Physical Address

304 North Cardinal St.
Dorchester Center, MA 02124

Respiratory System


General organization

The respiratory system can be divided into the upper airway (consisting of the nose and nasal cavity), pharynx, and lower airway (consisting of the larynx, trachea, and lungs).

Nose and nasal cavity

The two nasal cavities are the uppermost parts of the respiratory tract and contain the olfactory receptors. They are elongated wedge-shaped spaces with a large inferior base and a narrow superior apex ( Figs. 2.1 and 2.2 ) and are held open by a skeletal framework consisting mainly of bone and cartilage.

Fig. 2.1, Nasal cavities (anterolateral view). Relationship to other cavities.

Fig. 2.2, Nasal cavities. A. Floor, roof, and lateral walls. B. Conchae on lateral walls. C. Coronal section. D. Air channels in right nasal cavity.

The smaller anterior regions of the cavities are enclosed by the external nose, whereas the larger posterior regions are more central within the skull. The anterior apertures of the nasal cavities are the nares, which open onto the inferior 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, and

  • □

    from the cranial cavity above by parts of the frontal, ethmoid, and sphenoid bones.

Lateral to the nasal cavities are the orbits.

Each nasal cavity has a floor, roof, medial wall, and lateral wall ( Fig. 2.2A ).

Lateral wall

The lateral wall is characterized by three curved shelves of bone (conchae), which are one above the other and project medially and inferiorly across the nasal cavity ( Fig. 2.2B ). The medial, anterior, and posterior margins of the conchae are free.

The conchae divide each nasal cavity into four air channels ( Fig. 2.2C,D ):

  • □

    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 of the lateral wall and the respired air.

The openings of the paranasal sinuses, which are extensions of the nasal cavity that erode into the surrounding bones during childhood and early adulthood, are on the lateral wall and roof of the nasal cavities ( Fig. 2.3 ). In addition, the lateral wall also contains the opening of the nasolacrimal duct, which drains tears from the eye into the nasal cavity.

Fig. 2.3, Paranasal sinuses and nasolacrimal duct.

Regions

Each nasal cavity consists of three general regions—the nasal vestibule, the respiratory region, and the olfactory region ( Fig. 2.4 ):

  • □

    The nasal vestibule is a small dilated space just internal to the naris that is lined by skin and contains hair follicles.

  • □

    The respiratory region is the largest part of the nasal cavity, has a rich neurovascular supply, and is lined by respiratory epithelium composed mainly of ciliated and mucous cells.

  • □

    The olfactory region is small, is at the apex of each nasal cavity, is lined by olfactory epithelium, and contains the olfactory receptors.

Fig. 2.4, Regions of the nasal cavities.

In addition to housing receptors for the sense of smell (olfaction), the nasal cavities adjust the temperature and humidity of respired air by the action of a rich blood supply, and trap and remove particulate matter from the airway by filtering the air through hair in the vestibule and by capturing foreign material in abundant mucus. The mucus normally is moved posteriorly by cilia on epithelial cells in the nasal cavities and is swallowed.

Innervation and blood supply

Innervation of the nasal cavities is by three cranial nerves:

  • □

    Olfaction is carried by the olfactory nerve [I].

  • □

    General sensation is carried by the trigeminal nerve [V], the anterior region by the ophthalmic nerve [V 1 ], and the posterior region by the maxillary nerve [V 2 ].

  • □

    All glands are innervated by parasympathetic fibers in the facial nerve [VII] (greater petrosal nerve), which join branches of the maxillary nerve [V 2 ] in the pterygopalatine fossa.

Sympathetic fibers are ultimately derived from the T1 spinal cord level. They synapse mainly in the superior cervical sympathetic ganglion, and postganglionic fibers reach the nasal cavities along blood vessels, or by joining branches of the maxillary nerve [V 2 ] in the pterygopalatine fossa.

Blood supply to the nasal cavities is by:

  • □

    terminal branches of the maxillary and facial arteries, which originate from the external carotid artery, and

  • □

    ethmoidal branches of the ophthalmic artery, which originates from the internal carotid artery.

Skeletal framework

Bones that contribute to the skeletal framework of the nasal cavities include:

  • □

    the unpaired ethmoid, sphenoid, frontal, and vomer bones, and

  • □

    the paired nasal, maxillary, palatine, and lacrimal bones and inferior conchae.

