The External Nose
The external nose is a visible component of the face, projecting over and allowing entrance into the nasal cavity. This article will discuss the anatomy of the external nose – its skeletal structure, muscles, blood supply and innervation.
The external nose is said to have a pyramidal shape. The nasal root is located superiorly, and is continuous with the forehead. The apex of the nose ends inferiorly in a rounded ‘tip’. Spanning between the root and apex is the dorsum of the nose.
Located immediately inferiorly to the apex are the nares; piriform openings into the vestibule of the nasal cavity. The nares are bounded medially by the nasal septum, and laterally by the ala nasi (the lateral cartilaginous wings of the nose).
The skeleton of the external nose is made of both bony and cartilaginous components:
- Bony component – located superiorly, and is comprised of contributions from the nasal bones, maxillae and frontal bone.
- Cartilaginous component – located inferiorly, and is comprised of the two lateral cartilages, two alar cartilages and one septal cartilage. There are also some smaller alar cartilages present.
Whilst the skin over the bony part of the nose is thin, that overlying the cartilaginous part is thicker with many sebaceous glands. This skin extends into the vestibule of the nose via the nares. Here there are hairs which function to filter air as it enters the respiratory system.
More information can be found on the nasal skeleton here.
Clinical Relevance – Saddle Nose Deformity
The saddle nose deformity occurs primarily as a result of nasal trauma; whereby septal support to the nose is lost, and subsequently the middle part of the nose appears sunken. This is either a result of direct damage to the septal bone or cartilage, or a consequence of nasal septal haematoma.
As cartilage has no blood supply of its own, it relies on oxygen and nutrients diffusing from blood vessels in the surrounding perichondrium. A haematoma between these two structures can result in destruction of the septum, and therefore deformity of the nose.
A number of small muscles insert into the external nose, contributing to facial expression. All these muscles are innervated by branches of the facial nerve (CN VII).
The procerus muscle originates in the fascia overlying the nasal bone and lateral nasal cartilage, inserting into the inferior forehead. Contraction can depress the medial eyebrows, and wrinkles the skin of the superior dorsum.
The transverse portion of the nasalis muscle assists the procerus muscle in this action. Meanwhile the alar part of nasalis arises from the maxilla, inserting into the major alar cartilage. This allows the muscle to dilate the nares, “flaring” them. This action is assisted by the depressor septi nasi.
More information regarding these and surrounding muscles can be found in here.
Vessels and Lymphatics
The skin of the external nose receives arterial supply from branches of the maxillary and ophthalmic arteries. The septum and alar cartilages receive additional supply from the angular artery and lateral nasal artery. These are both branches of the facial artery (derived from the external carotid artery).
Venous drainage is into the facial vein, and then in turn into the internal jugular vein.
Lymphatic drainage from the external nose is via superficial lymphatic vessels accompanying the facial vein. These vessels, like all lymphatic vessels of the head and neck, ultimately drain into the deep cervical lymph nodes.
Clinical Relevance: Danger Triangle of the Face
The venous drainage of the nose and surrounding area is unique as a result of communication between the facial vein and cavernous sinus, via the ophthalmic vein.
As the cavernous sinus lies within the cranial cavity, this enables infections from the nasal area to spread to the brain. This retrograde spread of infection can therefore cause cavernous sinus thrombosis, meningitis or brain abscess.
Sensory innervation of the external nose is derived from the trigeminal nerve (CN V). The external nasal nerve, a branch of the ophthalmic nerve (CN V1), supplies the skin of the dorsum of nose, nasal alae and nasal vestibule. The lateral aspects of the nose are supplied by the infrorbital nerve, a branch of the maxillary nerve (CN v2).
Motor innervation to the nasal muscles of facial expression is via the facial nerve (CN VII).