Upper Respiratory Tract Anatomy Notes

Upper Respiratory Tract Anatomy

Overview

• The upper respiratory tract includes the nasal and oral cavities, pharynx, and larynx.
• Functions include:
  • Air conduction
  • Olfaction
  • Taste
  • Passage of food and liquid
• Important reflexes: swallowing, gag, cough.

Respiratory Tract Divisions

• Upper Respiratory Tract:
  • Nasal cavity (and oral cavity)
  • Pharynx
  • Larynx
• Lower Respiratory Tract:
  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli

Respiratory Epithelium

• Nasal cavity and superior pharynx: respiratory mucosa with mucous cells and mucus escalator.
• Inferior pharynx: stratified squamous epithelium for protection against abrasion and chemical attack.
• Lower respiratory tract: typical respiratory mucosa.
• Finer bronchioles: cuboidal epithelium.
• Gas exchange surfaces: delicate simple squamous epithelium (less than 1 \,\mu m between air and blood).

Nasal Cavity

• Elongated wedge-shaped spaces.
• Extends from the paired nares (nostrils) to the paired choanae.
  • Nares: Inferior aspect of the external nose with flexible borders, held open by alar and septal cartilages and maxillae margins; continuously open but dilatable/compressible.
  • Choanae: Rigid openings completely surrounded by bone; posterior opening communicating with the nasopharynx, formed by the sphenoid, vomer, and palatine bones.
• Boundaries:
  • Roof: frontal, ethmoid, and sphenoid bones.
  • Medial wall (nasal septum): septal cartilage, ethmoid, and vomer bones; Also includes the nasal crests of the maxilla and palatine bones inferiorly
  • Lateral wall: ethmoid, inferior nasal conchae bones; Also contains parts of the nasal, frontal, maxillary, lacrimal, palatine, and sphenoid bones
  • Floor: palatine process of maxillae and horizontal plate of palatine bones.
• Regions:
  • Nasal vestibule: space internal to the nares, lined with skin and hair follicles.
  • Respiratory region: large cavity, lined by respiratory epithelium, rich neurovascular supply.
  • Olfactory region: small, superiorly placed at the apex of the nasal cavity, lined by olfactory epithelium, contains olfactory receptors.
• Functions:
  • Warms and humidifies air.
  • Traps particles and prevents foreign matter from entering lungs.
  • Contains olfactory receptors.
  • Drains four paranasal sinuses and the lacrimal duct.
• Bones of the Nasal Cavities
  • External Nose: Nasal spine of frontal bone, nasal bones, frontal process of maxilla.
  • Nasal Septum: Ethmoid, vomer, nasal crest of maxilla and palatine, nasal cartilages.
  • Lateral Walls: Ethmoid, inferior concha, maxillae, lacrimal, sphenoid, palatine.
  • Posterior Wall: Sphenoid.

Ethmoid Bone

• Contributes to the roof, lateral, and medial walls.
• Contains ethmoidal cells (sinuses).
• Features: crista galli, olfactory foramina, cribriform plate, perpendicular plate, middle nasal concha, ethmoidal air cells, orbital plate.

Coronal Skull Cross Section

• Shows: perpendicular plate, superior/middle/inferior nasal conchae and meatuses, crista galli, frontal and maxillary sinuses, left orbit, vomer, oral cavity, maxilla.

Nasal Cavity Walls: Detailed Breakdown

• Floor:
  • Palatine process of maxillae, horizontal plate of palatine bones
• Roof:
  • Cribriform plate of ethmoid, nasal spine of frontal bone and nasal bones, surfaces of sphenoid, vomer and palatine bones
• Medial Wall (Nasal Septum): mucosa-covered surface of thin nasal septum, vertical plate of ethmoid bone, vomer, septal cartilage, nasal crest of maxillary and palatine bones.
  • Oriented vertically in the median sagittal plane and separates the nasal cavities.
• Lateral Wall:
  • Frontal process of maxilla, lacrimal bone, superior/middle/inferior conchae, uncinate process of ethmoid.
  • Contains bone, cartilage, and soft tissue covered with mucosa; complex and irregular contour characterized by conchae and four air channels; various structures drain (sinuses, nasolacrimal duct).

