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The extrinsic muscles are those that originate from the torso and attach to the bones of the shoulder, scapula, or humerus. They are located in the back and are also known as the superficial back muscles. The extrinsic muscles of the back include the trapezius, latissimus dorsi, rhomboid major and minor, levator scapulae, serratus posterior superior and inferior, and serratus anterior. The extrinsic muscles of the hand originate outside the hand but insert into structures within it, mostly in the forearm. The extrinsic muscles of the tongue do not change its shape but change its position. The extrinsic muscles of the shoulder include the trapezius and latissimus dorsi.
| Characteristics | Values |
|---|---|
| Definition | Muscles that originate outside a body part but insert into structures within it |
| Extrinsic back muscles | Trapezius, Latissimus Dorsi, Rhomboid Major and Minor, Levator Scapulae, Serratus Posterior Superior and Inferior |
| Extrinsic shoulder muscles | Trapezius, Latissimus Dorsi, Levator Scapulae, and Rhomboids |
| Extrinsic tongue muscles | Genioglossus, Hyoglossus, and Styloglossus |
| Extrinsic hand muscles | Originate in the forearm or the humerus |
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What You'll Learn
Trapezius
The trapezius is a large, flat, and triangular extrinsic back muscle that runs from the base of the neck down to the middle of the back. It is the most superficial of all the back muscles. The muscle is divided into three sections: the superior or descending, the inferior or ascending, and the middle or transverse. The trapezius has many attachment points, extending from the skull and vertebral column to the shoulder girdle. The upper 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. The middle fibres originate from the spinous processes of the T1-T4 vertebrae and run horizontally towards the shoulder. The inferior fibres originate from the spinous processes of the T4-T12 vertebrae. The trapezius muscle is involved in several movements of the shoulder girdle and is, therefore, considered a muscle of the upper limb.
The main function of the trapezius is to stabilize the scapula in its anatomical place and control its movement during the movement of the shoulder and upper limb. It assists in postural attributes, allowing and supporting the spinal column to remain erect when a person is standing. The trapezius works with several other muscles to produce coordinated movements, primarily involving the scapula. For example, the rhomboids (major and minor) work closely with the trapezius to retract and stabilize the scapula, playing a key role in shoulder movement and posture. The serratus anterior works in conjunction with the lower trapezius to rotate the scapula upward during arm elevation, allowing the arm to lift smoothly above shoulder height. The trapezius is also involved in the movement of the head and neck, such as turning the head to either side, elevating and depressing the shoulders, and internally rotating the arm.
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Latissimus dorsi
The latissimus dorsi is a large, flat muscle on the back that stretches to the sides, behind the arm, and is partly covered by the trapezius on the back near the midline. The word "latissimus dorsi" comes from Latin and means "broadest [muscle] of the back", derived from "latissimus" (Latin for broadest) and "dorsum" (Latin for back). The pair of muscles are often referred to as "lats", especially in bodybuilding circles.
The latissimus dorsi is the widest muscle in the human body. It is relatively thin and covers almost all back muscles at the posterior trunk, except the trapezius. It is one of the extrinsic muscles of the back, which means it originates from the myogenic cells in the developing upper limb buds rather than from the myotomal dorsal epaxial division of the somite, where the intrinsic (deep back) muscles originate.
The latissimus dorsi is responsible for extension, adduction, transverse extension (also known as horizontal abduction or horizontal extension), flexion from an extended position, and (medial) internal rotation of the shoulder joint. It also plays a role in the extension and lateral flexion of the lumbar spine. The muscle helps pull the torso superiorly and anteriorly when the arm is raised above the head.
The latissimus dorsi receives blood from the thoracodorsal artery, a continuation of the subscapular artery, which is a branch of the third part of the axillary artery. It also receives supply from the dorsal perforating branches of the inferior three posterior intercostal arteries and the superior three lumbar arteries.
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Rhomboid major and minor
The rhomboid major and minor are two of the extrinsic muscles of the back, which also include the trapezius, latissimus dorsi, levator scapulae, and serratus posterior superior and inferior muscles. The extrinsic muscles of the back are responsible for moving the upper extremity by controlling the movement of the scapula and humerus, which are important bones in the shoulder region.
The rhomboid muscles are located in the upper back, underneath the trapezius muscle. They are rhombus-shaped and participate in the movement of the scapula. The rhomboid minor is situated superiorly to the major. These muscles work together to draw the scapula superomedially, support the scapula, and rotate the glenoid cavity inferiorly.
