Membrane Potentials Flashcards
What are the 4 effects of caffeine?
- CNS stimulant.
- Diuretic.
- Phosphodiesterase inhibitor.
- Non-selective antagonist of adenosine receptors, therefore a competitive inhibitor of adenosine.
What can caffeine do that not many substances can?
It can cross the blood brain barrier (BBB).
What happens in the brain with continued caffeine intake?
An increased number of adenosine receptors are formed.
How does stress lead to glucose release?
- Stress results in the release of epinephrine from the adrenal medulla.
- Epinephrine binds to B2 receptors in the liver.
- Adenylyl cyclase is activated.
- ATP is converted into cAMP.
- cAMP stimulates the activation of protein kinase.
- Protein kinase activates phosphorylase b.
- Phosphorylase b acts on glycogen.
- Glycogen is converted into glucose-1-phosphate.
- Glucose-1-phosphate becomes glucose.
What does phosphodiesterase convert cAMP into?
5AMP.
What caffeine derivative inhibits phosphodiesterase?
Methyl xanthine.
What is membrane potential?
The electrical gradient across the cell membrane.
What 2 systems is membrane potential particularly important in?
- Nervous system.
- Muscular system.
What animal was first used to study membrane potential? Why?
- The giant squid.
- Few, large neurons that are easy to remove.
What 3 factors effect the electrical gradient of cells?
- Na+/K+ ATPase Pump.
- Differential membrane permeability.
- Non-diffusible anions inside the cell.
What is the membrane more permeable to: Na+ or K+?
K+.
What 2 diffusible anions are present in the cell?
- Phosphates (ATP).
- Amino acids (Proteins).
What are the functions of a nerve cell?
- Rapid depolarization of membranes.
- Conveying a message.
Where does the action potential originate?
In the cell body before traveling down the axon.
What is an action potential?
Rapid changes in the membrane potential that spread rapidly along the nerve fiber membrane.
What two changes occur to allow for the transmission of the action potential down the axon?
- Depolarization.
- Repolarization.
What is the average RMP of a nerve?
-70 to -90 mV.
What does the - in front of the mV when measuring RMP mean?
That the potential inside the membrane is 90 mv more negative than the potential in the ECF.
How does the Na+/K+ ATPase pump contribute to the RMP?
It pumps more positive ions out of the membrane than it brings in, resulting in a negative RMP.
*Is an electrogenic pump.
What is an electrogenic pump?
A pump that moves ions across a cell membrane creating a charge difference.
What is the concentration gradient for Na+?
0.1.
What is the concentration gradient for K+?
35.
How does K+ and Na+ leak through the membrane?
Through Na+-K+ channels.
How many times more permeable is the channel to K+ than to Na+?
50x-100x.
What does the leakage of Na+ and K+ help determine?
Normal RMP.
What is Nernst potential?
The diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through a membrane.
How is Nernst potential determined?
By the ratio of the concentration of specific ion on 2 sides of the membrane.
The greater the ratio when calculating Nernst potential…
The greater the tendency for the ion to diffuse in one direction and the greater the Nernst potential required to prevent additional net diffusion.
What is the equation for calculating for Nernst potential?
+/- 61*log(Concentration inside/Concentration outside).
What does Nernst potential demonstrate?
The membrane is highly permeable to K+ and only slightly permeable to Na+. Therefore, K+ contributes more to RMP than diffusion Na+.
Why is their a continual loss of positive charge from inside the membrane?
Due to the Na+/K+ ATPase pump pumping more Na+ out than K+ in.
*Additional -4mV charge.
What is most of the RMP a result of?
K+ diffusion.
How long does it take an action potential to move down an axon?
Few 10,000ths of a second.
What ion does the membrane become very permeable to during depolarization?
Na+.
How does Na+ cross the membrane?
Through Na+ channels.
Which direction does Na+ diffuse during depolarization?
Into the memebrane.
What happens to the RMP during depolarization?
It peaks at ~35mV due to the influx of Na+ ions.
What happens to Na+ channels during repolarization?
They begin to close as K+ channels begin to open.
What direction does K+ diffuse during repolarization?
Out of the membrane.
What does the movement of K+ allow for?
The re-establishment of the RMP to -70 to -90 mV.
How do voltage-gated channels operate?
When there is a shift in charge in the external environment, ~+/-20 mV, the gates on the channels open/close in response.