Conchae (Turbinates)

• Three curved shelves of bone: superior, middle, and inferior.
• Greatly increase the surface area of the mucosal epithelium (between tissue and respired air).
• Divide each nasal cavity into four air channels:
  1. Spheno-ethmoidal recess
  2. Superior meatus
  3. Middle meatus
  4. Inferior meatus

Paranasal Sinuses

• Four sinuses: frontal, maxillary, ethmoid, sphenoid.
• Extensions of nasal cavities.
• Lined by respiratory mucosa (ciliated and mucous-secreting).
• Open and drain into the nasal cavities via different meatuses (ostia).
• Innervated by ophthalmic and maxillary branches of CN V (trigeminal).
• Functions:
  • Lighten skull
  • Sound resonation
• Sinusitis = inflammation of the mucosa.
• Drainage Pathways and Locations:
  • Frontal sinus & anterior ethmoidal cells: frontonasal duct to middle meatus.
  • Middle ethmoidal cells: ethmoidal bulla in middle meatus.
  • Posterior ethmoidal cells: lateral wall of superior meatus.
  • Sphenoid sinus: spheno-ethmoidal recess.
  • Maxillary sinus: floor of hiatus semilunaris.
  • Nasolacrimal duct: inferior meatus.
• The maxillary sinus is the most commonly infected due to small ostia high on the superomedial walls causing poor drainage.

Arterial Supply

• Arterial supply to the nasal cavity arises from:
  • Anterior and posterior ethmoidal branches of the ophthalmic artery (from the internal carotid artery).
  • Lateral nasal and septal branches of the facial artery (from the external carotid artery).
  • Branches of the sphenopalatine and greater palatine branches of the maxillary artery (from the external carotid artery).
  • Kiesselbach's plexus: An area on the anterior septum of the nasal cavity where most of the above arteries anastomose and is a common site of nosebleeds.

Innervation

• Autonomic innervation to the glands of the mucosal glands of the nasal cavity are from cranial nerve 7 (the facial nerve), which arrive by ‘hitchhiking’ on branches of the maxillary nerve after they synapse in the pterygopalatine ganglion.
• General sensation of the nasal cavity occurs via branches of the 1st division of the trigeminal nerve (V1; e.g., the anterior ethmoidal nerve) and the 2nd division of the trigeminal nerve (cranial nerve V2; e.g., the internal nasal branch of the infraorbital nerve, nasal branch of the anterior superior alveolar nerve, and the nasopalatine nerve).

Pharynx

• Fibro-muscular C-shaped tube that provides a passageway for food to esophagus and air to trachea & lungs.
• Attached above to the base of skull and continues downwards to the cricoid cartilage and top of esophagus.
• The pharyngeal walls are attached anteriorly to the margin of the nasal cavity, oral cavity, and larynx. Based on this, it is subdivided into three regions.
• Down the posterior margin of the pharyngeal wall is the pharyngeal raphe (cord-like vertical ligament where the two sides weld together). Three constrictor muscles come off this median raphe.
• Regions:
  • Nasopharynx: posterior to nasal choanae & superior to soft palate; contains the pharyngeal tonsils (adenoids) & the opening of the pharyngotympanic tube.
  • Oropharynx: posterior to oral cavity, inferior to the soft palate & superior to epiglottis; the palatoglossus muscles mark the boundary from the oral cavity; contains the palatine tonsils.
  • Laryngopharynx: posterior to larynx & laryngeal inlet, extends from superior border of epiglottis to top of esophagus at cervical vertebral level 6 (CVI); contains the piriform fossae and the epiglottic valleculae.

Pharyngeal Arch Components

• Derivatives of the pharyngeal arch.
• Table 9-1 lists structures derived from pharyngeal arch components.
  • 1st Arch (Mandibular): Trigeminal (CN V); muscles of mastication, mylohyoid, anterior belly of digastric, tensor tympani, tensor veli palatini, malleus, incus; anterior ligament of malleus, sphenomandibular ligament.
  • 2nd Arch (Hyoid): Facial (CN VII); muscles of facial expression, stapedius, stylohyoid, posterior belly of digastric, stapes, styloid process, lesser cornu of hyoid bone; stylohyoid ligament, upper part of body of hyoid bone.
  • 3rd Arch: Glossopharyngeal (CN IX); stylopharyngeus, greater cornu of hyoid bone, lower part of body of hyoid bone.
  • 4th & 6th Arches: Superior laryngeal and recurrent laryngeal branches of Vagus (CN X); cricothyroid, levator veli palatini, constrictors of pharynx, intrinsic muscles of larynx, striated muscles of esophagus; thyroid cartilage, cricoid cartilage, arytenoid cartilage, corniculate/cuneiform cartilages.

