Excitable Membranes and potential gradients Flashcards
What are the four factors that establish the cell membrane resting potential?
- membrane permeability
- solute concentration gradients
- electrical conc gradients
- active molecular pumps
What does the Nerst equation assume to be zero?
Net flux
What are fixed anions?
negatively charge large mol that cannot leave the inside of the cell and exert a net negative source on the inside of the cell
Give an example of Donnan Equilibrium.
The net negative charge inside the cell pulls in K+ against its concentration gradient. At equilibrium the concentration of K+ is 20 times greater inside than outside.
Three features of active molecular pumps
- tansport can take place against a concentration gradient
- Transport is selective
- Use ATP
WHat is transported where in the sodium potassium pump?
3 sodium of and 2 potassium in
The charged ions moving through the electrolyte solution ie the cell membrane create a what?
constant current called a riogenic current
What is electrotonis?
the natural electrical resting state of the cell
What are the four physiological ions?
Na K Cl Ca
Cell membranes high permeability to what ion?
K
Cell membranes are not permeable to what ions?
Na Cl Ca
Sodium and chloride are how many times more concentrated on the outside than inside?
10 times
Calcium is how many orders of magnitude greater on the outside than inside?
2-7
What is the resting membrane potential?
-60mV to -70mV
What are the three types of tissue that have excitable membranes?
muscle
nervous
epithelial
What are the two fundamental states of excitable membranes?
resting and active
WHat does the Goldman adjustment take care of?
The Nerst equation for the trans membrane potential does not take into account all the ions in an excitable membrane. the Goldman adjustment specifically includes the permeability of Na and Cl and established the trans membrane potential as -60mV
What is the primary ion involved in creating an action potential?
Na
What is depolarization?
The complete reversal of charge of the inside to the outside of the cell from the effects of the membrane being permeable to Na for only a few microseconds.
What does a Na equilibrium across the membrane establish?
an Action Potential
Cll membranes designed to close quick or slow and what is this phenomenon known as?
ball and chain close fast!
How is sodium permeability controlled?
When a nerve is stimulated and depolarization occurs the sodium channels are only open for a very short period of time and only a few ions are allowed to cross through and only a few are needed to create an action potential so that the nerve can repolarize faster!
How does the membrane become permeable to sodium?
gated channels are opened
what are the three types of gated channels?
ligand gated channels
voltage geted channels
mechanically gated channels
What are mechanically gated channels?
The cell membrane is distorted and that deformation allows the Na to come in.
Good in stretch receptors on skin or joints. pressure sensors too.
What is the ligand gated channel?
Have specific receptors for certain types of molecules and when it comes in contact with that molecule the gate opens. Nerve Tracks
What are voltage gated channels?
It is the flow of a charged molecule that creates the amperage. When there is enough flow of ions the voltage gate will open.
What type of channel do we use the most?
voltage gated channels
When Na flows through ligand gated channels what other gates are opened?
voltage gated channels by the flow of the charged molecules
What is an action potential?
self propagating way of depolarization in a preferred direction.
What cycle can illustrate the series of events that take place during a depolarization?
Hodgkin’s Cycle
What are the events that are shown in the action potential?
sodium channels activated, overshoot, sodium channels deactivate, rectified potassium channels activate, hyper polarization
WHat is a local response?
A response that causes a little movement of ions but not enough to trip the voltage gates. Membrane reestablished itself almost instantly.
What is threshold value?
Once you reach threshold response cannot stop what happens it all relies on the membrane potential. Voltage gates open and reach 0 V and goes beyond to overshoot.
Why does the membrane over shoot the 0V?
Because there is a concentration and electrical gradient. Jaust because the electrical gradient is in equilibrium does not mean the concentration is in equilibrium as well.
At what voltage do the sodium gates close?
+55mV
WHat are the rectified potassium channels?
Specialized gates in cell membrane that allow potassium to move out faster to restore negative inside to outside relationship for another action potential to occur.
From the time threshold is reached to the time where the tangent on curve shifts another action potential will not be generated what is this point called?
absolute refractory period
Relative refractory period?
period where you can send another action potential but you must have a much stronger signal strength.
What is Accommodation?
slow gradual application of stimulus and therefore need a higher threshold…threshold event is changeable
What is adaptation? what is a better term for this?
Constant stimulus in certain neurons will cause a decrease in the frequency of depolarization. A better term would be habituation. ex puppy with color
