succs to?

Paralyzed Burn Crush injuries Bedridden

________ temporarily brings proper distance between RMP and TP during hyperkalemia

Calcium

When treating hyperkalemia- bicarb, insulin, and hyperventilation all DECREASE/INCREASE pH so that H+ is released to DECREASE/INCREASE pH. This leads to shuttling K+ back into the cell to maintain electrical neutrality

Bicarb , insulin, and hyperventilation Increase pH (alkalotic) H+ decreases pH (more acidic)

In hyperkalemia- Insulin and b2 agonist, albuterol, activate what that moves K= into the cell?

Na-K pump

What are the only treatments that truly decrease total body potassium?

Dialysis | Kaexelate retention enema