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 are dominant in the night (because, as physics states, 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 electrical 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 in 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 connection to the brain by the olfactory nerve, the first cranial nerve of the brain, just after the nasal turbinate of the nose warm, strain and
Touch, is felt by nerves in the Somatosensory system.
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 gives the awareness of the position and movement of the head. The receptors are maculae and cristae ampullaris. Maculae is located in utricle and saccule. Cristae ampullaris is found in semicircular canals.
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.
Sensation in fiction
Sensation is the fiction-writing mode for portraying a character's perception of the senses. According to Ron Rozelle, “. . .the success of your story or novel will depend on many things, but the most crucial is your ability to bring your reader into it. And that reader will be most completely in when you deliver the actual sensations of the many things that comprise your story.” (Rozelle 2005, p. 76) As stated by Jessica Page Morrell in Between the Lines, “You breathe life into fiction by translating the senses onto the page, producing stories rooted in the physical world . . . that creates a tapestry, a galaxy of interwoven sensory ingredients.” (Morrell 2006, p. 172)
Also according to Rozelle, “The sensation of what something feels like is used to describe everything from sensual pleasure to pain and torture. It’s a wide range, and your readers have actually experienced only some of those feelings. So your job is to either make them recall exactly what it feels like when something occurs in your story or, if they haven’t experienced it, what it would feel like if they did.” (Rozelle 2005, p. 86) Morrell describes a “sensory surround,” which when “coupled with drama tugs the reader into [the] story and forces him to keep reading.” (Morrell 2006, p. 173)
The importance of conveying sensation in fiction is widely accepted. However, recognition of sensation as a distinct fiction-writing mode is a matter of discussion. 
- Morrell, Jessica Page (2006). Between the Lines: Master the Subtle Elements of Fiction Writing. Cincinnati, OH: Writer's Digest Books. ISBN 1582973938.
- Rozelle, Ron (2005). Write Great Fiction: Description & Setting. Cincinnati, OH: Writer's Digest Books. ISBN 158297327X.