Cell Electrophysiology

Question 1

Describe the ionic composition of interstitial fluid and intracellular fluid

Answer 1

Interstitial fluid has Na+ and Cl- majority. Intracellular fluid has K+ and PO43- majority.

Question 2

What is the Gibbs Donnan Effect?

Answer 2

Small building blocks diffuse inside cells, and then form larger molecules that can’t diffuse out. Proteins ionise as anions (-ve), plus small ions (H+) than can diffuse out - leaving the cell negative (–ve RMP)

Question 3

Describe the membrane potential response.

Answer 3

1. Sub-threshold stimuli cause ligand gated Na+ channels to open, causing depolarisation. 2. When threshold is reached, voltage gated Na+ channels open, causing rapid depolarisation. 3. At peak MP, cell is highly positive and Na+ channels close and K+ channels open 4. K+ floods out of the cell, causing repolarisation 5. K+ channels are slower to close, causing ICF to be more negative than at rest.

Question 4

Describe the absolute refractory period and the relative refractory period.

Answer 4

Absolute = all Na+ channels are inactive, neurone can’t reach AP.

Relative = Some Na+ channels are inactive, greater stimulus required for neurone to reach AP.

Question 5

What is the purpose of refractory periods?

Answer 5

To ensure the AP travels in one direction.

Question 6

What is saltatory conduction?

Answer 6

Myelin insulated nerves (secreted by glial cells) have Schwann cells and Nodes of Ranvier.

APs jump from node to node - much quicker.