A stimulus is an energy source (chemical, pressure, light wave, etc.) that activates a receptor cell (specialized nerve cell) to transmit a nerve impulse, or sensation. If the sensation arrives in the conscious part of the brain, the cerebral cortex, a perception occurs. Perception is awareness of the stimulus.Pricking one’s finger, for example, is a stimulus that activates many receptor cells to send nerve impulses
to the brain. Once these sensations reach the cerebral cortex, a person perceives (feels) pain.
