Anatomy of the Larynx and Pharynx

Hyoid Bone and Related Structures

  • Hyoid Bone: A U-shaped bone located in the anterior neck.
  • Right Vagus Nerve: Vital for nerve signaling in the throat region.
  • Right Common Carotid Artery: Supplies blood to the right side of the head and neck.
  • Thyroid Cartilage: Framework of the larynx, prominently forms the laryngeal prominence (Adam's apple).
  • Cricoid Cartilage: The only complete cartilaginous ring in the airway, providing support.
  • Thyroid Gland: Endocrine gland with crucial metabolic functions.
  • Trachea: Main airway leading to the lungs.
  • External Carotid Artery: Supplies blood to the face, neck, and base of the skull.
  • Superior Laryngeal Nerve: Innervates parts of the larynx, including sensory and motor functions.
  • Inferior Ganglion of Vagus Nerve: Associated with the vagus nerve, involved in autonomic functions.
  • Left Internal Carotid Artery: Supplies blood to the left side of the head and brain.
  • External Branch of Superior Laryngeal Nerve: Innervates the cricothyroid muscle.
  • Left Vagus Nerve: Prominent nerve in throat operation and autonomic functions.
  • Left Common Carotid Artery: Supplies blood to the left side of the head and neck.
  • Esophagus: Muscular tube connecting the throat and stomach, involved in swallowing.
  • Right Recurrent Laryngeal Nerve: Branch of the vagus nerve, providing motor function.
  • Right Subclavian Artery: Supplies blood to the upper limb.
  • Left Recurrent Laryngeal Nerve: Provides motor function to the larynx and innervates the vocal cords.

Anatomy of the Larynx

  • Larynx: Also known as the voice box, it plays a crucial role in voice production and protects the air passages during swallowing.
  • Location: Situated in the anterior neck, spanning vertebral levels C3 to C6.
  • Structure: Extends from the laryngeal inlet to the level of the cricoid cartilage, interconnected with various parts of the pharynx.
  • Composition: Made up of cartilages, ligaments, and membranes.

Components of the Larynx

  • Cartilage Composition:
    • Unpaired Cartilages:
    • Thyroid Cartilage: Forms the anterior wall of the larynx.
    • Epiglottis: A flap covering the laryngeal inlet during swallowing.
    • Cricoid Cartilage: Forms the base of the larynx and encapsulates the airway.
    • Paired Cartilages:
    • Arytenoid Cartilages: Pyramid-shaped, involved in vocal fold movement.
    • Cuneiform Cartilages: Small, rod-like structures providing support within the larynx.
    • Corniculate Cartilages: Sit atop the arytenoids, contributing to laryngeal structure.

Detailed Structures Within the Larynx

Thyroid Cartilage

  • Location: Opposite the C4 vertebral level.
  • Structure: Composed of two laminae fused anteriorly, forming the laryngeal prominence (Adam's Apple).
  • Notch: Separated by the thyroid notch, with superior and inferior thyroid horns posteriorly.
  • Attachment: The thyrohyoid membrane connects superior horns, pierced by superior laryngeal vessels and nerves.
  • Articulation: The inferior horns articulate with the cricoid cartilage at the cricothyroid joint.

Cricoid Cartilage

  • Shape: Resembles a signet ring, with a broad posterior part (lamina) and a narrow anterior part (arch).
  • Articulations:
    • Cricothyroid Joint: Articulates with the thyroid cartilage, providing a synovial joint.
    • Cricocricoid Joint: Connects with arytenoid cartilages, allowing for joint movement.
  • Ligaments:
    • Cricotracheal Ligament: Connects cricoid to the first tracheal ring.
    • Conus Elasticus: Membrane between cricoid and thyroid, thickening to form ligaments.

Epiglottis

  • Shape: Heart-shaped cartilage covered by a mucous membrane.
  • Position: Superior end projects behind the mouth and hyoid bone; inferior stock attached to the thyroid cartilage.

Paired Cartilages

  • Arytenoid Cartilage: Pyramidal shape; base articulates with cricoid cartilage; features vocal and muscular processes.
  • Cuneiform and Corniculate Cartilages: Found in the aryepiglottic folds, aiding in laryngeal function.

