Muscles of the neck: An overview

Superficial muscles

Platysma

The platysma is a sheet-like muscle that lies within the subcutaneous tissue of the anterior neck, superficial to the investing layer of deep cervical fascia. It originates from the skin and fascia overlying the region of the clavicle and passes superiorly along the neck. The platysma inserts into several points, including the mandible, the skin of the lower face, lower lip and the corners of the mouth.

The platysma is innervated by the cervical branch of facial nerve (CN VII), and vascularized by the submental branch of the facial artery, and suprascapular branch of the thyrocervical trunk.

Due to its direct attachment to the skin of the lower face, the platysma functions mainly as a muscle of facial expression. For example, it contributes to producing an expression of sadness by pulling the corners of the mouth inferiorly.

Sternocleidomastoid muscle

The sternocleidomastoid is a large, two-headed muscle of the neck. Its clavicular head originates from the medial third of the clavicle, while its sternal head arises from the manubrium of sternum. The heads come together and ascend diagonally to insert onto the mastoid process of the temporal bone.

The sternocleidomastoid muscle is innervated by the accessory nerve (CN XI) and anterior rami of spinal nerves C2 and C3. Vascular supply to this muscle is derived from branches of the occipital, posterior auricular, superior thyroid and suprascapular artery.

The function of the sternocleidomastoid muscle depends on whether the muscle acts alone or together with its contralateral counterpart.

• Unilateral contraction produces lateral flexion of the neck on the same (ipsilateral) side and lateral rotation of the head to the opposite (contralateral) side.
• Bilateral contraction of the sternocleidomastoid muscles produce flexion of the neck, drawing the head towards the chest. When the head and neck are fixed, the sternocleidomastoid can also elevate the sternum and clavicle and thereby expand the thoracic cavity during forced inspiration.

Suprahyoid muscles

The suprahyoid muscles are four muscles located superior to the hyoid bone. They connect the hyoid bone to the mandible and the base of the skull and form the floor of the oral cavity. These muscles include the digastric, mylohyoid, geniohyoid and stylohyoid muscles.

Generally, the main function of these muscles is positioning of the hyoid bone and coordination of the movements of the floor of the mouth and the hyoid bone while swallowing or vocalization.

Digastric

The digastric muscle is a small muscle situated below the mandible, that extends from the mastoid process of temporal bone to the chin. The muscle is composed of a posterior and an anterior belly, connected by an intermediate tendon, which represents their common insertion point.

• The posterior belly arises from the medial surface of mastoid notch, a deep groove found on the mastoid process of temporal bone.
• The anterior belly arises from the digastric fossa of the lower border of mandible.

The muscle bellies both travel towards the hyoid bone and connect via the intermediate tendon, a fibrous tissue sling that is anchored to the superior aspect of the body of hyoid bone.

The digastric muscle has dual innervation. The anterior belly is innervated by the nerve to mylohyoid, a branch of the inferior alveolar nerve, while the posterior belly receives innervation from the digastric branch of the facial nerve. The blood supply for the digastric muscle is derived from the submental branch of the facial artery, and posterior auricular and occipital arteries.

The function of the digastric muscle depends on its point of action.

• If the mandible is fixed and the muscle is acting from below, it causes an elevation of the hyoid bone and larynx. This results in the closing of the epiglottis, preventing the inhalation of the food bolus during swallowing.
• If the hyoid bone is fixed and the muscle acts from above, it depresses the mandible, aiding the act of opening the mouth.

Mylohyoid

The mylohyoid is a sheet-like muscle that forms the majority of the floor of the mouth. The mylohyoid arises from the mylohyoid line on the inner surface of mandible, and inserts into the mylohyoid raphe and superior aspect of the body of hyoid bone.

The mylohyoid is innervated by the nerve to mylohyoid muscle that arises from the inferior alveolar branch of the mandibular nerve (CN V3). Its blood supply is derived from the sublingual, inferior alveolar and submental arteries.

Like the digastric muscle, the function of the mylohyoid depends on its point of action.

