Lecture 5

Question 1

Describe the properties of the action potential

Answer 1

Changes the voltage across a membrane. Dependent on ion gradients and relative permeability of the membranes. Will not occur if threshold potential is not reached.

Question 2

Explain the ionic basis of the action potential

Answer 2

The upstroke of the action potential is due to the increases of Na+ flowing inside the cell. The ions flow to make the membrane potential closer to that of the equilibrium potential.

Question 3

Explain how the ionic permeability of the membrane alters with time

Answer 3

When there is a small increase in membrane potential the sodium channels open and there is an influx of sodium ions, causing an even greater depolarisation. Once to membrane has reached the maximum potential the sodium channels are deactivated and the potassium channels open so there is an efflux of potassium ions, leading to a repolarisation of the membrane

Question 4

Describe some molecular properties of voltage-gated ion channels

Answer 4

A voltage gated Sodium ion channel has four repeats each with 6 subunits. The fourth subunit is positively charged and is a voltage sensor. The pore regions lie between the 5th and 6th domain. The deactivating particle lie between the 3rd and 4th.

A voltage-gated potassium ion channel has a similar structure but one alpha subunit is only a ¼ of the whole channel in this case.