Session 7: The Nose and Paranasal Sinuses Flashcards
Describe the multiple functions of the nose. What is respiratory epithelium?
The nose has multiple functions. It is an organ of olfaction (smell), the uppermost part of the respiratory tract and plays an important role in speech.
[*] The nose, nasal cavities and the paranasal sinuses constitute the upper part of the respiratory system superior to the hard palate.
- Inferiorly, the hard palate, made up of the palatine and maxillary bones, separates the nasal and oral cavities.
[*] Each nasal cavity comprises an area of olfaction (smelling) and an area of respiratory function (breathing).
[*] Other functions of the nose and nasal cavities include filtration of dust and humidification of inspired air.
[*] The nasal cavities receive secretions from the paranasal sinuses and the nasolacrimal ducts – drain and eliminate paranasal sinus and nasolacrimal duct secretions.
[*] The nasal cavities and the paranasal sinuses are lined by respiratory epithelium – **pseudostratified columnar ciliated. **
Apart from the olfactory region - Olfactory epithelium (with non-motile cilia in the lamina propria etc), olfactory nerves and olfactory bulb
Describe how the nasal cavities open into the nasopharynx
[*] The nasal cavities open into the nasopharynx (at inferior meatus) that contains the opening of the Eustachian tube.
[*] The nasopharynx has a ring of lymphoid tissue (adenoids – nasopharyngeal tonsils) that may be particularly large in children.
Describe the external nose including its skeleton
[*] The external nose is the visible portion that projects from the face. It has both bony and (predominantly) cartilaginous components and provides the opening into the nasal cavity. The nostrils are bounded laterally by alae and the skin covering the nose extends upwards into the vestibule.
- The limen nasi is a ridge marking the boundary between the nasal cavity proper and the vestibule of the nose.
- Large hairs provide mechanical impedance to any inhaled particulates into nasal cavity.
[*] The skeleton of the external nose comprises bony and cartilaginous parts
- The bony part consists of nasal bones, frontal processes of the maxillae, nasal part of the frontal bone (and its nasal spine) and the bony nasal septum
- The cartilaginous part consist of 5 cartilages (2 lateral, 2 alar and a septal cartilage)
Describe the floor and roof of the nasal cavity
- Each nasal cavity extends between the anterior nasal aperture (naris, nares pl.) and posterior nasal aperture (choana, choanae pl.).
- The cavity opens into the nasopharynx
- The roof of the cavity is formed by the cribriform plate of the ethmoid bone
- The floor is formed by the palatal shelf (palatine process) of the maxilla and the horizontal process of palatine bone
Describe the medial and lateral walls of the nasal cavity
- Medial wall: nasal septum (the main components of which are the perpendicular plate of the ethmoid, vomer, septal cartilage and the nasal crests of the maxillary and palatine bones).
- The lateral wall of the nasal cavity has three projections (turbinates or conchae) that divide the cavity into four passages within the cavity (one unpaired – the sphenoethmoidal recess - and three paired). The conchae curve inferomedially, hanging like short curtains from the lateral wall of the nasal cavity. The conchae are scroll-like structures that offer a vast surface area for heat exchange and create turbulence in the nasal cavity.
What bones are the conchae derived from?
The inferior concha is the longest and broadest and is formed by an independent bone (the Inferior Concha).
The middle and superior conchae are the **medial processes of the Ethmoid Bone. **
Describe the mucosal lining of the nasal cavity
The mucous membrane lining the turbinates is highly vascular, for the purpose of humidifying the inspired air. It is continuous with areas (paranasal sinuses) draining into the cavity. The nasal cavity is completely lined with this mucosal lining apart from the vestibule.
Describe the Sphenoethmoid Recess
The area between the superior turbinate and the cribriform plate of the ethmoid bone is called the sphenoethmoid recess.
- The lining epithelium of the mucous membrane in this region is modified for the purpose of olfaction; axonal processes of the olfactory cells pass through the cribriform plate and penetrate the meninges before entering the olfactory bulb.
- Each of the paired sphenoidal sinuses (or sometimes a person only has one) open into the roof of the nasal cavity via apertures on the posterior wall of the sphenoethmoidal recess, directly above the choana.
