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The muscles in the neck and back are responsible for moving the head. There are about 30 muscles in the neck that help stabilize and support the head and upper back, and they also assist with chewing, swallowing, and breathing. The neck muscles are skeletal muscles, meaning they are attached to bones by tendons, and they are voluntary muscles, meaning we control how they move and work. The major muscle that laterally flexes and rotates the head is the sternocleidomastoid, or SCM, which is a major head flexor along with the suprahyoid and infrahyoid muscles. The splenius capitis, a posterior neck muscle, also aids head extension, while unilateral contraction assists with lateral flexion and rotation to the same side.
| Characteristics | Values |
|---|---|
| Number of neck muscles | 30 |
| Neck muscle types | Lateral, posterior (superficial, suboccipital, transversospinalis), scalene, splenius, trapezius |
| Neck muscle functions | Stabilise and support the head, enable a range of movements, assist with chewing, swallowing, breathing, and <co: 2,11>facial expressions |
| Head muscle | Occipitofrontalis |
| Head muscle functions | Moves up the scalp and eyebrows |
| Bilateral neck muscles | Sternocleidomastoid (SCM), suprahyoid, infrahyoid |
| SCM functions | Bilateral contraction bends the head forward, unilateral contraction facilitates lateral flexion on the same side or head rotation to the opposite side |
| SCM origin | Sternum and clavicle |
| SCM insertion | Mastoid process of the temporal bone |
| Splenius capitis origin | Nuchal ligament and the C7 to T3 spinous processes |
| Splenius capitis insertion | Occipital and temporal bones |
| Splenius capitis functions | Bilateral contraction aids head extension, unilateral contraction assists lateral flexion and rotation to the same side |
| Oral muscles of facial expression | Orbicularis oris, buccinator |
| Extra-ocular muscles | Superior, inferior, medial and lateral recti muscles, superior and inferior oblique muscles |
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What You'll Learn
Neck muscles
The neck muscles are a complex group of structures that work together to enable a wide range of head movements, including rotation, flexion, extension, and lateral bending. There are about 30 muscles in the neck that help stabilise and support the head and upper back. They also assist with chewing, swallowing, and breathing.
The neck muscles can be categorised into three layers. The deepest layer includes the suboccipital muscles, which are located just below the occipital bone and aid in minor adjustments of head position. The suboccipital muscles are crucial for fine motor control and proprioception, the sense of self-movement and body position. The intermediate layer includes the splenius capitis and splenius cervicis muscles, which originate from the sides and back of the neck and extend to the head and cervical regions, respectively. These muscles can extend the head, laterally flex it, and rotate it. The superficial layer includes the trapezius muscle, which controls shoulder blade movements and assists in extending and tilting the head backward.
The major muscle that laterally flexes and rotates the head is the sternocleidomastoid (SCM). The SCM muscles originate at the sternum and clavicle and attach to the mastoid process of the temporal bone. When contracted bilaterally, the SCM helps bend the head forward, while unilateral contraction causes lateral flexion on the same side or head rotation to the opposite side.
Other muscles that contribute to head movement include the scalene muscles, which help move the head and stabilise the bones in the neck (cervical spine). The lateral neck muscles control head movements from the base of the skull and enable twisting and tilting of the cervical spine. The posterior neck muscles, such as the transversospinalis muscles, help move the head forward and backward and facilitate tilting from side to side.
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Lateral neck muscles
The neck muscles are responsible for the movement of the head in all directions. They also assist with chewing, swallowing, and breathing. There are about 30 muscles in the neck that are divided into three main groups based on their position in the neck: anterior, lateral, and posterior groups.
The lateral neck muscles, also known as the lateral vertebral muscles, pass obliquely along the lateral sides of the neck. They include the anterior, middle, and posterior scalene muscles, which extend between the cervical vertebrae's transverse processes and the first two ribs. The lateral neck muscles control head movements from the base of the skull, allowing the head to twist from side to side and tilt the cervical spine.
The anterior scalene muscle is the most anterior of the scalene muscles. It originates 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 the inferior thyroid artery.
The middle scalene muscles originate from the transverse processes of certain cervical vertebrae and attach to the first rib. The posterior scalene muscles originate from the cervical spine and attach to the second rib. Together, the scalenes flex the neck and can be recruited as accessory muscles of respiration.
The sternocleidomastoid is another important muscle of the neck. It is a large, two-headed muscle that originates from the medial third of the clavicle and the manubrium of the sternum. The heads come together and ascend diagonally to insert onto the mastoid process of the temporal bone. Unilateral contraction of the sternocleidomastoid produces lateral flexion of the neck on the same side and lateral rotation of the head to the opposite side. Bilateral contraction, on the other hand, produces flexion of the neck, drawing the head towards the chest.
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Posterior neck muscles
The neck muscles support the head and help in a variety of movements, such as chewing, swallowing, and breathing. There are about 30 muscles in the neck that can be categorized into three groups: anterior (front), lateral (side), and posterior (back).
The posterior neck muscles are located on the posterior aspect of the neck and connect the skull to the vertebral column and pectoral girdle. They can be subdivided into three groups: superficial, deep, and deepest.
