Larynx Anatomy and Function

Anatomy and Histology of the Nasal Cavity and Paranasal Sinuses,and Larynx

This document provides a comprehensive overview of the anatomy and histologyof the nasal cavity, paranasal sinuses, and larynx, key components of the respiratory system.

Functions of the Respiratory System

• Upper Respiratory Tract (Nose, Nasal Cavity, Paranasal Sinuses, Pharynx):

  • Conduction, warming, and filtering air.

  • Olfaction (smell) and detection ofodorants.

  • Common pathologies: Rhinitis, Sinusitis, Pharyngitis.

• Lower Respiratory Tract (Larynx, Trachea,Bronchial Tree, Lungs, Pleurae):

  • Conduction, warming, and filtering air.

  • Phonation (voice production).

  • Respiration, gaseous exchange (O2 and CO2) in the lungs.

  • Common pathologies: Laryngitis, Tracheitis, Bronchitis, Pneumonia, Pleuritis.

Nose:External Anatomy

• The external nose is comprised of both bony and cartilaginous structures.

• Root of the nose (Radix nasi): Formed by nasal bones and frontal process of maxilla (piriform aperture).

• Dorsum of the nose (Dorsum nasi): Formed by nasal cartilages (lateral processes).

• Ala of the nose (Ala nasi): Major alar cartilages, 3-4 minor cartilages.

• Nostrils (Nares): Entrance to nasal cavities, formed by medial and lateral crus of major alar cartilages; lead to the nasal vestibule (Vestibulum nasi).

• Apex of the nose.

External Nose: Neurovascular Supply

• Arteries:

  • Angular artery (from facial artery, external carotid).

  • Posterior nasal artery (from ophthalmic artery, internal carotid).

  • Infraorbital artery (from maxillary artery, external carotid).

• Veins:

  • Facial vein Internal jugular vein.

  • Superior ophthalmic vein Cavernous sinu.s

• Lymphatic Drainage: Drains to submandibular lymph nodes.

Nasal Cavity: General Features

• Separated intoright and left by the nasal septum.

• Roof: Floor of the anterior cranial fossa.

• Floor: Roof of the oral cavity.

• Surrounded by four pairs of paranasal sinuses: maxillary, frontal, sphenoid, ethmoid.

• Piriform Aperture: Bony entrance to the nasal cavity, bordered by maxilla, nasal bones, and anterior nasal spine.

• Choana: Posterior opening towards the pharynx.

Nasal Cavity: Walls

• Superior Wall (Roof):

  1. Nasal bone

  2. Nasal part of frontal bone

  3. Cribriform plate of ethmoidbone

  4. Body of sphenoid bone

• Inferior Wall (Floor):

  1. Palatine process of maxilla

  2. Horizontal plate of palatine bone

• Medial Wall (Nasal Septum): Divides nasal cavity.

  • Cartilaginous Part: Anteriorly septal cartilage and medial crus of alar cartilage.

  • Bony Part: Perpendicular plate of ethmoid bone (postero-superiorly), Vomer (postero-inferiorly), nasal crests of maxilla and palatine bone.

  • Membranous Part: Antermost part, lined by skin andfibrofatty tissue.

• Lateral Wall: Characterized by three curved shelves of bone called conchae.

  • Superior nasal concha

  • Middle nasal concha

  • Inferior nasalconcha

  • These divide the air passage into three meatuses: inferior, middle, and superior nasal meatus.

Nasal Cavity: Mucosal Landmarks

• Anterior NasalVestibule: Stratified keratinized squamous epithelium (skin).

• Respiratory Region: Pseudostratified, ciliated epithelium with mixed nasal glands.

• Olfactory Region (above superior nasal concha): Olfactory receptors, supporting cells, basal cells.

Nasal Cavity: Neurovascular Supply

• Arteries:

  • Anterior and posterior ethmoidal arteries (from ophthalmic artery, internal carotid)supply anterior and superior parts.

  • Sphenopalatine artery (from maxillary artery, external carotid) supplies posterior and inferior parts.

  • Greater palatine artery (from maxillary artery).

  • Septal branch of superior labial artery (from facial artery).

  • Kiesselbach's plexus (Little's Area): A vascular plexus formed by the anastomoses of these four arteries in the antero-inferior part of the nasal septum, a common site for nosebleeds.

• Veins: Correspond to arteries, draining into ophthalmic vein, pterygoid plexus, and facial vein.

• Nerve Supply: Ophthalmic nerve (V1) and Maxillary nerve (V2).

Paranasal Sinuses

• Four pairs of air-filled cavities named after surrounding bones:

  1. Frontal Sinus (Sinus frontalis)

  2. Sphenoid Sinus (Sinus sphenoidalis)

  3. Maxillary Sinus (Sinus maxillaris)

  4. Ethmoid Cells (Cellulae ethmoidales): anterior, middle, and posterior.

• Openings intoNasal Meatuses:

  Nasal Passage	Structures that open into the meatus
  Inferior meatus	Nasolacrimalduct
  Middle meatus	Frontal sinus, Maxillary sinus, Anterior ethmoid cells, Middle ethmoid cells
  Superior meatus	Posteriorethmoid cells
  Spheno-ethmoid recess	Sphenoid sinus

The Larynx (Voice Box)

• Short passageway connecting the laryngopharynx with the trachea.

• Located in the midline of the neck, anterior to C4-C6 vertebrae.

• Composed of eleven pieces of cartilage:

  • Single (3): Thyroid, Epiglottis, Cricoid.

