Lecture 3 - Membrane Potentials Flashcards
Define excitable cells and give an example of such
- Excitable cells are cells in which an action potential can be induced.
- Neurons, Skeletal muscle cells, Cardiac muscle cells, Smooth muscle cells
On one side of a neuron cell is the dendrite. Describe what is on the other side
- Each neuron has a single axon that is variable in length.
- Extension of the cell body and is typically opposite the side of the cell body where the dendrites are located
- Covered by the plasma membrane (referred to as the axolemma). The axolemma is characterized by the presence of voltage-gated ion channels and the ability to conduct an action potential.
- The distal end of the axon is characterized by the presence of membrane-bound vesicles filled with neurotransmitter molecules.
What is the permeability like in cell membranes lacking voltage channels
The membrane is only permeable to hydrophobic substances without channels of some sort. Ions need respective channels. But the permeability of ions is often based on ion concentration/charge.
Describe the permeability of calcium and potassium ions at rest
Sodium ion permeability: The membrane has low permeability to sodium ion when at rest.
Potassium ion permeability: The membrane is more permeable to potassium than sodium ion when at rest
What are the two biggest ways integral proteins selectively filter ions through the membrane?
- Size (and to a much lesser degree, shape) of the protein channel
- Charge of the amino acids lining them
There are 3 types of Gated Ion channels on the membrane. What are they called and how do they work?
Changes in voltage: Voltage-gated channels
Binding of specific molecules (ligands) to receptors: Ligand-gated channels
Mechanical deformation: Modality-gated channels
What is the definition and formula for Nernst potential
- The Nernst potential is the diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through the membrane (Force against diffusion)
What is the voltage difference (usually) between the inside of the cell, and the outside
I’m gonna fail to properly explain this, but because the exterior of the cell membrane is mostly positive and the inside mostly negative, there exists a voltage “drop” once inside the cell. (Usually around -90 mV). Since the recording electrode is inside the cell, the cell’s interior is regarded as negative potential difference. I don’t fully get it either.
Give the formula for the Nernst equation and define what each factor represents
E = 2.3 * (RT/F) * log(Co/Ci)
E = electrical difference potential between the inside and outside the neuron, or Nernst potential.
R = universal gas constant, T = absolute temperature.
F = electric charge per gram equivalent of univalent ions (Faraday’s constant).
Ci and Co= concentration of ions inside the membrane and outside the membrane.
Can the nernst equation measure for more than one type of ion at a time?
No. It's restricted to only one type of ion. There is another equation called the Goldman potential that can factor for multiple ions but that's past the scope of this class thankfully. - The nernst equation also assumes that the membrane Is permeable to that ion, and that the membrane potential must be in equilibrium for the equation to be accurate.
When the nernst potential is calculated at human body temperature, what simplified equation can be resulted from it?
EMF = z * (61.5) * log([Coutside]/[Cinside])
Where z = valence electron of the analyzed ion.
Look at the problem questions for Lecture 3 (Slides 30-50)
DO IT!!
What moves faster through water: Sodium ions, or chloride ions?
Sodium ions drag a larger electron cloud through water, so chloride ions will move somewhat faster. However, when comparing membranes, both should reach equilibrium relatively quickly.
