Neuro 4

Question 1

What is flux

Answer 1

Number of of molecule that cross a unit of area in a unit of time

Question 2

What is voltage

Answer 2

Potential difference. Generates a charge gradient. Produced by ions

Question 3

What is current

Answer 3

Movement of ions due to pd

Question 4

Importance of ion channels for the membrane potential

Answer 4

They selectively allow ions across. Movement of ions creates a charge difference

Question 5

What is electrochemical equilibrium

Answer 5

Movement of ions is balanced between the electrical gradient and the concentration gradient. Sometimes, flow of ions down their conc gradient is stopped due to the electrical gradient - like ions repelling.

It is achieved when the electrical force prevents further ion diffusion

Question 6

Equilibrium potential

Answer 6

The potential at which electrochemical equilibrium has been reached. It is the potential that prevents diffusion of the ion down its concentration gradient

Question 7

What does Nernst Equation do

Answer 7

measures potential difference of single ion across membrane

Question 8

What is Nernst equation

Answer 8

E(mV) = -61log(ion con inside/ion conc outside)

Question 9

What is role of lipid membrane in pd across a cell membrane

Answer 9

It is impermeable to ions, so ions cannot travel across, so it separates charge. Movement of ions = charge gradient made

Question 10

Values of extra and intracellular Na+ and K+

Answer 10

Na+ K+
Extra. 150 5
Intra. 10 150

Question 11

Why is Goodman bodkins Katz equation better

Answer 11

It includes permeability of all ions as membrane is slightly permeate to all ions always.
Real membrane potentials (Em) do not rest at EK (–90 mV) or ENa (+72 mV)
Typical Em is -70 mV
Why?
Membranes have mixed K+ and Na+ permeability (but at rest K+&raquo_space; Na+)

Question 12

Role of voltage independent channels

Answer 12

Set resting membrane potential as always open.

Question 13

What governs overall membrane potential

Answer 13

Permeability of the membrane to ions

Question 14

Why is K+ important in membrane potential

Answer 14

POTASSIUM is the main ion which controls resting membrane potential

Question 15

Changes in membrane potential definitions

Answer 15

Depolarisation = change in a positive direction 
Overshoot = change from 0 in a positive direction 
Repolarisation = change in a negative direction towards the resting potential 
Hyperpolarisation = voltage drops below resting potential

Question 16

Graded potential - how different from action potential

Answer 16

1. Graded potential changes depending on the stimulus and it can be bi-directional, cane depolarisation or hyperpolarisation
2. Weak stimulus = small potential; Strong stimulus = large potential, in AP, only 1 size of potential
3. Graded potentials decrease in size over time and with distance from its point of origin. They get smaller because the movement of charge across the axon will slowly leak over time resulting in a decrease in the size of the graded potential

Question 17

Where are graded potential found

Answer 17

Synapses

Sensory receptors

Question 18

Function of graded receptors

Answer 18

Initiate or stop action potential

Question 19

When is there no flux

Answer 19

at diffusion equilibrium