Anatomy and Function of the Larynx

Introduction to the Larynx

• Overview of learning objectives concerning the anatomy and function of the larynx.

• Breakdown of topics into manageable parts:

  • Cartilages of the larynx and the joints they form.

  • Ligaments and membranes between the cartilages.

  • Muscles of the larynx and their movements.

• Reassured that the complex structure can be mastered bit by bit.

Anatomy of the Larynx

Definition and Location

• The larynx is also called the voice box.

• Located in the anterior neck, anterior to the cervical part of the esophagus.

• Link between the pharynx (where both food and air pass) and the trachea (where only air passes).

• At rest, the larynx is located at the level of the third to sixth cervical vertebrae (higher in females and children).

• Larger in males; thyroid cartilage grows until age 40, forming the Adam's apple.

Functions of the Larynx

1. Protects airways from choking by large swallowed objects.

2. Regulates airflow into the lungs.

3. Involved in sound production (phonation).

General Anatomy Components

• Laryngeal Inlet: Entrance from the pharynx into the larynx.

  • Bordered by:

  • Anteriorly: Free edge of the epiglottis.

  • Laterally: Aryepiglottic folds.

  • Posteriorly: Cuneiform and corniculate tubercles; interarytenoid notch.

• Three main spaces of the larynx:

  • Vestibule: Superior space from the laryngeal inlet to the vestibular folds.

  • Ventricle: Space between the vestibular folds and the vocal folds.

  • Infraglottic cavity: Inferior space from the vocal folds to the first tracheal ring.

• Rhyma Glottidis: Opening between the vocal folds and arytenoid cartilages.

Cartilages of the Larynx

Overview of Cartilages

• Unpaired Cartilages:

  1. Epiglottis

  2. Thyroid cartilage

  3. Cricoid cartilage

• Paired Cartilages:

  1. Arytenoid cartilages

  2. Corniculate cartilages

  3. Cuneiform cartilages

  4. Triticeal cartilages (variable presence).

Detailed Description of Cartilages

• Epiglottis:

  • Leaf-shaped elastic cartilage.

  • Location: Posterior to the hyoid bone, anterior to the laryngeal inlet.

  • Function: Closes off the laryngeal inlet during swallowing.

  • Structure: Free edge (broad, occasionally notched) & stalk (attached via thyroepiglottic ligament).

  • Covered by important mucosa:

  • Anterior surface: Mucosa similar to tongue (contains taste buds).

  • Posterior surface: Ciliated mucosa typical of respiratory tract.

• Thyroid Cartilage:

  • Largest cartilage of the larynx, formed of two fused hyaline cartilage laminae.

  • Structure:

  • Inferior two-thirds form the Adam's apple (laryngeal prominence).

  • V-shaped superior thyroid notch above prominence.

  • Extends into superior/inferior horns (cornua).

  • Oblique line and tubercles noted on the surface.

• Cricoid Cartilage:

  • Complete ring of hyaline cartilage between thyroid cartilage and trachea.

  • Structure:

  • Anterior arch (curved) and posterior lamina (flattened).

  • Vertical ridge creating two concavities.

  • Articular surfaces for thyroid and arytenoid cartilages.

• Arytenoid Cartilages:

  • Pyramidal in shape with three surfaces; sits on cricoid cartilage base.

  • Projections:

  • Vocal process (sharp projection anteriorly).

  • Muscular process (rounded, posterolaterally).

• Corniculate Cartilages:

  • Elastic, conical cartilages on top of arytenoid cartilages.

• Cuneiform Cartilages:

  • Tiny elongated nodules of elastic cartilage in aryepiglottic folds.

• Triticeal Cartilages:

  • Elastic cartilages present in a variable number of individuals; found associated with thyrohyoid membrane.

Types of Cartilage

• Hyaline Cartilage:

  • Thyroid, cricoid, most arytenoid cartilages.

  • Composed of type II collagen; strong and firm.

• Elastic Cartilage:

  • Cuneiform, corniculate, and triticeal cartilages.

  • Contains elastic fibers; provides flexibility.

Joints of the Larynx

• Cricothyroid Joint:

  • Synovial joint formed between inferior cornu of thyroid cartilage and cricoid cartilage.

