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Nasal Cavity Explained
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Overview
The nasal cavity is a large, air-filled space that opens at the nostrils, which are the two openings of the nose. The nasal septum is a partition that divides the cavity into two separate cavities. The nasal cavity is lined with a mucus membrane that helps keep your nose moist. The openings to the nasal cavity at the nostrils are lined by modified skin and have short hairs called vibrissae. The nasal cavity has many important anatomical landmarks. It has a roof (the uppermost part of the cavity), projections of mucosa from either side called concha, and small empty spaces (sphenoethmoidal recess) which are lined with olfactory mucosa. These barriers give mechanical protection from the invasion of pathogens.
In this article, we will cover everything you need to know about the nasal cavity and what are the most common diseases associated with this body part.
Structure
This cavity is divided into two separate cavities by the nasal septum. Each cavity consists of a roof, floor, and two walls on the sides; medial wall, and lateral wall. Each cavity comprises a nasal vestibule (which is the area below the nostrils), respiratory section, olfactory(smell-related) region, and some surrounding structures.
Nasal Vestibule
The area just below the nostrils is called vestibule, lined with course hairs which filter dust, sand and other particles keeping them from entering the lungs.
Respiratory section
This section of the cavity refers to the passages through which air travels to reach the trachea and eventually the lungs. The respiratory section of each nostril contains four conchae (protrusions) covered by the nasal mucosa. Underlying these conchae are small holes. These openings connect to the paranasal sinuses surrounding the cavity.
Olfactory Region
The olfactory mucosa is located in the upper region of the nasal cavity, supporting the olfactory mucus membrane for the sensation of smell.
Surrounding Structures
The surrounding structures include:
- Paranasal sinuses – this is an air-filled space in the nasal cavity
- Nasolacrimal duct – also known as the “tear duct”, it drains tears from the eye, through the lacrimal sac to the nasal cavity
Function
Olfaction
Olfaction is the sense of smell that happens at the apex of the cavity (olfactory area). This portion of the nasal cavity is lined with the cells called exteroception epithelial tissue, and it is interspersed with neurons containing sensory cilia.
The pathway of olfactory conduction goes from the olfactory receptor cells to the olfactory bulb in the forebrain, via the olfactory nerve.
Sensations of smell are experienced when certain chemical substances become dissolved in the thin layer of fluid covering the surface of the mucous membrane of special cells called olfactory receptor cells which come in contact with the olfactory hairs, or cilia.
Respiration
The inhaled air must be warmed and humidified before it reaches the lungs. This is mainly done in the upper respiratory portion of the nasal cavity which is lined with special cells known as the ciliated pseudostratified epithelium.
The moisture of the mucus plays a role in the humidification of inhaled air. Also, the turbinates slow down the airflow keeping the air in the nasal passageways long enough to be warmed and humidified.
The cilia in the nasal cavity also play a role in defending the organism, as they move the mucus and eventual pathogens (germs and bacteria) towards the throat (pharynx) to eliminate them.
Blood Supply
The nose receives blood from the internal and external carotid artery arteries.
The internal carotid artery branches to supply:
• Anterior ethmoidal artery
• Posterior ethmoidal artery
The ethmoidal arteries descend into the cavity through openings in the frontal bone (the cribriform plate.) to reach the nasal cavity.
External carotid branches that supply the nasal cavity include:
• Sphenopalatine artery
• Greater palatine artery
• Superior labial artery
• Lateral nasal arteries
Nerve Supply
The innervation of the nose is often functionally divided into special and general innervation.
Unique sensory innervation refers to the power of the nose to smell. The exteroception nerves are responsible for this. Branches of the first cranial nerve run through the cribriform plate to produce special sensory innervation to the nose.
General sensory innervation to the septum and the lateral walls is delivered by the nasopalatine nerve and the nasociliary nerve (branch of the ophthalmic division of the trigeminal nerve; the fifth cranial nerve.)
Clinical Relevance and Associated Disorders
Rhinitis
The inflammation and swelling of the mucus membrane of the nose. It is characterized by a runny nose, sneezing, and stuffiness.
It can be treated by:
- Avoidance of irritants
- Anti-histamines
- Antibiotics
- Desensitization
- Surgery
Epistaxis
Epistaxis is simply an elaborated medical term for a bloody nose. The nasal cavity is very vascularized so any trauma to the nose, dry nasal passageways, certain medications like blood thinners, or chronic conditions like a sex-linked disorder can commonly cause bleeding from a part of the nasal septum called the Little’s area.
Deviated Septum
A deviated septum occurs when the thin wall (nasal septum) between your nasal passages is displaced to one side. A deviated septum can develop in utero, or while the fetus is still in the womb, as well as during the birthing process.
The presence of a deviated septum can cause frontal headaches and bleeding from the nose.
Enlarged Turbinate
Turbinates are small structures inside the nose that cleanse and humidify the air that passes through the nostrils into the lungs. They are made of bone and soft tissue and are located inside the nose near the septum. Enlarged turbinates are a reaction to seasonal allergens. Sometimes, the enlargement is caused by environmental irritants. Chronic sinusitis, which causes persistent inflammation in the nasal passages, may also trigger chronic swelling of the turbinate. The treatment for enlarged Turbinates is often surgical reduction.
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