Human nose
The human nose is the first organ of the respiratory system. It is also the principal organ in the olfactory system. The shape of the nose is determined by the nasal bones and the nasal cartilages, including the nasal septum, which separates the nostrils and divides the nasal cavity into two.
The nose has an important function in breathing. The nasal mucosa lining the nasal cavity and the paranasal sinuses carries out the necessary conditioning of inhaled air by warming and moistening it. Nasal conchae, shell-like bones in the walls of the cavities, play a major part in this process. Filtering of the air by nasal hair in the nostrils prevents large particles from entering the lungs. Sneezing is a reflex to expel unwanted particles from the nose that irritate the mucosal lining. Sneezing can transmit infections, because aerosols are created in which the droplets can harbour pathogens.
Another major function of the nose is olfaction, the sense of smell. The area of olfactory epithelium, in the upper nasal cavity, contains specialised olfactory cells responsible for this function.
The nose is also involved in the function of speech. Nasal vowels and nasal consonants are produced in the process of nasalisation. The hollow cavities of the paranasal sinuses act as sound chambers that modify and amplify speech and other vocal sounds.
There are several plastic surgery procedures that can be done on the nose, known as rhinoplasties available to correct various structural defects or to change the shape of the nose. Defects may be congenital, or result from nasal disorders or from trauma. These procedures are a type of reconstructive surgery. An elective procedure to change a nose shape is a type of cosmetic surgery.
Structure
Several bones and cartilages make up the bony-cartilaginous framework of the nose, and the internal structure. The nose is also made up of types of soft tissue such as skin, epithelia, mucous membrane, muscles, nerves, and blood vessels. In the skin there are sebaceous glands, and in the mucous membrane there are nasal glands. The bones and cartilages provide strong protection for the internal structures of the nose. There are several muscles that are involved in movements of the nose. The arrangement of the cartilages allows flexibility through muscle control to enable airflow to be modified.Bones
The bony structure of the nose is provided by the maxilla, frontal bone, and a number of smaller bones.The topmost bony part of the nose is formed by the nasal part of the frontal bone, which lies between the brow ridges, and ends in a serrated nasal notch. A left and a right nasal bone join with the nasal part of the frontal bone at either side; and these at the side with the small lacrimal bones and the frontal process of each maxilla. The internal roof of the nasal cavity is composed of the horizontal, perforated cribriform plate of the ethmoid bone through which pass sensory fibres of the olfactory nerve. Below and behind the cribriform plate, sloping down at an angle, is the face of the sphenoid bone.The wall separating the two cavities of the nose, the nasal septum, is made up of bone inside and cartilage closer to the tip of the nose. The bony part is formed by the perpendicular plate of the ethmoid bone at the top, and the vomer bone below. The floor of the nose is made up of the incisive bone and the horizontal plates of the palatine bones, and this makes up the hard palate of the roof of the mouth. The two horizontal plates join at the midline and form the posterior nasal spine that gives attachment to the musculus uvulae in the uvula.
The two maxilla bones join at the base of the nose at the lower nasal midline between the nostrils, and at the top of the philtrum to form the anterior nasal spine. This thin projection of bone holds the cartilaginous center of the nose. It is also an important cephalometric landmark.
Cartilages
The nasal cartilages are the septal, lateral, major alar, and minor alar cartilages. The major and minor cartilages are also known as the greater and lesser alar cartilages. There is a narrow strip of cartilage called the vomeronasal cartilage that lies between the vomer and the septal cartilage.The septal nasal cartilage, extends from the nasal bones in the midline, to the bony part of the septum in the midline, posteriorly. It then passes along the floor of the nasal cavity. The septum is quadrangular–the upper half is attached to the two lateral nasal cartilages, which are fused to the dorsal septum in the midline. The septum is laterally attached, with loose ligaments, to the bony margin of the anterior nasal aperture, while the inferior ends of the lateral cartilages are free. The three or four minor alar cartilages are adjacent to the lateral cartilages, held in the connective tissue membrane, that connects the lateral cartilages to the frontal process of the maxilla.
The nasal bones in the upper part of the nose are joined by the midline internasal suture. They join with the septal cartilage at a junction known as the rhinion. The rhinion is the midline junction where the nasal bone meets the septal cartilage. From the rhinion to the apex, or tip, the framework is of cartilage.