• If the mandible is fixed, the mylohyoid elevates the hyoid bone and the floor of the mouth, which aids the act of deglutition by pressing the tongue against the hard palate.
• If the hyoid bone is fixed, the muscle depresses the mandible and assists in opening the mouth.

Geniohyoid

The geniohyoid is a short muscle that arises from the inferior mental spine of the mandible and runs posteroinferiorly to insert into the superior border of the body of the hyoid bone.

The geniohyoid muscle is innervated by the anterior ramus of spinal nerve C1 via the hypoglossal nerve (CN XII) and vascularized by the sublingual branch of the lingual artery.

The main function of the geniohyoid is similar to other suprahyoid muscles:

• If the mandible is fixed, the muscle acts to elevate the hyoid bone and move the larynx and pharynx anterosuperiorly. The geniohyoid thus aids the act of deglutition and voice production.
• If the hyoid bone is fixed, the geniohyoid muscle depresses the mandible and assists in opening the mouth.

Stylohyoid

The stylohyoid is a thin muscle that extends between the temporal and hyoid bones. It originates from the posterior surface of the styloid process of temporal bone and passes anteroinferiorly and medially to attach on the body of hyoid bone.

The stylohyoid muscle is innervated by the stylohyoid branch of the facial nerve (CN VII). Its blood supply is derived from the facial, occipital and posterior auricular arteries.

The function of the stylohyoid is to elevate the hyoid bone and retract the tongue, which facilitates deglutition because it pushes the food bolus towards the soft palate. The stylohyoid also keeps the pharynx open during inspiration.

Infrahyoid muscles

The infrahyoid muscles are four muscles located inferior to the hyoid bone, that connect it to the larynx, sternum and scapula. These include the sternohyoid, omohyoid, sternothyroid and thyrohyoid muscles.

Generally, the main function of these muscles is positioning of the hyoid bone and movement of the thyroid cartilage of the larynx during vocalization, swallowing and mastication.

Sternohyoid

The sternohyoid muscle is a strap-like muscle found in the muscular triangle of the neck. It arises from the superior part of the manubrium of sternum and the posterior surface of the medial end of the clavicle. The sternohyoid then courses superiorly and medially to insert into the inferior border of the body of hyoid bone.

The sternohyoid is innervated by the anterior rami of the first three cervical spinal nerves via the ansa cervicalis, that arises from the cervical plexus. The muscle is vascularized by the superior thyroid branch of the external carotid artery.

The function of the sternohyoid muscle is to depress the hyoid bone and larynx after it has been elevated by the suprahyoid muscles. This action opens the airways again and reestablishes breathing after swallowing.

Omohyoid

The omohyoid is a narrow muscle that connects the scapula to the hyoid bone. The muscle is composed of two bellies connected by an intermediate tendon, similar to the digastric muscle.

• The inferior belly arises from the superior border of the scapula and runs anterosuperiorly to insert onto the intermediate tendon at the level of the arch of cricoid cartilage.
• The superior belly originates from the intermediate tendon at the level of the internal jugular vein and courses superiorly to insert at the lower border of the body of hyoid bone.

The nerve supply to the omohyoid is provided by the ansa cervicalis. Its blood supply stems from the superior thyroid branch of the external carotid artery, and inferior thyroid branch of the thyrocervical trunk.

As other infrahyoid muscles, the omohyoid functions to depress the hyoid bone and larynx to reopen the laryngeal inlet after swallowing. In addition, since the intermediate tendon of the omohyoid is connected to the carotid sheath, when the muscle contracts, it pulls on the sheath and decreases the pressure in the internal jugular vein. This action is convenient as it increases the venous return from the head to the superior vena cava.

Sternothyroid

The sternothyroid is a strap-like muscle that runs in the muscular triangle of the neck. It arises from the costal cartilage of the first rib and the posterior surface of the manubrium of the sternum. The muscle then courses superiorly to insert onto the oblique line of the thyroid cartilage.

The nerve supply to the sternothyroid muscle is derived from the ansa cervicalis (C1-C3). Its blood supply stems from the branches of the lingual and superior thyroid arteries.

