Читать книгу Neurobiology For Dummies - Frank Amthor - Страница 34

Skin sensation is composed of a group of different types of sensory capabilities controlled by different receptors in the skin and a few other places, such as the mouth and trachea. Mechanoreceptors detect shallow and deep pressure, applied constantly or intermittently. Cold and warm temperature receptors respond to skin temperatures below or above body temperature. Pain receptors respond to mechanical or chemical inputs likely to cause injury.

The sense of smell is mediated by several thousand different receptor types in the olfactory organ in the roof of the nasal cavity. Evolutionary evidence suggests that some of the earliest neocortex in mammals may have been devoted to sorting out and identifying what produced the smells detected by the olfactory receptors.

A dog has about one billion olfactory receptors, a number comparable to the total number of neurons in its entire brain. I’m sure my dogs sniffing around the yard every morning know what was there last night, and probably when, and probably what each critter did, from the smells left over.

The olfactory system is unique in being divided between a pathway that projects (although indirectly) through the thalamus, of which we are aware, and a pathway that is non-thalamic, which influences our behavior, but of which we are not directly aware.

The sense of taste is mediated by salt, sweet, sour, and bitter receptors located mostly on the tongue. Some taste researchers also include the MSG taste, umami, as a fundamental taste.