Of all the bones associated with the nasal cavities, the ethmoid is a key element.

Ethmoid bone

The single ethmoid bone is one of the most complex bones in the skull. It contributes to the roof, lateral wall, and medial wall of both nasal cavities, and contains the ethmoidal cells (ethmoidal sinuses).

The ethmoid bone is cuboidal in overall shape ( Fig. 2.5A ) and is composed of two rectangular box-shaped ethmoidal labyrinths, one on each side, united superiorly across the midline by a perforated sheet of bone (the cribriform plate). A second sheet of bone (the perpendicular plate) descends vertically in the median sagittal plane from the cribriform plate to form part of the nasal septum.

Fig. 2.5, Ethmoid bone. A. Overall shape. B. Coronal section through skull.

Each ethmoidal labyrinth is composed of two delicate sheets of bone, which sandwich between them the ethmoidal cells.

  • □

    The lateral sheet of bone (the orbital plate) is flat and forms part of the medial wall of the orbit.

  • □

    The medial sheet of bone forms the upper part of the lateral wall of the nasal cavity and is characterized by two processes and a swelling ( Fig. 2.5B )—the two processes are curved shelves of bone (the superior and middle conchae), which project across the nasal cavity and curve downward ending in free medial margins, while inferior to the origin of the middle concha, the middle ethmoidal cells form a prominent bulge (the ethmoidal bulla), on the medial wall of the labyrinth.

Extending anterosuperiorly from just under the bulla is a groove (the ethmoidal infundibulum), which continues upward, and narrows to form a channel that penetrates the ethmoidal labyrinth and opens into the frontal sinus. This channel is for the frontonasal duct, which drains the frontal sinus.

The superior surface of the ethmoidal labyrinth articulates with the frontal bone, which usually completes the roof of the ethmoidal cells, while the anterior surface articulates with the frontal process of the maxilla and with the lacrimal bone. The inferior surface articulates with the upper medial margin of the maxilla.

A delicate irregularly shaped projection (the uncinate process) on the anterior aspect of the inferior surface of the ethmoidal labyrinth extends posteroinferiorly across a large defect (maxillary hiatus) in the medial wall of the maxilla to articulate with the inferior concha.

The cribriform plate is at the apex of the nasal cavities and fills the ethmoidal notch in the frontal bone ( Fig. 2.5 ) and separates the nasal cavities below from the cranial cavity above. Small perforations in the bone allow the fibers of the olfactory nerve [I] to pass between the two regions.

A large triangular process (the crista galli) at the midline on the superior surface of the cribriform plate anchors a fold (falx cerebri) of dura mater in the cranial cavity.

The perpendicular plate of the ethmoid bone is quadrangular in shape, descends in the midline from the cribriform plate, and forms the upper part of the median nasal septum ( Fig. 2.5 ). It articulates:

  • □

    posteriorly with the sphenoidal crest on the body of the sphenoid bone,

  • □

    anteriorly with the nasal spine on the frontal bone and with the site of articulation at the midline between the two nasal bones, and

  • □

    inferiorly and anteriorly with the septal cartilage and posteriorly with the vomer.

External nose

The external nose extends the nasal cavities onto the front of the face and positions the nares so that they point downward ( Fig. 2.6 ). It is pyramidal in shape with its apex anterior in position. The upper angle of the nose between the openings of the orbits is continuous with the forehead.

Fig. 2.6, External nose.

Like posterior regions, the anterior parts of the nasal cavities found within the nose are held open by a skeletal framework, which is composed partly of bone and mainly of cartilage:

  • □

    The bony parts are where the nose is continuous with the skull—here the nasal bones and parts of the maxillae and frontal bones provide support.

  • □

    Anteriorly, and on each side, support is provided by lateral processes of the septal cartilage, major alar and three or four minor alar cartilages, and a single septal cartilage in the midline that forms the anterior part of the nasal septum.

Walls, floor, and roof

Medial wall

The medial wall of each nasal cavity is the mucosa-covered surface of the thin nasal septum, which is oriented vertically in the median sagittal plane and separates the right and left nasal cavities from each other.