Quadrangular Membrane

  • Extends from epiglottis to arytenoid cartilage.
  • Free Margins:
    • Vestibular Fold: Lower border.
    • Aryepiglottic Fold: Upper border with aryepiglottic muscles that close the inlet during swallowing.

Vocal Folds

  • Extend from the thyroid cartilage to the arytenoid cartilage, crucial in sound production.

Membranes and Ligaments

  • Thyrohyoid Membrane: Connects the hyoid bone to thyroid cartilage.
  • Hyoepiglottic Ligament: Anchors the epiglottis to the hyoid.

Cavity of the Larynx

  • Rima Glottidis: Space between the vocal folds; shape varies during breathing.
  • Cavity Divisions:
    • Vestibule or Supraglottis: From laryngeal inlet to vestibular folds.
    • Ventricle or Sinus: Between vestibular and vocal folds.
    • Infraglottic Cavity: Between vocal folds and cricoid cartilage.

Muscle Groups and Functions

Muscle Division

  • External Muscles: Elevate or depress the larynx during swallowing.
  • Internal Muscles: Adjust individual laryngeal components for breathing and phonation.

Extrinsic Muscles

  • Suprahyoid and Infrahyoid Groups:
    • Actions: Suprahyoid muscles and stylopharyngeus elevate; infrahyoid muscles depress the larynx.

Intrinsic Muscles

  • Control rima glottidis shape, vocal fold length, and tension.
  • Innervation:
    • Most intrinsic muscles (except cricothyroid) are innervated by the inferior laryngeal nerve (from recurrent laryngeal nerve).
    • Cricothyroid Muscle: Innervated by the external branch of the superior laryngeal nerve.

Specific Intrinsic Muscles Functions

Cricothyroid Muscle

  • Function: Stretches and tenses vocal ligaments for forceful speech.
  • Innervation: External laryngeal nerve.

Thyroarytenoid Muscle

  • Function: Relaxes vocal ligament for softer voice.
  • Innervation: Recurrent laryngeal nerve.

Posterior Cricoarytenoid Muscle

  • Function: Sole abductors of vocal folds; widens the rima glottidis.
  • Innervation: Recurrent laryngeal nerve.

Lateral Cricoarytenoid Muscle

  • Function: Major adductors of vocal folds; modulates tone and volume.
  • Innervation: Recurrent laryngeal nerve.

Transverse and Oblique Arytenoids

  • Function: Adduct arytenoid cartilages, narrowing the laryngeal inlet.
  • Innervation: Recurrent laryngeal nerve.

Phonation

  • Occurs during expiration when vocal folds are held together to vibrate.
  • Control: Degree of opening managed by muscles attached to arytenoid cartilages.
  • Pitch Control: Dependent on length and tension of vocal folds manipulated by thyroid and arytenoid movements.
  • Vocal Fold Characteristics: Generally, males have longer and heavier vocal folds, resulting in lower pitch.

Nerve Innervation

  • Vagus Nerve: Main innervator for laryngeal function.
  • Sensory Innervation:
    • Vocal Folds: Internal branch of superior laryngeal nerve.
    • Infraglottis: Recurrent laryngeal nerve.
  • Motor Innervation:
    • Mostly via recurrent laryngeal nerve; cricothyroid via external branch of superior laryngeal nerve.

Nerve Injury Implications

  • External Laryngeal Nerve Injury: Results in weakened phonation.
  • Recurrent Laryngeal Nerve Injury: Can lead to hoarseness if one is affected; may severely impair speech if both are damaged.

Anatomy of the Pharynx

  • Pharynx: Superior part of the gastrointestinal tract; posterior to the nose, mouth, and larynx.
  • Division:
    • Nasopharynx: Superior portion extending from the cranial base.
    • Oropharynx: Extends from soft palate to epiglottis.
    • Laryngopharynx: Lies posterior to the larynx.

Further Details on Pharynx

  • Components:

    • Nasopharynx: Contains pharyngeal tonsil (adenoids) and auditory tube openings.
    • Oropharynx: Contains palatine tonsils.
    • Laryngopharynx: Includes piriform recesses alongside the laryngeal inlet.

  • Muscle Types: Longitudinal and circular muscles; pharyngeal constrictors are key circular muscles.

  • Detailed Study: More intricate details of the pharynx are outlined in subsequent sections.