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The sternocleidomastoid (SCM) muscle 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 your neck and is easily visible and palpable. SCM syndrome, an acute or chronic condition, can cause neck stiffness, pain and trigger points. The SCM is innervated by the accessory nerve and has multiple functions. It is an important landmark in the neck, which divides it into anterior and posterior triangles. The SCM is also involved in respiration, helping to lift the breastbone and collarbone during inhalation.
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What You'll Learn
The sternocleidomastoid muscle is a two-headed neck muscle
The sternocleidomastoid muscle, also known as SCM or Sternomastoid, is a two-headed neck muscle. It is the most superficial and largest muscle in the front portion of the neck. The name sternocleidomastoid is derived from the Latin and Greek words for the parts of the body to which the muscle attaches: sterno- (sternum), cleido- (clavicle), and -mastoid (mastoid process).
The two heads of the sternocleidomastoid muscle originate from two locations: the manubrium of the sternum (sternal head) and the clavicle (clavicular head). They join together below the middle of the neck to form a thick, rounded muscle that inserts into the mastoid process of the temporal bone of the skull. The sternal head is tendinous in the front and fleshy behind, while the clavicular head can vary in breadth.
The sternocleidomastoid muscle has multiple functions, including rotating the head to the opposite side of contraction, flexing the neck laterally and anteriorly, and assisting in breathing by lifting the sternum and clavicle to expand the thoracic cavity. It also plays a role in maintaining posture and stabilising the neck.
The SCM is susceptible to various injuries, strains, and conditions such as trigger points, torticollis, and temporomandibular joint disorders (TMD). Treatment options for SCM issues include massage, osteopathic manipulation, physical therapy, and surgery in severe cases. Maintaining good posture, managing stress, and regular exercise can help prevent and manage SCM-related issues.
The SCM is a significant landmark in the neck, dividing it into anterior and posterior triangles. It is closely associated with several neurovascular structures, including the common carotid artery, accessory nerve, and brachial plexus.
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It is innervated by the accessory nerve
The sternocleidomastoid muscle is a powerful neck muscle that allows you to bend your neck and turn or tilt your head. It is one of the largest and most superficial cervical muscles. The primary actions of the muscle are rotation of the head to the opposite side and flexion of the neck. The muscle is closely related to certain neurovascular structures that pass through the neck on their way either to the head or to the periphery of the body.
The sternocleidomastoid muscle is innervated by the accessory nerve (cranial nerve XI), which is the eleventh paired cranial nerve. It has a purely somatic motor function and provides motor control of the sternocleidomastoid and trapezius muscles. The accessory nerve is tested by evaluating the function of the trapezius and sternocleidomastoid muscles. The trapezius muscle is tested by asking the patient to shrug their shoulders with and without resistance. The sternocleidomastoid muscle is tested by asking the patient to turn their head to the left or right against resistance.
The accessory nerve has two parts: the cranial part and the spinal part. The cranial component of the accessory nerve provides motor control to the muscles of the soft palate, larynx, and pharynx. The spinal component of the accessory nerve provides motor control of the sternocleidomastoid and trapezius muscles. The spinal accessory nerve continues alone and heads backward and downward after leaving the skull. It then pierces through the sternocleidomastoid muscle and sends motor branches to the muscle.
The sternocleidomastoid muscle is susceptible to strain and injury due to its size and complexity. Trigger points may develop in multiple places within the muscle, leading to neck stiffness, pain, and other symptoms associated with sternocleidomastoid syndrome. Treatment options for the SCM muscle include massage, osteopathic manipulation, physical therapy, and surgery in severe cases.
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It is the largest muscle in the front of the neck
The sternocleidomastoid (SCM) muscle is the largest muscle in the front of the neck. It is a powerful muscle that allows you to bend your neck and turn or tilt your head. It is a two-headed neck muscle that bears attachments to the manubrium of the sternum (sterno-), the clavicle (-cleido-), and the mastoid process of the temporal bone (-mastoid). The SCM muscle ends at the mastoid process, which is a section of bone located at the base of the skull behind the ears.
The SCM muscle is a long, bilateral muscle of the neck that helps to flex the neck both laterally and anteriorly, as well as rotate the head to the opposite side. It is a thick muscle that serves as a primary landmark of the neck, dividing it into anterior and posterior cervical triangles. These triangles help define the location of structures such as the lymph nodes for the head and neck. The SCM muscle is also an important protective structure, shielding the vertical neurovascular bundle of the neck, branches of the cervical plexus, deep cervical lymph nodes, and soft tissues of the neck from damage.
