The Resting Potential

Question 1

What is the threshold voltage?

Answer 1

Around -55 mV.

Question 2

The main ingredient of the intracellular and extracellular fluid?

Answer 2

Water, H2O

Question 3

What is a covalent bond?

E.g. water (H2O)

Answer 3

A covalent bond is when two atoms share of one or more pairs of electrons.

Example: Water (H2O). The two hydrogen atoms and the oxygen atom are bonded together covalently.

Question 4

What are ions?

Answer 4

Atoms or molecules that have a net electrical charge.

Question 5

A sphere of hydration (also called a solvation shell)

Answer 5

Clouds of water molecules that surround an ion. They isolate the ions from one another.

Each positively charged ion is covered by water molecules oriented so that the oxygen atoms (the negative pole) are facing the ion.
Likewise, each negatively charged ion is surrounded by water molecules with the hydrogen atoms (the positive poles) facing the ion.

Question 6

What are positively charged ions called?

Answer 6

Cations

Question 7

What are negatively charged ions called?

Answer 7

Anions

Question 8

What are the most important ions for cellular neurophysiology?

Answer 8

Sodium (Na+)
Potassium (K+)
Calcium (Ca2+)
Chloride (Cl-)

Question 9

Why is water (H2O) a polar molecule?

Answer 9

Because the oxygen atom has a negative charge and the hydrogen atoms have a positive charge.

This electrical polarity means that other polar or charged molecules tend to dissolve in water.

Question 10

Substances that dissolve in water are called …

Answer 10

Hydrophilic

Hydrophilic means “water-loving”

Question 11

Substances that do not dissolve in water are called …

Answer 11

Hydrophobic

Hydrophopic means “water-fearing”.

Hydrophobic substances are substances that have have no electrical charge.

Question 12

Examples of protein molecules in the neuron?

Three examples

Answer 12

• Enzymes that catalyze chemical reactions in the neuron.
• Cytoskeleton that gives the neuron its special shape.
• Receptors that are sensitive to neurotransmitters.

Question 13

What are the concentration gradients for sodium (Na+) and potassium (K+) at resting potential?

Answer 13

Potassium has a large concentration of ions inside the cell (100 mM) and a small concentration outside the cell (5 mM).
Sodium has a small concentration inside the cell (15 mM) and a large concentration outside the cell (150 mM).

Question 14

Which ion is the membrane most permeable to?

Answer 14

Potassium (K+).

Question 15

Voltage

Answer 15

The difference in electrical potential between two points. Measured in volts (V).

Question 16

What is the membrane potential?

Answer 16

The voltage across the membrane at any point in time. Caused by an imbalance of positive and negative charges close to the membrane that generates an electrical field across the membrane.

Question 17

A steady state

Answer 17

A balancing point at which the membrane potential will be stable. No single ion will be at its equilibrium but the total net flow of all charges into and out of the cell will be equal and opposite.

E.g. resting potential.

Question 18

The equlibrium potential

Answer 18

An individual ion’s potential at equilibrium, i.e. the membrane potential at which electrical forces and diffusion balance each other out. Calculated with the Nernst Equation.

Question 19

The resting potential

Answer 19

The membrane potential of a neuron “at rest”, meaning that it is not sending or receiving signals. Generally between -60mV and -70 mV.

Question 20

The GHK equation

To calculate what?
The equation

Answer 20

To calculate the membrane potential when the membrane is permeable to more than one ion.

The coefficients for permeability weight ther relative effects on the me

Question 21

Nernst Potential Equation

To calculate what?
Equation

Answer 21

To calculate an individual ion’s potential at equilibrium, i.e. the membrane potential at which electrical forces and diffusion balance each other out.

Question 22

The driving force

Answer 22

Ions will always flow in a direction that brings the current membrane potential closer to an ion’s own Nernst Potential. The driving force is a measure of how hard a given ion is getting pushed across the membrane. Thus, the driving force can tell us how far each ion is from its Nernst potential.

Driving force = Vmembrane - Eion

i.e. the difference betweent he current membrane potential at a given moment and the Nernst Potential.