The major alar cartilages are thin, U-shaped plates of cartilage on each side of the nose that form the lateral and medial walls of the vestibule, known as the medial and lateral crura. The medial crura are attached to the septal cartilage, forming fleshy parts at the front of the nostrils on each side of the septum, called the medial crural footpods. The medial crura meet at the midline below the end of the septum to form the columella and lobule. The lobule contains the tip of the nose and its base contains the nostrils. At the peaks of the folds of the medial crura, they form the alar domes the tip-defining points of the nose, separated by a notch. They then fold outwards, above and to the side of the nostrils forming the lateral crura. The major alar cartilages are freely moveable and can respond to muscles to either open or constrict the nostrils.
There is a reinforcing structure known as the nasal scroll that resists internal collapse from airflow pressure generated by normal breathing. This structure is formed by the junction between the lateral and major cartilages. Their edges interlock by one scrolling upwards and one scrolling inwards.
Muscles
The muscles of the nose are a subgroup of the facial muscles. They are involved in respiration and facial expression. The muscles of the nose include the procerus, nasalis, depressor septi nasi, levator labii superioris alaeque nasi, and the orbicularis oris of the mouth. As are all of the facial muscles, the muscles of the nose are innervated by the facial nerve and its branches. Although each muscle is independent, the muscles of the nose form a continuous layer with connections between all the components of the muscles and ligaments, in the nasal part of a superficial muscular aponeurotic system. The SMAS is continuous from the nasofrontal process to the nasal tip. It divides at level of the nasal valve into superficial and deep layers, each layer having medial and lateral components.The procerus muscle produces wrinkling over the bridge of the nose, and is active in concentration and frowning. It is a prime target for Botox procedures in the forehead to remove the lines between the eyes.
The nasalis muscle consists of two main parts: a transverse part called the compressor naris, and an alar part termed the dilator naris. The compressor naris muscle compresses the nostrils and may completely close them. The alar part, the dilator naris mainly consists of the dilator naris posterior, and a much smaller dilator naris anterior, and this muscle flares the nostrils. The dilator naris helps to form the upper ridge of the philtrum. The anterior, and the posterior dilator naris,, give support to the nasal valves.
The depressor septi nasi may sometimes be absent or rudimentary. The depressor septi pulls the columella, the septum, and the tip of the nose downwards. At the start of inspiration, this muscle tenses the nasal septum and with the dilator naris widens the nostrils.
The levator labii superioris alaeque nasi divides into a medial and a lateral slip. The medial slip blends into the perichondrium of the major alar cartilage and its overlying skin. The lateral slip blends at the side of the upper lip with the levator labii superioris, and with the orbicularis oris. The lateral slip raises the upper lip and deepens and increases the curve above the nasolabial furrow. The medial slip pulls the lateral crus upwards and modifies the curve of the furrow around the alae, and dilates the nostrils.
Soft tissue
The skin of the nose varies in thickness along its length. From the glabella to the bridge, the skin is thick, fairly flexible, and mobile. It tapers to the bridge where it is thinnest and least flexible as it is closest to the underlying bone. From the bridge until the tip of the nose the skin is thin. The tip is covered in skin that is as thick as the top section, and has many large sebaceous glands.The thickness of the skin varies but is still separated from the underlying bones and cartilage by four layers – a superficial fatty layer; a fibromuscular layer continued from the SMAS; a deep fatty layer, and the periosteum.
Other areas of soft tissue are found where there is no support from cartilage; these include an area around the sides of the septum – the paraseptal area – an area around the lateral cartilages, an area at the top of the nostril, and an area in the alae.
External nose
The nasal root is the top of the nose that attaches the nose to the forehead. The nasal root is above the bridge and below the glabella, forming an indentation known as the nasion at the frontonasal suture where the frontal bone meets the nasal bones. The nasal dorsum also known as the nasal ridge is the border between the root and the tip of the nose, which in profile can be variously shaped. The ala of the nose is the lower lateral surface of the external nose, shaped by the alar cartilage and covered in dense connective tissue. The alae flare out to form a rounded eminence around the nostril. Sexual dimorphism is evident in the larger nose of the male. This is due to the increased testosterone that thickens the brow ridge and the bridge of the nose making it wider.Differences in the symmetry of the nose have been noted in studies. Asymmetry is predominantly seen in wider left-sided nasal and other facial features.