Special Surgical Procedures II
LESSON 1: Eye, Ear, Nose, and Throat (EENT) Surgery
Section IV: THROAT, TONGUE, AND NECK SURGERY
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1-33. ANATOMY AND PHYSIOLOGY OF THE THROAT AND NECK
The word throat refers to those structures of the neck in front of the vertebral column, including the mouth, tongue, pharynx, tonsils, larynx, and trachea.
a. The Mouth. The mouth extends from the lips to the anterior pillars of the fauces. The portion of the mouth outside the teeth is known as the buccal cavity and that on the inner side of the teeth as the lingual cavity. The tongue occupies a large portion of the floor of the mouth. The hard and soft palates form the upper and posterior boundaries of the oral cavity, separating it from the nasal cavity and the nasopharynx. The soft palate emerges from the posterior border of the hard palate to form the uvula, a fingerlike movable projection. On either side, the uvula is adjacent to the base of the tongue anteriorly and the pharynx posteriorly.
b. The Pharynx.
(1) The pharynx serves as a channel for both the digestive and respiratory systems. It is situated behind the nasal cavities, mouth, and larynx. The food and air passages cross each other in the pharynx. The pharynx is a funnel-shaped structure, wide above and narrower below, about 12 cm in length. It is composed of muscular and fibrous layers and lined with mucous membrane. It is associated above with the sphenoid and the basilar part of the occipital bone. Below, it joins the esophagus. Seven cavities communicate with the pharynx: the two nasal cavities, the two tympanic cavities, the mouth, the larynx, and esophagus. The cavity of the pharynx may be subdivided from above downward into three parts: nasal, oral, and laryngeal. Infection may spread from the pharynx to the middle ear via the auditory tube. This auditory tube can be catheterized through the nostril.
(2) The nasopharynx communicates with the oropharynx through the pharyngeal isthmus, which is closed by muscular action during swallowing. The oropharynx and the laryngopharynx cannot be closed by muscular action during swallowing. The oropharynx and the laryngopharynx cannot be closed off from each other; both service respiratory and digestive functions.
(3) The pharynx is made up of three groups of constrictor muscles. Each muscle fits within the one below, and each inserts posteriorly in the median line with its mate from the opposite side. The constrictor muscles provide constriction of the pharynx for dilatation. Between the origins of the constrictor muscle groups, there are so-called intervals through which pass ligaments, nerves, and arteries. The recurrent laryngeal nerve is closely associated with the lower portion of the pharynx.
c. The Tonsils.
(1) The tonsils are situated one on each side of the oropharynx, lodged in a tonsillar fossa that is attached to folds of membrane containing muscle. One pair, the palatine tonsils, is the only lymphatic organ covered with stratified squamous epithelium. The lateral surface of each tonsil is usually covered with a fibrous capsule. The anterior and posterior tonsillar pillars join to form a triangular fossa, with the posterior lateral aspects of the tongue at its base. The so-called palatine tonsils are lodged in each fossa. The adenoids (pharyngeal tonsil) are suspended from the roof of the nasopharynx and consist of an accumulation of lymphoid tissue.
(2) The arteries of the tonsils enter the upper and lower poles. The tonsils are supplied with blood primarily by the tonsillar branch and the ascending palatine branch of the facial artery (branches of the external carotid artery). The external carotid artery on each side lies behind and lateral to each tonsil. The nerves supplying the tonsils are derived from the middle and posterior palatine branches of the maxillary and glossopharyngeal nerves.
d. The Larynx and Associated Structures.
(1) The larynx.
(a) The larynx is located at the upper end of the respiratory tract and is situated between the trachea and the root of the tongue, at the upper front part of the neck. The larynx has three main functions: a passageway for air, a valve for closing off air passages from the digestive system, and the pharynx, and a voice box on which sound and speech depend on to a degree.
(b) The larynx is a cartilaginous box, situated in front of the fourth, fifth, and sixth cervical vertebrae. The upper portion of the larynx is continuous with the pharynx above, and its lower portion joins the trachea. The skeletal structure provides for patency of the enclosed airway. The complex muscle action and arrangement of tissues within the structure provide for closure of the lumen for protection against trauma and entrance of foreign bodies and for phonation.
(2) Cartilages. The skeletal framework of the larynx consists of cartilages and membranes. There are nine separate cartilages-- three of them single and six arranged in pairs. The main
cartilages of the larynx include the thyroid, cricoid, epiglottis, two arytenoid, two corniculate, and two cuneiform. The thyroid cartilage (Adam's apple) forms the anterior portion of the voice box. The cricoid cartilage, which resembles a signet ring, rests beneath the thyroid cartilage and within the laryngotracheal space. The epiglottis is a slightly curled, leaf-shaped, elastic fibrous membrane. It is prolonged below into a slender process, attached in the midline to the upper border of the thyroid cartilage. When the cricothyroid muscle contracts, it pulls the thyroid cartilage and the cricoid cartilage, thereby tightening the vocal cords and, if unopposed, closing the glottis. The arytenoid cartilages, which rest above the signet ring portion of the cricoid cartilage, support the posterior portion of the true vocal cords.
(3) Laryngeal ligaments.
(a) The extrinsic ligaments of the larynx are those connecting the thyroid cartilage and epiglottis with the hyoid bone and the cricoid cartilage with the trachea. The intrinsic ligaments of the larynx are those connecting several cartilages of the organ to each other. They are considered the elastic membrane of the larynx.
(b) The mucous lining of the larynx blends with the fibrous tissue to form two folds on each side of the larynx. The upper set are known as the false cords. The lower set are called the true vocal cords because they are primarily concerned with the speaking voice and protection of the lower respiratory channels against the invasion of food and foreign bodies.
