|Anatomy and function of the nose|
With several different compartments, the nose is an intricate network of bones, cartilage, cells, blood vessels and nerves. The nose's form and function are closely related and all parts of the human nose work together to warm, filter and moisten the air that goes into the lungs, as well as send messages to the brain to enable the sense of smell.
Consisting of skin, bone, cartilage, blood vessels and nerves, the nose can be divided into two main parts - the external and the cavity. A wall called the nasal septum, which falls between the two nostrils and extends back behind the nose and into the nasal cavity, divides these sections vertically.
This term refers to the actual structure (similar to a three-sided pyramid) that protrudes from the face. The ridge that leads down from the forehead to the tip of the nose is called the bridge, or dorsum. The top-third section is made of bone and skin, while the bottom two-thirds are made of skin and cartilage. The skin of the dorsum and sides of the nose is thin, but is thicker over the tip and the nostrils. The skin also has more sweat and oil glands than other parts of the face. The cartilage that makes up the tip of the nose and nostrils is the most complex, as it is actually five separate pieces that are connected by membranes, and has a specific shape that varies for each person.
External at a glance:
• Located at the anterior margin of the ethmoid bone, the septal cartilage connects the nasal bones and forms the dividing wall of the nose.
• Situated below the inferior margin of the nasal bone, the lateral cartilage is flattened and triangular in shape. It connects the septal cartilage on either side.
• The greater alar cartilage is a thin, flexible plate that forms the tip of the nose and nostrils.
• Also known as the naris, a nostril is one of two openings to the nose.
• The columella is the strip of skin that separates the nostrils.
• The rhinion is the anterior tip at the end of the suture of the nasal bones.
The internal structure of the nose can be thought of as a tunnel with an opening on the face and an opening at the top of the throat. This tunnel, called the nasal cavity, is divided into a right and a left side by a bony and cartilaginous divider called the nasal septum. The top of the nasal cavity is divided from the anterior cranial cavity by a bone called the cribiform plate. The lateral walls on each side border with the maxillary, or cheek, bones. The floor of the nasal cavity is separated from the top of the mouth by the palatal bones.
The internal nasal valve involves the area bounded by upper lateral cartilage, septum, nasal floor, and anterior head of the inferior turbinate. This comprises the narrowest portion of the nasal airway in the leptorrhine nose. An angle wider than 15 degrees is generally needed in this area.
Inside the nose is lined with a moist, thin layer of tissue called a mucous membrane, which warms up the air and moistens it. This membrane makes mucous, which captures dust, germs and other small particles that could irritate the lungs.
The nose, being an air filter and conditioner for the lungs, contains hairs to keep out dust and microscopic particles that could hinder the breathing process. If something does get trapped in the nose, a sneeze is triggered to clear it out.
Further into the nose, smaller hairs called cilia move back and forth to keep the mucous out of the sinuses and back of the nose. Cilia can also be found lining the air passages to help move mucous out of the lungs. As the lungs need to be supplied with air that is about 35 degrees centigrade and 95 percent humidity, noses have to deliver air to the lungs at the right temperature. Hence, the cavity is also complete with shelves, called turbinates, which warm the air and add moisture to it before it reaches the lungs.
Internal at a glance:
• The olfactory nerve transmits the sense of smell from the nasal cavity to the brain.
• The hard palate separates the oral cavity from the nasal cavity, whereas the soft palate closes the nasal cavity from the oral cavity when swallowing.
• The passage that connects the nasal cavity to the top of the throat is called the nasopharynx.
• The Eustachian tube is the narrow channel that connects the middle ear and the nasopharynx.
• Also known as the superior nasal concha, the upper turbinate contains olfactory receptor cells.
• The middle turbinate is the spongy bone situated between the upper and lower meatuses.
• The lower turbinate, or inferior nasal concha, lies between the middle and lower meatuses.
• The upper, or superior, meatus is the nasal opening located between the upper and lower turbinates.
• The middle meatus runs from the anterior to the posterior end of the lower turbinate.
• The lower, or inferior, meatus is situated between the lower turbinate and the floor of the nasal cavity.
• A nasal meatus is one of the four portions (common, inferior, middle, and superior) of the nasal cavity on either side of the septum.
The sinuses are hollow areas within the bones of the skull that are lined with mucous membrane, also known as mucosa. By creating air-filled chambers within the skull bones, the sinuses may serve to decrease the weight of the head. They also add resonance to the voice.
Importantly, the sinuses help to cushion the eyes and brain in a severe injury to the face. They also help to warm and humidify the air that passes through the nasal passage.
Sometimes, the narrow openings that run from the nose to the sinuses become blocked and the lining of the sinuses becomes inflamed, which leads to sinusitis. This can cause many uncomfortable symptoms such as:
• Sensation of a build-up of pressure in the head
• Blocked or runny nose
• Feeling of nasal stuffiness
• Sore throat and cough.
A deviated septum may be caused by an injury or birth defect, and can be corrected through a procedure called septoplasty.
The nose has many physiologic functions, some of which include breathing, olfaction and taste.
Sense of smell
The nose is capable of distinguishing a large number of different odours. Some people have a great sense of smell, but others suffer from anosmia, a loss of the sense of smell.
It is common for individuals who have a cold or blocked nose and lose their sense of smell to report that food loses its taste. This is incorrect; the food has only lost its aroma, and taste (sweet, salty, sour, bitter) remains intact.
Evolution of the nose
The shape of an individual's nose seems to have evolved in response to environmental factors. In desert areas where the air is already heated but isn't moist enough, noses tend to be large and narrow. This is t ensure that air travelling up the nose has plenty of time to absorb moisture from the mucous membranes. In northern Europe, where the air is more humid but colder, noses are usually long and narrow to restrict airflow and give the air the time it needs to warm up before reaching the lungs. In more humid environments, shorter, wider noses enable the air to reach the lungs more quickly.