Dr Mitcheson lecture 1

Question 1

What types of electrical signalling occur within neurons?

Answer 1

Action Potentials - active process requiring energy to maintain electrical gradients. For example, maintenance of the sodium and potassium concentration gradients occur via the Na+/K+ ATPase.

Passive (electrotonic) conduction - No energy is required. For example, post synaptic potentials occur without the use of energy. Passive conduction is the underlying basis of neuronal signalling.

Question 2

When does current flow?

Answer 2

When there is a potential difference (V) between the two points and if they are connected via a conductor.

Question 3

What is current a flow of?

Answer 3

Charge (through ion movement)

Question 4

What is the symbol and unit of current?

Answer 4

Symbol = I units = Ampere (A)

Question 5

What is the symbol and unit of Charge?

Answer 5

Symbol = Q units = Coulomb (C)

Question 6

What is Ohm’s Law?

Answer 6

The amount of current through a conductor for a given potential difference is proportional to the conductor’s conductance and inversely proportional to its resistance.

Question 7

What equation is used to determine conductance?

Answer 7

G = 1/R

Question 8

What equations are used to determine current?

Answer 8

I = G . V
I = V / R

Question 9

What is the basis of the electrical properties of biological membranes?

Answer 9

The mobility of ions within the intracellular and extracellular solutions. This mobility allows for charge to be carried across the membrane.

Question 10

Which ions allow for charge to be carried across the membrane?

Answer 10

Na+, K+, Cl- and Ca2+.

Question 11

Why is the lipid bilayer a bad conductor?

Answer 11

Ions are unable to pass through the lipid bilayer as the membrane is impermeable to them. To cross they must be transported via ion channels.

Question 12

What determines membrane resistance?

Answer 12

The number of open ion channels

Question 13

What is a capacitor?

Answer 13

2 conductors separated by a thin insulator.

Question 14

Name the factors which affect capacitance.

Answer 14

Surface area - the bigger the cell the more charge can be stored across the membrane (proportional).

Insulator thickness - the thicker the insulator the less charge can be stored (inversely proportional).

Question 15

What is capacitance?

Answer 15

The store of charge which builds up on the membrane for a given voltage. It may also be thought of as the quantity of charge required to change the membrane potential by a given value. The membrane capacitance aids in slowing the change of membrane potential.

Question 16

Which equation, using capacitance, can be used to determine charge?

Answer 16

Q = C . V

Question 17

Which equation, using capacitance, can be used to determine current?

Answer 17

I = C(dV/dt)

dt = rate of change of voltage with respect to time
C = capacitance (farad)
dV = Voltage change (Volts)

Question 18

What factors affect the time course of changes to membrane potential?

Answer 18

Membrane capacitance and resistance

Question 19

Define the time constant

Answer 19

The time taken for the membrane potential to change by 63% of the membrane potential max.

Question 20

Give the equation for calculating the time constant.

Answer 20

t = Rm . Cm

Question 21

What time course does changes in membrane potential follow?

Answer 21

Exponential

Question 22

In which type of cell does membrane potential change more slowly?

Answer 22

Larger cells or cells with high membrane resistance.

Question 23

What increases linearly with subthreshold stimuli?

Answer 23

Current

Question 24

What is the length constant?

Answer 24

Distance from current injection point when voltage signal has decreased to 37%

Question 25

How does the voltage potential decrease with distance from injection site?

Answer 25

Exponentially

Question 26

Name the three components of resistance.

Answer 26

Rm, Ra and Rext

Question 27

What does flow of current along a nerve process depend upon?

Answer 27

The leakiness of the membrane relative to the resistance of the cytoplasm

Question 28

In which physiological conditions is the electrotonic conduction greatest?

Answer 28

High membrane resistance (low channel density or high insulation) as well as low axonial resistance (high membrane process diameter)

Question 29

What does electrotonic conduction apply to?

Answer 29

1) The spread of passively propagating voltage signals such as post synaptic potentials (IPSP & EPSP) moving along the dendrites.
2) The conduction velocity of APs. The greater the electrotonic conduction the faster the APs will propagate since spread of depolarisation occurs via electrotonic conduction.