EX1; Excitable Cells; Electricity Flashcards
The electrical charge difference between the inside and outside of a cell is what
voltage
The voltage of a resting cell is steady, therefore the plasma membrane must have what
resistance
When a resistance changes, ions cross the membrane and this is what
current
This is the reciprocal of resistance
conductance
These two things are membrane properties
conductance and resistance
There is a higher concentration of solutes in 1 but why is there no voltage difference
because the number of cations in 1 is the same as the number of anions in 1; and vice versa
Something causes permeability to increase, therefore X+ moves down the concentration gradient from 1 to 2, 1 aquires a negative charge and 2 aquires positive; but the movement of X+ stops before the concentration is equal, why?
a charge difference develops (voltage); the system attains an equilibrium state
the concentration difference and voltage difference are directed oppositely
What does the Nernst equation describe
it relates the voltage difference between 1 and 2 and the concentration difference between 1 and 2
What is the Nernst equation
Ex= (58/z) log10 ([X1]/[X2])
z = valence
What does the Nernst equation yield
the equilibrium potential or a single ionic species
This is the voltage across a cell membrane that exactly balances the force in the concentration gradient of a permeable ion
equilibrium potential
What is a diffusion potential and what does it mean to be transient
they are due to asymmetic ion flow - an imbalance in the flow of an ion or several ions between two compartments
they can disappear over time
What is an example of a transient diffusion potential
A membrane is equally permeable to Na and Cl, but Cl moves faster, therefore bringing the negative chage more into one compartment, one having an excess positive charge is a diffusion potential; eventually they will equal out
A diffusion potential can or cannot be maintained at a steady level over time
can be
What is an example of a steady diffusion potential
membrane becomes permeable to only K, the one compartment will have a high postive charge and the other a high negative chage; the change in voltage will slow the subsequent diffusion; when the concentration force is balanced by the electrical force diffusion potential stops changing
There is a high concentration of what inside the cell
K+
There is a higher concentration of what outside the cell
Na+
The membrane of a resting cell is most permeable to what ion
K+
What is the Pk/P(Na) ration
around 60; K+ ions diffuse across a typical membrane 60 times more readuly than Na+ when the cell is at rest
Equilibrium is reached with the force in the concentration gradient for K+ ions to move out of the cell is balanced by what
the opposing force in electrical gradient which favors keeping K+ ions inside the cell
This keeps the resting membrane potential slightly lower than Ek
Na+ diffuses into cell down both its concentration gradient and electrical gradient
What is the flow of ions when a cell is at rest
K+ ions diffuse out
Na+ ions diffuse in
The resting membrane potential is what; is not a transient diffusion potential
steady
The resting potential is not due to the instantaneous movement of ions, it is due to what
the fact the ions have moved across the membrane (specifically K+)
This protein moves K+ ions back into the cell and Na+ ions out of the cell when it is at rest; requires ATP
Na+/K+ ATPase pump
A change of the membrane potential toward 0mV is referred to as what
depolarization (or hypopolarization)
A change in the membrane potential away from 0mV, in the negative voltage direction is referred to as what
repolarization
An increase in membrane potential from the resting value (more negative toward resting potential; -70mV) is referred to as what
hyperpolarization
What is the resting potential
-70mV
True or False
The Na/K ATPase pump maintian concentration gradients for Na and K across membrane
True
What does the active transport via the Na/K ATPase pump counteract
the passive diffusion of ions; keeping the resting potential
The Na/K ATP-ase pump is an example of what
homeostasis
True or False
The number of ions that are required to cross the membrane, which results in large changes in the membrane potential is extremelly small compared to the total number of ions
True
True or False
The extracellular and intracellular concentrations of the ions that cross living cell plasma membranes, remain essentially unchanged, even during periods of intense excitation
True
