Sensation
In
psychology,
sensation is the first stage in the biochemical and neurologic events that begins with the impinging of a
stimulus upon the receptor cells of a sensory organ, which then leads to
perception, the mental state that is reflected in statements like "I see a uniformly blue wall."
A sensation that might lead to that statement could include the excitation of
cone cells in the
retina, spatially varying in the proportion of "blue" and "green" cone excitation due to portions of the wall receiving different proportions of yellowish artificial and bluish sky-light; it is common for these variations to be compensated for, within the brain, so that the non-uniform sensation yields a perception of uniform color.
In the West, the human body's
senses are divided into eight: visual, auditory, gustatory, olfactory, cutaneous, kinesthetic, vestibular, organic. The ways in which these
senses are divided from one another in concept, and combined in varying ratios in perceiving the world, differs based on individual physiology, social and cultural context, and physical surroundings. The whole sensory system, including both physical sensation and interpretation (or
cognition) of information from the senses, is referred to as a
sensorium.
Light enters to the eyes through
cornea. It then passes through the pupil, and is refracted by the
crystalline lens of the eyes. Light is then channeled through the vitreous humour and then on to the
retina. In the
retina, there are two kinds of cells,
rods and
cones. Rods see black-and-white colors, and is dominant in the night (because, as Physics state, there are no colors in the night, because what we see is the colors reflected from the atmosphere). Cones then, see colored structures. Cones are exceptionally abundant in the fovea. Cones are reactive to the three colors of red, blue, and green. Other colours are sensed as combinations of these.
Sound is received by the ear via the
pinna, the outer ear structure, which then leads the sound inside through the
external auditory meatus. After the sound passes through the meatus, it goes to the
eardrum, or tympanus, then vibrates its way through the tiny
ossicles, the hammer (malleus), anvil (incus), and stirrup (stapes), then to the
cochlea. The cochlea converts vibration into electical impulses which are transmitted to the brain.
Taste, or gustation, is the ability to detect sensory changes in the tongue, through the use of
taste buds, situated deep into the
papillae. Intriguingly, the sense called gustation is if fact comprised of varying ratios of multiple sensory systems, shifting in importance and attention as food is chewed, tasted and swallowed. These include the
taste buds, the sense of touch in the structures of the mouth and digestive system, chemical sensation of irritation in the trigeminal nerve system, and unique receptors for sensing the properties of water located at the rear of the oral cavity.
Smell, or olfaction, is received by the olfactory bulb and the connected to the brain by the olfactory nerve, the 1st cranial nerve of the brain, just after the nasal turbinates of the nose warm, strain and filter the air.
Please see the
skin article for more details.
The kinesthetic sense is the sense of posture and movement. It is also referred to as
proprioception.
The vestibular sense is the sense of balance. It is mediated by the action of the fluid inside the
Semicircular canals in the ear.
The organic sense, per se, refers only to sensation from the internal organs, or viscera, but can, however, be expanded to include certain physiological processes, such as
hunger, thirst, drowsiness and
air hunger. It is also referred to as
interoception.
