Muscles of the Neck: An Overview
The muscles in the neck are responsible for the movement of the head in the cervical region in all directions. The musculature of the neck is comprised of a number of different muscle groups. They can be divided into anterior, lateral and posterior groups based on their position in the neck. They are further divided into more specific groups based on a number of determinants; including depth, precise location, and function.
The position of the muscles in the neck generally relates to the function of the muscle or groups of muscles. For example, the muscles in the posterior neck are those which produce extension of the neck. The muscles of the neck are closely related to a number of important structures passing between the thorax and the head, including major blood vessels serving intra and extracranial regions, nerves, elements of the respiratory and gastrointestinal system and glands.
These are a group of 3 paired muscles in the anterior neck:
- the platysma
- subclavius muscles
Platysma is a superficial sheath-like muscle. It originates directly from the skin overlying the regions above and below the clavicle, passing superiorly to insert on to the skin overlying the region of the lower jaw. Due to its direct attachment to the skin, the platysma is involved in facial expression, pulling the corners of the mouth inferiorly, such as in expression of sadness. It is innervated by the cervical branch of the facial nerve. The platysma is the muscle that is used to stretch the skin, making it taut and providing a smoother surface for shaving the neck region.
Sternocleidomastoid is a large, superficial muscle of the neck. It is the muscle that appears to run diagonally beneath the skin when the head is turned to the opposite side. It originates as two heads from the medial clavicle and the sternum, and passes superiorly to insert onto the mastoid process on the posterior aspect of the temporal bone. Unilateral (or one-sided) contraction of the sternocleidomastoid muscle produces lateral rotation of the head. Bilateral (both sides) contraction of the muscle produces flexion of the neck. It is innervated by the accessory nerve (the 11th cranial nerve).
Subclavius is a small muscle located beneath the clavicle. It originates from the upper aspect of the 1st rib, and passes superiorly and laterally to insert onto the lower border of the clavicle. Its function is to pull the clavicle towards the sternum, reinforcing the sternoclavicular joint. Its innervation is the nerve to the subclavius, a branch of the upper trunk of the brachial plexus.
The suprahyoid muscles are a group of 4 paired muscles located above the hyoid bone in the neck. They all insert onto the hyoid bone and are involved in elevation of the bone during swallowing. Together, they partially form the floor of the oral cavity.
Digastric consists of two parts or bellies, as suggested by its name. The anterior and posterior bellies are connected by a central tendon that is attached to the hyoid bone. The anterior belly originates from the digastric fossa on the mandible; the posterior belly originates from the mastoid notch on the temporal bone. It’s insertion is onto the hyoid bone via the central tendon.
When the hyoid bone is fixed, the digastric muscle assists in opening the mouth. When both bellies contract simultaneously, the muscle elevates the hyoid bone. The anterior belly is innervated by the mylohyoid branch of the trigeminal nerve as the posterior belly is innervated by the facial nerve. The split innervation is due to the differing embryological origins of the bellies of the muscle.
Mylohyoid extends from the mylohyoid line on the inner mandible to the midline central tendon, called the midline raphe. The midline raphe continues to insert onto the hyoid bone. Mylohyoid elevates the hyoid bone, and is innervated by the mylohyoid nerve, a branch of the mandibular nerve.
Geniohyoid originates from the inferior mental spines on the inner surface of the mental symphysis. It also inserts onto the hyoid bone. It is innervated by the 1st cervical nerve and the hypoglossal nerve.
Stylohyoid extends from the styloid process of the temporal bone to the hyoid bone. It is innervated by the facial nerve.
The infrahyoids are a group of 4 paired muscles located inferior to the hyoid bone in the anterior neck. The sternohyoid, thyrohyoid and omohyoid depress the hyoid bone. This facilitates downward movement of the larynx after swallowing. They are supplied by the ansa cervicalis (C1-C3).
Sternohyoid is the most superficial of the infrahyoids, originating from the anterior surface of the sternoclavicular joint and manubrium and inserting onto the body of the hyoid bone.
Sternothyroid lies deep to sternohyoid. It originates from the posterior surface of the manubrium and inserts onto the oblique line of the thyroid cartilage.
Thyrohyoid is the continuation of the sternothyroid cartilage superiorly. It originates from the oblique line of the thyroid cartilage, and inserts onto the body and greater horn of the hyoid bone.
Omohyoid consists of two bellies: a superior and an inferior. It originates from the superior border of the scapula, and passes superomedially to a central tendon overlying the carotid sheath. It continues superiorly to insert onto the body of the hyoid bone.
The scalenes are a group of 3 paired muscles in the anterolateral neck. They extend from the cervical vertebrae to the first two ribs. The muscles elevate the ribs. Unilateral contraction produces lateral flexion of the neck, and bilateral contraction also produces anterior flexion of the neck.
Scalenus Anterior originates from the transverse processes of the C3-C6 cervical vertebrae and inserts onto the upper aspect of the 1st rib.