  • Paired (4 pairs): Arytenoid, Cuneiform, Triticeal, Corniculate.

• ExtrinsicMuscles: Connect cartilages to other throat structures.

• Intrinsic Muscles: Connect cartilages to each other.

• Laryngeal Cavity: Space from laryngeal entrance to inferior border of cricoid cartilage.

  • Laryngeal vestibule: Above vestibular folds.

  • Infraglottic cavity: Below vocal folds.

Laryngeal Cartilages in Detail

• Thyroid Cartilage (Hyaline):

  • Right and left laminae form the laryngeal prominence (Adam's apple).

  • Thyroid notch, superior/inferior horns, cricoid articular surface, inferior tubercle, oblique line.

• Cricoid Cartilage (Hyaline):

  • Lamina (posteriorly), arch (anteriorly).

  • Thyroid articular surface (junction of lamina and arch), arytenoid articular surfaces on superior border of lamina.

• Arytenoid Cartilages (Hyaline):

  • Pyramid-shaped, three surfaces.

  • Apex carries corniculate cartilage.

  • Base articulates with cricoid cartilage.

  • Tapers into two processes: muscular process (lateral/posterior) and vocalprocess (anterior, attachment for vocal ligament).

• Epiglottic Cartilage (Elastic):

  • Stalk (petiolus) attaches to thyroid cartilage.

  • Anterior surface (pharynx-facing): nonkeratinized, stratified squamous epithelium.

  • Posterior surface (laryngeal inlet-facing): respiratory epithelium.

• Cuneiform, Triticeal, Corniculate Cartilages: Smaller cartilages aiding in support and movement.

  • Cuneiform cartilages: Anterior to corniculate cartilages in aryepiglottic folds.

  • Triticeal cartilages: In lateral thyrohyoidligament.

  • Corniculate cartilages: Articulate with apices of arytenoid cartilages.

Laryngeal Joints

• Cricothyroid Joint:

  • Synovial joint between inferior cornua of thyroid cartilage and cricoid lamina.

  • Actions: anteroposterior sliding and rotation, which adjust vocal fold tension.

• Cricoarytenoid Joint:

  • Multiaxial articulation between arytenoids and cricoid cartilage.

  • Action: Changes distance between vocal processes and between vocal process and anterior commissure, crucial foradduction/abduction of vocal folds.

Ligaments of the Larynx

• Extrinsic Ligaments: Connect larynx to external structures.

  • Thyrohyoid membrane (median and lateral, contains triticeal cartilage).

  • Median cricothyroid ligament (part of conus elasticus).

  • Cricotracheal ligament.

  • Thyroepiglotticligament.

  • Hyoepiglottic ligament.

  • Cricopharyngeal ligament.

• Intrinsic Ligaments: Connect laryngeal cartilages.

  • Conus Elasticus (Cricovocal Membrane): Extends from cricoid to vocal processes of arytenoids and thyroid cartilage. Its superior free margin thickens to form the vocal ligament, which forms true vocal cords (vocal folds).

  • Quadrangular Membrane: Extends between epiglottis and arytenoid cartilages. Its inferior free margin thickens to form the vestibular ligament, forming false vocal cords (vestibular folds).

Laryngeal Cavity

• Tubular shape, lined with mucosa.

• Superior Aspect (Laryngeal inlet): Opens into pharynx.

• Inferior Aspect: Continuous with trachea.

• Divided into three major regions:

  • Vestibule: Between laryngeal inlet and vestibular folds.

  • Middle Portion (Glottis): Between vestibular and vocal folds. This is the voicebox.

  • Infraglottic Space: Between vocal folds and inferior opening into trachea.

• Laryngeal Ventricles: Lateral mucosal bulges between vestibular and vocal folds.

• Laryngeal Saccules: Anterosuperior extensions of ventricles, thought to contain many mucous glands.

• Rima Vestibuli: Triangular opening between the two vestibular folds.

• Rima Glottidis: Opening between true vocal cords (intermembranous part) and arytenoid cartilages (intercartilaginous part).

Laryngeal Muscles

• Extrinsic Laryngeal Muscles: M. cricothyroideus.

  • Innervation: External branch of superior laryngeal nerve (Vagus).

  • Action: Tightens vocal folds.

• IntrinsicLaryngeal Muscles:

  • M. cricoarytenoideus posterior.

  • M. cricoarytenoideus lateralis.

  • M. vocalis.

  • M. thyroarytenoideus.

  • M. arytenoideus obliquus.

  • M. arytenoideus transversus.

• Innervation (all intrinsic except cricothyroid): Recurrent laryngeal nerve (Vagus).

• Actions of Intrinsic Laryngeal Muscles:

Blood Supply of the Larynx

• Arteries:

  1. Superior laryngeal artery (from superior thyroid artery external carotid artery).

  2. Inferior laryngeal artery (from inferior thyroid artery subclavian artery).

• Veins: Drain into internal jugular vein and left brachiocephalic vein.

Nerves of the Larynx

• Superior Laryngeal Nerve (from vagus nerve):

  • External branch: Motor to cricothyroid muscle.

  • Internal branch: Sensory to laryngeal cavity down to vocal folds.

• Recurrent Laryngeal Nerve (from vagus nerve):

  • Motor to all intrinsic laryngeal muscles except cricothyroid.

  • Sensory to laryngeal cavity below vocal folds.

Lymph Nodes of the Larynx

• Superior Deep Cervical Nodes: Drain larynx above vocal folds.

• Inferior Deep Cervical Nodes:Drain larynx below vocal folds.