The digastric is a muscle located in the anterior region of the neck and that is made up of two portions or bellies, one anterior and one posterior. Both are connected to each other by means of a tendon.
The anterior belly of the muscle attaches to the mandible and the posterior to the temporal bone of the skull. While the tendon that joins them passes through a space formed by a fibrous band that inserts into the hyoid bone.
By Image: Gray385.png modified by Uwe Gille - Image: Gray385.png, Public Domain, The hyoid is a single, horseshoe-shaped bone located in the middle of the neck. It is characterized by being related to all the muscular and ligamentous structures of that cervical area, including the digastric muscle, without being articulated to any other bone.
The two bellies of the digastric muscle work synergistically during the chewing and swallowing processes. The anterior belly also works by helping to lower the jaw during speech, while the posterior belly contributes with other muscles in the extension movement of the head.
In surgical anatomy, the digastric muscle plays an important role since it is part of the limits of the triangular spaces that are recognized in the neck.
These spaces are traversed by vital vascular and neurological structures and serve as a guide for the surgeon to identify cervical elements.
Embryological origin
From the fourth week of gestation, the formation of the body's muscle groups begins. The muscles and other organs of the neck originate from the primitive structures called branchial arches.
By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See «Book» section below) Bartleby.com: Gray's Anatomy, Plate 41, Public Domain, https://commons.wikimedia.org/w/index. php? curid = 792240
There are six branchial arches, and different muscles, nerves, organs and vascular elements originate from each one, except for the fifth.
The anterior and posterior belly of the digastric muscle have a different origin. While the anterior belly comes from the first branchial arch together with the mylohyoid nerve, which provides motor skills, the posterior one originates from the second arch, together with the facial nerve.
By the eighth week of gestation, the neck muscles are fully formed and the cartilage that will form the hyoid bone can be seen.
Anatomy
Insertion
The digastric is a paired muscle that is located in the anterior region of the neck. It is found in the group of the so-called suprahyoid muscles, since it is located above the hyoid bone.
It is made up of two bellies, anterior and posterior, which are joined in the middle by a common tendon.
The anterior belly is attached to the lower edge of the jaw in a groove called the digastric fossa, while the posterior belly is attached to a protrusion of the temporal bone of the skull, known as the mastoid process.
By Berichard - travail personnel (own work) d'après Gray's Anatomy public, CC BY-SA 3.0, Both portions are joined by its intermediate tendon which, in most cases, makes its way through the stylohyoid muscle and passes through a fibrous tunnel that is fixed to the hyoid bone.
The embryological origin of the two portions that make up the digastric muscle is not the same, which is why each belly is independent in terms of its irrigation and innervation, receiving these supplies from different structures.
In that sense, each segment of the digastricus behaves like an individual muscle.
Irrigation and innervation
The anterior belly of the muscle is supplied by the sub-mental artery, which is a direct branch of the facial artery; while the posterior belly receives the occipital artery and the posterior auricular artery, both direct branches of the external carotid artery.
Regarding the neurological endings, the anterior belly is innervated by the mylohyoid nerve, which has the same embryological origin.
This ending is a branch of the inferior alveolar nerve that comes from the mandibular branch of the trigeminal nerve.
By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See «Book» section below) Bartleby.com: Gray's Anatomy, Plate 1210, Public Domain, https://commons.wikimedia.org/w/index. php? curid = 564825
The trigeminal nerve is one of the twelve cranial nerves, nerves that originate directly from the brain.
For its part, the posterior belly is innervated by the facial nerve. Another of the most important cranial nerves for the mobility of the face.
Features
The digastric muscle is one of the four muscles that lie above the hyoid bone. These are known as the suprahyoid muscles, which are part of the floor of the mouth and provide stability to the hyoid to perform different important tasks, such as swallowing and breathing.
By User: Mikael Häggström - Image: 386.png, Public Domain, Contraction of the anterior digastric belly helps stabilize and lower the hyoid at the time of swallowing. In addition, it works by collaborating with the rest of the suprahyoid muscles in the opening of the mouth and the descent of the jaw when chewing and speaking.
As for the posterior belly, its activation participates in the process of extension of the head, along with other cervical muscles.
The digastric muscle also serves a guiding role for the surgeon when manipulating the cervical area.
The neck is a complex structure that houses important vascular and neurological structures and different vital organs. To make its study more practical and understandable, it is divided into triangles that are delimited by muscles and bone structures.
The digastric muscle is part of the boundaries of two triangles in the anterior region of the neck, which house important structures such as the submaxillary gland, the facial vein, and the external carotid artery.
By Olek Remesz (wiki-pl: Orem, commons: Orem) Modified by user: madhero88 - Own work, CC BY 3.0, Knowing the insertion points of the muscle and the content of these triangles is of great importance for the surgeon since it reduces the possibility of injuring the structures that are within them.
The anterior belly of the muscle can be used as a flap in reconstructions of the floor of the mouth, in those patients with malignant diseases that involve major surgeries in which the lower support of the tongue may be lost.
Injuries
Digastric muscle dysfunction can occur from damage during a surgical procedure, especially in emergency surgeries, or from excessive scarring or burn from radiation therapy.
This type of injury causes problems chewing and swallowing food, difficulty articulating words when speaking and opening the mouth.
The hardening, fibrosis or calcification of the digastric muscle is a pathology that should be taken into account in those patients who present with chronic neck pain with difficulty or pain when mobilizing the tongue.
This condition is sometimes associated with irritation of the cervical nerves and its resolution is surgical.
References
- Tranchito, E. N; Bordoni, B. (2019). Anatomy, Head and Neck, Digastric Muscle. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov
- Khan, Y. S; Bordoni, B. (2019). Anatomy, Head and Neck, Suprahyoid Muscle. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov
- Kim, S. D; Loukas, M. (2019). Anatomy and variations of digastric muscle. Anatomy & cell biology. Taken from: ncbi.nlm.nih.gov
- Carvallo, P; Carvallo, E; del Sol, Mariano. (2017). Digastric Muscle or Digastricomastoid Muscle ?. International Journal of Morphology. Taken from: scielo.conicyt.cl
- Roesch, Z. K; Tadi, P. (2019). Anatomy, Head and Neck, Neck. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov
- AlJulaih, G. H; Menezes, RG (2019) Anatomy, Head and Neck, Hyoid Bone. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov