The scalene muscles are a group of three

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

s on each side of the

neck The neck is the part of the body in many vertebrates that connects the head to the torso. It supports the weight of the head and protects the nerves that transmit sensory and motor information between the brain and the rest of the body. Addition ...

, identified as the anterior, the middle, and the posterior. They are innervated by the third to the eighth cervical

spinal nerves A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into ...

(C3-C8). The anterior and middle scalene muscles lift the first rib and bend the

to the side they are on. The posterior scalene lifts the second rib and tilts the neck to the same side. The muscles are named from the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

(), meaning 'uneven'.

Structure

The scalene muscles are attached at one end to bony protrusions on

vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

C2 to C7 and at the other end to the first and second

rib In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the ...

Anterior scalene

The anterior scalene muscle (), lies deeply at the side of the neck, behind the

sternocleidomastoid muscle The sternocleidomastoid muscle 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 Anatomical terms of motion#Flexion and extension, flexion of the neck. ...

. It arises from the anterior tubercles of the

transverse processes Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

of the third, fourth, fifth, and sixth

cervical vertebrae In tetrapods, cervical vertebrae (: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In saurop ...

, and descending, almost vertically, is inserted by a narrow, flat tendon into the scalene tubercle on the inner border of the first rib, and into the ridge on the upper surface of the first rib in front of the

subclavian groove On the medial part of the clavicle The clavicle, collarbone, or keybone is a slender, S-shaped long bone approximately long that serves as a strut between the scapula, shoulder blade and the sternum (breastbone). There are two clavicles, one ...

. It is supplied by the

anterior ramus The ventral ramus (: rami) (Latin for 'branch') is the anterior division of a spinal nerve. The ventral rami supply the antero-lateral parts of the trunk and the limbs. They are mainly larger than the dorsal rami. Shortly after a spinal nerve e ...

cervical nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into t ...

5 and 6.

Middle scalene

The middle scalene, (), is the largest and longest of the three scalene muscles. The middle scalene arises from the posterior tubercles of the transverse processes of the lower six cervical vertebrae. It descends along the side of the

vertebral column The spinal column, also known as the vertebral column, spine or backbone, is the core part of the axial skeleton in vertebrates. The vertebral column is the defining and eponymous characteristic of the vertebrate. The spinal column is a segmente ...

to insert by a broad attachment into the upper surface of the first rib, posterior to the subclavian groove. The

brachial plexus The brachial plexus is a network of nerves (nerve plexus) formed by the anterior rami of the lower four Spinal nerve#Cervical nerves, cervical nerves and first Spinal nerve#Thoracic nerves, thoracic nerve (cervical spinal nerve 5, C5, Cervical spi ...

and the

subclavian artery In human anatomy, the subclavian arteries are paired major arteries of the upper thorax, below the clavicle. They receive blood from the aortic arch. The left subclavian artery supplies blood to the left arm and the right subclavian artery suppli ...

pass anterior to it. Scalenus posterior04

Posterior scalene

The posterior scalene, () is the smallest and most deeply seated of the scalene muscles. It arises, by two or three separate tendons, from the posterior tubercles of the transverse processes of the fourth, fifth and sixth cervical vertebrae, and is inserted by a thin tendon into the outer surface of the second rib, behind the attachment of the anterior scalene. It is supplied by cervical nerves C5, C6 and C7. It is occasionally blended with the middle scalene.

Variation

A fourth muscle, the (Sibson's muscle), is sometimes present behind the lower portion of the anterior scalene.

Function

The anterior and middle scalene muscles lift the first rib and bend the

to the same side as the acting muscle; the posterior scalene lifts the second rib and tilts the neck to the same side. Because they elevate the upper ribs, they also act as

accessory muscles of respiration The muscles of respiration are the muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration duri ...

, along with the

sternocleidomastoids The sternocleidomastoid muscle 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 sternocleidomastoid is innervated by the acces ...

