WEEK 2

Question 1

Galvani

Answer 1

discovered that the NS uses electrical activity to perform its functions while studying frogs.

Question 2

Electrophysiology

Answer 2

science and recording of electrical activity.

uses a wide range of techniques that can be grouped under 2 headings:
1) invasive
2) non-invasive

Question 3

Electroplaques (rays + eels)

Answer 3

• specialist cells that have membrane sodium and potassium exchanges. at rest, these exchanges use ATP to alter the ion distribution across the membrane. this generates a potential difference across the electroplaque.
• when the fish want to give a shock, the electroplaques are activated by a nerve. The nerve releases acetalcholine onto receptors that are ligand-gated ion channels. these channels allow the flow of sodium into the plaque, depolarizing it, and generating a brief potential change of 120 mV.
• electroplaques are stacked in thousands in electric organs (5k) and the sum of these can generate hundreds of volts.

Question 4

5 extracellular recording types

Answer 4

1) field potentials

2) whole nerve activity

3) multiunit activity

4) single unit activity

5) multielectrode arrays (MEAs)

• in each case the electrode is outside but close to neurons. it picks up only field potentials and low frequency filtered APs. it does not record Vmrest or PSPs.

Question 5

2 intracellular recording types

Answer 5

1) sharp electrodes

2) patch suction electrodes

• measures activity within single cells

Question 6

Somatic population spike

Answer 6

the sum of many APs of cells

Question 7

Whole nerve activity

Answer 7

the compound AP of a whole nerve can be recorded extracellularly.

• the outer chambers are sealed with silicon grease and filled with olive oil to electrically isolate the nerves: only the AP traveling down the individual axons will be recorded.
• increasing the intensity of the stimulation increases the compound AP size: the stronger the stimulation, the more axons are recruited to fire APs.

Question 8

Multi-electrode Arrays (MEAs)

Answer 8

• electrodes are embedded in the bottom of a dish. individually, they are inert to the cells, so they don’t affect them, but they can pick up extracellular activity.
• we can grow the neurons inside these dishes in an incubator, and we can monitor electrical activity in a non-invasive manner.

Question 9

Current vs. voltage clamp

Answer 9

1) current-clamp: we’re injecting the current and recording the voltage.

2) voltage-clamp: we are looking at current flow through the membrane after applying different voltages.

Question 10

Applications of electrophysiological techniques

Answer 10

1) humans in-vivo
- extracellular recording, only as part of an existing treatment

2) non-humans in-vivo
- extracellular recording (implanted/anaesthetic)
- intracellular recording (anaesthetic)
- single cell recording (anaesthetic)

3) in-vitro (can use human tissue)
- extracellular recording
- intracellular recording
- single cell recording