Anatomy

Laryngeal Neuromuscular Anatomy (Fig. 3—1)

• Extrinsic Depressors: (C1—C3) sternohyoid, sternothyroid, thyrohyoid, and omohyoid muscles

• Extrinsic Elevators: geniohyoid (C1), digastric (CN V and CN VII), mylohyoid (CN V), stylohyoid (CN VII) muscles

• Posterior Cricoarytenoid (PCA): (RLN) only vocal fold ABductor

• Lateral Cricoarytenoid (LCA): (RLN) vocal fold ADduction

Figure 3—1. The intrinsic laryngeal muscles and their vector action: (1) posterior cricoarytenoid muscle; (2) interarytenoid muscle; (3) vocalis (medial aspect of thyroarytenoid); (4) thyroarytenoid muscle; (5) lateral cricoarytenoid muscle; (6) cricothyroid muscle. (copyright 1989 Novartis. Adapted with permission from The Atlas ofHuman Anatomy, illustrated by Frank H. Netter, MD. All rights reserved.)

Figure 3—1. The intrinsic laryngeal muscles and their vector action: (1) posterior cricoarytenoid muscle; (2) interarytenoid muscle; (3) vocalis (medial aspect of thyroarytenoid); (4) thyroarytenoid muscle; (5) lateral cricoarytenoid muscle; (6) cricothyroid muscle. (copyright 1989 Novartis. Adapted with permission from The Atlas ofHuman Anatomy, illustrated by Frank H. Netter, MD. All rights reserved.)

• Thyroarytenoid (TA): (RLN) increases vocal fold tension, vocal fold ADduction, the medial aspect of the TA is called the vocalis

• Cricothyroid: (external branch of SLN) ADduction, increases vocal fold tension and length (chief pitch-changing muscle)

• Interarytenoid: (RLN) only unpaired muscle, ADduction

Laryngeal Cartilage

• Thyroid, Cricoid, and Arytenoids: hyaline cartilage (hyaline cartilage is the most common, found in most articular cartilage)

• Epiglottis: fibroelastic cartilage (less strength, elastin), attaches to thyroid cartilage

• Corniculate Cartilage: fibroelastic cartilage, above arytenoid cartilage, provides rigidity to A-E folds

• Cuneiform Cartilage: fibroelastic cartilage, within A-E folds, provides rigidity

• Trieceous Cartilage: sometimes found in thyrohyoid ligament, may be mistaken on x-ray as a foreign body when calcified

Laryngeal Joints

• Cricothyroid Joints: synovial, rocks (hinge)

• Cricoarytenoid Joints: synovial, rocking motion (anteromedially for vocal fold ADduction and posterolaterally for vocal fold ABduction)

Vocal Fold Layers (from superficial to deep, Fig. 3—2)

1. Squamous Epithelium: stratified, nonkeratinizing

2. Superficial Lamina Propria (SLP, Reinke's Space): loose fibrous matrix (few fibroblasts), gelatinous consistency permits fluency of vocal fold vibration (mucosal wave)

3. Intermediate Lamina Propria: elastin (some fibroblasts)

4. Deep Lamina Propria: fibroblasts and collagen (dense)

5. Thyroarytenoid Muscle Complex: thyromuscular bundle (thyroarytenoid muscle) and thyrovocalis bundle (vocalis muscle)

NOTE: the squamous epithelium and superficial layer of the lamina propria form the vocal fold cover, the intermediate and deep lamina propria form the vocal ligament (transition zone), the thyroarytenoid muscle complex forms the vocal fold body

NOTE: The gelatinous consistency of the SLP allows for fluency of vibration of the cover over the body during voicing (cover-body concept of vocal fold vibration). This vibratory activity can be readily visualized using videostroboscopy and is referred to as the mucosal wave.

Vocal Fold Cover

Squamous Epithelium

Lamina Propria

Superficial

(Reinke's space)

Vocal I" Intermediate

Ligament Deep

Vocal Fold Thyroarytenoid Body Muscle Complex

Squamous Epithelium

Figure 3-2. Histological layers of the true vocal fold.

Pediatric Airway Anatomy

• neonates and all non-humans have their epiglottis engage the soft palate forming a central tunnel for airway and the lateral sides for food to allow for simultaneous respiration and deglutition; in humans, the epiglottis descends during infancy

• >90% of neonates are obligate nasal breathers until 2 months because of lack of coordination of oral/respiratory functions and epiglottis location

• the epiglottis at birth is omega (ft) shaped

• superior margin of the infant's larynx is at the level of cervical spine C1 and the cricoid cartilage at C4; as the larynx descends the cricoid cartilage aligns to C6—7 by puberty

• 1 mm of laryngeal edema in the neonate can reduce airway by 60%

• endotracheal tube size = (age + 16)/4; bronchoscope size = age/4

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