Relations

The scalene muscles have an important relationship to other structures in the neck. The

and

pass between the anterior and middle scalenes. The

subclavian vein The subclavian vein is a paired large vein, one on either side of the body, that is responsible for draining blood from the upper extremities, allowing this blood to return to the heart. The left subclavian vein plays a key role in the absorption ...

and

phrenic nerve The phrenic nerve is a mixed nerve that originates from the C3–C5 spinal nerves in the neck. The nerve is important for breathing because it provides exclusive motor control of the diaphragm, the primary muscle of respiration. In humans, t ...

pass anteriorly to the anterior scalene as the muscle crosses over the first rib. The phrenic nerve is oriented vertically as it passes in front of the anterior scalene, while the subclavian vein is oriented horizontally as it passes in front of the anterior scalene muscle. The passing of the

and the

through the space of the anterior and middle scalene muscles constitute the scalene hiatus (the term "scalene fissure" is also used). The region in which this lies is referred to as the scaleotracheal fossa. It is bounded by the

clavicle The clavicle, collarbone, or keybone is a slender, S-shaped long bone approximately long that serves as a strut between the scapula, shoulder blade and the sternum (breastbone). There are two clavicles, one on each side of the body. The clavic ...

inferior anteriorly, the trachea medially, posteriorly by the

trapezius The trapezius is a large paired trapezoid-shaped surface muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the human spine, spine and laterally to the spine of the scapula. It moves the scapula and ...

, and anteriorly by the platysma muscle.

Clinical significance

The anterior and middle scalene muscles can be involved in certain forms of thoracic outlet syndrome as well as

myofascial pain syndrome Myofascial pain syndrome (MPS), also known as chronic myofascial pain (CMP), is a syndrome characterized by chronic pain in multiple myofascial trigger points ("knots") and fascial (connective tissue) constrictions. It can appear in any body part. ...

, the symptoms of which may mimic a

spinal disc herniation A disc herniation or spinal disc herniation is an injury to the intervertebral disc between two vertebrae, usually caused by excessive strain or trauma to the spine. It may result in back pain, pain or sensation in different parts of the body, ...

of the

. Since the nerves of the brachial plexus pass through the space between the anterior and middle scalene muscles, that area is sometimes targeted with the administration of regional anesthesia by an anesthesia provider. The nerve block, called an interscalene block, may be performed prior to arm or shoulder surgery. According to the medical codes in the 2016 Procedural Coding Expert, published by the American Academy of Professional Coders, for

Current Procedural Terminology The Current Procedural Terminology (CPT) code set is a procedural code set developed by the American Medical Association (AMA). It is maintained by the CPT Editorial Panel. The CPT code set describes medical, surgical, and diagnostic services and ...

(CPT) and other medical codes, the scalenus anticus muscle can be divided by reparative or reconstructive surgery, with (# 21705) or without (# 21700) resection of the

cervical rib Cervical ribs are the ribs of the neck in many tetrapods. In most mammals, including humans, cervical ribs are not normally present as separate structures. They can, however, occur as a pathology. In humans, pathological cervical ribs are usually no ...

History

The scalenes used to be known as the ''lateral vertebral muscles''.

Etymology

The muscles are named from

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

(), meaning 'uneven'

Mosby's Medical, Nursing & Allied Health Dictionary ''Mosby's Dictionary of Medicine, Nursing & Health Professions'' is a dictionary of health-related topics. The 11th edition, published in 2021, contains 2,080 pages and 2,450 illustrations. It includes some encyclopaedic definitions and 12 appendi ...

, Fourth Edition, Mosby-Year Book Inc., 1994, p. 1395 as the pairs are all of differing length.

Additional images

File:Musculi coli base.svg, Musculi colli base File:Slide1ABBA.JPG, Scalene muscles. Muscles of the neck. Lateral view. File:Slide2ABBA.JPG, Scalene muscles. Muscles of the neck. Lateral view. File:Gray384.png, Section of the neck at about the level of the sixth cervical vertebra. Showing the arrangement of the fascia colli.

References

{{Authority control Human anatomy Muscles of the head and neck