Lecture 3: Electrical Potential of Cells

Question 1

Potential difference

Answer 1

The ability of separated opposing charges to do work, aka electrical potential

Question 2

Current

Answer 2

Movement of charge

Question 3

Resistance

Answer 3

Hindrance to electrical charge movement

Question 4

Resting membrane potential of neurons

Answer 4

-70 mV

Question 5

Contributors to membrane potential

Answer 5

Na+ outside, K+ inside (salty bananas); chloride somewhat as well. Negligible amounts compared to total compartment concentrations.

Question 6

Equilibrium potential

Answer 6

Potential at which net flux due to concentration balances net flux due to charge. A larger concentration gradient means a larger equilibrium potential. Differs between ions.

Question 7

Nernst Equation

Answer 7

61 combines R, physiological temperature, Faraday constant

Question 8

Goldman-Hodgkin-Katz Equation

Answer 8

= -70 mV. Expanded Nernst that factors in permeabilities; note that Cl- is reversed because it’s an anion.

Question 9

How do different ions’ equilibrium potentials influence membrane potential?

Answer 9

The ions with highest permeability influence the resting potential the most via their equilibrium potentials. K+ has a high permeability due to leak channels, which is why membrane potential is so close to E_K (-90 mV).

Question 10

Electrogenic pump

Answer 10

A pump that moves net charge and thus directly contributes to membrane potential (small effect in most cells).

Question 11

How are equilibrium potentials created?

Answer 11

Concentration gradients across semipermeable membranes.

Question 12

Excitable cell

Answer 12

Cells that can produce electrical signals along their membranes via gated ion channels

Question 13

Graded potential

Answer 13

Potential of variable amplitude/duration conducted decrementally. Triggered by chemical stimulus opening ion channels.

Question 14

Types of graded potentials

Answer 14

1. Receptor: produced at receptor cells/peripheral ends of afferent neurons in response to stimulus.
2. Synaptic: produced in post-synaptic neuron in response to neurotransmitter release and binding.
3. Pacemaker: spontaneously occurring, occurs in specialized cells

Question 15

Driving force of an ion

Answer 15

= Membrane potential - ion equilibrium potential. Depends on electrochemical gradient.

Question 16

Ionic current

Answer 16

= g (Vm - E). Ions move only when there is a driving force AND a conductance/permeability (g) for that ion.

Question 17

Depolarization

Answer 17

Potential moving from resting membrane potential to less negative value

Question 18

Overshoot

Answer 18

Reversal of membrane polarity (inside becomes more positive than out)

Question 19

Repolarization

Answer 19

Potential returns to RMP from depolarized state

Question 20

Hyperpolarization

Answer 20

Potential becomes more negative than RMP.

Question 21

What defines the conductance of the membrane?

Answer 21

Open and closed ion channels.

Question 22

Time constant τ

Answer 22

τ = Rm * Cm (membrane resistance and capacitance). Defined as amount of time post-current injection for potential to rise to 63% of its final value OR drop to 37% of its initial value. Shows how quickly membrane depolarizes and affects temporal summation.

Question 23

Length constant λ

Answer 23

λ = sqrt(r_m / r_i)
(membrane/internal or axonal resistance per unit length). Defined as distance from sit of injection where potential falls to 37% of its initial value. Indicates how far a depolarizing current will spread/how leaky the membrane is. Determines decremental propagation.

Question 24

How does length constant λ affect neurons?

Answer 24

λ determines synaptic efficiency. Synapsing to a larger dendrite is more likely to initiate an AP.

Question 25

What affects internal (axonal) resistance?

Answer 25

Internal resistance relates to how easily charge flows within a neuron. It is highest with larger diameter neurons.

Question 26

Equilibrium potentials of Na+, K+, Cl-, Ca2+

Answer 26

Na+: +60-70 mV
K+: -90 mV
Cl-: -65 mV
Ca2+: +130 mV