Nasa Cavity:Divisions and Boundaries:Skeleton and cartilages:Paranasal air sinuses:Neurovascular supply Olaleye O.O. 2B10
Introduction:The nasal cavities are the uppermost parts of the respiratory tract which contain theolfactory receptors.They are elongated wedge-shaped spaces with a large inferior base and a narrowsuperior apex.They are held open by a skeletal framework consisting mainly of bone and cartilage.The smaller anterior regions of the cavities are enclosed by the external nose whereasthe larger posterior regions are more central within the skull.The anterior apertures of the nasal cavities are the NARES, which open onto theinferior surface of the nose.The posterior apertures are the CHOANAE, which open into the nasopharynx.
The nasal cavities are separated:•from each other by a midline, NASAL SEPTUM;•from the oral cavity below by the HARD PALATE;•from the cranial cavity above by parts of the •FRONTAL, •ETHMOID, •SPHENOID BONESLateral to the nasal cavities are the ORBITS.
Boundaries of the Nasal CavityEach nasal cavity has;• a floor,• roof,•medial wall, and•lateral wall
Lateral wall: The lateral wallis characterized by threecurved shelves of boneCONCHAE, which are oneabove the other and projectmedially and inferiorlyacross the nasal cavity. Themedial, anterior andposterior margins of theconchae are free.
The conchae divide each nasal cavity into four air channels;•an inferior nasal meatus between the inferior concha and the nasal floor;•a middle nasal meatus between the inferior and middle concha;•a superior nasal meatus between the middle and superior concha; and•a spheno-ethmoidal recess between the superior concha and the nasal roof.
These conchae, increase the surface area of contact between tissues ofthe lateral wall and the respired air.The openings of the paranasal sinuses, which are extensions of the nasalcavity that erode into the surrounding bones during childhood and earlyadulthood, are on the lateral wall and roof of the nasal cavities.In addition, the lateral wall also contains the opening of the nasolacrimal duct,which drains tears from the eye into the nasal cavity.
Regions of the Nasal CavitiesEach nasal cavity consists of three general regions- •the nasal vestibule, •the respiratory region, and •the olfactory region.
The nasal vestibule is a small dilated space just internal to the naristhat is lined by skin and contains hair follicles.The respiratory region is the largest part of the nasal cavity, has a richneurovascular supply, and is lined by respiratory epithelium composedmainly of ciliated and mucous cells.The olfactory region is small, is at the apex of each nasal cavity, islined by olfactory epithelium, and contains the olfactory receptors.NB: In addition to housing receptors for the sense of smell (olfaction),the nasal cavities adjust the temperature and humidity of respired air,and trap and remove particulate matter from the airway.
Innervation and blood supplyThree cranial nerves innervates the nasal cavities.•olfaction is carried by the olfactory nerve [I];•general sensation is carried by the trigeminal nerve [V], • the anterior region by the ophthalmic nerve [V1], • and the posterior region by the maxillary nerve [V2];•All glands are innervated by parasympathetic fibers in the facial nerve [VII] (greaterpetrosal nerve), which joins branches of the maxillary nerve [V2] in the pterygopalatinefossa.
Sympathetic fibers are ultimately derived from the T1 spinal cord level. Theysynapse mainly in the superior cervical sympathetic ganglion andpostganglionic fibers reach the nasal cavities along blood vessels, or byjoining branches of the maxillary nerve [V2] in the pterygopalatine fossa.
Blood supply to the nasal cavities is by:•terminal branches of the maxillary and facial arteries, which originate fromthe external carotid artery;•from ethmoidal branches of the ophthalmic artery, which originates from theinternal carotid artery.
Skeletal frameworkBones that contribute to the skeletal framework of the nasal cavitiesinclude:•the unpaired ethmoid, sphenoid, frontal bone, and vomer;•the paired nasal, maxillary, palatine and lacrimal bones, and inferiorconchae.Of all the bones associated with the nasal cavities, the ethmoid is akey element.
Ethmoid bone: The single ethmoid bone is one of the most complex bones inthe skull. It contributes to the roof, lateral wall, and medial wall of both nasalcavities, and contains the ethmoidal cells, ethmoidal sinuses. The ethmoidbone is cuboidal in overall shape and is composed of two rectangular box-shaped, ethmoidal labyrinths, one on each side, united superiorly across themidline by a perforated sheet of bone ,the cribriform plate. A second sheet ofbone, perpendicular plate, descends vertically in the median sagittal plane fromthe cribriform plate to form part of the nasal septum.
