The memory is just storage of information and it does not sense anything.

Senses are the physiological methods of 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 sensory system dedicated to each sense.





[edit] Definition of sense
There is no firm agreement among neurologists as to the number of senses because of differing definitions of what constitutes a sense. One definition states that a sense is a faculty by which outside stimuli are perceived.[1] The conventional five senses are sight, hearing, touch, smell, taste: a classification traditionally attributed to Aristotle.[2] However, humans have at least nine different senses, and there are at least two other senses in other organisms.

A broadly acceptable definition of a sense would be "a system that consists of a group sensory cell types that responds to a specific physical phenomenon, and that corresponds to a particular group of regions within the brain where the signals are received and interpreted." Disputes about the number of senses arise typically regarding the classification of the various cell types and their mapping to regions of the brain.


[edit] Five classical senses

[edit] Sight
Sight or vision is the ability of the brain and eye to detect electromagnetic waves within the visible range (light) interpreting the image as "sight." There is disagreement as to whether this constitutes one, two or three senses. Neuroanatomists generally regard it as two senses, given that different receptors are responsible for the perception of colour (the frequency of photons of light) and brightness (amplitude/intensity - number of photons of light). Some argue[citation needed] that stereopsis, the perception of depth, also constitutes a sense, but it is generally regarded as a cognitive (that is, post-sensory) function of brain to interpret sensory input and to derive new information. The inability to see is called blindness.


[edit] Hearing
Hearing or audition is the sense of sound perception and results from tiny hair fibres in the inner ear detecting the motion of a membrane which vibrates in response to changes in the pressure exerted by atmospheric particles within (at best) a range of 9 to 22000 Hz, however this changes for each individual. Sound can also be detected as vibrations conducted through the body by tactition. Lower and higher frequencies than that can be heard are detected this way only. The inability to hear is called deafness.


[edit] Taste
Taste or gustation is one of the two main "chemical" senses. It is well-known that there are at least four types of taste "bud" (receptor) on the tongue and hence there are anatomists who argue that these constitute four or more different senses, given that each receptor conveys information to a slightly different region of the brain. The inability to taste is called ageusia.

The four well-known receptors detect sweet, salt, sour, and bitter, although the receptors for sweet and bitter have not been conclusively identified. A fifth receptor, for a sensation called umami, was first theorised in 1908 and its existence confirmed in 2000[3]. The umami receptor detects the amino acid glutamate, a flavor commonly found in meat and in artificial flavourings such as monosodium glutamate.


[edit] Smell
Smell or olfaction is the other "chemical" sense. Unlike taste, there are hundreds of olfactory receptors, 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.


[edit] Touch
Touch, also called tactition or mechanoreception, is the sense of pressure perception, generally in the skin. There are a variety of pressure receptors that respond to variations in pressure (e.g., firm, brushing, and sustained). The inability to feel anything or almost anything is called anesthesia. Paresthesia is a sensation of tingling, pricking, or numbness of a person's skin with no apparent long term physical effect.