Page 78 - Teknik Menjawab Soalan PSPM Biologi

Describe how the axon membrane resting potential is established

1. In unstimulated neuron, sodium-potassium pump is activated.
+
• For every 3 sodium ions (Na ) pumped to the outside, 2 potassium
+
ions (K ) is pumped into the axon.
• By active transport against their concentration gradient.
+
• Causing sodium ion (Na ) concentration is higher outside the axon
• And potassium ion (K ) concentration is higher inside the axon
+

+
2. Axon membrane is less permeable to sodium ion (Na ) but more
+
permeable to potassium ion (K ).
• This cause potassium ion is able to diffuse outward via potassium

• channel
These diffusions cannot reach equilibrium because the sodium
potassium gradient is maintained by sodium potassium pump

3. In axon, there are many anions that is too large to diffuse out
• Causes the electrical charge in axon becomes relatively more

negative than outside
• This electrochemical gradient creates an electrical potential across

• the axon membrane
Potential difference across the membrane is about -70mV
• Membrane is in resting potential
• Since the inner membrane is negatively charged during resting

potential, membrane is in polarized state