Pharyngeal Muscles

• The pharyngeal wall is formed by skeletal muscles and fascia.
• Muscles split into two groups:
  • Constrictor muscles: circular direction (superior, middle, inferior)
  • Longitudinal muscles: vertically oriented (salpingopharyngeus, palatopharyngeus, stylopharyngeus)

Constrictor Muscles

• Superior, middle, inferior; all constrict the pharynx.
• Common posterior attachment: pharyngeal raphe.
• Anterior attachments:
  • Superior: pterygomandibular raphe
  • Middle: hyoid bone
  • Inferior: oblique line of thyroid cartilage & cricoid cartilage
• All innervated by CN X (vagus).

Longitudinal Muscles

• Salpingopharyngeus, palatopharyngeus, stylopharyngeus; all elevate the pharynx.
• Named according to their origin; all insert onto pharyngeal wall.

Pharyngeal Blood Supply

• Branches of the external carotid artery:
  • Ascending pharyngeal artery
  • Facial artery
  • Maxillary artery (pharyngeal branch supplies roof of nasopharynx)
  • Lingual artery
• Pharyngeal branches of the inferior thyroid artery from the thyrocervical trunk.

Pharyngeal Innervation

• All muscles of the pharynx are innervated by the vagus nerve (CN X), except stylopharyngeus - glossopharyngeal (CN IX).
• Each region of the pharynx has a different sensory innervation:
  • Nasopharynx: sensory [V2]
  • Oropharynx: sensory [IX]
  • Laryngopharynx: sensory [X]

Muscles of the Soft Palate

• Tensor veli palatini
  • Origin: scaphoid fossa of the medial pterygoid plate, spine of the sphenoid bone, and cartilage of the Eustachian tube.
  • Insertion: palatine aponeurosis of soft palate
  • Action: tenses soft palate and opens Eustachian tube during yawning to equalize pressure either side of the tympanic membrane
  • Innervation: mandibular division of the trigeminal nerve (cranial nerve V3)
• Levator veli palatini
  • Origin: cartilage of the Eustachian tube and petrous temporal bone
  • Insertion: palatine aponeurosis
  • Action: elevates soft palate during swallowing and yawning
  • Innervation: vagus nerve (cranial nerve X)
• Musculus uvulae
  • Origin: posterior border of hard palate
  • Insertion: palatine aponeurosis
  • Action: shapes uvula
  • Innervation: vagus nerve (cranial nerve X)
• Palatoglossus
  • Origin: inferior surface of palatine aponeurosis
  • Insertion: lateral margin of tongue (is an extrinsic tongue muscle)
  • Action: depresses palate, moves palatoglossal arch toward midline, and elevates pharynx
  • Innervation: vagus nerve (cranial nerve X)
• Palatopharyngeus
  • Origin: hard palate and palatine aponeurosis
  • Insertion: pharyngeal wall
  • Action: elevate pharynx and larynx during swallowing and speaking, closes oropharyngeal isthmus, and depresses palate
  • Innervation: vagus nerve (cranial nerve X)

Larynx

• Part of the respiratory system.
• Acts as both a valve to close respiratory tract and a sound-producing instrument (phonation).
• Extends from root of tongue to trachea and is suspended from the hyoid bone.
• Hollow structure made up of a framework formed by cartilages, ligaments, membranes, & intrinsic muscles.
• Mucous membrane of pharynx reflects over these cartilages & ligaments forming vestibular and vocal folds.
• Hyoid Bone: The only bone that doesn’t form an articulation with another bone, and is found in the neck posterior to the mandible and superior to the thyroid cartilage. Muscles attached to the hyoid bone include the suprahyoid and infrahyoid muscles.

