Logan Steele
The neck muscles are responsible for rotating the head. There are about 30 neck muscles that support and stabilise the head, neck, and upper spine, and they also assist with chewing, swallowing, and breathing. The neck muscles can be sub-categorised into anterior, lateral (prevertebral), and posterior neck muscles. The cervical spine, which is the most superior portion of the vertebral column, also plays a crucial role in allowing for head rotation while protecting the spinal cord. The sternocleidomastoid (SCM) muscles, in particular, are key muscles involved in head rotation and neck movement. Other muscles that contribute to head rotation include the longus capitis, splenius muscles, and various transversospinalis muscles.
| Characteristics | Values |
|---|---|
| Number of neck muscles | 30 |
| Functions | Support and stabilise head, neck and upper spine, enable head movement, assist with chewing, swallowing and breathing |
| Types | Anterior, lateral (prevertebral), and posterior |
| Muscles enabling head rotation | Sternocleidomastoid (SCM), longus capitis, splenius muscles, semispinalis capitis and cervicis, rotatores cervicis, interspinales, intertransversarii, scalene muscles, suboccipital muscles, transversospinalis muscles |
| SCM origin | Collarbone/clavicle and breastbone/manubrium |
| SCM contraction | Turns/rotates head to the opposite side, tilts head to the ipsilateral side, turns face upward, brings chin down towards breastbone |
| SCM impairment | Weakness or paralysis, atrophy, difficulty in turning the head and bending the neck |
| SCM treatment | Strengthening exercises, nerve repair, cervical isometrics, posture improvement, stretching and strengthening of SCM and surrounding muscles |
| SCM condition | Cervical dystonia, or spasmodic torticollis, rotational deformity, positional plagiocephaly, facial asymmetry, dysplasia of skull, atlas, and axis |
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What You'll Learn
The role of the sternocleidomastoid muscle
The sternocleidomastoid muscle is a two-headed neck muscle that plays a crucial role in head and neck movements. Its name is derived from its attachments to the sternum, clavicle, and mastoid process of the temporal bone. This muscle is responsible for rotating the head and neck, flexing the neck, and extending the head.
The function of the sternocleidomastoid muscle depends on whether it acts alone or in conjunction with its counterpart on the other side. When the muscle contracts unilaterally, it flexes the cervical vertebral column to the same side and rotates the head to the opposite side. This lateral flexion of the neck and lateral rotation of the head are important movements that allow us to turn our heads from side to side.
On the other hand, when both sides of the sternocleidomastoid muscle act together, it results in neck flexion, drawing the head towards the chest, and head extension. This bilateral contraction is essential for maintaining stability and allowing us to look straight ahead.
The sternocleidomastoid muscle is also involved in respiration as an accessory muscle. It works in conjunction with the scalene muscles of the neck to facilitate breathing. Additionally, this muscle serves as a primary landmark in the neck, dividing it into anterior and posterior cervical triangles. This distinction helps define the locations of important structures, such as the lymph nodes for the head and neck.
Furthermore, the sternocleidomastoid muscle is associated with certain medical conditions, such as cervical dystonia or spasmodic torticollis. This condition arises from an abnormal contraction of the muscle, leading to a rotational deformity and a head tilt toward the affected side. Treatment options for torticollis include passive stretching, Botox injections, and surgical procedures to release the muscle and prevent permanent deformities.
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The trapezius muscle
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. 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. The trapezius muscle works in conjunction with several muscles to produce coordinated movements, primarily involving the scapula.
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The splenius muscles
The splenius capitis muscle is a deep, intrinsic muscle of the back of the neck. It gets its name from the Greek word 'splenion', meaning bandage, and the Latin word 'caput', meaning head, thus describing its bandage-like appearance. The splenius capitis originates from the spinous processes of the seventh cervical vertebra and the superior three thoracic vertebrae (C7-T3) and the nuchal ligament. The muscle fibres run superiorly and laterally to insert into the mastoid process of the temporal bone. The mastoid process is a pyramidal-shaped eminence on the base of the skull. The splenius capitis also inserts in part onto the external surface of the occipital bone, below the lateral section of the superior nuchal line. The blood supply to the splenius capitis arises from the muscular branches of the occipital artery, a branch of the external carotid artery.
Bilateral contraction of the splenius capitis results in the extension of the head on the neck. When the splenius capitis contracts unilaterally, it works in synergy with the contralateral sternocleidomastoid muscle, resulting in lateral flexion and rotation of the head towards the ipsilateral side. This muscle also assists in supporting the head in the erect position. Dysfunction of the splenius capitis may be associated with mechanical chronic neck pain or whiplash disorders.
