Sensation
A sensation is excitement, or something that produces excitement. A new song or a new play might be termed a "sensation" or producing "sensation". A thrilling ride on a roller coaster might be described as "sensational".
Psychology
In psychology, sensation is the process by which the sensory system processes inputs from sense organs. It is the first stage in the biochemical and neurologic events:
It begins with 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.
In the West, the human body's senses have sometimes been divided into five, but nowadays are more often 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.
Sensory system
The sensory system provides many ways to be aware of the world.
- In the visual system Light enters the eyes through the 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.
- in the Auditory system 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 connected to the brain by the olfactory nerve, the first cranial nerve of the brain, just after the nasal turbinates of the nose warm, strain and filter the air.
- 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.
- 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.