Dominic Stone
The trapezius muscle is a large, triangular, broad, and thin muscle that covers the upper back, shoulders, and neck. It is responsible for several functions, including moving the head, neck, and upper back, as well as maintaining and adjusting posture. While trapezius muscle pain is commonly caused by overuse, injuries, and nerve damage, some people also experience an absence or underdevelopment of the trapezius muscle, which can be genetic and is associated with Poland Syndrome. This topic will explore the genetic influences on the trapezius muscle and how genetic variations can impact its structure and function.
| Characteristics | Values |
|---|---|
| Trapezius muscle shape | Triangular, broad, and thin |
| Trapezius muscle location | Two muscles on either side of the upper back |
| Trapezius muscle function | Stabilize and move the scapula |
| Trapezius muscle movement | Movement of the scapulae when the spinal origins are stable; movement of the spine when the scapulae are stable |
| Trapezius muscle injury | Injury to the spinal accessory nerve (cranial nerve XI) can result in loss of motor function of the trapezius |
| Trapezius muscle pain | Common causes include overuse, injuries, and nerve damage |
| Trapezius muscle absence | Absence of the trapezius muscle is rare and has been associated with Poland Syndrome |
| Trapezius muscle genetic tracing | Genetic tracing of the trapezius muscle has been performed using Cre lines and β-galactosidase (β-gal) positive cells |
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What You'll Learn
Trapezius muscle absence is rare but can be genetic
The trapezius muscle is a large, triangular, broad, and thin muscle that covers the upper back, shoulders, and neck. It is responsible for several important functions, including maintaining and adjusting posture, moving the head, neck, and upper back, and assisting in various motions. While trapezius muscles are common, their absence is considered rare.
In rare cases, the absence or underdevelopment of the trapezius muscle can occur, and this condition has been associated with genetic factors. Genetic tracing studies have been conducted on trapezius muscles, and the muscle's development has been observed in embryos. The trapezius muscle can be affected by genetic factors, as evidenced by its presence or absence in family members. For instance, a clinical report described the absence of the inferior portion of the trapezius muscle in three family members, confirmed by magnetic resonance imaging.
The trapezius muscle is one of the muscles commonly impacted in facioscapulohumeral muscular dystrophy (FSHD), with the lower and middle fibers typically affected first. Absence or dysfunction of the trapezius muscle can result in issues such as winged scapula, abnormal mobility or function of the scapula (scapular dyskinesia), and neck pain.
Additionally, the trapezius muscle is associated with Poland Syndrome, a condition characterized by breast and pectoralis muscle hypoplasia. The absence of the trapezius muscle is a rare feature of Poland Syndrome, further highlighting the genetic component associated with the muscle's development.
In summary, the absence of the trapezius muscle is uncommon but can be influenced by genetic factors. Genetic tracing studies, clinical observations within families, and associations with genetic syndromes like FSHD and Poland Syndrome provide evidence for the genetic influence on the development and presence of the trapezius muscle.
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The trapezius muscle has three sections
The trapezius muscle is a large, triangular, paired muscle located on the posterior aspect of the neck and thorax. The muscle is named after its shape, which forms a trapezoid (a four-sided shape with two parallel sides) or a kite. The trapezius muscle has three sections: the upper (superior) section, the middle (transverse) section, and the lower (inferior) section. These sections run from the base of the neck down to the middle of the back.
The upper trapezius arises from the occipital bone at the back of the skull and the nuchal line at the back of the neck. It also has attachments to the cervical levels of the spine, from the first through the sixth vertebrae. The upper trapezius elevates or brings up the shoulder girdle and helps extend, tilt, and rotate the neck. This rotation brings the head back, to the side, and turns it to the opposite side of the muscle.
The middle trapezius fibres originate from the spinous processes of the T1-T4 vertebrae and their intervening supraspinous ligaments. These fibres are directed horizontally, running laterally towards the shoulder. The middle trapezius helps bring the shoulder blades back towards the spine, aiding in the retraction of the scapula. It also helps stabilize the shoulder during certain arm movements, such as lifting the arm above the head.
The lower trapezius fibres originate from the spinous processes of the T4-T12 vertebrae and their respective supraspinous ligaments. The lower trapezius performs the opposite action of the upper trapezius, bringing the shoulder girdle down and depressing the medial part of the scapula, thus lowering the shoulder. It also acts with the upper trapezius to rotate the shoulder blade upward, which occurs when lifting the arm to the side.
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The muscle's main function is to stabilise and move the scapula
The trapezius muscle is a large, paired trapezoid-shaped surface muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula. It is one of the broadest and most superficial muscles of the upper back and trunk. The trapezius muscle has several origin points along the midline of the posterior neck and back. The superior fibres attach to the medial third of the superior nuchal line, the external occipital protuberance of the occipital bone, and the nuchal ligament, which is attached to the spinous processes of the C1-C6 vertebrae. These fibres have a descending course towards their insertion point, which is why this part of the trapezius is referred to as the descending part.
The main function of the trapezius muscle is to stabilise and move the scapula. The upper fibres of the trapezius elevate and upwardly rotate the scapula and extend the neck. The descending muscle fibres of the trapezius muscle internally rotate the arms. The middle fibres of the trapezius adduct (medially retract) the scapula. The transverse muscle fibres retract the scapulae. The middle fibres originate from the spinous processes of T1-T4 vertebrae and their intervening supraspinous ligaments. These fibres are directed horizontally, running laterally towards the shoulder. Thus, these fibres represent the transverse part of the trapezius.
