The Anterior Triangle of the Neck
To examine the musculoskeletal, nervous, respiratory, digestive, endocrine, lymphatic, and cardiovascular systems, you need knowledge of neck anatomy. The anterior triangle of the neck, or the front of the neck, is bordered by the sternocleidomastoid muscle, the midline of the neck from the chin to the manubrium, and the bottom of the mandible.
Many muscles are located in the anterior triangle of the neck, and they’re classified according to their relationship to the hyoid bone. The hyoid bone is a horseshoe-shaped bone located in the anterior part of the neck below the chin. It serves as an anchor for muscles that help you swallow and move your tongue.
Hyoid muscles: Located above (suprahyoid) and below (infrahyoid) the hyoid bone, these muscles move the hyoid bone and larynx.
Suprahyoid muscles: These muscles connect the hyoid bone to the cranium. They form the floor of the mouth and assist the larynx during speaking. Following are the four suprahyoid muscles:
The mylohyoid originates on the mylohyoid line of the mandible and inserts onto the body of the hyoid. It elevates the hyoid, the floor of the mouth, and the tongue.
The geniohyoid originates on the inferior mental spine of the mandible and inserts onto the body of the hyoid. It pulls the hyoid anteriorly and superiorly and shortens the floor of the mouth.
The stylohyoid originates on the styloid process of the temporal bone and inserts onto the body of the hyoid. It elevates and retracts the hyoid to elongate the floor of the mouth.
The digastric has two portions. The anterior belly originates on the mandible, and the posterior belly originates on the temporal bone of the skull. The digastric inserts onto the body and the greater horn of the hyoid. It works with the infrahyoid muscles to depress the mandible against resistance and elevates the hyoid.
Infrahyoid muscles: These muscles are below the hyoid bone. They provide a base for the tongue and help stabilize the hyoid during swallowing and speaking.
The omohyoid originates on the superior border of the scapula and inserts onto the inferior border of the hyoid. It depresses and retracts the hyoid.
The sternohyoid originates on the manubrium and medial end of the clavicle and inserts onto the body of the hyoid. It depresses the hyoid after elevation during swallowing.
The sternothyroid originates on the posterior surface of the manubrium and inserts onto the thyroid cartilage. It depresses the hyoid and larynx.
The thyrohyoid originates on the thyroid cartilage and inserts onto the inferior border of the body and greater horn of the hyoid. It depreses the hyoid and elevates the larynx.
Two cranial nerves, the vagus and glossopharyngeal, have branches in the anterior cervical triangle. Two more nerves are located here:
The transverse cervical nerve innervates the skin over the anterior triangle of the neck.
The hypoglossal nerve travels to the tongue.
The anterior triangle of the neck is also home to a couple of well-known blood vessels, plus a few more. Carotid arteries include the common carotid artery and the internal and external carotid arteries. The common carotid artery travels upward within the carotid sheath and then forks into the internal and external carotid arteries.
Several arteries branch off the external carotid artery:
Superior thyroid artery: Provides blood flow to the thyroid gland and the larynx
Ascending pharyngeal artery: Supplies blood to the pharyngeal wall
Lingual artery: Takes blood to the tongue
Facial artery: Supplies blood to parts of the face
Occipital artery: Takes blood to the back of the scalp
Posterior auricular artery: Supplies the scalp and the auricle
Superficial temporal artery: Also sends blood to the scalp
Maxillary artery: Goes up to the skull and supplies blood to the middle areas of the face
The internal jugular vein is formed as the dural venous sinuses leave the skull through the internal jugular foramen. It continues inferiorly until it joins the subclavian vein to form the brachiocephalic vein.
The anterior triangle of the neck has an interesting bit of tissue called the carotid body. You can find it near the bifurcation of the common carotid artery. Near the bifurcation of the common carotid artery is also a small dilation of the internal carotid artery, called the carotid sinus. The carotid sinus has baroreceptors that detect changes in blood pressure. When they’re stimulated, they cause a slowing of heart rate and a decrease in blood pressure. The carotid sinus is innervated by cranial nerves IX and X.
The carotid body is a chemoreceptor, which is a sensory receptor that monitors chemical changes in the blood. The carotid body monitors the amounts of oxygen and carbon dioxide in the blood, and when the amount of oxygen starts to get too low, it triggers a response that changes your heart rate and breathing rate. It’s innervated by cranial nerves IX and X.