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41 Cards in this Set

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gradient
As used here, the gradual continuous increase or decrease in solute concentration from one region to another.
membrane potential
The electrical potential, or voltage, across a cell membrane that results from the separation of charged particles across the membrane.
Na+ - outside
K+ - inside
CI- - outside
Which of these ions have a high concentration outside the cell and which have a high concentration inside the cell? Na+, K+, Cl-
through ion channels
What is the only way that ions can get across the cell membrane?
it lets certain ions through, but prevents others from crossing
What does it mean to say that cells exhibit selective permeability with respect to ions.
K+
Which ion are most cells in the body permeable to?
They are selectively permeable towards ions

??
How do neurons differ from most of the other cells in the body with respect to ion permeability?
Excitable cells are very permeable to potassium & slightly permeable to sodium.
What's the difference between a neuron's permeability to sodium and potassium?
1. # of channels
2. the ease w/which the ion can move through that channel
What two factors will affect the permeability of a cell for a particular ion?
gated channels
What mechanism used by the nervous system to produce rapid changes in membrane permeability?
K+
As opposed to neurons, simple, non-excitable cells are permeable only to one ion. What is that ion?
gradient (high to low concentrations)
What major factor causes ions to move through ion channels?
a chemical force
What type of force is the concentration gradient?
When ions move out of the cell, it makes more + outside, and more - inside.
How does the cell membrane become more positive outside and more negative inside?
electrical potential (voltage)
What type of force is the separation of charge?
+
-
diffuse ?
As potassium diffuses out of a cell, the outside of the cell becomes more _______ and the inside of the cell becomes more ________. Since opposite charges attract each other, and potassium is positive, the potassium will __________.
electrical potential
The force that is responsible for the movement of positive potassium ions back into the cell, where it is more negative is called the _________.
electrical potential
voltage
What are two alternative names for the electrical force?
1. the concentration gradient or chemical force
2. The electrical potential (force)
What are the two parts of the electrochemical gradient?
chemical force causes K+ to diffuse out of the cell.

electrical force pulls K+ back into the cell.
.) What effect does both the chemical force and the electrical force have on K+?
when K+ is at equalibrium
When is there no net movement of K+ across a membrane?
Yes
When there is no net movement, does that mean that ions are not moving across the membrane?
What is a membrane potential?
The electrical potential or voltage, across a cell membrane that results from the sep. of charged particles across the membrane.
millivolts
In what units is both the concentration and the membrane potential measured?
-90mV
What is the equilibrium potential in general?
150mM K+ inside and 5mM K+ outside. This means that K+ is equal and opposite when the membrane potential is 90 mV.
What is the equilibrium potential for K+ in a non-excitable cell? What does this mean?
Chemical force pull Na+ into the cell, because it has a net neg. charge K+ in the cell. Wants to pull Na+ into the cell. Electrical force pulls Na+ into cell, because the charge sep. acts as the force.
Neurons are slightly permeable to sodium ions. a. In which direction is the chemical force for sodium? Why? b. In which direction is the electrical force for sodium? Why?
The electrical potential & chemical potential. It pulls Na+ into the cell.
What is the electrochemical gradient for sodium a combination of ? In which direction is the electrochemical gradient for sodium?
Ty means that the neuron is at rest. A typical value is -70mV.
What does the term "resting membrane potential" in a neuron mean. What is a typical value for the resting membrane potential.
The non-excitable cells only depend on K+. K+ comes to equalibrium when membrane potential is -90mV. The resting membrane potential depend ob both Na+ and K+ across cell membrane.
Why do non-excitable cells have a membrane potential of -90 mV while neurons have a resting membrane potential of -70 mV?
Because the chemical force out of the cell is greater than the electical force back into the neuron.
.) At -70 millivolts, the resting membrane potential, why does potassium leak out of the neuron?
Because the force is very large, but neuron only slightly is permeable to Na+.
At -70 millivolts, the resting membrane potential, why does sodium slowly leak into the neuron?
K+/Na+ pump
What compensates for the leakage of sodium and potassium ions?
against their chemical gradients
Does the sodium-potassium pump move sodium and potassium with or against their gradients?
ATP
What provides the energy to pump sodium and potassium against their gradients?
3
2
The sodium-potassium pump pumps out ______ sodiums for every _____ potassiums that are pumped in.
It maintains Na+ & K+ leaks
How does the sodium-potassium pump keep the resting membrane potential at -70 millivolts.
B
The sodium–potassium pump ___________.
a. creates the membrane potential
b. maintains the membrane potential
concentration gradient
The difference in the concentration of a particular substance between two adjacent areas.
electrical potential
An electrical force across a cell membrane that results from the separation of charged particles across that membrane.
electrochemical gradient
The combined electrical and chemical forces on an ion. This force determines the net movement of charged particles.