The superficial layer is composed of the trapezius and the two splenius muscles (capitis and cervicis). The trapezius primarily functions to produce lateral flexion and contralateral rotation of the head if contracting unilaterally, or extension of the head if contracting bilaterally. It also stabilizes and moves the scapula in different directions, depending on which fibers contract. The splenius muscles cause lateral flexion and ipsilateral rotation of the head and neck when contracting unilaterally, or extension of the head and neck when contracting bilaterally.
The deep layer is composed of the transversospinales muscles of the cervical region: semispinalis capitis, semispinalis cervicis, and multifidus cervicis. The primary function of this group is lateral flexion and contralateral rotation of the head and neck when contracting unilaterally and extension of the head and neck when contracting bilaterally.
The deepest layer consists of the suboccipital muscles (rectus capitis posterior major, rectus capitis posterior minor, obliquus capitis superior, and obliquus capitis inferior), interspinales cervicis, and intertransversarii colli. The primary function of the suboccipital muscles is to produce movements of the head (extension, lateral flexion, and rotation) and maintain posture. The small size of the interspinales cervicis and intertransversarii colli muscles makes them primarily proprioceptive and stabilizer muscles, although they also assist other muscles in neck extension and lateral flexion, respectively.
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Sternocleidomastoid
The sternocleidomastoid (SCM) is a powerful neck muscle that allows you to bend your neck and turn or tilt your head. It is the largest muscle in the front of the neck and can be felt on both the right and left sides. The SCM is a superficially palpable muscle and acts as an important anatomical landmark within the neck region. It divides the neck into anterior and posterior cervical triangles, helping to define the location of structures such as the lymph nodes for the head and neck.
The SCM is innervated by the accessory nerve (CN XI) of the same side, which supplies only motor fibres. The signalling process to contract or relax the SCM begins in the accessory nerve nucleus, located in the anterior horn of the spinal cord around C1-C3. From here, the nerve fibres travel upward to enter the cranium via the foramen magnum and reach the SCM. The SCM shares its nerve supply with the trapezius muscle.
The SCM helps stabilise the neck and is involved in various movements, including:
- Turning the head left or right
- Tilting the head toward either shoulder
- Tilting the head backward, chin up
- Tilting the head forward, chin to chest
The SCM also assists in breathing by working with other neck muscles to lift the breastbone and collarbone during inhalation, creating space for the lungs to take in air. Additionally, it supports the temporomandibular joint (TMJ), which connects the jaw to the skull and enables the opening and closing of the mouth.
Injuries, tension, and strain on the SCM can lead to pain, stiffness, and conditions such as torticollis (wry neck) or sternocleidomastoid syndrome, which may require treatment through stretching, physical therapy, osteopathic manipulation, or surgery in severe cases. Maintaining good posture, managing stress, and regular exercise can help care for the SCM.
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Splenius muscles
The splenius muscles are a group of deep muscles located in the back of the neck. They are made up of two parts: the splenius capitis and splenius cervicis. These muscles are responsible for extending and rotating the head and neck.
The splenius capitis muscle is a deep muscle that originates from the lower half of the nuchal ligament and the spinous processes of the seventh cervical vertebra and the superior three thoracic vertebrae (C7-T3). The muscle fibres run superiorly and laterally, inserting into the mastoid process of the temporal bone and the occipital bone of the skull. The name "splenius capitis" comes from the Greek word "splenion," meaning bandage, and the Latin word "caput," meaning head, reflecting its bandage-like appearance. This muscle acts as an extensor and lateral flexor of the neck, assisting with its rotation. It also forms part of the floor of the posterior triangle of the neck.
The splenius cervicis muscle has a similar origin to the splenius capitis, arising from the upper thoracic and lower cervical spinous processes. However, it differs in its insertion point and function. The splenius cervicis helps to extend and rotate the neck, working in conjunction with other muscles in the region.
Bilateral contraction of the splenius capitis results in the extension of the head on the neck. When it contracts unilaterally, it works together with the contralateral sternocleidomastoid muscle to produce lateral flexion and rotation of the head towards the same side. This unilateral contraction gives rise to the term "shaker of the head" for the splenius capitis.
The splenius muscles are just one part of the intricate network of neck muscles that enable a wide range of movements. These muscles not only support the head but also assist with essential functions such as chewing, swallowing, and breathing. Maintaining the health and strength of these muscles is crucial for overall well-being.
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Frequently asked questions
The neck muscles are the primary movers of the head. There are about 30 muscles in the neck that help stabilise and support the head and upper back. These include the splenius capitis, splenius cervicis, suboccipital muscles, and the bilateral sternocleidomastoid (SCM), which is a major head flexor.
Neck muscles are skeletal muscles, meaning they are attached to bones by tendons. They are voluntary muscles, so you control how they move and work. They help with chewing, swallowing, and breathing.
The SCM muscles originate at the sternum and clavicle and attach to the mastoid process of the temporal bone. When contracted bilaterally, the SCM helps bend the head forward. When contracted unilaterally, it causes lateral flexion on the same side or head rotation to the opposite side.
