Comprehensive Study Notes on Head and Neck Anatomy
Introduction to Head and Neck Anatomy
These study notes are based on the lectures provided by Monica A. Pessina, Ph.D., JMEOTR. The material covers a comprehensive overview of the head and neck, including the muscles of facial expression, the parotid region, the nasal cavity and paranasal sinuses, the oral region, select muscles of the neck, the pharynx, the larynx, regional blood supply, and the anatomical triangles of the neck.
Muscles of Facial Expression
The facial muscles, also known as the muscles of facial expression, are located within the subcutaneous tissue of the anterior and posterior scalp, the face, and the neck. These muscles are unique because they move the skin and change facial expressions to convey various moods. Additionally, they play an essential role in eating and speech production.
The occipitofrontalis is a flat digastric muscle consisting of two parts: the occipital belly and the frontal belly. The action of these bellies is independent; the contraction of the occipital belly retracts the scalp, while the contraction of the frontal belly protracts the scalp. This muscle is innervated by the facial nerve (CN VII).
The orbicularis oris is a muscle that encircles the mouth and forms the lips. It is responsible for closing the mouth and compressing or protruding the lips (often referred to as the pucker). Like other muscles of facial expression, it is innervated by the facial nerve (CN VII).
The buccinator is a thin, flat, rectangular muscle that sits deep to the oral cavity and comes forward to form the lateral wall of the oral cavity. Its primary action is to press the cheek against the molar teeth, thereby holding food on the chewing surfaces of the teeth during mastication. It is innervated by the facial nerve (CN VII).
Specific Facial Muscles for Lip and Eye Movement
The levator labii superioris muscle arises from the area below the orbit and inserts into the upper lip. Its primary action is to raise the upper lip. It is innervated by the facial nerve (CN VII).
The depressor labii inferioris muscle arises from the mandible and inserts into the skin of the lower lip. Its primary action is to depress the lower lip. It is innervated by the facial nerve (CN VII).
The orbicularis oculi is the muscle responsible for closing the eyelids. Its fibers form concentric circles around the orbital margin and the eyelids. It consists of two distinct parts with different actions: the palpebral portion is responsible for gentle blinking, while the orbital portion is used for forceful closing of the eyes. This muscle is innervated by the facial nerve (CN VII).
The zygomaticus muscles arise from the zygomatic bone. Their primary action is to draw the angle of the mouth upward and backward, facilitating smiling. They are innervated by the facial nerve (CN VII).
Clinical Correlates of the Head and Scalp
Scalp lacerations or cuts can frequently appear to gape open due to the tension of the occipitofrontalis muscle. These injuries require closure using sutures or medical staples. Immediate first aid care for a scalp laceration involves applying direct pressure for to stop any bleeding and washing the cut thoroughly with soap and water.
In the field of nasal soft tissue reconstruction, the "forehead flap" is considered the gold standard for surgical repair. This procedure is documented in research by authors such as Baker SR, Menick FJ, and others in publications like "Seminars in Plastic Surgery" (May 2013).
The Parotid Gland and Region
The parotid gland is a major salivary gland located anterior to the ear and the mastoid process of the temporal bone. It is the largest of the salivary glands. The parotid duct passes from the anterior side of the gland and travels across the anterior border of the masseter muscle. It سپس pierces the buccinator muscle and enters the oral cavity. The opening of the parotid duct is located in the oral vestibule, specifically opposite the second maxillary molar tooth.
Several important structures are embedded within the parotid gland, including the facial nerve (CN VII) and its various branches, as well as the external carotid artery. Clinical interest in this region includes rare cases such as a "tuba player with air in the parotid gland," where computed tomography (CT scanning) revealed air within the parotid duct (pneumoparotid) and lateral to the gland.
The Nasal Cavity and Paranasal Sinuses
The nasal cavity relates to numerous regions of the head. It is bounded above by the perforated cribriform plate of the ethmoid bone. Below, the floor of the nasal cavity is formed by the hard palate, which serves as a partition separating the oral cavity from the nasal cavity above. Posteriorly, the nasal cavity is continuous with the pharynx.
Nasogastric (NG) tube placement is a common procedure, but it carries reported complications. These include perforation of the esophagus and misplacement in the airway (tracheobronchial placement). Notably, there have been reported cases of intracranial placement of NG tubes, typically occurring when there is a fracture in the cribriform plate.
Paranasal sinuses are air-filled extensions of the respiratory part of the nasal cavity into the surrounding skull bones. These sinuses are lined with a mucous membrane and all drain into the nasal cavity. The maxillary sinuses are the largest of the paranasal sinuses and occupy the bodies of the maxillae. A unique feature of the maxillary sinus is that the opening for drainage is located superiorly, which can make drainage difficult when the head is upright.