The nasal septum ( Fig. 2.7 ) consists of:

  • □

    the septal nasal cartilage anteriorly,

  • □

    posteriorly, mainly the vomer and the perpendicular plate of the ethmoid bone,

  • □

    small contributions by the nasal bones where they meet in the midline, and the nasal spine of the frontal bone, and

  • □

    contributions by the nasal crests of the maxillary and palatine bones, rostrum of the sphenoid bone, and the incisor crest of the maxilla.

Fig. 2.7, Medial wall of the nasal cavity—the nasal septum.

Floor

The floor of each nasal cavity ( Fig. 2.8 ) is smooth, concave, and much wider than the roof. It consists of:

  • □

    soft tissues of the external nose, and

  • □

    the upper surface of the palatine process of the maxilla and the horizontal plate of the palatine bone, which together form the hard palate.

Fig. 2.8, Floor of the nasal cavity (superior view).

The naris opens anteriorly into the floor, and the superior aperture of the incisive canal is deep to the mucosa immediately lateral to the nasal septum near the front of the hard palate.

Roof

The roof of the nasal cavity is narrow and is highest in central regions where it is formed by the cribriform plate of the ethmoid bone ( Fig. 2.9 ).

Fig. 2.9, Roof of the nasal cavity.

Anterior to the cribriform plate the roof slopes inferiorly to the nares and is formed by:

  • □

    the nasal spine of the frontal bone and the nasal bones, and

  • □

    the lateral processes of the septal cartilage and major alar cartilages of the external nose.

Posteriorly, the roof of each cavity slopes inferiorly to the choana and is formed by:

  • □

    the anterior surface of the sphenoid bone,

  • □

    the ala of the vomer and adjacent sphenoidal process of the palatine bone, and

  • □

    the vaginal process of the medial plate of the pterygoid process.

Underlying the mucosa, the roof is perforated superiorly by openings in the cribriform plate, and anterior to these openings by a separate foramen for the anterior ethmoidal nerve and vessels.

The opening between the sphenoidal sinus and the spheno-ethmoidal recess is on the posterior slope of the roof.

Lateral wall

The lateral wall of each nasal cavity is complex and is formed by bone, cartilage, and soft tissues.

Bony support for the lateral wall ( Fig. 2.10A ) is provided by:

  • □

    the ethmoidal labyrinth, superior concha, middle concha, and uncinate process,

  • □

    the perpendicular plate of the palatine bone,

  • □

    the medial pterygoid plate of the sphenoid bone,

  • □

    the medial surfaces of the lacrimal bones and maxillae, and

  • □

    the inferior concha.

Fig. 2.10, Lateral wall of the nasal cavity. A. Bones. B. Covered with mucosa. C. Conchae broken away at attachment to lateral wall.

In the external nose, the lateral wall of the cavity is supported by cartilage (lateral process of the septal cartilage and major and minor alar cartilages) and by soft tissues. The surface of the lateral wall is irregular in contour and is interrupted by the three nasal conchae.

The inferior, middle, and superior conchae ( Fig. 2.10B ) extend medially across the nasal cavity, separating it into four air channels, an inferior, middle, and superior meatus and a spheno-ethmoidal recess. The conchae do not extend forward into the external nose. The anterior end of each concha curves inferiorly to form a lip that overlies the end of the related meatus.

Immediately inferior to the attachment of the middle concha and just anterior to the midpoint of the concha, the lateral wall of the middle meatus elevates to form the dome-shaped ethmoidal bulla ( Fig. 2.10C ). This is formed by the underlying middle ethmoidal cells, which expand the medial wall of the ethmoidal labyrinth. Clinically, these middle ethmoidal cells are now considered part of the anterior group of ethmoidal cells.

Inferior to the ethmoidal bulla is a curved gutter (the semilunar hiatus), which is formed by the mucosa covering the lateral wall as it spans a defect in the bony wall between the ethmoidal bulla above and the uncinate process below.

The anterior end of the semilunar hiatus forms a channel (the ethmoidal infundibulum), which curves upward and continues as the frontonasal duct through the anterior part of the ethmoidal labyrinth to open into the frontal sinus.

The nasolacrimal duct and most of the paranasal sinuses open onto the lateral wall of the nasal cavity ( Fig. 2.10C ):

  • □

    The nasolacrimal duct opens onto the lateral wall of the inferior nasal meatus under the anterior lip of the inferior concha—it drains tears from the conjunctival sac of the eye into the nasal cavity and originates at the inferior end of the lacrimal sac on the anteromedial wall of the orbit.