Laryngeal Cartilages

• 9 cartilages:
  • 3 unpaired: cricoid, thyroid, epiglottis.
  • 3 paired: arytenoid, corniculate, cuneiform.
• Unpaired Cartilages:
  • Cricoid: Forms base of larynx; ring-like cartilage; posterior broad lamina, anterior narrow arch; 2 sites for articulations on both sides.
  • Thyroid: Largest of the laryngeal cartilages; 2 horns: superior & inferior; laryngeal prominence = Adam’s apple.
  • Epiglottis: Leaf-shaped cartilage; attached to thyroid between laryngeal prominence & inferior thyroid notch; forms lid for the glottis.
• Paired Cartilages:
  • Arytenoid: Pyramid-shaped with 3 surfaces; base articulates with cricoid, apex with corniculate; medial surface faces each other; anterolateral surface has 2 depressions for attachments (vocalis muscle, vestibular ligament).
  • Corniculate: Articulate with apices of arytenoid; point posteromedially.
  • Cuneiform: Club-shaped; suspended in fibroelastic membrane between arytenoid & epiglottis.

Ligaments of Larynx

• Extrinsic Ligaments: Attach to other structures other than the cartilages.
  • thyrohyoid membrane/ligament
  • Hyo-epiglottic ligament
  • Cricotracheal ligament
• Intrinsic Ligaments: Complete the architectural framework of the larynx - fibroelastic membranes that link the laryngeal cartilages together.
  • Cricothyroid ligament: free edge forms the vocal ligament under the vocal folds of the larynx (true vocal cord).
  • Quadrangular membrane: lower free edge forms the vestibular ligament under the vestibular fold of the larynx (false vocal cord).

Laryngeal Spaces and Folds

• Aryepiglottic fold
• Vestibule (supraglottic cavity)
• Vestibular fold
• Laryngeal ventricle and saccule
• Vocal fold
• Infraglottic/subglottic space

Laryngeal Muscles

• Framework is moved by various muscles that change its dimensions; divided into:
  • Extrinsic muscles: pass from larynx to neighboring structures; move the larynx as a whole and alter voice quality; elevators (suprahyoid muscles) and depressors (infrahyoid muscles).
  • Intrinsic muscles: pass between the cartilages of the larynx; move the cartilages of the larynx changing the length and tension of the vocal cords, the size and shape of the rima glottidis and rima vestibuli, and facilitate closing of the laryngeal inlet.

Extrinsic Laryngeal Muscles

• Suprahyoid muscles = elevate larynx and include:
  • Digastric
  • Geniohyoid
  • Mylohyoid
  • Stylohyoid
• Infrahyoid muscles = depress hyoid and larynx and include:
  • Sternohyoid
  • Sternothyroid
  • Omohyoid
  • Thyrohyoid
• Stylopharyngeus

Intrinsic Laryngeal Muscles

• Cricothyroid, thyroarytenoid, vocalis, lateral cricoarytenoid, posterior cricoarytenoid, transverse arytenoid, oblique arytenoid, aryepiglottic, thyroepiglottic.

Main Movements of Vocal Cords

• Adduction of vocal cords: Closes airway (lateral cricoarytenoids).
• Abduction of vocal cords: Opens airway (posterior cricoarytenoids).
• Change in tension of vocal folds: Vocalis, thyroarytenoids & cricothyroid.
• Closure/narrowing of laryngeal inlet: Aryepiglottic, thyroepiglottic, oblique arytenoids.

Laryngeal Blood Supply

• Superior laryngeal artery: branch of superior thyroid artery.
• Inferior laryngeal artery: branch of inferior thyroid artery.

Laryngeal Innervation

• Sensory and motor innervation is by two branches of the vagus nerve (CN X):
  • Superior laryngeal nerve (external and internal branches).
  • Recurrent laryngeal nerve.
• All intrinsic muscles of larynx are innervated by the recurrent laryngeal nerve, except cricothyroid (external branch of superior laryngeal nerve).
• Sensory innervation:
  • Above vocal cord area: internal branch of superior laryngeal nerve.
  • Below vocal cord area: recurrent laryngeal nerve.
• Vagus Nerve Main Branches:
  • Pharyngeal branch: supplies the pharyngeal constrictors, longitudinal muscles of the pharynx, the majority of the muscles of the soft palate (except for tensor veli palatini) as well as the striated esophagus.
  • Superior laryngeal branch:
    • Internal branch: supplies the mucosa of the oropharynx (including the valleculae).
    • External branch: supplies the cricothyroid muscle.
  • Recurrent laryngeal branch: supplies the intrinsic laryngeal muscles and mucosa below the vocal cords (infraglottic cavity).