A sensory homunculus or cortical homunculus is a distorted representation of the human body, based on a neurological “map” of the areas and proportions of the human brain dedicated to processing motor functions, or sensory functions, for different parts of the body. Basically, this is how our brain sees or interprets the body and through it senses its environment and surroundings.
A sense is a physiological capacity of organisms that provides data for perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology (or cognitive science), and philosophy of perception. The nervous system has a specific sensory nervous system, and a sense organ, or sensor, dedicated to each sense.
The 5 Senses
The five senses make up human’s multitude of sensors: Sight (vision), hearing (audition), taste (gustation), smell (olfaction) and touch (somatosensation) are the five traditionally recognized senses.
Sight or vision (adjectival form: visual/optical) is the capability of the eye(s) to focus and detect images of visible light on photoreceptors in the retina of each eye that generates electrical nerve impulses for varying colors, hues, and brightness. There are two types of photoreceptors: rods and cones. Rods are very sensitive to light, but do not distinguish colors. Cones distinguish colors, but are less sensitive to dim light. Some argue that stereopsis, the perception of depth using both eyes, also constitutes a sense, but it is generally regarded as a cognitive (that is, post-sensory) function of the visual cortex of the brain where patterns and objects in images are recognized and interpreted based on previously learned information. This is called visual memory.
Hearing or audition (adjectival form: auditory) is the sense of sound perception. Hearing is all about vibration. Mechanoreceptors turn motion into electrical nerve pulses, which are located in the inner ear. Since sound is vibration, propagating through a medium such as air, the detection of these vibrations, that is the sense of the hearing, is a mechanical sense because these vibrations are mechanically conducted from the eardrum through a series of tiny bones to hair-like fibers in the inner ear, which detect mechanical motion of the fibers within a range of about 20 to 20,000 hertz with substantial variation between individuals. Hearing at high frequencies declines with an increase in age. Inability to hear is called deafness or hearing impairment.
Taste or gustation (adjectival form: gustatory) is one of the traditional five senses. It refers to the capability to detect the taste of substances such as food, certain minerals, and poisons, etc. The sense of taste is often confused with the “sense” of flavor, which is a combination of taste and smell perception. Flavor depends on odor, texture, and temperature as well as on taste. Humans receive tastes through sensory organs called taste buds, or gustatory calyculi, concentrated on the upper surface of the tongue. There are five basic tastes: sweet, bitter, sour, salty and umami (it has been described as brothy or meaty). Other tastes such as calcium and free fatty acids may also be basic tastes but have yet to receive widespread acceptance. The inability to taste is called ageusia.
Smell or olfaction (adjectival form: olfactory) is the other “chemical” sense. Unlike taste, there are hundreds of olfactory receptors (388 according to one source), each binding to a particular molecular feature. Odor molecules possess a variety of features and, thus, excite specific receptors more or less strongly. This combination of excitatory signals from different receptors makes up what we perceive as the molecule’s smell. In the brain, olfaction is processed by the olfactory system. Olfactory receptor neurons in the nose differ from most other neurons in that they die and regenerate on a regular basis. The inability to smell is called anosmia. Some neurons in the nose are specialized to detect pheromones.
Touch or somatosensation (adjectival form: somatic), also called tactition (adjectival form: tactile) or mechanoreception, is a perception resulting from activation of neural receptors, generally in the skin including hair follicles, but also in the tongue, throat, and mucosa. A variety of pressure receptors respond to variations in pressure (firm, brushing, sustained, etc.). The touch sense of itching caused by insect bites or allergies involves special itch-specific neurons in the skin and spinal cord. The loss or impairment of the ability to feel anything touched is called tactile anesthesia. Paresthesia is a sensation of tingling, pricking, or numbness of the skin that may result from nerve damage and may be permanent or temporary.
As you see above, the “Five Senses” is also a set of allegorical paintings created at Antwerp in 1617–18 by Jan Brueghel the Elder and Peter Paul Rubens, with Brueghel being responsible for the settings and Rubens for the figures.
The 6th Sense(s)
There are two senses which are commonly accepted to be human’s 6th sense:
- Equilibrioception (sense of balance) and proprioception (sense of body position), commonly accepted physiological senses in addition to the usually considered “five senses”.
- Extrasensory perception, ESP or Esper, also called sixth sense or second sight, includes claimed reception of information not gained through the recognized physical senses but sensed with the mind.
The 7th Sense
Then, there’s the 7th sense: The common sense. Unfortunately, not all people have it – or have it developed to some certain extent but do not use it.
The 8th Sense
Last but not least: The sense of humor is the tendency of particular cognitive experiences to provoke laughter and provide amusement. The term derives from the humoral medicine of the ancient Greeks, which taught that the balance of fluids in the human body, known as humours (Latin: humor, “body fluid”), controlled human health and emotion.
That might all be nonsense but by applying the 8th sense above, you might sense that this all does make sense. If not, why not rethink how we use our senses? Believe it or not: Everything’s not at all senseless after all.