Ion Gradients and Nerve Transmission

Question 1

What kind of transport does the sodium-potassium pump work by and what does it do?

Answer 1

Active Transport - Requires energy.

Moves three sodium ions out of the cell and two potassium ions in.

Question 2

Describe the stages of the sodium-potassium pump.

Answer 2

1) It is in its first confomational change with its ion binding sites exposed to the cytoplasm and a high affinity for sodium ions. 3 sodium ions bind.
2) The transporter protein hydrolysis ATP to ADP and phosphate. The phosphate then attaches to the protein, phosphorylating it and this causes a conformational change.
3) This new conformation has its ion binding sites exposed to the outside of the cells and it has a low affinity for sodium ions so they are released out of the cell.
4) Since the protein now has a high affiity for potassium ions, 2 bind the the binding sites and this triggers dephosphorylation.
5) This causes the protein to return to its original conformation state with its binding sites exposed to the cytoplasm and the potassium ions are released.
6) The protein has a high affinity for sodium again so begins again.

Question 3

Why is the sodium-potassium pump so important?

Answer 3

1) Maintaining the osmotic balance in animal cells - The pump lowers the overall ion concentration and so increases the net water concentration.
2) Sodium ion gradient generated for glucose symport - A sodium ion gradient from intestine to lining cell is generated enabling the glucose symport to absorb sodium ions and glucose.
3) Sodium ion gradient generated for kidney tubules - Sodium ion gradient formed from lumen of tubule into the cell, enabling a glucose symport to absorb sodium ions and glucose from the filtrate.
4) Generation and maintainance of ion gradients for resting potential in neurons.

Question 4

What is the resting potential in nerve cells?

Answer 4

The resting potential is when there is an imbalance of electrical charge across the neuron membrane due to neurons having potassium channels which let some potassium ions leak back out of the cell to give a positive charge outside the cell.

Question 5

What does a nerve impulse pass along a neuron as?

Answer 5

A nerve impulse passes along a neuron as a wave of depolarisation of the resting potential due to sodium ion influx (entry) into the neuron.

Question 6

Describe in stages how a neurotransmitter triggers a nerve impulse.

Answer 6

1) The neurotransmitter is released into the synapse and it binds to the transmemrane receptor protein on the surface of the next neuron (ligand-gated channel).
2) This causes the ligand gated channel to open and sodium ions to diffuse into the neuron.
3) If enough sodium ion movement occurs, the voltage change across the membrane reaches a critical level and the membrane is depolarised.
4) This voltage change causes the neighbouring voltage-gated sodium ion channels to open and a domino effect is reached. The effect travels along the nerves as a wave of depolarisation.

Question 7

Describe in stages how the resting potential is reset.

Answer 7

1) The voltage from sodium ion channels reaches a critical level which causes the voltage-gated sodium ion channels to close and the potassium voltage gated channels to open.
2) The potassium ions diffuse back out of the neuron, restoring the resting potential.
3) When the resting potential is reached, the potassium channels close again.
4) The sodium-potassium pump also helps to restore the resting potential.