How do sensory receptors communicate the intensity of a stimulus to the CNS?

Answer 1

This can happen at least two different ways. First, it should be known that senses are not governed by single neurons, they have multiple neuronal receptors that can communicate individually or communicate with other neurons as well.

In some cases, the level of intensity may cause only a few of the many nerve endings to fire an action potential (signal) to the brain. The more intense the sensation - generally the more neurons will fire and relate that intensity to the Central Nervous System (CNS).

Another way is the repeated firing of the same neurons sending a constant signal (action potential) to the CNS and the more signals increase the magnitude of the sensation in the CNS.

There are many other ways that stimulus intensity can be sensed by the CNS. You may want to look up signal transduction in neurons or similar questions aspects. An opposing (opposite) example would be how we are better able to see in the dark after spending more time there. It has nothing to do with our eyes "getting used" to the dark, but rather a buildup in the chemical gradient of the rods in your eye that is normally dissipated with light. The build-up of that chemical allows for better night vision as darkness continues, but a single flash of light can disrupt the system and force the entire process to begin again.