The muscles of the neck can be divided into four main groups. The first are the suboccipital muscles, which act to rotate the head and extend the neck. The two main suboccipital muscles are rectus capitis posterior major and rectus capitis posterior minor, both of which attach the inferior nuchal line of the occiput to the C2 and C1 vertebrae respectively. Additionally, obliquus capitis superior attaches the occiput to C1, while obliquus capitis inferior attaches C2 to C1.
The second set of muscles, the scalenes, form the floor of the posterior triangle. Anterior and middle scalenes originate from the transverse processes of certain cervical vertebrae and attach to the first rib, while the posterior scalene originates from the cervical spine and attaches to the second rib. The scalenes are very important because they flex the neck, and can also be recruited as accessory muscles of respiration.
The third group of muscles, the suprahyoid muscles, all attach to the hyoid bone from superior origins. These muscles are responsible for elevating the hyoid during swallowing. Mylohyoid and geniohyoid both originate from the internal surface of the mandible, with mylohyoid flattening the floor of the mouth and geniohyoid depressing the mandible. Digastric muscle is also responsible for depressing the mandible; it has two bellies, which are connected to each other and the hyoid bone via an intermediate ligament. Lastly, stylohyoid runs superiorly from the styloid process of the temporal bone to the posterior belly of digastric.
The fourth and final group of muscles are the infrahyoid muscles. These muscles mainly act to depress the hyoid. Sternohyoid and omohyoid originate from the sternum and scapula respectively, and both have an intermediate tendon between their two bellies that is anchored to the clavicle. Sternothyroid is found deeper, running from the sternum to the thyroid cartilage, and continues toward the hyoid as a thin band called the thyrohyoid. The thyrohyoid is the only infrahyoid muscle not innervated by the ansa cervicalis; instead, it is supplied by fibres from the hypoglossal nerve.
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