What is the difference between a channel and a carrier?
A channel is like a tube
A carrier is only open on one side at a time
In the Na/K pump, what does sodium take out of the cell with it?
Glucose
Electric potentials are generated across what?
The membranes of neurons, and all cells
Why/how is an electric potential generated across membranes?
There are difference in the concentrations of specific ions across nerve cell membranes
The membranes are selectively permeable to some of these ions
How are the resting membrane potentials, action potentials, the synaptic potentials and receptor potentials generated?
By the channels and active transporters working against each other
In which cell domain are voltage gated channels found?
Axonal domain
In which cell domain are ligand-gated ion channels found?
Somatodendritic domain
What part of the cell is the action potential generation zone?
Axon hillock
Which part of the neuron has only voltage-gated Na and K channels?
Axon
Which part of the neuron has voltage-gated Na, K and Ca channels?
Nerve termini
Is the concentration of Na higher in the cell, or out of the cell?
Outside of the cell
Is the K concentration higher in or out of the cell?
In the cell
Where is the potential difference found?
In the cell membrane
What two factors influence the actual voltage of a membrane potential?
Ionic concentration gradient
Membrane permeability
In almost all cases, the resting membrane potential is primarily due to what?
The leak of K ion out of the cell without a counter ion balancing the charge
The rate of ion flux across a membrane is a function of what?
The driving force acting on the solute/ion
The permeability of that ion across the membrane
The driving force acting on a solute/ion is a function of what?
Concentration gradient
Membrane potential
Passive flux of all solutes will continue until what occurs?
The solute is at equilibrium across the membrane
What is the net flux of a solute across a membrane at equilibrium?
0
Ions come into “electrochemical equilibrium” where net flux of the ion may equal zero, and what may still be present?
A concentration gradient
What is the electrochemical gradient?
A combination of the chemical gradient (concentration) and the electrical gradient (membrane potential)
How is the membrane potential generated?
By differential ionic permeabilities across the membrane - generally due to selective permeability of the membrane for specific solutes
As K moves between chambers, it adds a small amount of ___ charge on the one side, and leaves a small amount of ___ charge on the other.
Positive
Negative
Which equation is used to calculate the equilibrium potential?
Nernst equation
Voltage is not the same for all cells, and may very over time. Why?
Vm is a function of 2 parameters:
- Concentration gradients of those ions across the membrane
- Permeability of the various ions
Under resting conditions, what is the most permeable ion?
K
What does the Goldman-Hodgkin-Katz equation take into account?
All ion concentrations both inside and outside of the cell
Is Ex a real or theoretical value?
Theoretical value - provides a theoretical boundary for Vm if permeability for one ion predominates
Vm will vary based on what?
Cell type
What does TEPD stand for?
TransEpithelial Potential Difference
The magnitude of the TEPD is proportional to what?
The tightness of the tight junctions
