Question

that neurons are electrically charged or not, depending on the pres... or absence of a myelin sheath.
that neurons work together or not at all. they do not fire unless their neighbors are firing.
that neurons are either on or off. there are no intermediate states.
that neurons receive input from other neurons or shut off. they do not adjust their sensitivity depending on what is happening around them.

Explanation:

To solve this, we analyze each option based on neuron function:

1. First option: Myelin sheath affects signal speed, not neuron’s electrical charge presence. Incorrect.
2. Second option: Neurons fire based on their own threshold, not just neighbors. Incorrect.
3. Third option: Neurons operate as “all - or - none”—they either fire (on) or don’t (off), with no intermediate states. This matches the all - or - none principle of neural firing. Correct.
4. Fourth option: Neurons do adjust sensitivity (e.g., through synaptic plasticity) based on input. Incorrect.

Answer:

That neurons are either on or off. There are no intermediate states.