A diagram illustrating the human nose generally encompasses both its external and internal components. On the outside, it displays the nasal bridge, tip, nares (nostrils), alae (the sides of the nostrils), and columella (the tissue that divides the nostrils). Internally, the nasal cavity is partitioned by the septum and contains turbinates (conchae) and sinuses.
External Nose:
Nasal Bridge: The bony upper section of the nose.
Nasal Tip: The soft, rounded extremity of the nose.
Nares (Nostrils): The two apertures that permit air to enter the nasal passage.
Alae: The curved edges of the nostrils.
Columella: The tissue that divides the nostrils.
Internal Nose:
Nasal Cavity: The area within the nose, separated into two by the nasal septum.
Nasal Septum: A structure composed of bone and cartilage that divides the left and right portions of the nasal cavity.
Turbinates (Conchae): Bony projections lined with mucous membrane that assist in warming and humidifying the air.
Sinuses: Air-filled spaces within the skull that are connected to the nasal cavity.
The upper air passages pertain to the respiratory organs located in the human head. These include the nose and throat (pharynx). When breathing in, air first enters through the nose, where it is initially filtered by a hair-like structure. A bifurcated network of blood vessels within the nasal mucous membrane serves to warm the incoming air. Additionally, mucous droplets from the nasal mucous membrane help to moisten the air. This process prepares the air for the conditions found within the lungs (pulmo). The paranasal sinuses (sinus paranasales), which are connected to the nasal cavity, also play a role in this adaptation. From the nose, the air travels to the throat, which comprises various sections, with the esophagus and windpipe intersecting in the medial throat (mesopharynx). The inhaled air continues through the throat to the larynx (larynx) and then to the lower air passages. In contrast to the sense of taste, the sense of smell is capable of distinguishing a far greater variety of sensations. The qualitative categorization seen in taste (bitter, sweet, sour, salty) does not apply as straightforwardly to smell. Instead, scent classes are utilized to convey the experience (pungent, sweaty, rotten, etc.). The sensory receptors of the olfactory organ (organum olfactus) are situated at the beginning of the respiratory tracts and are approximately the size of a dime, located on the upper nasal wall and the septum. Due to pigmentation, the olfactory region appears yellow, which contrasts with the red membrane. It remains uncertain whether this pigmentation plays a role in the sense of smell. However, it is noted that animals lacking pigmentation (albinos) do not possess a sense of smell. The tissue within the olfactory region, containing over 10 million receptor cells, is approximately 50 µm thicker than the epithelium of the respiratory tracts. The olfactory cells feature very fine hairs (cilia), with up to 12 per cell, and are coated in mucus. Nerve processes from the olfactory cells bundle together as fibers leading to the anterior section of the olfactory cortex at the base of the frontal brain. The olfactory cells are separated from the olfactory cortex by a very thin bone known as the sieve.. The olfactory cells are separated from the olfactory cortex by very thin bone, the sieve, through which the nerve fibers pass through small openings. After appropriate processing of the olfactory information, the smell becomes known.
Olfactory cells are chemical receptors, i.e. the stimulus of the olfactory cells is the result of a chemical process on the surface of the hairs. How the molecular reaction occurs, with which hundreds of different smells are distinguished, is unclear. Gaseous substances are easier to smell. A water-soluble property increases the ability to smell because the smell molecules enter the air through evaporation.
