Electrophysiology II: The Basis of Bioelectricity

Question 1

What are the differences between ion pumps and channels?

Answer 1

Pumps require ATP and active transport to maintain ion flow but channels cause the change in membrane potential, which is driven by the stored energy in the electrochemical gradients generated by the pumps

Question 2

What role do pumps have on neuronal signalling?

Answer 2

No role, they are not directly involved in neuronal signalling, they just maintain the [X] over a long time

Question 3

What is the relationship between the Na+ and action potential?

Answer 3

No relationship, you need the pump to establish conditions of AP but doesn’t cause AP or restore membrane potential

Question 4

What is charge in terms of the cell?

Answer 4

Q, the ions

Question 5

What is current in terms of the cell?

Answer 5

I, the movement of charge

Question 6

What is voltage in terms of the cell?

Answer 6

V, the separation of charge (Vm)

Question 7

What is resistance in terms of the cell?

Answer 7

R, the ion channels

Question 8

What is capacitance in terms of the cell?

Answer 8

C, the lipid bilayer

Question 9

What is the principle of electroneutrality?

Answer 9

If you have a solution of charged ions (e.g -ve), then you must have the same amount of oppositely charged ions too (+ve)

Question 10

What is the voltage across the membrane due to?

Answer 10

Due to small separation of charge, not the change in [X] across a membrane

Question 11

What is the equilibrium potential?

Answer 11

The voltage

Question 12

What can be used to determine the equilibrium potential?

Answer 12

Nernst Equation

Question 13

What is net flow like at equilibrium?

Answer 13

At equilibrium, inward and outward flow are equal. If driving force due to concentration is inward, driving force due to voltage must be outward

Question 14

What happens if Vm is different to Eion?

Answer 14

There is a net difference in the electrochemical driving force

Question 15

What is the electrochemical driving force?

Answer 15

• A potential that drives ion flow across the membrane, where potential is voltage and ion flow is current
• It is the difference between Vm and Eion, the greater the difference, the greater the driving force

Question 16

Compare the function of ion transporters and ion channels:

Answer 16

Transporters:

• Actively move ions against concentration gradient
• Create ion concentration gradients

Ion channels:

• Allow ions to diffuse down concentration gradient
• Cause selective permeability to certain ions

Question 17

Define the electrical terms = Q, I, V, R and C along with their units:

Answer 17

Q = charge, Units = coulombs

I = current = movement of charge, Units = amps

V = voltage = separation of charge, Units = volts

R = resistance, Units = ohms

C = capacitance = capacity to store and separate charge, Units = farads

Question 18

Describe the use of the Nerst equation:

Answer 18

Used to find cell potential at any moment during a reaction

Or at conditions other than standard state

Question 19

Define Vm:

Answer 19

Electrical potential difference across the cell membrane

That exactly balances the concentration gradient for an ion

Question 20

Describe the link between ionic equilibrium potential and [ion]:

Answer 20

Ionic equilibrium potential is proportional to the log of concentration ratio for that ion

Question 21

What is Ek with normal physiological concentration:

Answer 21

At eq = net out and inflows are equal

Driving force due to known concentration gradient is outward

Thus, at eq, force due to voltage gradient must be inward (due to Vin being more negative)

Question 22

What is Ena with normal physiological concentration:

Answer 22

At eq = net out and inflows are equal

Driving force due to known concentration gradient is inward

Thus, at eq, force due to voltage gradient must be outward (due to Vout being more negative)

Question 23

What happens if Vm is different from Eion (describe net flow):

Answer 23

Force due to voltage gradient will be towards whichever (Vin/Vout) is more negative, in the case of K+ will be inward

Force due to known concentration gradient will be outward (for K+)

Net flow will be the difference = known as electrochemical driving force

Question 24

Describe the link between absolute difference and driving force:

Answer 24

A potential that drives ion flow across the membrane

Potential: voltage

Ion flow: current

Driving force is difference between Vm and Eion

The greater the absolute of this difference, the greater the driving force

Question 25

Describe the link between conductance to a given ion and Vm:

Answer 25

An ionic current ‘tries’ to change Vm so that it is closer to the equilibrium (reversal) potential for that ion This means that if there is an increase in conductance to a given ion Then the change in Vm will be towards the equilibrium potential for that ion

Question 26

Describe how to calculate ion current:

Answer 26

More formally, from Ohm’s law I = V/R = gV (since conductance (g) is the reciprocal of resistance (g = 1/R) ) So ionic current is membrane conductance for that ion times the driving force on that ion I_ion = g_ion (Vm – E_ion)

Question 27

Describe a synaptic potential:

Answer 27

Potential difference across postsynaptic membrane that results from the action of neurotransmitters at a neuronal synapse “incoming” signal that a neuron receives Two forms of synaptic potential: excitatory and inhibitory

Question 28

Describe the function of EPSPs and IPSPs with relation to each other:

Answer 28

EPSPs depolarize membrane and move potential closer to threshold for AP to be generated IPSPs hyperpolarize membrane + move potential farther away from threshold Decreasing the likelihood of an action potential occurring. In order to depolarize a neuron enough to cause an action potential There must be enough EPSPs to both depolarize the postsynaptic membrane from its resting membrane potential to its threshold And counterbalance the concurrent IPSPs that hyperpolarize the membrane