Special Sense Organs: Nose.
Introduction:
The sense of smell or olfaction originates in the superior part of the nasal cavity.
The nose contains 10-100 millions receptors for the sense of smell.
Olfactory receptors react to odorant molecules in inspired air of the nasal cavity.
The sense of smell may affect the appetite. If the odours are pleasant the appetite may improve and vice versa.
From the olfactory portion of nasal cavity nerve fibres pass through the cribriform plate of the ethmoid bone to the olfactory bulb. From this region nerve fibres are passed to the olfactory area in the temporal lobe of the cerebral cortex. In this area the impulses are interpreted and odour perceived.
‘Sniffing’ concentrates more molecules in the roof of the nose. This increases the stimulation of the olfactory receptor and the perception of the smell.
Nose:
Nose, the prominent organ between the eyes that act as the entrance to the respiratory tract and contains the olfactory receptors.
It provides air for respiration, serves the sense of smell, conditions the air by filtering, warming, and moistening it, and cleans itself of foreign debris extracted from inhalations.
The nose has two cavities, separated from one another by a wall of cartilage called the septum. The external openings are known as nares or nostrils. The roof of the mouth and the floor of the nose are formed by the palatine bone, the mouth part of which is commonly called the hard palate; a flap of tissue, the soft palate, extends back into the nasopharynx, the nasal portion of the throat, and during swallowing is pressed upward, thus closing off the nasopharynx so that food is not lodged in the back of the nose.
Structure of Nasal Cavity:
The shape of the nasal cavity is complex.
The forward section, within and above each nostril, is called the vestibule.
Behind the vestibule and along each outer wall are three elevations, running generally from front to rear.
Each elevation, called a nasal concha or turbinate, hangs over an air passage.
Beside and above the uppermost concha is the olfactory region of the nasal cavity.
The rest of the cavity is the respiratory portion.
The respiratory area is lined with a moist mucous membrane with fine hairlike projections known as cilia, which serve to collect debris.
Mucus from cells in the membrane wall also helps to trap particles of dust, carbon, soot, and bacteria. Sinus cavities are located in the bony skull on both sides of the nose.
In the olfactory (smelling) portion of the nose, most of the lining is mucous membrane.
A small segment of the lining contains the nerve cells that are the actual sensory organs.
Fibres, called dendrites, which project from the nerve cells into the nasal cavity, are covered only by a thin layer of moisture.
The moisture dissolves microscopic particles that the air has carried into the nose from odour-emitting substances, and the particles dissolved in the fluid stimulate the olfactory nerve cells chemically.
Commonly Asked Questions:
Write in short about the organ of Smell.