Summary
Highlights
The sensory system is how we gather information from our surroundings and send it to our brain. Our brain interprets simple nerve signals, or action potentials, in complex ways. An optical illusion demonstrates how the brain can interpret the same color differently based on context.
Nerve signals are action potentials, which are always identical in size and shape. The brain differentiates signals based on their origin (which nerves) and their frequency (number of action potentials). For example, a louder sound generates more action potentials.
We have far more than five senses, including balance, temperature, pain, acceleration, and kinesthetic sense (body awareness), as well as numerous internal senses, totaling around 25 different senses.
Smell works by chemical sensors in the olfactory bulb in the nose. Odors dock with olfactory neurons, causing interactions that send action potentials to the brain. The more interactions, the stronger the perceived smell. The brain can also habituate to smells.
Vision involves light entering the pupil, focusing through a lens, and being projected onto the retina at the back of the eye. The brain then flips this inverted image right-side up. Rods and cones on the retina convert light into action potentials.
Rods contain rhodopsin, a chemical that changes conformation when hit by light, sending an action potential to the brain. More light hitting rhodopsin means more signals. When light is absent, rhodopsin returns to its original conformation, reducing signals. This is why our eyes adjust to sudden changes in light.
Hearing involves compressional sound waves vibrating the eardrum, which mechanically amplifies the vibrations through a series of bones to the oval window. This transfers vibrations to the fluid within the cochlea.
Inside the unwound cochlea, fluid vibrations stimulate nerves at different points depending on the sound's pitch, sending action potentials to the auditory nerve and then to the brain, which interprets them as sound. Specialized cochleas allow animals to hear different frequency ranges.
Regardless of the sense, the brain receives action potentials. The specific part of the brain these signals go to determines how they are perceived. Sometimes, signals can get 'crossed', leading to phenomena like synesthesia where sounds are perceived as colors.