The SCM muscle is innervated by the accessory nerve (Cranial Nerve XI) and direct branches of the cervical plexus (C2-C3). The signalling process to contract or relax the SCM muscle begins in the accessory nerve nucleus in the anterior horn of the spinal cord (C1-C3), with lower motor neuron fibres marking its origin. After a signal reaches the accessory nerve nucleus, it is conveyed to motor endplates on the muscle fibres located at the clavicle. Acetylcholine (ACH) is then released from vesicles and sent over the synaptic cleft to receptors on the postsynaptic bulb, initiating an action potential that travels along the muscle fibre.
The SCM muscle is susceptible to various conditions, including injuries, sprains, strains, atrophy, and tumours. Sternocleidomastoid syndrome, for example, is a condition involving neck stiffness, pain, and other symptoms. It occurs when the SCM muscle develops tightened, sensitive areas, or trigger points. Torticollis (wryneck) is another condition that can result from shortened, tightened SCM muscles, causing the head to naturally turn or tilt to one side. Treatment options for SCM-related conditions include massage, osteopathic manipulation, physical therapy, and, in severe cases, surgery.
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It is an important landmark in the neck
The sternocleidomastoid muscle is a powerful neck muscle that allows you to bend your neck and turn or tilt your head. It is one of the largest and most superficial cervical muscles, and it is easily visible and palpable. The muscle is thick and thus serves as a primary landmark in the neck.
The sternocleidomastoid is within the investing fascia of the neck, along with the trapezius muscle, with which it shares its nerve supply (the accessory nerve). It divides the neck into anterior and posterior cervical triangles (in front and behind the muscle, respectively), which helps define the location of structures such as the lymph nodes for the head and neck. The anterior triangle is further divided into the submental, submandibular, carotid, and muscular triangles.
The triangle formed by the clavicle and the sternal and clavicular heads of the sternocleidomastoid muscle is used as a landmark in identifying the correct location for central venous catheterization. The medial edge of the sternocleidomastoid muscle serves as a lead structure when putting a central venous catheter (CVC). The carotid pulse may be felt in the middle third of the front edge of the sternocleidomastoid region.
The sternocleidomastoid muscle is closely related to certain neurovascular structures that pass through the neck on their way to the head or to the periphery of the body. Many important structures relate to the sternocleidomastoid, including the common carotid artery, accessory nerve, and brachial plexus.
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It is susceptible to strain and injury
The sternocleidomastoid (SCM) muscle is the largest muscle in the front of the neck. It is a two-headed neck muscle, with its name derived from its attachments to the manubrium of the sternum (sterno-), the clavicle (-cleido-), and the mastoid process of the temporal bone (-mastoid). The SCM muscle is susceptible to strain and injury due to its size, complexity, and involvement in various functions and movements.
The SCM muscle plays a crucial role in neck flexion and rotation, allowing us to bend, turn, and tilt our heads. It also assists in maintaining posture, breathing, and chewing. However, its size and complexity make it prone to strain and injury. SCM syndrome, also known as sternocleidomastoid syndrome, is a condition that can develop as a result of SCM muscle strain or injury. It is characterised by neck stiffness, pain, and the development of trigger points within the muscle.
SCM syndrome can be acute or chronic, causing tightened, sensitive areas within the muscle. These trigger points can lead to referred pain in the SCM muscle, even when the tightness originates in another part of the body. Additionally, SCM muscle strain or injury can contribute to temporomandibular joint disorders (TMD), where the muscles and ligaments supporting the temporomandibular joint (TMJ) become irritated or damaged.
Certain factors can increase the susceptibility of the SCM muscle to strain and injury. For example, occupations that require maintaining uncomfortable postures for extended periods, such as violinists, painters, and carpenters, can strain the SCM muscle over time. Poor posture, frequent sleeping on the stomach, neck trauma (whiplash), weightlifting, incorrect swimming styles, and abrupt sit-ups can also contribute to SCM muscle strain and injury.
To prevent and manage SCM muscle strain and injury, it is essential to prioritise stress management, regular exercise, adequate sleep, and the practice of yoga or meditation. Maintaining good posture is crucial, especially when using digital devices, reading, and performing physical activities like sit-ups. Daily neck stretches are highly beneficial, especially for those who sit for long periods during the day.
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Frequently asked questions
The Sternocleidomastoid is a two-headed neck muscle that allows you to bend your neck and turn or tilt your head. It is the largest muscle in the front of your neck.
The Sternocleidomastoid muscle helps you bend your neck and turn and tilt your head. It also helps with breathing by working with other neck muscles to lift your breastbone and collarbone when you inhale.
Sternocleidomastoid syndrome is caused by trigger points, which are small, sensitive areas in the muscle that can refer pain to other parts of the body. This can be caused by stress, anxiety, ageing, pillow height, and frequent sleeping on the stomach, among other factors.
Sternocleidomastoid syndrome can be treated with massage, osteopathic manipulation, physical therapy, and surgery in severe cases. It is also important to manage stress and anxiety through techniques like meditation, relaxation, yoga, and light exercise.