  • □

    The frontal sinus drains via the frontonasal duct and ethmoidal infundibulum into the anterior end of the semilunar hiatus on the lateral wall of the middle nasal meatus—the anterior ethmoidal cells drain into the frontonasal duct or ethmoidal infundibulum (in some cases, the frontal sinus drains directly into the anterior end of the middle nasal meatus and the frontonasal duct ends blindly in the anterior ethmoidal cells).

  • □

    The middle ethmoidal cells open onto or just above the ethmoidal bulla.

  • □

    The posterior ethmoidal cells usually open onto the lateral wall of the superior nasal meatus.

  • □

    The large maxillary sinus opens into the semilunar hiatus, usually just inferior to the center of the ethmoidal bulla—this opening is near the roof of the maxillary sinus.

The only paranasal sinus that does not drain onto the lateral wall of the nasal cavity is the sphenoidal sinus, which usually opens onto the sloping posterior roof of the nasal cavity.

Nares

The nares are oval apertures on the inferior aspect of the external nose and are the anterior openings of the nasal cavities ( Fig. 2.11A ). They are held open by the surrounding alar cartilages and septal cartilage, and by the inferior nasal spine and adjacent margins of the maxillae.

Fig. 2.11, Nares. A. Inferior view. B. Associated muscles.

Although the nares are continuously open, they can be widened further by the action of the related muscles of facial expression (nasalis, depressor septi nasi, and levator labii superioris alaeque nasi muscles; Fig. 2.11B ).

Choanae

The choanae are the oval-shaped openings between the nasal cavities and the nasopharynx ( Fig. 2.12 ). Unlike the nares, which have flexible borders of cartilage and soft tissues, the choanae are rigid openings completely surrounded by bone, and their margins are formed:

  • □

    inferiorly by the posterior border of the horizontal plate of the palatine bone,

  • □

    laterally by the posterior margin of the medial plate of the pterygoid process, and

  • □

    medially by the posterior border of the vomer.

Fig. 2.12, Choanae (posterior view). A. Overview. B. Magnified view.

The roof of the choanae is formed:

  • □

    anteriorly by the ala of the vomer and the vaginal process of the medial plate of the pterygoid process, and

  • □

    posteriorly by the body of the sphenoid bone.

Gateways

There are a number of routes by which nerves and vessels enter and leave the soft tissues lining each nasal cavity ( Fig. 2.13 ), and these include the cribriform plate, sphenopalatine foramen, incisive canal, and small foramina in the lateral wall, and around the margin of the nares.

Fig. 2.13, Gateways to the nasal cavities.

Cribriform plate

The fibers of the olfactory nerve [I] exit the nasal cavity and enter the cranial cavity through perforations in the cribriform plate. In addition, small foramina between the cribriform plate and surrounding bone allow the anterior ethmoidal nerve, a branch of the ophthalmic nerve [V 1 ], and accompanying vessels to pass from the orbit into the cranial cavity and then down into the nasal cavity.

In addition, there is a connection in some individuals between nasal veins and the superior sagittal sinus of the cranial cavity through a prominent foramen (the foramen cecum) in the midline between the crista galli and frontal bone.

Sphenopalatine foramen

One of the most important routes by which nerves and vessels enter and leave the nasal cavity is the sphenopalatine foramen in the posterolateral wall of the superior nasal meatus. This foramen is just superior to the attachment of the posterior end of the middle nasal concha and is formed by the sphenopalatine notch in the palatine bone and the body of the sphenoid bone.

The sphenopalatine foramen is a route of communication between the nasal cavity and the pterygopalatine fossa. Major structures passing through the foramen are:

  • □

    the sphenopalatine branch of the maxillary artery,

  • □

    the nasopalatine branch of the maxillary nerve [V 2 ], and

  • □

    superior nasal branches of the maxillary nerve [V 2 ].

Incisive canal

Another route by which structures enter and leave the nasal cavities is through the incisive canal in the floor of each nasal cavity. This canal is immediately lateral to the nasal septum and just posterosuperior to the root of the central incisor in the maxilla. The two incisive canals, one on each side, both open into the single unpaired incisive fossa in the roof of the oral cavity and transmit:

  • □

    the nasopalatine nerve from the nasal cavity into the oral cavity, and

  • □

    the terminal end of the greater palatine artery from the oral cavity into the nasal cavity.