The splenius cervicis is another muscle within the splenius group. It arises from the transverse processes of the first three thoracic vertebrae (T1-T3) and inserts onto the spinous processes of the second to fifth cervical vertebrae (C2-C5). The splenius cervicis acts to extend the spine through bilateral contraction and produces lateral flexion of the spine through unilateral contraction.
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The semispinalis capitis and cervicis
The semispinalis capitis arises from the articular processes of vertebrae C4 to C7 and the transverse processes of vertebrae T1 to T6. It follows an upward path to insert itself between the superior and inferior nuchal lines of the occipital bone. The semispinalis capitis is involved in maintaining the balance of the head on the neck and plays a key role in cervical lordosis, which is essential for maintaining the normal curvature of the neck.
The semispinalis cervicis, on the other hand, arises from the transverse processes of vertebrae T1 to T6 and inserts into the spinous processes of vertebrae C2 to C5. It is thicker than the semispinalis thoracis and has a predominantly muscular structure. The semispinalis cervicis is involved in the extension, lateral flexion, and rotation of the head, neck, and thoracic spine.
Both the semispinalis capitis and cervicis muscles contribute to the complex system of neck muscles that enable a wide range of movements. They work in coordination with other muscles, such as the sternocleidomastoid and the trapezius, to allow for smooth and controlled head rotations and maintain stability during these movements.
The cervical spine, which includes the first two cervical vertebrae (C1 and C2) or the atlas and axis, respectively, plays a crucial role in supporting and cushioning the head and neck while allowing for rotation. It also protects the spinal cord, which extends from the brain. Any injury to the cervical spine or associated muscles, including the semispinalis capitis and cervicis, can have significant implications and must be carefully evaluated.
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Torticollis and its impact
The muscles that enable head rotation include the sternocleidomastoid, longus capitis, longus colli, splenius muscles, and trapezius. The sternocleidomastoid muscle, in particular, plays a crucial role in rotating the head to the opposite side during unilateral contraction and drawing the head towards the chest during bilateral contraction.
Torticollis, also known as wryneck, is a condition characterised by a twisted neck that causes the head to rotate and tilt at an unusual angle. It can be congenital (present at birth) or acquired later in infancy or childhood. Congenital torticollis is the most prevalent type, affecting firstborn children more frequently. It is typically painless for infants, and parents may not notice it until their baby gains better head control after a few weeks.
The exact cause of torticollis is often unclear, but it is believed that congenital torticollis occurs due to extra pressure on one side of the sternocleidomastoid (SCM) muscle, causing it to tighten and making it challenging for the baby to turn their neck. This pressure may result from the baby's position in the uterus, leading to injury or abnormal development of the SCM. Acquired torticollis, on the other hand, can be caused by irritation to the cervical ligaments from viral infections, injuries, or vigorous movements. It may also be associated with swelling in the child's throat, allowing the vertebrae to move out of position.
The primary symptom of torticollis is a stiff neck, making it difficult or painful to turn the head. Other signs include a flat spot on the head (positional plagiocephaly) from lying in one direction and facial asymmetry. In some cases, a small neck lump or bump may develop due to tense muscles.
If left untreated, torticollis can lead to permanent rotational deformities, facial asymmetry, and dysplasia of the skull and vertebrae. Treatment typically involves gentle muscle stretches, position changes, physical therapy, and, in some cases, surgery to lengthen the SCM muscle. Early intervention is crucial to prevent long-term issues.
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Frequently asked questions
The neck muscles are responsible for rotating the head. There are about 30 neck muscles that extend from the base of the skull and jaw down to the collarbone and shoulder blades. These muscles include the sternocleidomastoid (SCM), splenius, semispinalis capitis and cervicis, longus capitis, and the trapezius muscles.
The sternocleidomastoid (SCM) is a superficially located neck muscle that plays a crucial role in tilting and rotating the head. It also helps with neck extension and flexion. SCM impairment or injury can cause difficulty in turning the head.
The splenius muscles, including the splenius capitis and splenius cervicis, originate at the midline and run laterally and superiorly to their insertions. They help extend the head, provide lateral flexion, and enable rotation of the head.
Cervical rotation refers to the act of turning the head to the left or right. It is facilitated by the cervical spine, which supports and cushions the head and neck while allowing for rotation. The cervical spine also aids in swallowing and elevating the rib cage during inhalation.
