RMP

Question 1

How is stimulus intensity encoded in the nervous system? Why?

Answer 1

Stimulus intensity is encoded in spiking frequency because action potentials have fixed size and duration.

Question 2

What is the main difference between pumps and exchangers?

Answer 2

The energy source that drives the active transport. In pumps, the hydrolysis of ATP powers the the movement of ions against the electrochemical gradient, whereas exchangers are fueled by the transport of other ions/solutes down the electrochemical gradient .

Question 3

Which factors influence ionic movement through ion channels?

Answer 3

Electrochemical gradient: diffusion (concentration gradient) and electricity (difference in electrical potential)

Question 4

When do ions diffuse across the membrane?

Answer 4

When there is a concentration gradient across the membrane and there are channels permeable to the ions.

Question 5

Which factors determine the electrical current?

Answer 5

Electrical potential/voltage (force per charge, reflects charge difference, Volts) and electrical conductance/resistance (relative ability/inability of charge to migrate, Siemens/Ohms)

Question 6

Ohm’s law

Answer 6

I=gV or I=V/R

Question 7

What is an (ionic) equilibrium potential?

Answer 7

The electrical potential difference that exactly balances an ionic concentration gradient.

Question 8

How does the neuronal membrane at rest separate electrical charge?

Answer 8

Ionic concentration gradient and selective permeability

Question 9

True or false: large changes in membrane potential are caused by minuscule changes in ion concentration

Answer 9

True

Question 10

Where does charge separation occur?

Answer 10

At the inside and outside surfaces of the membrane

Question 11

What is the ionic driving force?

Answer 11

Ionic current is proportional to the ionic driving force, the difference between membrane potential and equilibrium potential (Vm-E)

Question 12

How can we calculate the equilibrium potential knowing the ionic concentration difference?

Answer 12

Nernst equation: E=(RT/Fz)ln([out]/[in])

Question 13

Limitations of Nernst equation?

Answer 13

Applies only to 1 given ion (provided the membrane is permeable to that single ion)

Question 14

What determines the resting membrane potential?

Answer 14

Distribution of ions across the membrane (concentration gradients for every ion) and selective membrane permeability

Question 15

Provided that the driving force propelling Na+ into the cell is very high at the RMP, is there much Na+ entering neurons at rest? And what is the relative contribution
of Na+ and K+ movements across the membrane to the RMP?

Answer 15

No, due to the very low membrane permeability to Na+ at rest. Since the RMP is much closer to E(K+) than to E(Na+), we conclude that the permeability at rest is much higher for K+ (40x higher than for Na+ due to leak K+ channels). However, RMP is slightly higher than E(K+) due to steady leak of Na+ into the cell (residual permeability due to random channel opening).

Question 16

What is the role of the Na+/K+ pump?

Answer 16

To maintain (NOT establish) the RMP which, otherwise, would gradually dissipate due to the Na+ leakage into the cell and K+ efflux out of the cell.

Question 17

What is the Goldman-Hodgkin-Katz equation?

Answer 17

To determine the RMP, the concentration difference and
membrane permeability of each ion that can cross the membrane must be taken into account: Em=(RT/F)ln{(Pk+[K+out]+Pna+[Na+out]+Pcl-[Cl-in])/(Pk+[K+in]+Pna+[Na+in]+Pcl-[Cl-out])}

Question 18

Increasing extracellular K+ depolarizes neurons. The membrane is particularly sensitive to changes in K+ concentration. Why? How is [K+] regulated.

Answer 18

Because of the high K+ permeability. [K+] is regulated, for instance, by the blood-brain barrier and astrocytes (K+ spatial buffering).