Small foramina in the lateral wall

Other routes by which vessels and nerves get into and out of the nasal cavity include the nares and small foramina in the lateral wall:

  • □

    Internal nasal branches of the infra-orbital nerve of the maxillary nerve [V 2 ] and alar branches of the nasal artery from the facial artery loop around the margin of the naris to gain entry to the lateral wall of the nasal cavity from the face.

  • □

    Inferior nasal branches from the greater palatine branch of the maxillary nerve [V 2 ] enter the lateral wall of the nasal cavity from the palatine canal by passing through small foramina on the lateral wall.

Vessels

The nasal cavities have a rich vascular supply for altering the humidity and temperature of respired air. In fact, the submucosa of the respiratory region, particularly that related to the conchae and septum, is often described as “erectile” or “cavernous” because the tissue enlarges or shrinks depending on the amount of blood flowing into the system.

Arteries

Arteries that supply the nasal cavity include vessels that originate from both the internal and external carotid arteries ( Fig. 2.14 ):

  • □

    Vessels that originate from branches of the external carotid artery include the sphenopalatine, greater palatine, superior labial, and lateral nasal arteries.

  • □

    Vessels that originate from branches of the internal carotid artery are the anterior and posterior ethmoidal arteries.

Fig. 2.14, Arterial supply of the nasal cavities. A. Lateral wall of the right nasal cavity. B. Septum (medial wall of right nasal cavity).

Sphenopalatine artery

The largest vessel supplying the nasal cavity is the sphenopalatine artery ( Fig. 2.14 ), which is the terminal branch of the maxillary artery in the pterygopalatine fossa. It leaves the pterygopalatine fossa and enters the nasal cavity by passing medially through the sphenopalatine foramen and onto the lateral wall of the nasal cavity.

Posterior lateral nasal branches supply a large part of the lateral wall and anastomose anteriorly with branches from the anterior and posterior ethmoidal arteries, and with lateral nasal branches of the facial artery.

Posterior septal branches of the sphenopalatine artery pass over the roof of the cavity and onto the nasal septum where they contribute to the blood supply of the medial wall. One of these latter branches continues forward down the nasal septum to anastomose with the terminal end of the greater palatine artery and septal branches of the superior labial artery.

Greater palatine artery

The terminal end of the greater palatine artery enters the anterior aspect of the floor of the nasal cavity by passing up through the incisive canal from the roof of the oral cavity ( Fig. 2.14 ).

Like the sphenopalatine artery, the greater palatine artery arises in the pterygopalatine fossa as a branch of the maxillary artery. It passes first onto the roof of the oral cavity by passing down through the palatine canal and greater palatine foramen to the posterior aspect of the palate, then passes forward on the undersurface of the palate, and up through the incisive fossa and canal to reach the floor of the nasal cavity. The greater palatine artery supplies anterior regions of the medial wall and adjacent floor of the nasal cavity, and anastomoses with the septal branch of the sphenopalatine artery.

Superior labial and lateral nasal arteries

The superior labial artery and the lateral nasal artery originate from the facial artery on the front of the face.

The superior labial artery originates from the facial artery near the lateral end of the oral fissure and passes medially in the lip, supplying the lip and giving rise to branches that supply the nose and nasal cavity. An alar branch supplies the region around the lateral aspect of the naris and a septal branch passes into the nasal cavity and supplies anterior regions of the nasal septum.

The lateral nasal artery originates from the facial artery in association with the margin of the external nose and contributes to the blood supply of the external nose. Alar branches pass around the lateral margin of the naris and supply the nasal vestibule.

Anterior and posterior ethmoidal arteries

The anterior and posterior ethmoidal arteries ( Fig. 2.14 ) originate in the orbit from the ophthalmic artery, which originates in the cranial cavity as a major branch of the internal carotid artery. They pass through canals in the medial wall of the orbit between the ethmoidal labyrinth and frontal bone, supply the adjacent paranasal sinuses, and then enter the cranial cavity immediately lateral and superior to the cribriform plate.

The posterior ethmoidal artery descends into the nasal cavity through the cribriform plate and has branches to the upper parts of the medial and lateral walls.