The lower fibres of the trapezius depress and aid the upper fibres in upwardly rotating the scapula. The inferior or lower (or ascending) fibres of the trapezius arise from the spinous processes of the remaining thoracic vertebrae (T4-T12). From this origin, they proceed upward and laterally to converge near the scapula and end in an aponeurosis, which glides over the smooth triangular surface on the medial end of the spine, to be inserted into a tubercle at the apex of this smooth triangular surface. The ascending muscle fibres medially rotate the scapulae. Along with the descending part, the ascending fibres also produce a rotation of the scapula around an axis that runs anteroposteriorly through the base of the scapular spine.
The trapezius muscle is also responsible for upward rotation of the scapula, along with the serratus anterior muscle. This allows us to raise our arm above our heads beyond the level of the shoulder. The trapezius muscle is one of the commonly affected muscles in facioscapulohumeral muscular dystrophy (FSHD). The lower and middle fibres are affected initially, and the upper fibres are commonly spared until late in the disease.
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The trapezius is triangular, broad, and thin
The trapezius muscle is a large, triangular, paired muscle located on the posterior aspect of the neck and thorax. It is one of the broadest and most superficial muscles of the upper back and trunk. It covers the upper back of the shoulders and neck. Its broad shape allows it to assist in postural attributes, such as supporting the spinal column to remain erect when a person is standing. The trapezius also enables active movements like side bending, rotation of the head, elevating and depressing the shoulders, and internally rotating the arm.
The trapezius muscle has several origin points along the midline of the posterior neck and back. The superior fibres attach to the medial third of the superior nuchal line, the external occipital protuberance of the occipital bone, and the nuchal ligament. These fibres descend towards their insertion point, forming the descending part of the trapezius. The middle fibres, or transverse part, originate from the spinous processes of T1-T4 vertebrae and their intervening supraspinous ligaments, running horizontally towards the shoulder. The inferior fibres, or ascending part, arise from the spinous processes of the remaining thoracic vertebrae (T4-T12) and move upward and laterally to converge near the scapula.
The trapezius muscle is involved in the movement and stabilisation of the scapula. The upper fibres elevate the scapulae, the middle fibres retract them, and the lower fibres depress them. Together, the upper and lower fibres also induce upward rotation of the scapula. The trapezius further assists in abduction of the shoulder by rotating the glenoid upward. Injury to the trapezius can result in winged scapula or scapular dyskinesia, characterised by abnormal mobility or function of the scapula.
The trapezius muscle is essential for various physical activities and movements. For example, it helps in throwing objects and performing an overhead press. Exercises such as the clean, particularly the hang clean, and the shoulder shrug can develop the upper portion of the trapezius, while pulling the shoulder blades together works the middle fibres. The lower part of the trapezius can be strengthened by drawing the shoulder blades downward while keeping the arms straight and stiff.
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The trapezius is one of the commonly affected muscles in FSHD
The trapezius muscle is a large, paired trapezoid-shaped surface muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula. It is responsible for moving the scapula and supporting the arm. The trapezius muscle is also the only muscle of the upper limb that does not receive its innervation from the brachial plexus. Instead, motor innervation is conveyed by the accessory nerve.
Facioscapulohumeral muscular dystrophy (FSHD) is a genetic illness that affects skeletal muscle tissue in affected individuals. FSHD characteristically starts proximally in the face and spreads to other muscle groups. The trapezius muscle is one of the commonly affected muscles in FSHD. The lower and middle fibres of the trapezius are affected initially, and the upper fibres are commonly spared until the later stages of the disease.
The deltoid muscle is often spared in FSHD, and the combination of the deltoid and trapezius involvement manifests as a poly hill sign, in which musculature gives the appearance of consecutive peaks and valleys. In FSHD, muscle involvement then moves towards the legs, affecting the distal-most muscles first, primarily the gastrocnemius and tibialis anterior. As the trunk and spine muscles are affected, FSHD patients can present with accentuated lumbar lordosis.
FSHD patients may also experience facial muscle involvement, including lagophthalmos, a decrease in brow folds, a flattened or asymmetric smile, and an inability to tense the superficial muscles of the head and neck. In the upper extremities, muscle wasting of the shoulder girdle muscles with an anterior rounding pattern may be observed. The trapezius muscle is one of the muscles of the shoulder girdle, and its dysfunction can result in winged scapula, abnormal mobility or function of the scapula (scapular dyskinesia), and neck pain.
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Frequently asked questions
Your trapezius muscles are two big muscles on either side of your upper back. They help you move your head, neck, and upper back, and maintain and adjust your posture.
Genetic tracing of the trapezius and sternocleidomastoid neck muscles has been performed using a Tbx1-Cre allele. The trapezius and sternocleidomastoid muscles are also genetically labelled using a Cre line, as shown on whole-mount X-gal-stained embryos.
Although rare, underdevelopment or absence of the trapezius has been reported to correlate with neck pain and poor scapular control that are not responsive to physical therapy. Absence of the trapezius has been reported in association with Poland syndrome.