The rhomboid major and minor muscles are innervated by the dorsal scapular nerve, a branch of the brachial plexus. The dorsal scapular artery supplies blood to these muscles, although in some people, a deep branch of the transverse cervical artery provides circulation.
The rhomboid muscles work with the trapezius to retract the scapula to the posterior midline, stabilising the shoulders during motion. This retraction of the scapula by the rhomboids and trapezius enables complex actions such as reaching, lifting, pulling, and pushing.
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Levator scapulae
The levator scapulae is a small, strap-like extrinsic muscle of the upper back. It is located in the posterior triangle of the neck, underneath the trapezius muscle. The levator scapulae originates from the transverse processes of the C1-C4 vertebrae and attaches to the medial border of the scapula. The superior aspect of the levator scapulae is covered by the sternocleidomastoid, while its inferior part is covered by the trapezius. The muscle is innervated by the cervical nerve (C3-C4) and the dorsal scapular nerve (C5), and it receives its blood supply from the dorsal scapular artery.
The primary function of the levator scapulae is to elevate the scapula and tilt the glenoid cavity inferiorly by rotating the scapula downward. When the scapula is fixed, contraction of the levator scapulae leads to lateral flexion of the cervical vertebral column to the side and stabilizes the vertebral column during rotation. If the cervical spine is fixed, contraction of the muscle results in lateral flexion and rotation of the neck to the same side. Bilateral contraction of both levator scapulae muscles can lead to extension of the cervical spine.
The length and tension of the levator scapulae can be assessed by placing a patient in a supine position and stabilising the ipsilateral scapula. Trigger points are common in this muscle and can cause pain or discomfort, which can be relieved through various modalities and active movements.
The levator scapulae is clinically significant in surgical procedures such as the Modified Eden-Lange procedure, where it is attached to the spine of the scapula. It is also important to recognise and release the aponeurosis covering the levator scapulae during thoracotomy for lung excision to avoid dynamic shoulder instability.
The levator scapulae is one of the muscles within the floor of the posterior triangle of the neck. It is bounded in front by the scalenus medius and behind by the splenius cervicis. The spinal accessory nerve crosses laterally in the middle of the muscle, and it may lie deep to or pass through the dorsal scapular nerve. The number of attachments varies, with possible extensions to the occipital, mastoid, trapezius, scalene, serratus anterior, or the first or second rib.
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Serratus posterior superior and inferior muscles
The serratus posterior superior and inferior muscles are two of the extrinsic muscles of the back. The extrinsic back muscles are those that connect the posterior aspect of the axial skeleton with the superior appendicular skeleton. They are involved in moving the upper extremity by controlling the movement of the scapula and humerus, which are important bones in the shoulder region.
The serratus posterior superior muscle is located superficial to the thoracic part of the thoracolumbar fascia, which covers the splenius cervicis. It lies deep to the rhomboids and the trapezius muscle. The muscle is involved in respiration by elevating the ribs and thus supporting inspiration.
The serratus posterior inferior muscle is situated at the junction of the thoracic and lumbar regions. It lies superficial to the erector spinae muscle group and the thoracolumbar fascia, and deep to the latissimus dorsi muscle. It arises from the vertebrae T11 through L2 or L3 and is inserted into the lower border of the 9th through 12th ribs. This muscle also plays a role in respiration by depressing the ribs during expiration.
The serratus posterior superior and inferior muscles receive blood from the intercostal arteries. The serratus posterior superior is innervated by the intercostal nerves T2-T5, while the serratus posterior inferior is innervated by the anterior rami of the T9-T11 spinal nerves, as well as the subcostal nerves (T12).
The disproportionate use of the serratus posterior superior and other back muscles, such as cradling the phone between the ear and shoulder, can result in a condition known as scapulocostal syndrome. This condition is characterised by pain and paresthesia along the medial border of the scapula, radiating to the neck, chest, and upper extremities.
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Frequently asked questions
Extrinsic muscles are those that originate outside the hand but insert into structures within it. They are also referred to as superficial back muscles.
Some examples of extrinsic muscles in the back include the trapezius, latissimus dorsi, rhomboid major and minor, levator scapulae, and serratus posterior superior and inferior muscles.
The principal function of the extrinsic muscles of the back is to move the upper extremity by controlling the movement of the scapula and humerus, which are important bones in the shoulder region.
The trapezius is the most superficial extrinsic back muscle. It is a broad, flat, and triangular muscle that forms a trapezoid shape.
Some examples of extrinsic muscles in the head and neck include the genioglossus, hyoglossus, and styloglossus muscles.