- Openings: Cribiform plate (where olfactory nerve runs), sphenopalatine foramine, incisive foramen, foramen cecum (nasal veins to superior sagittal sinus in some individuals run here)
Describe the Superior Meatus
The area, which lies between the superior and middle turbinate, is called the superior meatus; the posterior ethmoidal air sinuses (cells) open into this area via one or more openings.
Describe the Middle Meatus
The middle meatus, lying between the middle and inferior turbinate has the opening of the frontal air sinus anteriorly and the opening of the maxillary air sinus posteriorly.
Both these openings lie at either end of a crescenteric groove, the semilunar hiatus.
The anterior ethmoidal air sinuses (cells) also open into the middle meatus.
Describe the Inferior Meatus
The inferior meatus, lying underneath the inferior turbinate, is a horizontal passage containing the opening of the nasolacrimal duct that drains tears from the orbit.
Describe the Nasal Septum
- The anterior portion of the nasal septum is cartilaginous
- The central portion is formed by the perpendicular plate of the ethmoid bone
- The posterior portion is formed by the vomer bone
Describe the blood supply to the nasal cavity and where an epitaxis occurs
The arterial blood supply to the medial and lateral wall of the nasal cavity is very rich.
- Branches of the Ophthalmic Artery (branch of the internal carotid artery) and Branches of the Maxillary and Facial arteries (branches of the external carotid artery) are involved.
- Facial Artery => Branch Superior Labial Artery
- Maxillary Artery => Sphenopalatine artery and Greater palatine artery
- Opthalmic Artery => Anterior ethmoidal artery and posterior ethmoidal artery
The anterior part of the nasal septum has an area (Kiesselbach or Little’s area) that is rich in capillaries where all the arteries supplying the septum anastomose.
It is in this area where profuse bleeding occurs during “nose bleeds’.
- Rupture of blood vessels leads to spurting blood
Describe the venous drainage to the nasal cavity
A rich submucosal venous plexus, deep to the nasal mucosa, drains into the
- Cavernous Sinus
- Facial Vein
- Pterygoid plexus
Describe the innervation of the nose and nasal mucosa
Special Sensory (smell)
- Olfactory nerve (CN I)
General Sensory – Posteroinferior Nasal Mucosa
- Maxillary Division of the Trigeminal Nerve (V2)
- Greater palatine nerve branch of maxillary nerve => supplies lateral wall
- Nasopalatine Nerve branch of maxillary nerve => supplies septum
General Sensory – Anterosuperior Nasal Mucosa
- Ophthalmic Division of the Trigeminal Nerve (CN V1)
- Anterior and Posterior Ethmoidal Nerves (branches of the nasociliary nerve which is a branch of the ophthalmic nerve)
General Sensory – External Nose
- External Nasal Nose (CN V1)
- Infraorbital Nerve (CN V2)
Compare the epithelium of the respiratory region with the olfactory region
- Respiratory Region: pseudostratified columnar ciliated with goblet cells
- Olfactory Region: olfactory cells with olfactory receptors – non-motile cilia in the lamina propria. The olfactory cells are bipolar neurons which congregate to form the olfactory nerves which terminate at the olfactory bulb. The apical poles of these neurons are covered with non-motile cilia, with the plasma membrane containing odorant-binding proteins acting as olfactory receptors. The incoming odorants are made soluble by the serous secretion from Bowman’s glands, located in the lamina propria of the mucosa.
Describe the Ethmoid Bone in detail
[*] The crista galli is a median ridge of bone that projects from the cribiform plate of the ethmoid bone.
[*] The falx cerebri is a strong fold of dura mater that descends vertically in the longitudinal fissure between the cerebral hemispheres. It is narrow in front, where it is attached to the crista galli of the ethmoid; and broad behind, where it is connected with the upper surface of the tentorium cerebelli.
[*] Olfactory bulbs lie on either side of the crista galli on top of the cribiform plate. This is how olfactory nerve fibres enter the cranial cavity.
[*] The nasal cavity is connected to the anterior cranial fossa through the cribiform plate – potential route for spread of infection.
