Biology · Neural Control and Coordination · NEET
No. This is the most common mix-up. The pump does NOT fire the impulse. It works quietly in the background to build and maintain the resting ionic gradient (high Na+ outside, high K+ inside). The actual impulse (action potential) happens when Na+ channels open and Na+ rushes IN by diffusion, not by the pump. Think of the pump as charging the battery; the action potential is spending that stored charge.
For every ATP used, the pump moves 3 Na+ outward and 2 K+ inward. Because 3 positive charges leave and only 2 positive charges enter, there is a net loss of one positive charge from inside the cell each cycle. This unequal (electrogenic) transport helps make the inside of the axon slightly more negative, supporting the polarised resting state. NCERT states this exact 3:2 ratio.
It is ACTIVE transport. NCERT calls it 'active transport of ions by the sodium-potassium pump.' It moves Na+ and K+ AGAINST their concentration gradients (pushing Na+ out even though Na+ is already high outside, and pulling K+ in even though K+ is already high inside). Moving ions uphill against a gradient always needs energy, so ATP is spent. Passive diffusion, in contrast, is downhill and free.
Without ATP the pump stops. The ionic gradients slowly leak away, Na+ builds up inside and K+ leaks out, the difference in charge disappears, and the membrane loses its resting potential. A neuron that cannot stay polarised cannot generate or conduct impulses. This is why nerve function depends heavily on energy supply.
A channel is a passive gate: when it opens, ions simply diffuse through, down their gradient, with no energy used. The pump is a carrier that spends ATP to force ions the wrong way (against the gradient). Channels create the fast changes during an impulse; the pump restores and maintains the long-term gradient the channels depend on.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It transports 3 sodium ions (Na+) outward and 2 potassium ions (K+) inward per cycle, using ATP. This exact 3:2 ratio is stated in NCERT and is a favourite one-mark point in NEET.
Potassium (K+) is high inside the axon, along with negatively charged proteins. Sodium (Na+) is high outside. The pump helps maintain this arrangement.
Yes. Because it removes 3 positive charges and brings in only 2, there is a net movement of one positive charge out per cycle, which slightly adds to the negative charge inside. This makes it electrogenic.
Its main job in NCERT is to maintain the ionic concentration gradients across the resting membrane. The resting potential value itself mainly comes from the membrane being more permeable to K+ at rest; the pump keeps the gradients that make this possible.
Because ions constantly leak across the membrane. Without the pump using ATP to push Na+ out and K+ in against their gradients, the gradients would run down and the neuron could no longer stay polarised or conduct impulses.
