L53. GA - Nasal Cavity & PT Fossa

Functional Anatomy of the Nasal Cavity

• Filters and humidifies air and regulates air temperature as it passes toward the trachea
• Contains olfactory sensory neurons for the sense of smell
• Related anatomically and functionally to the paranasal sinuses, which affect voice resonance and alter the shape of the face
• Functions as a site of mucosal swelling and mucus secretion during illness
• Contains two chambers separated by a nasal septum composed of cartilage and bone
• Features three bony shelves called conchae: superior, middle, and inferior
• Passages inferior to each concha are called meatuses, named superior, middle, and inferior accordingly
• The passage superior to the superior concha is called the spheno-ethmoidal recess, which contains olfactory sensory neurons in its mucosa
• Communicates anteriorly with the external environment via the nostrils (nares)
• Communicates posteriorly with the nasopharynx via the choanae

Skeletal Framework of the Nasal Cavity

• Includes several bones that contribute to the overall structure
• Ethmoid, sphenoid, frontal, and vomer are unpaired bones
• Nasal, maxillary, palatine, lacrimal, and inferior conchae are paired bones
• Ethmoid bone is the dominant skeletal structure, positioned in medial and lateral walls, and part of the roof
• The ethmoid bone consists of a perpendicular plate that forms part of the nasal septum
• The cribriform plate is the location of olfactory neuronal fibers passing from the roof of the nasal cavity into the anterior cranial fossa
• The crista galli serves as an attachment for the anterior portion of the falx cerebri to the skull
• The superior concha and middle concha are also components of the ethmoid bone
• Ethmoid air cells (labyrinth) form the anterior, middle, and posterior ethmoid sinuses
• Contains openings for drainage from some of the paranasal sinuses
• The nasal septum has bony and cartilaginous parts
• Perpendicular plate of ethmoid contributes superiorly to the bony part of the nasal septum
• Vomer contributes inferiorly to the bony portion, and it is its own bone
• Septal cartilage forms the anterior cartilaginous part of the nasal septum
• The lateral nasal wall consists of bony and cartilaginous parts

Bony Parts of the Lateral Nasal Wall

• Superior and middle concha of the ethmoid bone
• Inferior concha (its own bone)
• Maxilla
• Nasal bone
• Lacrimal bone
• Perpendicular plate of the palatine bone
• Medial pterygoid plate of the sphenoid bone are all bony parts

Cartilaginous Parts of the Lateral Nasal Wall

• Lateral process of septal cartilage shapes part of the nasal bridge
• Alar cartilages shape part of the nostrils

Mucosal Covering

• The nasal cavity is lined by the same mucosa as the oral cavity and pharynx
• The inferior and middle conchae are easily observed, while the superior concha is smaller
• Inferior to the sphenoid bone (and sinus) is the transition from the nasal cavity to the nasopharynx

Blood Supply to the Nasal Cavity

• The maxillary artery provides sphenopalatine and greater palatine arteries
• The facial artery provides superior labial and lateral nasal arteries
• The ophthalmic artery provides anterior and posterior ethmoidal arteries
• The anterior region of the medial wall contains an area of extensive anastomoses with vessels close to the surface
• This region is known as Kiesselbach's Area, a major site for nose bleeds (epistaxis)

Innervation of the Nasal Cavity

• Olfactory (CN I) uses epithelium at the level of the sphenoethmoid recess to detect chemicals dissolved in the nasal mucosa
• Signals are sent via primary olfactory axons through the cribiform plate of the ethmoid bone to the olfactory bulb for the sense of smell (SSA)
• Trigeminal (CN V) - Ophthalmic (V1) division provides the nasociliary nerve that sends anterior and posterior ethmoid nerve branches into the nasal cavity
• The anterior ethmoid nerve innervates the anterior nasal cavity, with a branch going to the surface as the external nasal nerve to innervate the nose
• The posterior ethmoid nerve supplies the sphenoid and ethmoid sinuses
• These nerves provide somatosensory information to the brainstem as part of the trigeminal system (SA)
• Trigeminal (CN V) - Maxillary (V2) division uses nasal branches to supply the lateral and septal walls of each nasal cavity posteriorly
• The largest is the nasopalatine nerve that supplies the nasal septum
• A terminal branch of this nerve passes through the incisive foramen to the hard palate to supply oral mucosa behind the incisor teeth
• These nerves provide somatosensory information to the brainstem as part of the trigeminal system (SA)

Functional Anatomy of the Paranasal Sinuses

• Paranasal sinuses develop as outgrowths of the nasal cavities
• Further air humidification and temperature regulation is provided
• Affect voice resonance and the shape of the face
• There are 4 paired paranasal sinuses: frontal, ethmoidal, maxillary, and sphenoidal

Drainage Locations

• Conchae have been cut to show drainage locations within the nasal cavity.
• Note the ethmoid bulla and semilunar hiatus inferior to the bony shelf of the middle concha.
• There are 4 drainage locations here.
• The sphenoethmoid recess drains the sphenoid sinus
• The superior meatus drains the posterior ethmoid sinus
• The middle meatus drains the frontal sinus (semilunar hiatus), anterior ethmoid sinus (semilunar hiatus), maxillary sinus (semilunar hiatus), and middle ethmoid sinus (ethmoid bulla)
• The inferior meatus drains the nasolacrimal duct

Functional Anatomy of the Pterygopalatine (PT) Fossa

• Serves as a gateway for distribution of Maxillary Nerve (V2) branches
• Acts as a gateway for terminal branches of the Maxillary artery
• Contains the PT Ganglion, which provides PANS to mucous glands of the oral and nasal cavities, as well as the lacrimal gland

