Ionic Movement, Membrane Potentials, And Action Potentials Flashcards
Permeability of cell membrane
Selectively permeable
-some things can diffuse through membrane (small, non polar molecules, steroids, oxygen)
Most solutes in the body and the cell membrane
Most solutes in body are large and/or charged and cannot cross the membrane
Conductance is by use of what?
Transport porteins and ion channels
Amount able to cross membrane is based on what?
Number and activity of these proteins
_____ are small holes that allow specific size/charge of ion to cross
Ion channels
Conductance of ions is based on what
The number of channels that are ‘open’
Ion channels and ionic movement are specific to what
Ionic size and charge
Size example of size exclusion in ion channel
A sodium channel can exclude a calcium/potassium ions due to different molecule size
charge exclusion in ion channel
Interior of channel will be lined with charged amino acids, will prevent like ions from crossing
Flow of ions depends on what?
Number of open channels
Leak channels
- always open
- some K+ channels and Cl- channels
Examples of gated channels
Ligand, 2nd messenger, voltage, mechanical, light, etc
These types of gates remain closed until proper ligand is present
Ligand gated
These types of ligands remains open as long as ligand is around, closes when removed
Ligand gated
Example of ligand gated channels
Nicotinic receptors in skeletal muscles neuromuscular junction
-binds acetylcholine, allows Na+ (mostly) and K+ (little) to flow down gradients
What type of channel remains open as long as 2nd messenger is around, closes when removed?
2nd messenger gated
How much messenger will be made until when?
Until receptor is no longer stimulated
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)
What type of channel remain closed until membrane potential reaches specific value?
Voltage gated
What type of channel remains open depending on the membrane potential and channel properties?
Voltage gated channels
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
Which type of channel would have the most rapid effect on ionic flow?
Ligand gated
What type of channel could lead to a more varied cellular response?
2nd messenger
What happens when ions move down a concentration gradient?
They generate a current
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