Like other infrahyoid muscles, the function of the sternothyroid muscle is to depress the hyoid bone and larynx, and thereby open the laryngeal inlet and reestablish breathing after swallowing. In addition, the sternothyroid muscle can pull the thyroid cartilage away from the hyoid bone and further open the laryngeal inlet, which can aid forced inspiration.

Thyrohyoid

The thyrohyoid is a quadrilateral muscle located in the muscular triangle of the neck. It arises from the oblique line of the lamina of thyroid cartilage, and courses superiorly to insert onto the lower border of the greater horn and the adjacent body of hyoid bone.

The thyrohyoid muscle is innervated by the anterior rami of the first cervical spinal nerve (C1) via the hypoglossal nerve (CN XII). Its blood supply is derived from the infrahyoid and superior laryngeal branches of the superior thyroid artery, and the lingual branch of the external carotid artery.

In conjunction with other infrahyoid muscles, the thyrohyoid functions to depress the hyoid bone following its elevation during the act of swallowing and vocalization. However, the thyrohyoid has an additional function when the hyoid bone is fixed, in which it elevates the larynx. This action is important for persons that need to sing high notes, such as vocalists.

Anterior vertebral muscles

The anterior vertebral muscles are a deep group of muscles located just anterior to the cervical vertebral column. These include the rectus capitis anterior, rectus capitis lateralis, longus capitis and longus colli. These muscles are surrounded by the prevertebral fascia of the neck, which is why they are commonly referred to as prevertebral muscles. The principal function of these muscles is flexion of the head to varying degrees.

Rectus capitis anterior

The rectus capitis is a short strap muscle that arises from the anterior surface of the lateral mass of atlas (C1 vertebra) and inserts on the basilar part of the occipital bone, anterior to the foramen magnum.

The innervation of this muscle comes from the anterior rami of spinal nerves C1 and C2, while its blood supply is provided by branches of the vertebral and ascending pharyngeal arteries.

The function of the rectus capitis anterior is to flex the head at the atlanto-occipital joint, as well as to stabilize this joint.

Rectus capitis lateralis

The rectus capitis lateralis is a small muscle that arises from the superior surface of the transverse process of the atlas (C1) and ascends superiorly to insert onto the inferior surface of the jugular process of occipital bone.

The muscle is innervated by branches of the anterior rami of spinal nerves C1 and C2, and vascularized by the ascending pharyngeal, vertebral and occipital arteries.

The function of the rectus capitis lateralis is to flex the head laterally at the atlanto-occipital joint, and to help stabilize this joint during movement.

Longus capitis

The longus capitis is a long, flat muscle that arises from the anterior tubercles of transverse processes of vertebrae C3-C6 as four thin muscle strips. These muscle strips travel superiorly and medially to insert onto the inferior surface of the basilar part of the occipital bone.

The muscle is innervated by anterior rami of spinal nerves C1-C3, and vascularized by the ascending pharyngeal artery, ascending cervical branch of the inferior thyroid artery and the muscular branches of the vertebral artery.

The longus capitis functions as a weak flexor of the head when acting bilaterally, while unilateral contraction of the muscle produces ipsilateral rotation of the head.

Longus colli

The longus colli, also called the longus cervicis, is a long muscle that spans the entire length of the cervical spine and the upper vertebrae of the thoracic spine. It is divided into three parts:

• The superior part arises from the anterior tubercles of transverse processes of vertebrae C3-C5 and inserts into the anterior tubercle of vertebra C1.
• The intermediate part arises from the anterior surface of bodies of vertebrae C5-T3 and inserts into the anterior surface of bodies of vertebrae C2-C4.
• The inferior part arises from the anterior surface of bodies of vertebrae T1-T3 and inserts into the anterior tubercles of transverse processes of vertebrae C5-C6.

The muscle is innervated by the anterior rami of the spinal nerves C2-C6. Its blood supply stems from branches of the vertebral, inferior thyroid and ascending pharyngeal arteries.

The main function of the longus colli is to flex the neck. In addition, the inferior part of the muscle can produce a weak ipsilateral flexion and contralateral rotation of the neck.

