Lecture 1 - Electrophysiology

Question 1

What is the membrane potential?

Answer 1

The potential difference between the inside of the cell and the outside
e.g neurons have a membrane potential of -70mV because the inside is 70mV less than the outside

Question 2

How is the resting potential of a neuron established?

Answer 2

Na+/K+ pumps bring K+ in and Na+ out
Leaky K+ channels allow K+ to flow out 
down concentration gradient
Anions cannot follow, electrical gradient builds up in the opposite direction 
Reaches an electrochemical equilibrium

Question 3

What 3 preparations can electrophysiology be carried out on?

Answer 3

Dissociated neuronal cultures - neurons taken from rat embryo and grown into artificial networks on a cover slip
Acute brain slices
Whole animal

Question 4

Give a pro and a con of dissociated neuronal networks

Answer 4

Pro - Easy to record from intracellularly
Con - Recordings aren’t taken under normal physiological conditions, neurons haven’t been developed in normal physiological conditions, can only be used to study early stage embryonic neurons, don’t know exactly what type of neuron it is

Question 5

Give a pro and a con of acute brain slices

Answer 5

Pro - Local circuits remain intact

Con - Recordings aren’t taken under normal physiological conditions

Question 6

Give a pro and a con of whole animal recordings

Answer 6

Pro - All circuits intact, can correlate brain activity with behaviour
Con - Technically very difficult

Question 7

Briefly explain the two methods by which you can take intracellular recordings of the membrane potential

Answer 7

Sharp electrode - high resistance tip, pokes hole in cell body
Patch pipette - low resistance tip, wide tip sucks up part of cell membrane until it bursts, cytoplasm becomes continuous with inside of pipette

Question 8

What is a benefit of using a patch pipette over a sharp electrode?

Answer 8

Patch pipettes allow you to perfuse the cell contents with a solution, to change ion concentrations
Allows you to carry out voltage clamp recordings

Question 9

What is Ohms law? (with units)

Answer 9

Voltage (volts) = Current (amps) x Resistance (Ohms)

Question 10

What affects resistance?

Answer 10

How easily current can pass through the membrane

Few ion channels, or closing ion channels, will lead to higher resistance

Question 11

What is a current clamp recording?

Answer 11

The cell is stimulated by injecting a current
The voltage is recorded
This can be used to calculate resistance

Question 12

When would you use a current clamp recording?

Answer 12

Monitors the effect of manipulations (drugs) on the membrane potential (voltage)
e.g. applying a drug that opens ion channels will decrease the resistance

Question 13

How are EPSPs/IPSPs recorded?

Answer 13

Using a patch pipette, recording from the cell body of the neuron

Question 14

During an EPSP, will the EPSC be positive or negative, and why?

Answer 14

Negative, as the amplifier must inject negative current to oppose the flow of positively charged ions

Question 15

What is a voltage clamp recording?

Answer 15

Measures the current required to keep the voltage at a fixed level
The voltage/membrane potential is fixed at a certain voltage
The ion channel of interest is opened
The amount of current needed to counteract the flow of ions and keep the voltage fixed is measured

Question 16

When would you use a voltage clamp recording?

Answer 16

To study the underlying biophysical properties of ion channels in the membrane, and the effects of manipulations (drugs) on these
e.g. at what membrane potential does a specific ion channel open

Question 17

What is a single unit recording?

Answer 17

Recording the voltage of many neurons at once
Recorded from the extracellular space
Records a field EPSP

Question 18

What is the equilibrium potential of an ion channel?

What will happen if you open an ion channel?

Answer 18

The membrane potential at which there is no net flow of that ion
Opening the ion channel allows membrane potential to match the equilibrium potential

Question 19

What is the Nernst equation?

Answer 19

Equation for calculating equilibrium potential, using the valance, intracellular concentration and extracellular concentration

Question 20

What happens to the equilibrium potential if you change the intracellular and extracellular concentrations of an ion to match?

Answer 20

Becomes zero

Question 21

Why is the equilibrium potential of chloride different in adult neurons and young neurons?

Answer 21

The KCC2 (K+/Cl- cotransporter) is not expressed in early development
So the intracellular Cl- concentration is higher
When you open the Cl- channels, Cl- exits and causes depolarisation
The membrane potential rises
Opposite in adult neurons, as the KCC2 is fully developed