The anterior ethmoidal artery passes forward, with the accompanying anterior ethmoidal nerve, in a groove on the cribriform plate and enters the nasal cavity by descending through a slit-like foramen immediately lateral to the crista galli. It gives rise to branches that supply the medial (septal) and lateral wall of the nasal cavity and then continues forward on the deep surface of the nasal bone, and terminates by passing between the nasal bone and lateral nasal cartilage to emerge on the external nose as the external nasal branch to supply skin and adjacent tissues.

Vessels that supply the nasal cavities form extensive anastomoses with each other. This is particularly evident in the anterior region of the medial wall where there are anastomoses between branches of the greater palatine, sphenopalatine, superior labial, and anterior ethmoidal arteries, and where the vessels are relatively close to the surface ( Fig. 2.14B ). This area is the major site of nosebleeds, or epistaxis.

Veins

Veins draining the nasal cavities generally follow the arteries ( Fig. 2.15 ):

  • □

    Veins that pass with branches that ultimately originate from the maxillary artery drain into the pterygoid plexus of veins in the infratemporal fossa.

  • □

    Veins from anterior regions of the nasal cavities join the facial vein.

Fig. 2.15, Venous drainage of the nasal cavities.

In some individuals, an additional nasal vein passes superiorly through a midline aperture (the foramen cecum), in the frontal bone anterior to the crista galli, and joins with the anterior end of the superior sagittal sinus. Because this nasal vein connects an intracranial venous sinus with extracranial veins, it is classified as an emissary vein. Emissary veins in general are routes by which infections can track from peripheral regions into the cranial cavity.

Veins that accompany the anterior and posterior ethmoidal arteries are tributaries of the superior ophthalmic vein, which is one of the largest emissary veins and drains into the cavernous sinus on either side of the hypophyseal fossa.

Innervation

Nerves that innervate the nasal cavities ( Fig. 2.16 ) are:

  • □

    the olfactory nerve [I] for olfaction, and

  • □

    branches of the ophthalmic [V 1 ] and maxillary [V 2 ] nerves for general sensation.

Fig. 2.16, Innervation of the nasal cavities. A. Lateral wall of right nasal cavity. B. Medial wall of right nasal cavity.

Secretomotor innervation of mucous glands in the nasal cavities and paranasal sinuses is by parasympathetic fibers from the facial nerve [VII], which mainly join branches of the maxillary nerve [V 2 ] in the pterygopalatine fossa.

Olfactory nerve [I]

The olfactory nerve [I] is composed of axons from receptors in the olfactory epithelium at the top of each nasal cavity. Bundles of these axons pass superiorly through perforations in the cribriform plate to synapse with neurons in the olfactory bulb of the brain.

Branches from the ophthalmic nerve [v 1 ]

Branches from the ophthalmic nerve [V 1 ] that innervate the nasal cavity are the anterior and posterior ethmoidal nerves, which originate from the nasociliary nerve in the orbit.

Anterior and posterior ethmoidal nerves

The anterior ethmoidal nerve ( Fig. 2.16 ) travels with the anterior ethmoidal artery and leaves the orbit through a canal between the ethmoidal labyrinth and the frontal bone. It passes through and supplies the adjacent ethmoidal cells and frontal sinus, and then enters the cranial cavity immediately lateral and superior to the cribriform plate. It then travels forward in a groove on the cribriform plate and enters the nasal cavity by descending through a slit-like foramen immediately lateral to the crista galli. It has branches to the medial and lateral wall of the nasal cavity and then continues forward on the undersurface of the nasal bone. It passes onto the external surface of the nose by traveling between the nasal bone and lateral nasal cartilage, and then terminates as the external nasal nerve, which supplies skin around the naris, in the nasal vestibule, and on the tip of the nose.

Like the anterior ethmoidal nerve, the posterior ethmoidal nerve leaves the orbit through a similar canal in the medial wall of the orbit. It terminates by supplying the mucosa of the ethmoidal cells and sphenoidal sinus and normally does not extend into the nasal cavity itself.

Branches from the maxillary nerve [v 2 ]

A number of nasal branches from the maxillary nerve [V 2 ] innervate the nasal cavity. Many of these nasal branches ( Fig. 2.16 ) originate in the pterygopalatine fossa, which is just lateral to the lateral wall of the nasal cavity, and leave the fossa to enter the nasal cavity by passing medially through the sphenopalatine foramen or through smaller foramina in the lateral wall:

  • □

    A number of these nerves (posterior superior lateral nasal nerves) pass forward on and supply the lateral wall of the nasal cavity.