Anterior scalene muscle

The anterior scalene muscle is the most anterior of the scalene muscles. It arises from the anterior tubercles of the transverse processes of vertebrae C3-C6, and inserts onto the scalene tubercle and the superior border of the first rib.

The anterior scalene muscle is innervated by the anterior rami of the spinal nerves C4-C6, and vascularized by the ascending cervical branch of inferior thyroid artery.

The function of the anterior scalene muscle depends on its point of action and whether the muscle acts alone or together with its contralateral counterpart.

• When the ribs are fixed and the muscle is acting from below, bilateral contraction of the anterior scalene causes flexion of the neck. In turn, unilateral contraction of the muscle causes lateral flexion of the neck to the same side.
• When the vertebral column is fixed, the muscle produces elevation of the 1st rib, which combined with the action of the external intercostals expands the antero-posterior diameter of the thoracic cage. This action is important during forced respiration.

Middle scalene muscle

The middle scalene is the largest of the scalene muscles, that arises from the transverse processes of axis (C2) and atlas (C1), and the posterior tubercles of transverse processes of the vertebrae C3-C7. The muscle then passes posterolaterally to insert onto the superior border of the first rib.

The middle scalene muscle receives its nerve supply from the anterior rami of cervical spinal nerves C3-C8. Its blood supply stems from the ascending cervical branch of the inferior thyroid artery.

The main function of the middle scalene muscle is to produce an ipsilateral flexion of the neck, when acting from below. When the cervical part of the vertebral column is fixed and the muscle is acting from above, it stabilizes or raises the 1st rib during forced inspiration.

Posterior scalene muscle

The posterior scalene is the smallest and most posterior of the scalene muscles that arises from the posterior tubercles of transverse processes of cervical vertebrae C4-C6. It then extends posterolaterally and inserts into the external surface of the second rib.

The nerve supply to the posterior scalene muscle is derived from the anterior rami of spinal nerves C6-C8, while its blood supply comes from the ascending cervical branch of the inferior thyroid artery and the transverse cervical branch of the thyrocervical trunk.

Similar to the middle scalene, the main function of the posterior scalene is ipsilateral flexion of the neck when acting from below, and stabilization or elevation of the second rib when acting from above.

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Superficial layer

Trapezius

The trapezius is a large, flat, triangular muscle that forms a diamond shape with its contralateral counterpart. The muscle extends over the posterior aspect of the neck and the superior part of the thorax. Based on the orientation of its fibers, the trapezius is divided into three parts; descending, transverse and ascending part, each of them having distinct attachments.

• The descending part is composed of the superior fibers of trapezius, that originate from the medial third of the superior nuchal line and the external occipital protuberance of the occipital bone. These fibers pass downwards to insert onto the posterior border of the lateral third of the clavicle.
• The transverse part is composed of the middle fibers of trapezius, that originate from the nuchal ligament of the spinous processes of vertebrae C1-C6, and spinous processes and supraspinous ligaments of vertebrae C7-T3. These fibers pass horizontally to insert onto the medial acromial margin and the superior crest of the scapular spine.
• The ascending part is composed of the inferior fibers of trapezius, that originate from the supraspinous ligaments and spinous processes of the vertebrae T4-T12. These fibers pass upwards and laterally to insert onto the lateral apex of the medial end of the scapular spine.

The trapezius muscle is innervated by the accessory nerve (CN XI). Its blood supply stems from branches of the occipital, superficial cervical, transverse cervical and dorsal scapular arteries.

The main function of the trapezius is to produce lateral flexion and contralateral rotation of the head when acting unilaterally, and extension of the head when acting bilaterally. In addition, the trapezius muscle stabilizes and produces movements of the scapula. Depending on which part of the trapezius contracts, these movements may be elevation, depression, retraction and rotation of the scapula.

Splenius muscles

The superficial muscles of the posterior neck are the splenius muscles; the splenius capitis and splenius cervicis. These muscles also belong to the superficial layer of the deep (intrinsic) back muscles.

