- always open - some K+ channels and Cl- channels

Ionic Movement, Membrane Potentials, And Action Potentials Flashcards by Sarah Heath

Permeability of cell membrane

Selectively permeable

-some things can diffuse through membrane (small, non polar molecules, steroids, oxygen)

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Most solutes in the body and the cell membrane

Most solutes in body are large and/or charged and cannot cross the membrane

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Conductance is by use of what?

Transport porteins and ion channels

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Amount able to cross membrane is based on what?

Number and activity of these proteins

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_____ are small holes that allow specific size/charge of ion to cross

Ion channels

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Conductance of ions is based on what

The number of channels that are ‘open’

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Ion channels and ionic movement are specific to what

Ionic size and charge

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Size example of size exclusion in ion channel

A sodium channel can exclude a calcium/potassium ions due to different molecule size

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charge exclusion in ion channel

Interior of channel will be lined with charged amino acids, will prevent like ions from crossing

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Flow of ions depends on what?

Number of open channels

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Leak channels

always open

- some K+ channels and Cl- channels

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Examples of gated channels

Ligand, 2nd messenger, voltage, mechanical, light, etc

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These types of gates remain closed until proper ligand is present

Ligand gated

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These types of ligands remains open as long as ligand is around, closes when removed

Ligand gated

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Example of ligand gated channels

Nicotinic receptors in skeletal muscles neuromuscular junction
-binds acetylcholine, allows Na+ (mostly) and K+ (little) to flow down gradients

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What type of channel remains open as long as 2nd messenger is around, closes when removed?

2nd messenger gated

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How much messenger will be made until when?

Until receptor is no longer stimulated

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Example of 2nd messenger gated channel

Ca2+ channels in smooth muscle cells. Angiotensin II binds to its receptor causing production of IP3 which binds to and open Ca2+ channels (InsP3R)

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What type of channel remain closed until membrane potential reaches specific value?

Voltage gated

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What type of channel remains open depending on the membrane potential and channel properties?

Voltage gated channels

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Example of voltage gated channels

Sodium channel (Nav) in muscles. Once membrane potential gets above certain point, they open. When it reaches a 2nd set point, they close

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Which type of channel would have the most rapid effect on ionic flow?

Ligand gated

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What type of channel could lead to a more varied cellular response?

2nd messenger

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What happens when ions move down a concentration gradient?

They generate a current

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What is diffusion potential?

- measured in mV | - only moves until the charge changes, not big change in concentration

Potential difference (charge) required to stop ionic movement

Equilibrium potential

Ions move in response to what?

Concentration and charge

How many ions need to move to make a charge difference across a membrane?

Very few Basis for resting membrane potential and the nervous systme

What does movement of charged particles generate?

An electrical potential

What equation do we use to determine the equilibrium potential?

Nernst equation

What does the charge on each ion (Ena=+65mV) mean?

Inside of cell membrane is negative at rest. Must equal this number to make it permeable to that specific ion

Driving force

mV=Em-Ex EM is actual membrane potential Ex is equilibrium potential Na+ mV=-70-65. mV=135

Ionic current: GX (driving force)

Hx=conductance (measure of the # of open channels)

Account for what to get the resting membrane potential (RMP)

Account for all ionic concentration gradients and membrane permeability and you get the resting membrane potential (RMP) -Goldman equation or chord equation

Charge difference across cell membranes due to concentration gradients of permanent ions

Resting membrane potential

What does each ion try to do to the RMP?

Tries to push it towards its own Eq potential

Inside of cell is considered ______ compared to outside of cell

Negative

What is the charge of the inside of the cell

Ranges from -20 to -100mV

What kind of tissue can rapidly change the RMP to send signals and start conduction?

Excitable tissue (muscle and nerves)

Increasing permeability of ________ to 100% would likely result in the greatest change in resting membrane potential

Calcium (+120)

Rapid changes in membrane potential

Action potential

What do action potentials consist of?

Depolarization from RMP and repolarization to RMP

Types of actions potentials in different tissues

All APs look the same in similar tissue, but the AP of two different tissues is different

When does AP occur?

