The voltage each ion wants

Science · The Human Body · ages 18-19

Name ______________________ Date ____________

Pumps build up more sodium outside the cell and more potassium inside.
Circle one: True False
What sets one ion's equilibrium voltage?
- The thickness of the membrane
- Its inside and outside concentrations
- The length of the axon
At rest the membrane is most open to which ion?
- Sodium
- Calcium
- Potassium
Why does rest sit a little way off the potassium equilibrium?
- The pumps stop working at rest
- Small flows of other ions drag it away
- Potassium stops moving at rest
Outside potassium is raised. What happens to the resting voltage?
- It grows less negative
- It grows more negative
- It stays exactly fixed
Two ions pull rest in opposite directions. What decides the winner?
- Which ion is larger
- Which ion arrived first
- Which ion the membrane lets through best
The resting voltage is simply the potassium equilibrium under another name.
Circle one: True False
A drug makes rest far more open to sodium. What happens?
- Rest moves toward the sodium equilibrium
- Rest locks onto potassium forever
- The gradients vanish at once

Answer key

For grown-ups. Fold this page away before handing over the rest.

True · Those stored gradients power all the voltages that follow.
Its inside and outside concentrations · The balance of gradient and voltage follows the two concentrations.
Potassium · Rest favours potassium, so potassium leaking out sets the negative rest.
Small flows of other ions drag it away · Sodium and other small flows pull rest off the potassium ideal.
It grows less negative · A smaller gradient shifts the equilibrium upward and rest follows.
Which ion the membrane lets through best · Rest is a compromise weighted by each ion's permeability.
False · Rest is a weighted compromise, not one ion's private value.
Rest moves toward the sodium equilibrium · Higher sodium permeability gives the sodium pull more weight.