  • □

    Others (posterior superior medial nasal nerves) cross the roof to the nasal septum and supply both these regions.

  • □

    The largest of these nerves is the nasopalatine nerve, which passes forward and down the medial wall of the nasal cavity to pass through the incisive canal onto the roof of the oral cavity, and terminates by supplying the oral mucosa posterior to the incisor teeth.

  • □

    Other nasal nerves (posterior inferior nasal nerves) originate from the greater palatine nerve, descending from the pterygopalatine fossa in the palatine canal just lateral to the nasal cavity, and pass through small bony foramina to innervate the lateral wall of the nasal cavity.

  • □

    A small nasal nerve also originates from the anterior superior alveolar branch of the infra-orbital nerve and passes medially through the maxilla to supply the lateral wall near the anterior end of the inferior concha.

Parasympathetic innervation

Secretomotor innervation of glands in the mucosa of the nasal cavity and paranasal sinuses is by preganglionic parasympathetic fibers carried in the greater petrosal branch of the facial nerve [VII]. These fibers enter the pterygopalatine fossa and synapse in the pterygopalatine ganglion (see Fig. 2.17 ). Postganglionic parasympathetic fibers then join branches of the maxillary nerve [V 2 ] to leave the fossa and ultimately reach target glands.

Fig. 2.17, Nerve of the pterygoid canal. A. Overview. B. In relationship to the pterygopalatine ganglion.

FLOAT NOT FOUND FLOAT NOT FOUND

Sympathetic innervation

Sympathetic innervation, mainly involved with regulating blood flow in the nasal mucosa, is from spinal cord level T1. Preganglionic sympathetic fibers enter the sympathetic trunk and ascend to synapse in the superior cervical sympathetic ganglion. Postganglionic sympathetic fibers pass onto the internal carotid artery, enter the cranial cavity, and then leave the internal carotid artery to form the deep petrosal nerve, which joins the greater petrosal nerve of the facial nerve [VII] and enters the pterygopalatine fossa.

Like the parasympathetic fibers, the sympathetic fibers follow branches of the maxillary nerve [V 2 ] into the nasal cavity.

Fig. 2.18, Pterygoid plexus of veins.

Fig. 2.19, Pterygopalatine fossa. A. Anterolateral view. B. Lateral view.

Lymphatics

Lymph from anterior regions of the nasal cavities drains forward onto the face by passing around the margins of the nares ( Fig. 2.20 ). These lymphatics ultimately connect with the submandibular nodes.

Fig. 2.20, Lymphatic drainage of the nasal cavities.

Lymph from posterior regions of the nasal cavity and the paranasal sinuses drains into upper deep cervical nodes. Some of this lymph passes first through the retropharyngeal nodes.

Paranasal sinuses

There are four paranasal air sinuses—the ethmoidal cells, and the sphenoidal, maxillary, and frontal sinuses ( Fig. 2.21A,B ). Each is named according to the bone in which it is found.

Fig. 2.21, Paranasal sinuses. A. Anterior view. B. Posteroanterior skull radiograph. C. Paramedian view of right nasal cavity. D. Lateral skull radiograph.

The paranasal sinuses develop as outgrowths from the nasal cavities and erode into the surrounding bones. All of the paranasal sinuses:

  • □

    are lined by respiratory mucosa, which is ciliated and mucus secreting,

  • □

    open into the nasal cavities, and

  • □

    are innervated by branches of the trigeminal nerve [V].

Frontal sinuses

The frontal sinuses, one on each side, are variable in size and are the most superior of the sinuses ( Fig. 2.21A–C ). Each is triangular in shape and is in the part of the frontal bone under the forehead. The base of each triangular sinus is oriented vertically in the bone at the midline above the bridge of the nose and the apex is laterally approximately one-third of the way along the upper margin of the orbit.

Each frontal sinus drains onto the lateral wall of the middle meatus via the frontonasal duct, which penetrates the ethmoidal labyrinth and continues as the ethmoidal infundibulum at the front end of the semilunar hiatus.

The frontal sinuses are innervated by branches of the supra-orbital nerve from the ophthalmic nerve [V 1 ]. Their blood supply is from branches of the anterior ethmoidal arteries.