(4) Laryngeal muscles.
(a) The laryngeal muscles perform two distinct functions. There are muscles (extrinsic type) that open and close the glottis and those (intrinsic type) that regulate the degree of tension of the vocal cords.
(b) It should be noted that the spoken voice also depends on the sphincter action of the soft palate, tongue, and lips. The muscle action of the larynx permits the glottis to close either voluntarily or involuntarily by reflex action. The closure of the inlet by this mechanism protects the respiratory passages. The closure of the glottis and the action of the vocal cords are precisely coordinated to produce the spoken voice.
(c) Two branches of the vagus nerve supply the intrinsic muscles. The recurrent laryngeal nerve branch of the vagus nerve is the important motor nerve of the intrinsic muscles of the larynx. The sensory nerve, which is derived from the branches of the superior laryngeal nerve, supplies the mucous membrane of the larynx.
(d) When both the recurrent laryngeal nerves become divided or paralyzed, the glottis remains closed so tightly that air cannot be drawn into the lungs. As a lifesaving measure, an endotracheal or tracheostomy tube is inserted immediately.
(e) The larynx derives its blood supply from the branches of the external carotid and subclavian arteries.
e. Trachea. The trachea, a cylindrical tube about 15 cm in length and from 2 to 2.5 cm in diameter, begins in the neck and extends from the lower part of the larynx, on a level with the sixth cervical vertebra, to the upper border of the fifth thoracic vertebra. The tube descends in front of the esophagus, enters the superior mediastinum, and divides into right and left main bronchi. The trachea is composed of a series of incomplete rings of hyaline cartilage. The carina is a ridge on the inside at the bifurcation of the trachea. It is a landmark during bronchoscopy and separates the upper end of the right main branches from the upper end of the left main branches of the bronchi. Branches given off from the arch of the aorta--the brachiocephalic (innominate) and left common carotid arteries--are in close relation to the trachea. The cervical portion of the trachea is related anteriorly to the sternohyoid and sternothyroid muscles and to the isthmus of the thyroid gland.
f. Salivary Glands.
(1) The salivary glands consist of three paired glands: the sublingual, submaxillary, and parotid. They communicate with the mouth and pour their secretions into its cavities. The combined secretion of all these glands is termed saliva. The salivary glands consist of tissue found in the mucosa of the cheek, tongue, palate, floor of the mouth, pharynx, lip and paranasal sinuses. A tumor of a salivary gland may occur in any of these structures.
(2) The external carotid artery supplies the salivary glands and divides into its terminal branches: the internal maxillary and superficial temporal. The superficial temporal and internal maxillary veins unite to form the posterior facial vein.
(3) The sublingual gland lies on the undersurface of the tongue beneath the mucous membrane of the floor of the mouth at the side of the frenulum linguae, in communication with the sublingual depression on the inner surface of the mandible. It is supplied with blood from the submental arteries. Its nerves are derived from the sympathetic nerves. The many tiny ducts of each gland separately enter into the oral cavity on the sublingual fold.
(4) The submandibular gland lies partly above and partly below the posterior half of the base of the mandible and on the mylohyoid and hyoglossus muscles. This gland is closely associated with the lingual veins and the lingual and hypoglossal nerves. The external maxillary artery lies on the posterior border of the gland. Its duct (Wharton's duct) enters the mouth at the frenulum of the tongue.
(5) The parotid gland, the largest of the salivary glands, lies below the zygomatic arch in front of the mastoid process and behind the ramus of the mandible. This gland is enclosed in fascia, attached to surrounding muscles, and divided into two parts--a superficial and a deep portion--by means of the facial nerve. The parotid duct (Stensen's duct) pierces the buccal pad of fat and the buccinator muscle, finally opening into the oral cavity opposite the crown of the upper second molar tooth. The superficial temporal artery and small branches of the external carotid arise in the parotid gland behind the neck of the mandible.
g. General Structures of the Neck.
(1) The general topography of the organs lying in front of the prevertebral facial has been described. A layer of deep cervical fascia surrounds the neck like a collar and is attached to the trapezius and sternocleidomastoideus (sternocleidomastoid) muscles. In front of the neck, the deep fascial layer is attached to the lower border of the mandible.
(2) The pretracheal fascia of the neck lies deep in the strap muscles (sterno-thyroid, sternohyoid, and omohyoid) and partially encloses the thyroid gland, trachea, and larynx. The pretracheal fascia is pierced by the thyroid vessels. It fuses with the front of the carotid sheath on the deep surface of the sternocleido-mastoid. The carotid sheath consists of a network of areolar tissue surrounding the carotid arteries and vagus nerve.
(3) Laterally, the carotid sheath is fused with the fascia on the deep surface of the sternocleidomastoideus; anteriorly, it is fused with the middle cervical fascia along the lateral border of the sternothyroideus muscle. Lying between the floor and roof of this triangular formation of muscles are the lymph glands and the accessory nerve. Arteries and nerves traverse and pierce this triangle.
h. Lymphatic System of the Neck. The lymph glands of the neck are closely associated with the salivary glands and the lymph plexus. The submaxillary nodes, located in the submaxillary triangle, drain the cheek, side of the nose, upper lip, side of the lower lip, gums, side of the tongue, and medial palpebral commissure. Lymph from the facial and submental nodes also drains to these glands. The superficial cervical nodes, following the external jugular vein, drain the ear and parotid area to the superior deep cervical nodes. The cervical nodes are in close contact with the larynx, thyroid gland, nasal cavities, ear, nasopharynx, palate, esophagus, and skin and muscles of the neck.
