Anatomy of Larynx, Trachea, Respiratory Center

Anatomy of Larynx, Trachea, Respiratory Center

Larynx

• Location: Located between the pharynx and trachea, in the anterior part of the neck, opposite the cervical vertebrae III, IV, V and VI.

• Sex difference: Before puberty, the larynx of both sexes is not much different. After puberty, the male larynx develops more than the female larynx.

• Structure: It is made up of cartilages connected to each other by ligaments, membranes and joints. Cartilages are moved by muscles.

• Laryngeal cartilages:

• Thyroid cartilage: Single cartilage, book-shaped, consisting of 2 right and left pieces attached to each other in front by the laryngeal prominence, the pieces are separated by the superior thyroid notch. The posterior edge of each piece is extended into the superior horn and the inferior horn. The inferior horn of the thyroid cartilage articulates with the lateral surface of the cricoid cartilage at the cricothyroid joint.

• Cricoid cartilage: Single cartilage, ring-shaped, located under the thyroid cartilage, consisting of the cricoid lamina posteriorly and the cricoid arch anteriorly. The two lateral surfaces have the cricothyroid joint. The upper border articulates with the arytenoid cartilage, the lower border connects to the first tracheal ring by the cricotracheal ligament.

• Epiglottis: Single cartilage, leaf-shaped, the stem of the epiglottis is attached to the angle between the two pieces of thyroid cartilage.

• Arytenoid cartilage: Paired cartilage, located at the upper edge of the cricoid cartilage, pyramid-shaped with 3 sides. The apex articulates with the corniculate cartilage, the base has the cricoarytenoid joint. The base has 2 processes: vocal process, muscular process. The outer surface has the attachment of the vestibular ligament and vocal muscle. The vocal process provides the structure for the vocal ligament attachment. The muscular process is the attachment site of some laryngeal muscles.

• Corniculate cartilage: Paired small cartilages located at the apex of the two arytenoid cartilages.

• Cartilage connection: The laryngeal cartilages are attached to the hyoid bone above and the tracheal cartilages below.

• Laryngeal membrane:

• Thyrohyoid membrane: Stretches from the body and greater horn of the hyoid bone to the upper border of the thyroid cartilage. The upper border of the quadrate membrane is covered by the epiglottic fold. The lower border of the quadrate membrane is the vestibular ligament which is covered by the vestibular fold. The vestibular ligament runs from the angle of the thyroid cartilage to the anterolateral surface of the cricoid cartilage. The posterior border of the quadrate membrane attaches to the corniculate cartilage and arytenoid cartilage. The anterior border of the quadrate membrane attaches to the angle of the thyroid cartilage and the epiglottis.

• Cricovocal membrane (elastic cone): The lower border of the cricovocal membrane is attached to the upper border of the cricoid cartilage. The vocal ligament is actually the upper border of the cricovocal membrane, running from the angle of the thyroid cartilage to the vocal process and is covered by the vocal fold.

• Ligaments:

• Median cricothyroid ligament: Stretches from the upper border of the cricoid arch to the lower border of the thyroid cartilage.

• Cricotracheal ligament: Stretches from the lower border of the cricoid cartilage to the first tracheal ring.

• Cricoarytenoid ligament: Stretches from the posterior part of the upper border of the cricoid lamina to the posterior border of the base of the arytenoid cartilage.

• Laryngeal muscles:

• Extrinsic muscles:

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

• Infrahyoid muscles (thyrohyoid, omohyoid, sternohyoid, sternothyroid)

• Role: Elevate, depress, fix the larynx.

• Intrinsic muscles:

• Posterior cricoarytenoid muscles (2): Origin: Posterior surface of the cricoid lamina. Insertion: Muscular process of the arytenoid cartilage. Action: Pulls the muscular process backwards and rotates the vocal process outwards –> opens the rima glottidis.

• Lateral cricoarytenoid muscles (2): Origin: Upper border of the cricoid arch. Insertion: Muscular process of the arytenoid cartilage. Action: Pulls the muscular process forwards and rotates the vocal process inwards –> closes the rima glottidis.

• Cricothyroid muscles (2): Origin: Outer surface of the cricoid arch. Insertion: Lower border of the thyroid lamina. Action: Contraction –> thyroid cartilage pulled downwards and forwards, tenses the vocal ligament, closes the vocal fold.

• Thyroarytenoid muscles (2): Origin: Inner surface of the thyroid lamina and the elastic cone. Insertion: Muscular process of the arytenoid cartilage. Action: Closes the glottis and relaxes the vocal ligament.

• Vocal muscles (2): Origin: Angle between the 2 pieces of thyroid cartilage. Insertion: Vocal process of the arytenoid cartilage. Action: Alters the tension of the vocal fold during phonation.

• Transverse and oblique arytenoid muscles (2): Origin: Arytenoid cartilage on this side. Insertion: Opposite arytenoid cartilage. Action: Closes the glottis.

• Laryngeal inlet: Communicates with the pharynx, limited by:

• Anterior: Upper border of the epiglottis.

• Posterior: Interarytenoid fold.

• Lateral: Aryepiglottic folds.

• Laryngeal cavity: From top to bottom consists of:

• Inlet.

• Laryngeal vestibule.

• Vestibular fold.

• Ventricle of larynx.

• Vocal fold.

• Subglottic cavity.

• Rima glottidis: Narrower than the rima vestibuli and is the narrowest part of the laryngeal cavity.

• Glottis: Includes rima glottidis + vocal fold + arytenoid cartilage + interarytenoid fold.

• Blood supply:

• Superior laryngeal artery (branch of the superior thyroid artery).

• Inferior laryngeal artery (branch of the inferior thyroid artery).

• Nerve supply:

• Superior laryngeal nerve: Supplies the cricothyroid muscle and sensation to the upper part of the vocal fold.

• Recurrent laryngeal nerve: Supplies the remaining intrinsic muscles and the lower part of the vocal fold.

Trachea

• Limits: Lower border of the cricoid cartilage (level of the sixth cervical vertebra) –> level of the IV-V thoracic vertebrae.

• Structure: Tubular, flattened posteriorly, formed by stacked cartilaginous rings.

• Relationships:

• In the neck: Located anterior to the esophagus, in the middle of the carotid sheath, posterior to the isthmus of the thyroid gland and infrahyoid muscles.

• In the thorax: Located in the superior mediastinum, between the two pleural cavities, posterior to the aortic arch, anterior to the left brachiocephalic vein and thymus.

• Area for tracheostomy in the neck: Tracheostomy site (only covered by skin and fascia).

• Tracheal carina: Vertical ridge separating the two main bronchi at the end of the trachea.

• Inner surface: Usually smooth, pink and clearly visible cartilaginous ring ridges.

• Structure:

• Outer: Fibrocartilaginous and smooth muscle layer.

• Inner: Mucosa.

• Fibrocartilaginous smooth muscle layer: Consists of 16-20 C-shaped cartilaginous rings, deficient posteriorly, stacked on top of each other. Includes 2 layers covering the outer and inner surfaces of the cartilaginous ring and connecting the cartilaginous rings. Posterior to the tracheal ring are muscle fibers and elastic fibers stretching between the two ends of the cartilaginous ring –> forming a membrane.

• Main bronchus:

• Right main bronchus: Wider, shorter and more vertical than the left main bronchus.

• Left main bronchus: Lies above the aortic arch.

Respiratory center

• Divided into:

• Medullary respiratory center.

• Pontine respiratory center (dorsal + ventral group).