Skeletal Framework of PT Fossa

• Located posterior-superior to the maxilla
• Lateral to the palatine bone
• Medial to zygomatic bone & arch
• Anterior to sphenoid bone & IT (infratemporal) fossa
• It is associated with the foramen rotundum, pterygoid canal, palatovaginal canal, palatine canal, sphenopalatine foramen, and inferior orbital fissure

Sphenoid Bone Relationships

• The anterior surface of the isolated sphenoid bone has three passageways: foramen rotundum, pterygoid canal, and palatovaginal groove.
• The posterior view shows the internal carotid artery located in the cavernous sinus.
• Lateral is the foramen rotundum transmitting the maxillary nerve (V2).
• The pterygoid canal is covered by cartilage of the auditory tube, filling foramen lacerum.
• The greater petrosal nerve (branch of CN VII) carries preganglionic PANS fibers destined for the PT ganglion

Gateway Connections that connect the PT fossa to other regions

• Sphenopalatine foramen connects to the nasal cavity
• Inferior orbital fissure connects to the floor of the orbit
• Pterygomaxillary fissure connects to the infratemporal fossa
• Foramen rotundum connects to the cranial cavity (middle cranial fossa)
• Pterygoid canal connects to the cranial cavity (middle cranial fossa)
• Palatovaginal canal connects to the nasopharynx
• Palatine canal connects to the roof of the oral cavity (palate)

Maxillary Nerve (V2) Branches in the PT Fossa

• Palatine Nerves serve as sensory input to the hard palate (greater palatine) & soft palate (lesser palatine) via the palatine canal
• Nerves enter the oral cavity via greater and lesser palatine foramina
• Nasal Nerves provide sensory input to the nasal cavity via the sphenopalatine foramen
• The nerve to the medial wall is called the nasopalatine nerve
• Pharyngeal Nerves provide sensory input to the nasopharynx
• Zygomatic Nerve provides sensory input to the zygomatic and temporal regions of the face via a small foramen
• Leaves the PT fossa via the inferior orbital fissure
• Orbital Nerves provide sensory input to the orbital wall and sphenoid and ethmoid nasal sinuses via the inferior orbital fissure
• Posterior Superior Alveolar Nerve provides sensory input to the upper molars and surrounding gingiva, as well as the maxillary sinus
• Enters the maxilla via a small alveolar foramen
• Infra-Orbital Nerve constitutes a continuation of V2 through the inferior orbital fissure and supplies anterior and middle superior alveolar nerves to upper teeth and gingiva, as well as the maxillary sinus
• Emerges on the face just below the orbit as the infra-orbital nerve via the infra-orbital foramen, supplying the nose, lower eyelid, cheek, and upper lip

PT Ganglia & Associated Autonomic Nerves

• The pterygopalatine ganglion is suspended from V2 and contains cell bodies of postganglionic PANS neurons that innervate glands of the nasal cavity, palate, & lacrimal gland
• Both SANS and PANS fibers enter the PT fossa via the pterygoid canal
• PANS preganglionic neurons are located in the caudal pons and project axons that travel with CN VII into the internal acoustic meatus
• These fibers exit the temporal bone as the greater petrosal nerve and travel into the pterygoid canal before synapsing in the PT ganglion
• PANS postganglionic fibers travel on branches of V2 to target glands of the palate, nasal cavity, and nasopharynx
• Branches destined for the lacrimal gland eventually use V1 branches
• SANS preganglionic neurons are located in the lateral horn of the spinal cord at the top of the sympathetic cell column (T1)
• They leave the spinal cord via T1 ventral roots, enter the sympathetic trunk via white rami communicans, ascend the sympathetic trunk of the neck until reaching the superior cervical sympathetic ganglion where they synapse
• SANS postganglionic neurons of the superior cervical ganglion send axons that leave the ganglion as the internal carotid nerve and form a plexus on the surface of the internal carotid artery, travelling with the artery into the skull via the carotid canal
• As the internal carotid artery enters the cavernous sinus, the SANS postganglionic axons form the deep petrosal nerve that enters the pterygoid canal
• At the point of entry into the pterygoid canal, both postganglionic SANS fibers of the deep petrosal nerve join with preganglionic PANS fibers of the greater petrosal nerve to form the nerve of the pterygoid canal (contains both SANS & PANS)
• PANS preganglionics stop to synapse in the PT ganglion while SANS postganglionics travel through the ganglion and use branches of V2 to travel to targets of the palate, nasal cavity, and nasopharynx
• Branches destined for the lacrimal gland eventually use V1 branches
• SANS function is mainly vasoconstriction, which decreases gland secretions
• PANS function is opposite, to increase gland secretions

Maxillary Artery Terminal Branch Relationships

• After giving off branches within the IT fossa, the maxillary artery crosses the pterygomaxillary fissure to enter the PT fossa
• There, it ends by providing a number of branches that traverse the various gateways of the PT fossa to the nasal cavity, nasopharynx, orbit, oral cavity, and face

Terminal Branches of Maxillary Artery Related to PT Fossa

• Posterior superior alveolar artery enters the foramen of the same name on the posterior surface of the maxilla and supplies upper molar and premolar teeth
• Descending palatine artery descends in the palatine canal to the palate region and divides into greater & lesser palatine arteries to supply the hard and soft palate respectively
• Sphenopalatine artery traverses the sphenopalatine foramen to supply both lateral and medial walls of the nasal cavity
• Infraorbital artery travels in the floor of the orbit within the inferior orbital fissure
• The Infraorbital artery gives off the anterior superior alveolar artery to supply upper canine and incisor teeth
• Branches are provided to structures in the floor of orbit (inferior rectus, inferior oblique, lacrimal sac)
• Exits the infraorbital foramen to supply structures of the face near the foramen