The person and animals perceive smells by means of the olfactory analyzer which includes receptors of a mucous membrane of a nasal cavity and also olfactory nerves and structures of a brain.
Instruction
1. Molecules of substances irritate olfactory receptors, and nervous fibers of an olfactory nerve carry out impulses to a brain in which there passes the analysis of force and quality of a smell.
2. The majority of animals perceive smells by means of specialized organs of smell which are located in the top part of respiratory tract. The nose consists of an external nose and a nasal cavity with additional bosoms. The cavity of a nose is reported with a frontal bosom, a maxillary cavity and pneumatic cells of a trellised bone of a facial skeleton.
3. The external nose forms the bone and cartilaginous skeleton covered with muscles and skin. The nasal partition divides a nose cavity into two half. With the external environment this cavity is reported through nostrils, and with a nasopharynx — through back openings which call hoanam.
4. The mucous membrane of a cavity of a nose is covered by a vibrating epithelium, also it contains receptors of an olfactory nerve. In a nasal cavity of mammals the area of an olfactory epithelium is increased at the expense of nasal olfactory sinks which have an openwork interlacing of a trellised bone. Tissues of a nose are plentifully supplied with blood.
5. At impact of odorous substance on an olfactory epithelium its surface becomes electronegative. The shift of potential of a cellular membrane arising at the same time brings to emergence of a nervous impulse or change of its frequency. Receptors have various selectivity, to some substances they can be irresponsive.
6. The level of development of sense of smell at animals very strongly differs. The sense of smell helps them by search of food and sexual partners, serves for biocommunication and orientation. Distinguish from mammals the makrosomatik possessing keen sense of smell, marsupials, insectivorous, hoofed animals and predatory treat them. The animals who are poorly distinguishing smells are called by mikrosomatikam, primacies, including the person, whales and Pinnipedia treat them. For example, at a dog in 45 times more olfactory receptors, than at the person.
7. For sense of smell of the person various sensitivity in relation to different smells is characteristic. High concentration of odorous substance can irritate a mucous membrane of a nose, cause sneezing and even spasms of bronchial tubes. The sense of smell worsens or disappears at atrophic changes of a mucous membrane of a nose and also at a trauma of some departments of a brain. At violation of sense of smell the decrease in perception of smells or its aggravation is observed.