Scalenus Medius extends from the transverse processes of the C3-C7 to the first rib, inserting posterior to scalenus anterior.
Scalenus Posterior originates from the transverse processes of the C5-C7 and inserts onto the second rib.
Lateral Neck (Prevertebrals)
The prevertebral muscles are a group of paired deep muscles in the neck, enclosed by the prevertebral layer of deep cervical fascia. They are active in flexion and lateral flexion of the neck in the cervical region, and flexion at the atlanto-occipital joint. They play an important role in the stabilization of the cervical vertebral column, counteracting the cervical extensors.
Rectus Capitis anterior and lateralis. Rectus capitis anterior originates from the lateral mass of the atlas and inserts anterior to the foramen magnum on the base of the occipital bone. Rectus capitis lateralis extends from the transverse process of the atlas to the internal aspect of the jugular process on the occipital bone. Both muscles are innervated by the anterior rami of C1-C2 spinal nerves.
Longus Capitis originates from the anterior tubercles of the transverse processes of C3-C6. It inserts onto the inferior surface of the basilar region of the occipital bone. It is innervated by the anterior rami of C1-C4 spinal nerves.
Longus Colli, also known as longus cervicis originates from the C5-T3 vertebrae. It inserts onto C2-C4, the anterior tubercles of C5-C6, and the tubercle of the anterior arch of the atlas. It is innervated by the anterior rami of C2-C8.
Splenius capitis and splenius cervicis are a pair of superficial muscles in the back of the neck. Bilateral contraction of these muscles produces extension of the neck. Unilateral contraction produces lateral flexion and rotation to the same side. They are innervated by the dorsal rami of the middle and lower cervical nerves.
Splenius Capitis originates from the spinous processes of C5-T3 via the nuchal ligament. It inserts onto the mastoid process of the temporal bone.
Splenius Cervicis extends from the spinous processes of T3-T6 to the transverse processes of C1-C3.
The suboccipital muscles are a compartment of 4 small paired muscles inferior to the external nuchal protuberance and the inferior nuchal line. They are mainly postural muscles of the cervical region, but are involved in movements of the head including extension, lateral flexion, and rotation at the atlantoaxial joint. They are all innervated by the suboccipital nerve.
Rectus Capitis Posterior Major originates from the spinous process of the axis. It inserts onto the lateral aspect of the inferior nuchal line. It produces extension and ipsilateral rotation.
Rectus Capitis Posterior Minor originates from the tubercle on the posterior arch of the atlas and inserts onto the median aspect of the inferior nuchal line. It produces extension and ipsilateral rotation.
Obliquus Capitis Inferior originates from the spine of the axis and inserts onto the transverse process of the atlas. It produces rotation to the ipsilateral side.
Obliquus Capitis Superior extends from the transverse process of the atlas to the superior and inferior nuchal lines of the occipital bone. It produces extension and lateral flexion.
The transversospinalis muscles are a group of muscles extending across all levels of the vertebral column. They are divided into subgroups depending on the region in which they are active. For example, the rotatores (spinae) muscles are divided into rotatores cervicis, thoracis and lumborum groups. The transversospinalis muscles are involved in rotation and extension of vertebral column. They are innervated throughout their course by the dorsal rami of the spinal nerves.
Semispinalis Capitis originates from the transverse processes of the upper thoracic and lower cervical vertebrae and inserts between the superior and inferior nuchal line on the occipital bone.
Semispinalis Cervicis originates from the transverse processes of the upper thoracic vertebrae and inserts onto the spinous processes of C1-C5.
Rotatores Cervicis originates from the transverse processes of the cervical vertebrae and inserts onto the laminae and transverse processes of the vertebrae 1-2 levels above.
Interspinales in the cervical region extends from the spinous process of the cervical vertebrae to the spinous process of the adjacent vertebra.
Intertransversarii in the cervical region extend between the transverse processes of adjacent cervical vertebrae.
Torticollis is a condition resulting in asymmetrical positioning of the neck. The name is derived from the latin words tortus, meaning ‘twisted’ and collis, which means ‘neck’. It is caused by damage to and effectively, shortening of the sternocleidomastoid muscle in the lateral neck. In relation to the affected sternocleidomastoid muscle, torticollis presents as an ipsilateral (same side) head tilt, and contralateral (opposite side) rotation of the face and chin. Presenting at childbirth, congenital muscular torticollis (CMT) is the most common presentation of torticollis. Contracture of the sternocleidomastoid muscle as a result of a traumatic childbirth is regarded as one of the most frequent causes of CMT.
Accessory Nerve Test
The integrity of the accessory nerve can be examined by testing the function of the sternocleidomastoid muscle. This is done by rotating the head against resistance. The clinician will place their hand on the side of the head and ask the patient to turn the head towards the side where the hand is place. The ability to produce this movement indicates that the accessory nerve is intact and functional as far as the level at which the motor supply to sternocleidomastoid branches.