24.4 the nerve impulse

Question 1

how is movement of (K+) and (Na+) ions across the axon membrane controlled

Answer 1

1) phopholipid bilayer does not allow the ions to directly diffuse across it
2) intrinsic proteins; contain channels
- some are premenantly open
- others are voltage gated; opening and closing depending on the potential difference
3) carrier proteins that use active transport to transport (K+) ions in and (Na+) ions out of the axon membrane

Question 2

resting potential

Answer 2

• when inside of axon is more negative then the outside
• value of -65 mV
• axon is said to be polarised

Question 3

establishment of resting potential

1) active transport of ions

Answer 3

• 3 (Na+) ions are actively transported out of the axon by sodium-potassium pumps
• 2 (K+) ions are actively transported into the axon by sodium-potassium pumps

Question 4

establishment of resting potential

2) chemical gradient

Answer 4

• outward movement of (Na+) ions is greater than inward movement of (K+) ions
• therefore, there are more (Na+) ions in the tissue fluid surrounding the axon than in the cytoplasm
• there are more (K+) ions in the cytoplasm than in the tissue fluid
• chemical gradient created

Question 5

establishment of resting potential

3) diffusion of (Na+) ions

Answer 5

-