How many gates does the voltage-gated Na+ channel have?
2.
In a voltage-gated Na+ channel, what is the gate nearer to the outside of the channel called?
Activation gate.
In a voltage-gated Na+ channel, what is the gate nearer to the inside of the channel called?
Inactivation gate.
What does the voltage-gated Na+ channel look like when the membrane is at rest?
The activation gate is closed, preventing Na+ entry, and the inactivation gate is open.
What does the voltage-gated Na+ channel look like in an activated state?
A conformational change occurs in the activation gate as a result of a 20 mV increase in membrane potential, causing the activation gate to flip to the open position and allow Na+ to pour in.
What does the voltage-gated Na+ channel look like in an inactivated state?
The steadily increasing voltage peaking at ~35 mV causes a conformational change in the inactivation gate that cause it to flip to the closed position. This prevents Na+ from flowing into the membrane.
How soon after the activation gate opens does the inactivation gate close?
A few 10,000ths of a second.
Which conformational change happens slower: the one that opens the activation gate or the one that closes the inactivation gate?
The one that closes the inactivation gate.
What occurs once the inactivation gate is closed?
Repolarization.
How many gates does the voltage-gated K+ channel have?
1.
What does the voltage-gated K+ channel look like in resting state?
The gate is closed.
What happens to change the conformation of the voltage-gated K+ channel?
The membrane potential increases to 0mV, causing the K+ channel to open.
What does the simultaneous decreased Na+ entry and increased K+ exit cause?
Increased repolarization for the full recovery to RMP in a few 10,000ths of a second.
What is transient hyperpolarization?
When the K+ channels do not close fast enough following repolarization, allowing extra K+ to exit the membrane.
What cannot occur as long as the membrane is still depolarized?
A new action potential.
What do the channels look like during the absolute refractory period?
Voltage-gated Na+ channel activation gates are open but are beginning to inactivate and voltage gated K+ channels are starting to open.
What do the channels look like during the relative refractory period?
Voltage-gated K+ channels are still open and Na+ channels are in the resting state.
Can an action potential be generated during the relative refractory period?
Yes, but it will require a larger than normal stimulus.
What is the function of the Na+/K+ ATPase pump?
To re-establish the Na+ and K+ ionic gradients.
What does a single action potential do to the Na+ and K+ ionic gradients?
It shifts them minutely, but over time with multiple action potentials, a reset is needed.
What are anions?
Ions with a negative charge.
Where are anions normally found: inside or outside the membrane?
Inside.
What does a deficit of positive ions inside the membrane cause to occur?
An excess of negative charge inside the membrane, due to anions being unable to move through channels, lowering the RMP.
What ion is the Ca2+ pump partially permeable to?
Na+.
Where does the Ca2+ pump pump Ca2+ ion to?
The exterior of the cell or into the ER.
*Into the SR in muscle.
How fast does the Ca2+ channel open compared to the Na+ channel?
Slower than the Na+ channel.
Where are a large number of Ca2+ channels found?
- Smooth muscle.
- Cardiac muscle.
What does the Ca2+ concentration in the ECF effect?
The voltage-gated Na+ channels efficiency.
What does a deficiency of Ca2+ cause?
Na+ channels become activated by very little increase in membrane potential from normal value, making the nerve fibers more excitable than normal.
*Can lead to repetitive discharge w/o stimulus.
How do Ca2+ ions impact ion channels?
They bind to the exterior surface, altering the voltage required to open the Na+ gate.
What are the 3 factors that change the level of threshold stimulus required for an AP?
- Alter cell membrane permeability to Na+.
- Alter cell membrane permeability to K+.
- Alter Ca2+ concentration in the ECF.
What is the function of the drug Veratrine?
Increased permeability to Na+, reducing the level of stimulus required for an action potential.
What does a high dose of Veratrine result in?
Spontaneous impulses.
What is low Ca2+ tetany a result of?
Low Ca2+ in the ECF leading to spontaneous nerve firing and muscle spasms.
How does high Ca2+ impact membranes?
Decreased membrane permeability to Na+ and even blocking Na+ channels.
What do local anesthetics do to the cell membrane?
They decrease its permeability to Na+ to the point that the nerve impulses cannot pass through the area.
*Threshold cannot be attained.
What does low ECF K+ result in?
Increased negativity of RMP called hyperpolarization.
How is familial periodic paralysis treated?
K+ and IV fluids.