Each ethmoidal labyrinth is composed of two delicate sheets of bone, whichsandwich between them the ethmoidal cells.•the lateral sheet of bone, the orbital plate, is flat and forms part of themedial wall of the orbit;
•the medial sheet of bone forms the upper part of the lateral wall of the nasal cavityand is characterized by two processes and a swelling; the two processes are curvedshelves of bone (the superior and middle conchae), which project across the nasalcavity and curve downwards ending in free medial margins, while inferior to the originof the middle concha, the middle ethmoidal air cells form a prominent bulge,ethmoidal bulla, on the medial wall of the labyrinth.
Paranasal sinuses: There are four paranasal air sinuses;•the ethmoidal cells,•the sphenoidal,•maxillary, and•frontal sinusesEach is named according to the bone in which it is found.
The paranasal sinuses develop as outgrowths from the nasalcavities and erode into the surrounding bones.All paranasal sinuses are:•Lined by respiratory mucosa, which is ciliated and mucussecreting;•Open into the nasal cavities;•Innervated by branches of the Trigeminal nerve [V].
Frontal sinuses:•one on each side,• are variable in size and• they are the most superiorof the sinuses.•Each is triangular in shapeand•is in the part of the frontalbone under the forehead.
Each frontal sinus drains onto the lateral wall of the middle meatus via thefrontonasalduct, which penetrates the ethmoidal labyrinth and continues as the ethmoidalinfundibulum at the front end of the hiatus semilunaris.They are innervated by branches of the ophthalmic nerve (V1).Their blood supply is from branches of the anterior ethmoidal arteries
Ethmoidal cells:The ethmoidal cells on each side fill the ethmoidal labyrinth. Each cluster of cells is separated fromthe orbit by the thin orbital plate of the ethmoidal labyrinth, and from the nasal cavity by the medialwall of the ethmoidal labyrinth. The ethmoidal cells are formed by a variable number of individualair chambers, which are divided into anterior, middle, and posterior ethmoidal cells based onthe location of their apertures on the lateral wall of the nasal cavity:•the anterior ethmoidal cells open into the ethmoidal infundibulum or the frontonasal duct;•the middle ethmoidal cells open onto the ethmoidal bulla, or onto the lateral wall just above thisstructure;•the posterior ethmoidal cells open onto the lateral wall of the superior nasal meatus.Because the ethmoidal cells often erode into bones beyond the boundaries of the ethmoidallabyrinth, their walls may be completed by the frontal, maxillary, lacrimal, sphenoid, and palatinebones.
The ethmoidal cells are innervated by:•the anterior and posterior ethmoidal branches of the nasociliary nervefrom the ophthalmic nerve [V1];•the maxillary nerve [V2] via orbital branches from the pterygopalatineganglion.
The ethmoidal cells receive their blood supplythrough branches of the• anterior and•posterior ethmoidal arteries.
Maxillary sinuses:•one on each side,•largest of the paranasal sinuses•completely fill the bodies of the maxillae.•Each is pyramidal in shape (with the apex directed laterally and the base deep to thelateral wall of the adjacent nasal cavity).The medial wall or base of the maxillary sinus is formed by the maxilla, and by parts ofthe inferior concha and palatine bone that overlie the maxillary hiatus.The opening of the maxillary sinus is near the top of the base, in the center of the hiatussemilunaris, which grooves the lateral wall of the middle nasal meatus.
Relations of the maxillary sinus are as follows:•the superolateral surface (roof) is related above to the orbit;•the anterolateral surface is related below to the roots of the upper molarand premolar teeth and in front to the face;•the posterior wall is related behind to the infratemporal fossa.The maxillary sinuses are innervated by infra-orbital and alveolarbranches of the maxillary nerve [V2], and receive their blood throughbranches from the infra-orbital and superior alveolar branches of themaxillary arteries.
Sphenoidal sinuses:•One on either side•Within the body of the sphenoid,•Open into the roof of the nasal cavity via apertures on the posterior wallof the spheno-ethmoidal recess.The apertures are high on the anterior walls of the sphenoid sinuses.
The sphenoidal sinuses are related:•Above to the cranial cavity, particularly to the pituitarygland and to the optic chiasm;•Laterally, to the cranial cavity, particularly to the cavernoussinuses;•Below and in front, to the nasal cavities.