• Cricoarytenoid Joints:

  • Synovial joints between cricoid cartilage and bases of arytenoid cartilages.

• Arytenocorniculate Joints:

  • Can be synovial or cartilaginous.

Ligaments and Membranes of the Larynx

Extrinsic Structures

• Thyrohyoid Membrane:

  • Connects thyroid cartilage to hyoid bone.

  • Thickened in the middle (median thyrohyoid ligament) and at lateral edges (lateral thyrohyoid ligaments).

  • Contains triticeal cartilages.

• Cricotracheal Ligament:

  • Connects cricoid cartilage to the first tracheal ring.

• Hyoepiglottic Ligament:

  • Attaches hyoid bone to epiglottis.

Intrinsic Structures

• Quadrangular Membrane:

  • Connects lateral edges of epiglottis to arytenoid cartilages.

  • Forms aryepiglottic fold (superior) and vestibular fold (false vocal cords, inferior).

• Thyroepiglottic Ligament:

  • Connects stalk of epiglottis to thyroid cartilage.

• Cricothyroid Membrane:

  • Connective tissue between cricoid and thyroid cartilages.

  • Contains:

  • Median cricothyroid ligament (anterior).

  • Conus elasticus (lateral), with vocal ligaments at upper edge.

Muscles of the Larynx

Overview

• Muscles divided into intrinsic and extrinsic groups:

  • Extrinsic: Elevate or depress larynx during swallowing/speech (attached to hyoid).

  • Intrinsic: Move components of the larynx (modulating voice).

Extrinsic Muscles

• Depressors:

  • Infrahyoid muscles (sternohyoid, sternothyroid, omohyoid).

• Elevators:

  • Suprahyoid muscles (digastric, stylohyoid, geniohyoid, mylohyoid).

  • Thyrohyoid (depresses hyoid; elevates larynx).

Intrinsic Muscles

• Cricothyroid Muscle:

  • Innervated by external laryngeal nerve.

  • Increases pitch by lengthening/stretching vocal ligaments.

• Adductors of Arytenoid Cartilages:

  • Transverse Arytenoid Muscle:

  • Unpaired, adducts arytenoid cartilages.

  • Oblique Arytenoid Muscles:

  • Superficial to transverse; also adducts.

• Lateral Cricoarytenoid Muscle:

  • Swivels muscular process laterally, adducts and shortens vocal folds.

  • Allows whispering-type phonation.

• Posterior Cricoarytenoid Muscle:

  • Primary abductor, pulls muscular process medially.

  • Opens rima glottidis for air flow.

• Aryepiglottic Muscle:

  • Extension of oblique arytenoid; closes rima glottidis.

• Thyroarytenoid Muscle:

  • Draws arytenoid cartilages anteriorly, shortens vocal ligament, lowers pitch.

• Vocalis Muscle:

  • Adjusts pitch minutely via fine tuning of vocal folds.

• Thyroepiglottic Muscle:

  • Widens laryngeal inlet, often considered part of thyroarytenoid.

Grouping by Function

• Adductors: Close rima glottidis (lateral cricoarytenoid, transverse, oblique arytenoid muscles).

• Abductor: Opens rima glottidis (posterior cricoarytenoid).

• Tensors and Relaxers: Control pitch (cricothyroid = tensor; thyroarytenoid = relaxer; vocalis = fine adjustments).

• Protective Function: Several intrinsic muscles act together to protect the laryngeal inlet from foreign material.

Clinical Applications

Muscle Tension Dysphonia (MTD)

• Difficulty or pain in sound production (dysphonia).

• Symptoms: Change in vocal quality, effort in sound production, voice fatigue, pain, and potential aphonia (inability to speak).

• Two types:

  • Primary MTD: Causes unclear (allergies, emotional distress).

  • Secondary MTD: Due to underlying physical problems (nodules, polyps, vocal fold paresis).

• Diagnosis involves examination of neck muscle tenderness and laryngoscopy.

• Treatment involves voice therapy and addressing underlying causes in secondary MTD.

Conclusion

• Comprehensive overview covered cartilages, ligaments, and muscles of the larynx, establishing their functions and anatomy.

• Emphasis on their relevance in both health and clinical practice, particularly in sound production and speech disorders.