Sensation

Sensation is the process or the result of obtaining information through the senses. In this process, the senses, which are bodily systems, transform external or internal stimuli into nervous signals. These signals travel to the brain and there produce the result of the process, that is, a sensation, a conscious feeling corresponding to the sense involved. When the term 'sensation' is used to refer to this result, its usage is similar to that of the word 'perception.'

The process just mentioned can be described as formed by the following elements: a stimulus, a sense organ or system, a way by which impulses travel to the brain, and an area of the brain that converts the impulse into a sensation. The list given by Aristotle of the senses: sight, hearing, smell, taste, and touch, has been expanded to include sensations of pain, temperature, balance, etc. The organs corresponding to these senses are located in the skin, the ears, the muscles, and other body systems.

There are instances in which impulses generated by the sense organ do not arrive to the brain, but are immediately processed producing a reflex act. These instances are not usually perceived as sensations, nor are those internal adjustments of body conditions like blood pressure that result from the information provided by internal sensors.

Animals differ in the information they can gather from the environment. For instance, humans can detect only a segment of the electromagnetic spectrum, which is called the visible spectrum. Snakes can detect lower (infrared) frequencies of the spectrum, and certain insects detect higher (ultraviolet) frequencies.

The sense organ function is to transform the external signal into an electric potential in a set of nerve cells. These cells are connected to the spinal cord, and this in turn to the brain. In the brain, the electric impulse arrives to the cerebral cortex where, by a process that is still a mystery, it is transformed into a specific sensation. The type of organ sending the impulse, and the area of the brain to which it is sent, undoubtedly play an important role in this decoding.

The sense organs, that can produce information on such different conditions as pain, hunger, thirst, and fatigue, in addition to the five classical ones, can be located in the exterior of the body, in the visceral organs, or in the muscular system. By way of experimentation, artificial sensations have been produced by the stimulation of the nerves or the brain itself. It has been determined that damaged caused to particular regions of the brain may result in the loss of selected sensory capacities.

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