Humans have far more than five senses, perhaps as many as 17
Sight, hearing, smell, taste and touch are just the famous ones. Your body also senses balance, the position of your limbs, pain, hunger, thirst and even rising blood pressure. Split the big senses into their component channels and researchers count up to 17 distinct sensory modalities in total.
A sense is a biological system for gathering information about the world by detecting stimuli. Sense organs catch signals such as light, sound or chemicals and transduce them, converting them into electrical impulses that nerves carry to the brain's sensory cortices, where they are interpreted. Receptor cells come in several types, including mechanoreceptors, photoreceptors, chemoreceptors and thermoreceptors, and they can be bare nerve endings, endings wrapped in connective tissue for extra sensitivity, or specialised cells.
Scientists divide the senses into outward-facing and inward-facing systems. Exteroception relies on eyes, ears, skin, nose and mouth. Interoception monitors the body itself: proprioception tracks where your limbs are, nociception registers pain, equilibrioception handles balance, and receptors in the aorta and carotid sinus notice climbing blood pressure. Chemical and fluid sensors underlie feelings of hunger, thirst, suffocation and nausea.
Each broad sense breaks down further. Touch alone includes light pressure, deep pressure, vibration, itch, pain, temperature and the movement of hairs. Taste separates into sweet, salty, sour, bitter, spicy and umami, each triggered by different chemicals binding to sensory neurons. The senses also blend: through multimodality, information from one can change how another is perceived.
Other species live in different sensory worlds. Most mammals smell far better than people do. Some animals detect electric or magnetic fields, humidity or polarised light, while others navigate by echolocation, and some process familiar signals in very unfamiliar ways. Recent theories even suggest that plants and robots may take in and interpret information from their surroundings in ways loosely comparable to animals. Fields from psychophysics and neurobiology to cognitive science study how sensation becomes perception.
Source: Sense