The Oral Region and Palate
The oral region is divided into two parts: the vestibule and the oral cavity proper. The vestibule is the space between the inner surface of the lips and cheeks and the outer surface of the teeth and gingiva. It includes a midline feature known as the philtrum. The muscles of facial expression, innervated by the facial nerve, control this area. The oral cavity proper is the space mostly filled with the tongue.
The palate forms the roof of the oral cavity proper and the floor of the nasal cavity. It has two distinct parts: the hard palate (bone), which acts as a firm structural backdrop for tongue-assisted food manipulation and sound formation, and the soft palate (muscle), which elevates during swallowing to seal off the nasal cavity from the oral cavity.
The floor of the oral cavity is formed primarily by the mylohyoid muscles. These muscles run from the mandible to the hyoid bone, filling the U-shaped gap between the sides and body of the mandible. The tongue, which has a dorsal and ventral (sublingual) surface, is composed of intrinsic muscles (to change the shape of the tongue) and extrinsic muscles (to move the tongue).
Neck Muscles and the Pharynx
The sternocleidomastoid (SCM) muscle is a key landmark in the neck. Its attachments are the mastoid process of the temporal bone and the sternum and clavicle. It is innervated by the accessory nerve (CN XI). Unilateral contraction of the SCM causes lateral flexion to the same side and rotation of the head to the opposite side. Bilateral contraction results in cervical flexion.
The pharynx is the common passageway for both the respiratory and digestive systems, leading to the larynx and esophagus. Muscles of the pharynx compress and move food inferiorly. From the pharynx, air travels to the larynx, then the trachea and lungs, while food travels to the esophagus.
The Larynx and Laryngeal Skeleton
The larynx is a structure necessary for voice production and serves a vital function in guarding the airway. It is located in the anterior neck, suspended from the hyoid bone, and is composed of cartilages connected by membranes and ligaments. These cartilages are moved by several muscles.
The thyroid cartilage is the largest of the laryngeal cartilages, formed by two portions that fuse in the midline to form the laryngeal prominence (Adam's apple). The vocal folds (cords) attach inside the thyroid cartilage and on the vocal process of the arytenoid cartilages. A chondrolaryngoplasty is a surgical procedure that reduces the size of the laryngeal prominence, often utilized as part of gender-affirming facial surgery.
Other cartilages of the larynx include the epiglottic cartilage, which is "free" at its superior end and attached to the thyroid cartilage at its inferior end, bending to cover the airway during swallowing. The cricoid cartilage is the most inferior cartilage and is shaped like a signet ring, completely encircling the airway. The arytenoid cartilages are two pyramid-shaped cartilages that articulate with the cricoid cartilage. Each has a vocal process (anterior attachment for vocal folds) and a muscular process (lateral attachment for muscles).
Regional Blood Supply
The blood supply to the head and neck originates from the arch of the aorta. On the right side, the brachiocephalic trunk branches into the right common carotid artery and the right subclavian artery. On the left side, the left common carotid artery and the left subclavian artery arise directly from the aortic arch.
The carotid pulse is palpated by positioning the fingers between the larynx and the anterior border of the sternocleidomastoid muscle at the level of the cricoid cartilage (). A normal pulse rate is . The common carotid artery bifurcates into the internal and external carotid arteries at the level of the superior border of the thyroid cartilage.
The internal carotid arteries become the main supply for the brain and orbit. The external carotid artery and its branches generally supply structures external to the skull. One terminal branch of the external carotid artery is the superficial temporal artery, and another is the maxillary artery. The external carotid is also embedded within the parotid gland.
Venous Drainage of the Head and Neck
The principal venous drainage for the head and neck involves the jugular veins. The external jugular vein (EJV) drains most of the scalp and side of the face and delivers blood to the subclavian vein. The internal jugular vein (IJV) is the main venous structure in the neck; it terminates by uniting with the subclavian vein to form the brachiocephalic vein.
The left and right brachiocephalic veins (BCV) are formed posterior to the sternoclavicular joints. These two veins unite to form the superior vena cava (SVC) at the inferior border of the first right costal cartilage. The SVC returns all blood from structures superior to the diaphragm to the heart, with the exception of the lungs and the heart itself.
Anatomical Triangles of the Neck
The neck is divided into regions known as triangles for clinical and anatomical description. The Anterior Triangle is bordered by the midline of the neck, the anterior border of the sternocleidomastoid muscle, and the inferior border of the mandible. Select contents of this triangle include the submandibular gland, the common carotid artery, the vagus nerve (CN X), and the hypoglossal nerve (CN XII).
The Posterior Triangle is bordered anteriorly by the sternocleidomastoid muscle, posteriorly by the trapezius muscle, and inferiorly by the clavicle. Select contents of the posterior triangle include the external jugular vein, the subclavian vessels, the spinal accessory nerve (CN XI), and the roots and trunks of the brachial plexus.