5.3.3 Resting Potentials

Question 1

What is the resting potential?

Answer 1

The negative electric potential inside of a resting axon compared to the outside of it is called the resting potential.

Usually -70mV, about 70mV lower than the outside

Question 2

What factors contribute to maintaining the resting potential?

Answer 2

• Active transport of sodium and potassium ions
• Differential membrane permeability

Question 3

How is the electrochemical gradient established in an axon?

Answer 3

• Sodium ions and potassium ions are pumped in and out
• Carrier proteins called sodium-potassium pumps are present in membranes of neurones
• Pumps use ATP to actively transport 3 sodium ions out for every 2 potassium ions that are actively transported in
• So a larger concentration of positive ions outside the axon than inside
• The movement of ions via the sodium potassium pump establishes the electrochemical gradient

Question 4

How does the differential membrane permeability affect the electrochemical gradient of an axon?

Answer 4

• Some sodium-potassium pumps are less permeable to sodium ions than potassium ions
• So potassium ions can diffuse back down concentration gradient out of axon at a faster rate than sodium ions