Innervation of the sphenoidal sinuses is provided by:•The posterior ethmoidal branch of the ophthalmic nerve [V1];•The maxillary nerve [V2] via orbital branches from the pterygopalatineganglion.The sphenoidal sinuses are supplied by branches of the pharyngealarteries from the maxillary arteries.
Walls, floor, and roofMedial wall: The medial wall of each nasal cavity is the mucosa-covered surface of thethin nasal septum, which is oriented vertically in the median sagittal plane and separates theright and left nasal cavities from each other.The nasal septum consists of:1. The septal nasal cartilage anteriorly;2. Posteriorly, mainly the vomer and the perpendicular plate of the ethmoid bone;3. Small contributions by the nasal bones where they meet in the midline, and the nasal spine of the frontal bone;4. Contributions by the crests of the maxillary and palatine bones, rostrum of the sphenoid bones, and the incisor crest of the maxilla.
Floor: the floor of each nasal cavity is•Smooth,•Concave, and•Much wider than the roof.It consists of:•Soft tissues of the external nose;•The upper surface of the palatine process of the maxilla, and the horizontalplate of the palatine bone, which together form the hard palate.•The naris opens anteriorly into the floor, and the superior aperture of theincisive canal is deep to the mucosa immediately lateral to the nasal septumnear the front of the hard palate.
Roof of the Nasal cavity•Narrow and highest in central regions where it is formed by the cribriform plate of theethmoid bone.• Roof slopes inferiorly to the nares which is anterior to the cribriform plate the and isformed by: 1. The nasal spine of the frontal bone and the nasal bones; 2. The lateral processes of the septal cartilage and 3. Major alar cartilages of the external nose.Posteriorly, the roof of each cavity slopes inferiorly to the choanae and is formed by: 1. The anterior surface of the sphenoid bone; 2. The ala of the vomer and adjacent sphenoidal process of the palatine bone; and 3. The vaginal process of the medial plate of the pterygoid process.
Underlying the mucosa, the roof is perforated superiorly by openings in thecribriform plate, and anterior to these openings by a separate foramen for theanterior ethmoidal nerve and vessels.The opening between the sphenoidal sinus and the spheno-ethmoidal recessis on the posterior slope of the roof.
Lateral wall: The lateral wall of each nasal cavity is complex and is formedby bone, cartilage, and soft tissues. Bony support for the lateral wall isprovided by:•the ethmoidal labyrinth and uncinate process;•the perpendicular plate of the palatine bone;•the medial plate of the pterygoid process of the sphenoid bone;•the medial surfaces of the lacrimal bones and maxillae;•the inferior concha.
Vessels: The nasal cavities have a rich vascular supply for altering the humidityand temperature of respired air. In fact, the submucosa of the respiratory region,particularly that related to the conchae and septum, is often described aserectile or cavernous in nature because the tissue enlarges or shrinksdepending on the amount of blood flowing into the system.
ArteriesInclude vessels that originate from both the internal and external carotidarteries:•Vessels that originate from branches of the external carotid artery include thesphenopalatine, greater palatine, superior labial, and lateral nasal arteries;•Vessels that originate from branches of the internal carotid artery are theanterior and posterior ethmoidal arteries.
Veins: Veins draining the nasal cavities generally follow the arteries:•veins that pass with branches that ultimately originate from the maxillary artery draininto the pterygoid plexus of veins in the infratemporal fossa;•veins from anterior regions of the nasal cavities join the facial vein.
In some individuals, an additional nasal vein passes superiorly through amidline aperture ,the foramen caecum, in the frontal bone anterior to the cristagalli, and joins with the anterior end of the superior sagittal sinus. Because thisnasal vein connects an intracranial venous sinus with extracranial veins, it isclassified as an emissary vein. Emissary veins in general are routes by whichinfections can track from peripheral regions into the cranial cavity. Veins thataccompany the anterior and posterior ethmoidal arteries are tributaries of thesuperior ophthalmic vein, which is one of the largest emissary veins and drainsinto the cavernous sinus on either side of the hypophysial fossa.
Innervation: Nerves that innervate the nasal cavities are:•the olfactory nerve [I] for olfaction;•branches of the ophthalmic [V1] and maxillary [V2] nerves for generalsensation.Secretomotor innervation of mucous glands in the nasal cavities andparanasal sinuses is by parasympathetic fibers from the facial nerve[VII], which mainly join branches of the maxillary nerve [V2] in thepterygopalatine fossa.