January 07, 2007

Anatomy of Human Nose


Anatomically, a nose is a protuberance in vertebrates that houses the nostrils, or nares, which admit and expel air for respiration.

As an interface between the body and the external world, the nose and associated structures frequently perform additional functions concerned with conditioning entering air (for instance, by warming and/or humidifying it) and by mostly reclaiming moisture from the air before it is exhaled (as occurs most efficiently in camels).

The visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils.
Adapted from: Wikipedia

Skin and soft tissues
Like the underlying bony-cartilaginous framework of the nose, the overlying skin may also be divided into vertical thirds. The skin of the upper third is fairly thick but tapers into a thinner mid-dorsal region. The inferior third regains the thickness of the upper third owing to the more sebaceous nature of the skin in the nasal tip. The dorsal skin is usually the thinnest of the 3 sections of the nose. The difference in the skin thickness must be appreciated during dorsal reduction.

The nasal muscles are encountered deep to the skin and comprise 4 principal groups: the elevators, the depressors, the compressor, and the dilators. The elevators include the procerus and levator labii superioris alaeque nasi. The depressors are made up of the alar nasalis and depressor septi nasi. The compressor of the nose is the transverse nasalis, whereas the dilators are the dilator naris anterior and posterior. The muscles are interconnected by an aponeurosis termed the nasal superficial musculoaponeurotic system (SMAS).

The internal nasal lining consists of squamous epithelium in the vestibule. This transitions to pseudostratified ciliated columnar respiratory epithelium with abundant seromucinous glands within the nose.

Blood supply
The nose, like the rest of the face, has an abundant blood supply. The arterial supply to the nose may be principally divided into (1) branches from the internal carotid, namely the branches of the anterior and posterior ethmoid arteries from the ophthalmic artery, and (2) branches from the external carotid, namely the sphenopalatine, greater palatine, superior labial, and angular arteries.

The external nose is supplied by the facial artery, which becomes the angular artery coursing over the superomedial aspect of the nose. The sellar and dorsal regions of the nose are supplied by branches of the internal maxillary artery (namely the infraorbital) and ophthalmic arteries (which are from the internal carotid system).

Internally, the lateral nasal wall is supplied by the sphenopalatine artery posteroinferiorly and by the anterior and posterior ethmoid arteries superiorly. The nasal septum also derives its blood supply from the sphenopalatine and the anterior and posterior ethmoid arteries with the added contribution of the superior labial artery (anteriorly) and the greater palatine artery (posteriorly). The Kiesselbach plexus, or the Little area, represents a region in the anteroinferior third of the nasal septum, where all 3 of the chief blood supplies to the internal nose converge.

Veins in the nose essentially follow the arterial pattern. They are significant for their direct communication with the cavernous sinus and for their lack of valves; these features potentiated the intracranial spread of infection. Even with the abundant blood supply of the nose, smoking does compromise postoperative healing.

Lymphatics arise from the superficial mucosa and drain posteriorly to the retropharyngeal nodes and anteriorly to the upper deep cervical nodes and/or submandibular glands

The sensation of the nose is derived from the first 2 branches of the trigeminal nerve. The following outline effectively delineates the respective sensory distribution of the nose and face of the trigeminal nerve.

Ophthalmic division
Lacrimal - Skin of lateral orbital area except lacrimal gland
Frontal - Skin of forehead and scalp
Supraorbital - Eyelid skin, forehead, and scalp
Supratrochlear - Medial eyelid and medial forehead
Nasociliary - Skin of the nose and mucous membrane of anterior nasal cavity
Anterior ethmoid - Anterior half of nasal cavity: (1) internal - ethmoid and frontal sinuses and (2) external - nasal skin from rhinion to tip
Posterior ethmoid - Superior half of nasal cavity, namely the sphenoid and ethmoids
Intratrochlear - Medial eyelids, palpebral conjunctiva, nasion, and bony dorsum
Maxillary division
Infraorbital - External nares
Superior posterior dental
Superior anterior dental - Mediates sneeze reflex
Sphenopalatine - Divides into lateral and septal branches and conveys sensation from posterior and central regions of the nasal cavity

The parasympathetic supply is derived from the greater superficial petrosal (GSP) branch of cranial nerve VII. The GSP joins the deep petrosal nerve (sympathetic supply), which comes from the carotid plexus to form the vidian nerve in the vidian canal. The vidian nerve travels through the pterygopalatine ganglion (with only the parasympathetic nerves forming synapses here) to the lacrimal gland and glands of the nose and palate via the maxillary division of the trigeminal nerve.

Bony anatomy
Superiorly, the paired nasal bones are attached to the frontal bone. Superolaterally, they are connected to the lacrimal bones, and inferolaterally, they are attached to the ascending processes of the maxilla. Posterosuperiorly, the bony nasal septum is composed of the perpendicular plate of the ethmoid. Posteroinferiorly lies the vomer, which in part forms the choanal opening into the nasopharynx. The floor comprises the premaxilla and the palatine bones.

The lateral nasal walls contain 3 pairs each of small, thin, shell-like bones: the superior, middle, and inferior conchae, which form the bony framework of the turbinates. Lateral to these curved structures lies the medial wall of the maxillary sinus.

Inferior to the turbinates lies a space called a meatus, with names corresponding to the above turbinate, eg, superior turbinate, superior meatus. The roof of the nose internally is formed by the cribriform plate of the ethmoid. Posteroinferior to this structure, sloping down at an angle, is the bony face of the sphenoid sinus.

Cartilaginous pyramid
The cartilaginous septum extends from the nasal bones in the midline above to the bony septum in the midline posteriorly, then down along the bony floor. It assumes a quadrangular shape. Its upper half is flanked by 2 triangular-to-trapezoidal cartilages: the upper lateral cartilages. These upper lateral cartilages are fused to the dorsal septum in the midline and attached to the bony margin of the pyriform aperture laterally by loose ligaments. The inferior ends of the upper lateral cartilages are free. The internal area or angle formed by the septum and upper lateral cartilage constitutes the internal valve. Adjacent sesamoid cartilages may be found lateral to the upper lateral cartilages in the fibroareolar connective tissue. These are found variably.
Beneath the upper lateral cartilages lie the lower lateral cartilages. The paired lower lateral cartilages swing out from medial attachments to the caudal septum in the midline, called the medial crura, to an intermediate crus area. They finally flare out superolaterally as the lateral crura. These cartilages are frequently mobile, in contradistinction to the upper lateral cartilages.

In some individuals, evidence of a scroll may exist, that is, an outcurving of the lower borders of the upper lateral cartilages and an incurving of the cephalic borders of the alar cartilages. Several variations exist.

Adapted from: EMedicine