An AP either occurs or it does not - all or none - if membrane reached specific voltage (threshold) then an AP will occur

Stages of action potential: at rest

RMP

Stages of action potential: local depolarization

Membrane moves closer to 0mV

Stages of the action potential: threshold (about -60mV)

Point at which AP has to occur

Stages of the action potential: overshoot

Interior becomes + relative to outside

Stages of the action potential: repolarization

Membrane begins to move back towards 0 and negative

Stages of action potentials: hyperpolarization

Membrane becomes more negative

Stages of action potential: at rest

RMP is reattained

What are the steps of action potential

``` Rest Local depolarization Threshold Overshoot Repolarization Hyperpolarization Rest ```

Membrane potential at rest

-70mV

What is the RMP maintained by?

K+ leak currents (Eq is about -85) Dependent upon K+ conductance

What is necessary for RMP?

Na-K ATPase - 3Na+ out - 2K+ in - more negative now - maintains large K+ gradient so small flux can occur and generate the RMP

Stability of RMP

Stable in most cell types | -unstable in rhythm generating cells (heart/intestines)

What is the major contributor to RMP?

K+ current through leak channels

Local depolarization

- stimulation occurs-usually gated Na+ channel - local membrane moves closer to 0mV - stimulated

Local hyperpolarization

Stimulation occurs-usually ligand gated Cl- channels - local membrane becomes more negative - inhibited

Where is the threshold?

About -60mV

Threshold

- IF local depolarization reaches this level, then action potential HAS to occur - voltage gated Na+ channels open

What is responsible for the depolarization of AP?

Voltage gated Na+ channels (Nav) | -rapidly opened and closed due to two sets of gates

What are the two sets of gates in voltage gated sodium channels?

Inactivation | Activation

Where is the inactivation gate for the voltage gated sodium channels?

Inside

Where is the activation gate for the voltage gated sodium channel?

Outside

At rest, what is the state of the two voltage gated sodium channels?

- activation is closed | - inactivation is open

When is the activation gate of the voltage gated sodium channel open?

At threshold

When is the inactivation gate of the voltage gated sodium channel closed?

At overshoot

What is required for action potential?

Voltage gated sodium channels

If the voltage gated sodium channels ar blocked, what happens?

No AP will occur, paralysis

What are some examples of things that block voltage gated sodium channels and cause paralysis?

Tetrodotoxin (blowfish) | Lidocaine

Overshoot is due to what

Rapid influx of Na+

Where does overshoot usually peak?

+35mV

What happens at overshoot?

Inactivation gate closes, no more Na+

What kind of channels open at overshoot?

Voltage gated K+ channels open

How many gates are involved with voltage gated K+ channels?

One | Much slower to close

What happens when the voltage gated K+ channels open?

K+ flux out of cell begins to repolarize - losing positive charges - blocked by TEA

What happens are repolarization

- Na conductance slows, K conductance rises | - more positive charges leave the cell

What happens are hyperpolarization

- membrane becomes more negative than RMP | - will hyperpolarize closer to the K+ Eq point

When is RMP re-established?

As K+ gates close | -leak channels and Na-K ATPase

When is there a K+ flux through leak channels?

At rest RMP

When does stimulation occur-ligand gated Na channel?

Local depolarization

When do Nav channels open?

Threshold (about -60mV)

When is there a Na+ flux?

Overshoot

When does Na+ slow and K+ rise?

Repolarization

When is there more K+ leaving?

Hyperpolarization

When is RMP re-established?

Due to K+ leaks

RMP and APs are based on what

Ionic gradients | -at rest, only open channels are K+ so RMP is sensitive to alterations in plasma levels

Too much K

Hyperkalemia - less negative - hypopolarizes RMP(more positive)

Not enough K

Hypokalemia | -higher gradient-hyperpolarizes (more neg) RMP

Slowly depolarizing and AP

Can stop APs from being generated

What does slow depolarization occur due to?

Inactivation gates closing before activation opens No Na+ no AP

What is accommodation of AP?

Inactivation gates closing before activation opens (no Na+ no AP) - can be the result of persistent hyperkalemia - decreased gradient, raises RMP towards 0

No AP = what?

Paralysis of muscles, death

The more K+

present, the less negative the membrane potential

Which of the following could be a consequence of acute hyperkalemia

Less steep repolarization slope Increases K, more positive

What affect would hypernatremia have on the RMP?

No change No sodium channels open at rest -almost no affect on RMP

What are APs used for?

To send information

What are refractory periods due to

Cells inability to depolarize again | -channels not reset

Absolute Refractory period

No AP | -activation gate of NA, not closed

Relative refractory period

Need a greater than normal stimulus | -Kv flux hyperpolarizes cell, harder to get to threshold