Describe the foramen in the nasal cavity
- The sphenopalatine foramen is a foramen in the skull that connects the nasal with the pterygopalatine fossa. It transmits the sphenopalatine artery and vein and the posterior superior lateral nasal nerve and nasopalatine nerves.
- The incisive foramen, aka the anterior palatine foramen, is a funnel-shaped opening in the bone of the oral hard palate immediately behind the incisor teeth. It is continuous with the incisive canal, this foramen or group of foramina are located posterior to the central incisor teeth in the incisive fossa of the maxilla. The incisive foramen receives the nasopalatine nerves from the floor of the nasal cavity along with the sphenopalatine artery, supplying the oral mucosa covering the hard palate of the mouth.
- Foramen cecum may not be present in some individuals.
Describe the Frontal Sinuses
[*] The Right and Left Frontal Sinuses are between the outer and inner tables of the frontal bone, posterior to the superciliary arches and the root of the nose.
[*] They are usually detectable in children by 7 years of age (not present at birth). Variable in size
[*] They each drain through a Frontonasal Duct into the ethmoidal infundibulum (effectively the duct travels through the ethmoid bone), which opens into the semilunar hiatus of the Middle Nasal Recess.
[*] The frontal sinuses are innervated by branches of the supra-orbital nerves (CN V1).
Describe the Ethmoidal Sinuses
[*] The Ethmoidal cells (sinuses) are small invaginations of the mucous membrane of the middle and superior nasal recesses into the Ethmoid bone. The small cavities are located in the lateral mass of the ethmoid bone between the nasal cavity and the orbit.
[*] The Ethmoidal cells usually are not visible in plain radiographs before 2 years of age.
[*] The Anterior Ethmoidal Cells drain directly or indirectly into the middle nasal recess through the ethmoidal infundibulum.
[*] The Middle Ethmoidal Cells open directly into the middle nasal recess (meatus)
[*] The Posterior Ethmoidal Cells, which form the ethmoidal bulla, open directly into the superior nasal recess (meatus). NB: the superior meatus is the smallest of the passageways within the nasal cavity.
[*] The ethmoidal sinuses are supplied by the anterior and posterior ethmoidal branches of the nasociliary nerves (CN V1)
Describe the Sphenoidal Sinuses
[*] The Sphenoidal Sinuses are located in the body of the sphenoid (unevenly divided by a bony septum) and may extend into the wings of the bone (in elderly people).
[*] The body of the sphenoid is fragile (because of the sinuses), and only thin plates of bone separate the sinuses from several important structures (optic nerves and chiasm, the pituitary gland, internal carotid arteries and cavernous sinuses). Related to:
- Pituitary fossa (pituitary glands lies in the sella turcica in the sphenoid bone), belongs to middle cranial fossa
- Cavernous sinus and ICA
- Posterior cranial fossa and pons
- (Effectively forms) roof of nasopharynx
[*] The posterior ethmoidal artery and nerve supply the sphenoidal sinuses.
[*] They are small at birth, enlarging after puberty
[*] They drain directly into the Sphenoethmoidal Recess
Describe the Maxillary Sinuses§
Of all the paranasal sinuses, the maxillary sinus is the largest and occupies almost the whole of the maxilla. Because of the superior location of this opening, it is impossible for the sinus to drain when the head is erect until the sinus is full.
[*] They drain by one or more openings, the Maxillary Ostium (ostia), into the middle nasal recess by way of the semilunar hiatus.
[*] Roof = floor of orbit
[*] Floor = alveolar part maxilla. The roots of the maxillary teeth, particularly the first two molars, often produce conical elevations in the floor of the maxillary sinus.
[*] Poteriorly = Pterygopalatine and infratemporal fossae
[*] Present at birth, enlarging from about 8 years
[*] The arterial supply of the maxillary sinus is mainly from superior alveolar branches of the maxillary artery; however branches of the greater palatine artery supply the floor of the sinus.
[*] Innervation of the maxillary sinus mucosa is from the anterior, middle and posterior superior alveolar nerves, branches of CN V2
Summarise where all the sinuses drain into. What epithelium do they have?