• The splenius capitis originates from the spinous processes of vertebrae C7-T3 and the nuchal ligament, and inserts just below the lateral superior nuchal line of the occipital bone, and the mastoid process of temporal bone.
• The splenius cervicis arises from the spinous processes of vertebrae T3-T6 and inserts onto the transverse processes of vertebrae C1-C3.

The splenius muscles are innervated by the posterior rami of middle and lower cervical spinal nerves. The blood supply to the splenius muscles is by the occipital and transverse cervical arteries.

The function of the splenius muscles is to extend the head when contracted bilaterally, whereas unilateral contraction produces lateral flexion and rotation of the head to the same side.

Deep layer

Cervical transversospinalis muscles

The transversospinalis muscles are a large group of muscles that also belong to the deep layer of the intrinsic muscles of the back. This group of muscles comprise the semispinalis, multifidus, and rotatores muscles. All of these muscles are subdivided further according to the region they span.

The ones that span the posterior aspect of the neck are the:

• Semispinalis capitis, that arises from the articular processes of vertebrae C4-C7 and transverse processes of vertebrae T1-T6. It then courses upwards to insert between the superior and inferior nuchal lines of the occipital bone.
• Semispinalis cervicis, that arises from the transverse processes of vertebrae T1-T6 and inserts onto the spinous processes of vertebrae C2-C5.
• Multifidus cervicis, that arises from the articular processes of vertebrae C4-C7 and inserts onto the spinous processes of vertebrae 2-5 levels above the origin.

The semispinalis capitis is innervated by the descending branches of the greater occipital nerve (C2) and spinal nerve C3, while the semispinalis cervicis and multifidus cervicis are innervated by the medial branches of posterior rami of spinal nerves. These muscles receive their blood supply via branches of the vertebral, deep cervical and occipital arteries.

The function of the cervical transversospinalis muscles is to extend the head and neck during bilateral contraction, and to laterally flex and rotate the head to the opposite side during unilateral contraction.

Deepest layer

Suboccipital muscles

The suboccipital muscles are four small muscles found in the suboccipital region, deep to the semispinalis muscles. These are:

• Rectus capitis posterior major, that arises from the spinous process of axis and inserts onto the lateral part of the inferior nuchal line.
• Rectus capitis posterior minor, that arises from the posterior tubercle of atlas and inserts into the medial part of the inferior nuchal line.
• Obliquus capitis inferior, that arises from the spinous process of axis and inserts on the transverse process of atlas.
• Obliquus capitis superior, that arises from the transverse process of atlas and inserts on the occipital bone, between the superior and inferior nuchal lines.

All four of the suboccipital muscles are innervated by the suboccipital nerve (C1), and vascularized by the vertebral artery and the deep descending branches of the occipital artery.

The main function of the suboccipital muscles is reflected in maintaining posture, but they can also produce movements of the head. Depending on which muscle of the group contracts, the suboccipital muscle can produce an extension, lateral flexion and rotation of the head at the atlanto-axial joint.

Interspinales cervicis

The interspinales cervicis is the cervical part of the interspinales muscle group. It is composed of six pairs of muscles that span the space between the tips of the spinous processes of successive vertebrae. Thus, they arise from the superior aspect of spinous processes of vertebrae C3-T1 and insert onto the spinous processes of vertebrae C2-C7.

The interspinales cervicis are innervated by the posterior rami of spinal nerves, and vascularized by branches of the occipital, vertebral and deep cervical arteries.

The main function of the interspinales cervicis muscles aid in the extension of the neck.

Intertransversarii colli

The intertransversari colli represent the cervical portion of the intertransversarii muscles, which belong to the deepest layer of the intrinsic back muscles. The intertransversarii colli are composed of anterior and posterior sets of short slips of muscles that arise from the superior border of transverse processes of vertebrae C1-T1 and insert into the inferior border of the transverse processes of the superior adjacent vertebrae.

The intertransversarii colli are innervated by the anterior and posterior rami of cervical spinal nerves, and vascularized by the occipital, deep cervical and vertebral arteries.

Due to their small size, the function of these muscles is to only assists in lateral flexion of the head and to stabilize the cervical spine during movement.

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