Ethmoidal cells

The ethmoidal cells on each side fill the ethmoidal labyrinth ( Fig. 2.21A,B ). Each cluster of cells is separated from the orbit by the thin orbital plate of the ethmoidal labyrinth, and from the nasal cavity by the medial wall of the ethmoidal labyrinth.

The ethmoidal cells are formed by a variable number of individual air chambers, which are divided into anterior, middle, and posterior ethmoidal cells based on the 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 this structure.

  • □

    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 ethmoidal labyrinth, their walls may be completed by the frontal, maxillary, lacrimal, sphenoid, and palatine bones.

The ethmoidal cells are innervated by:

  • □

    the anterior and posterior ethmoidal branches of the nasociliary nerve from the ophthalmic nerve [V 1 ], and

  • □

    the maxillary nerve [V 2 ] via orbital branches from the pterygopalatine ganglion.

The ethmoidal cells receive their blood supply through branches of the anterior and posterior ethmoidal arteries.

Maxillary sinuses

The maxillary sinuses, one on each side, are the largest of the paranasal sinuses and completely fill the bodies of the maxillae ( Fig. 2.21A,B ). Each is pyramidal in shape with the apex directed laterally and the base deep to the lateral wall of the adjacent nasal cavity. The medial wall or base of the maxillary sinus is formed by the maxilla, and by parts of the 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 semilunar hiatus, which grooves the lateral wall of the middle nasal meatus.

Relationships 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 molar and 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 alveolar branches of the maxillary nerve [V 2 ], and receive their blood through branches from the infra-orbital and superior alveolar branches of the maxillary arteries.

Sphenoidal sinuses

The 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 wall of the spheno-ethmoidal recess ( Fig. 2.21C,D ). 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 pituitary gland and to the optic chiasm,

  • □

    laterally, to the cranial cavity, particularly to the cavernous sinuses, and

  • □

    below and in front, to the nasal cavities.

Because only thin shelves of bone separate the sphenoidal sinuses from the nasal cavities below and hypophyseal fossa above, the pituitary gland can be surgically approached through the roof of the nasal cavities by passing first through the anteroinferior aspect of the sphenoid bone and into the sphenoidal sinuses and then through the top of the sphenoid bone into the hypophyseal fossa.

Innervation of the sphenoidal sinuses is provided by:

  • □

    the posterior ethmoidal branch of the ophthalmic nerve [V 1 ], and

  • □

    the maxillary nerve [V 2 ] via orbital branches from the pterygopalatine ganglion.

The sphenoidal sinuses are supplied by branches of the pharyngeal arteries from the maxillary arteries.

Pharynx

The pharynx is a musculofascial half-cylinder that links the oral and nasal cavities in the head to the larynx and esophagus in the neck ( Fig. 2.22 ). The pharyngeal cavity is a common pathway for air and food.

Fig. 2.22, Pharynx.

The pharynx is attached above to the base of the skull and is continuous below, approximately at the level of vertebra CVI, with the top of the esophagus. The walls of the pharynx are attached anteriorly to the margins of the nasal cavities, oral cavity, and larynx. Based on these anterior relationships the pharynx is subdivided into three regions, the nasopharynx, oropharynx, and laryngopharynx:

  • □

    The posterior apertures (choanae) of the nasal cavities open into the nasopharynx.

  • □

    The posterior opening of the oral cavity (oropharyngeal isthmus) opens into the oropharynx.

  • □

    The superior aperture of the larynx (laryngeal inlet) opens into the laryngopharynx.

In addition to these openings, the pharyngeal cavity is related anteriorly to the posterior one-third of the tongue and to the posterior aspect of the larynx. The pharyngotympanic tubes open into the lateral walls of the nasopharynx.

Lingual, pharyngeal, and palatine tonsils are on the deep surface of the pharyngeal walls.

The pharynx is separated from the posteriorly positioned vertebral column by a thin retropharyngeal space containing loose connective tissue.

Although the soft palate is generally considered as part of the roof of the oral cavity, it is also related to the pharynx. The soft palate is attached to the posterior margin of the hard palate and is a type of “flutter valve” that can:

  • □

    swing up (elevate) to close the pharyngeal isthmus, and seal off the nasopharynx from the oropharynx, and

  • □

    swing down (depress) to close the oropharyngeal isthmus and seal off the oral cavity from the oropharynx.

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here

Related Posts