Deep back muscles
The deep back muscles are a group of skeletal muscles located within the deepest part of the dorsal trunk, closest to the spine. They are sometimes referred to as the intrinsic back muscles or true back muscles as they control the movement and posture of the vertebral column.
The deep back muscles extend superiorly from the pelvis to the cranium and are arranged into four layers. They are enclosed in a deep fascia that has medial attachments to the nuchal ligament, tips of the spinous processes, supraspinous ligament, and the median sacral crest. The fascia also has lateral attachments to the transverse processes of the cervical and lumbar vertebrae as well as the angle of the ribs.
|Superficial layer||Splenius capitis and splenius cervicis|
|Intermediate layer (erector spinae group)||
Iliocostalis, longissimus, and spinalis
Mnemonic: I Like Standing
|Deep layer (transversospinales group)||Semispinalis, multifidus, rotatores breves and rotatores longi|
|Deepest layer||Interspinales, intertransversarii, levatores costarum|
|Blood supply||Vertebral, deep cervical, occipital, transverse cervical, superior intercostal, posterior intercostal, subcostal, lumbar, and lateral sacral arteries|
|Innervation||Branches of the dorsal rami of the spinal nerves|
Control movement of the vertebral column – bilateral muscle contraction causes dorsal extension; unilateral contraction causes lateral flexion and/or head rotation
Understanding spinal muscle anatomy can be tricky because there are so many origins and insertions to cover. For that reason, this article will present you with deep back muscle anatomy in an easy-to-understand model. Hopefully, in the end, you will be more confident in this area of anatomy.
- Superficial layer
- Intermediate layer
- Deep layer
- Deepest layer
- Blood supply
The most superficial layer of the intrinsic back muscles includes the splenius group of muscles. They extend along the posterior and lateral aspects of the neck and upper part of the thorax. Some texts include the erector spinae in this layer of muscles, while others place it in its own layer. For the purpose of this article, it will be discussed in its own layer. The splenius muscles are regionally divided into the capitis and cervicis subgroups.
Splenius capitis is a paired muscle that resides between the trapezius and two deeper muscles called semispinalis capitis and longissimus capitis. The proximal part of the muscle is located deep to sternocleidomastoid, where it contributes to the formation of the floor of the posterior triangle of the neck.
The muscle originates from the apices of the spinous process of C7 to T3 (seventh cervical to the third thoracic vertebra) along with the supraspinous ligament. The tendons of the cranial fibers of the muscle interlace with the dorsal raphe of the nuchal ligament (ligamentum nuchae). The caudal fibers take a superolateral course to insert on the lateral superior nuchal line of the occipital bone and the mastoid process of the temporal bone.
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When splenius capitis is activated on only one side (e.g. on the left) it works synergistically with the sternocleidomastoid muscle of the opposite side (e.g. the right) to turn the head ipsilaterally (e.g. to the left). Unilateral contraction of splenius capitis also results in lateral flexion of the neck. When the muscle acts in consort with its partner on the opposite side, the muscles work to extend the head. It receives motor innervation from the lateral branches of the posterior rami of the second and third cervical spinal nerves (C2-C3).
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Splenius cervicis, also called splenius colli, is a paired muscle located deep to the superior fibers of serratus posterior, rhomboids and trapezius muscles. It is, however, superficial to the caudal semispinalis muscles and erector spinae. Essentially, the muscle occupies the same plane as the splenius capitis muscle. The only exception is that it covers the lower regions of the neck and thorax.
This muscle emerges from the spinous processes of T3 to T6 vertebrae. Like the splenius capitis, the fibers of splenius cervicis also travel inferomedially as it travels around other deep neck muscles. It eventually inserts on the transverse process of the atlas and the tip of the transverse process of the axis. It also partly attaches to the posterior tubercle of the transverse process of the third cervical vertebra (C3).
Unilateral activation of splenius cervicis aids in turning the neck toward the same side by rotating the upper cervical vertebra. Therefore, it works in consort with the other splenius muscle. It also helps with lateral flexion of the neck. Bilateral activation of the splenius cervicis muscle will extend the head. The lower cervical dorsal rami (C4 – C7) provides motor innervation to this muscle.
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The intermediate layer of the intrinsic back muscles lies deep to the splenius group of muscles but superficial to the other intrinsic back muscles.
This intermediate layer is occupied by the erector spinae muscle group, which is the main extensor of the vertebral column. It is distributed craniocaudally and occupies a groove that is bounded laterally by the angle of the ribs and medially by the spinous processes of the vertebral column. The erector spinae muscle group is divided into three distinct columns or fascicles, from medial to lateral: spinalis, longissimus, and iliocostalis muscles. Each fascicle can be further subdivided according to the region of the vertebral column that it inserts in. For example, lumborum, thoracis, cervicis, and capitis for those that insert in the lumbar, thoracic and cervical vertebrae or the base of the skull, respectively.
The muscles are innervated by the lateral branches of the dorsal rami arising from the cervical, thoracic, and lumbar spinal nerves.
The spinalis group is the most medial column of the erector spinae muscle group. There are three subdivisions of this muscle arranged craniocaudally – capitis, cervicis, and thoracis. Spinalis thoracis is the most consistent of the three parts of this muscle. The muscle fascicles originate from the spinous processes of T11 – L2 vertebrae and insert on the spinous processes of the proximal thoracic vertebrae (T2 – T8).
Whenever spinalis cervicis (spinalis colli) is present, it originates from the caudal part of the nuchal ligament and from the spinous processes of C7 – T1. In turn, the muscle inserts into the spinous processes of C2 - C4 vertebrae. The spinalis capitis fibers are actually inconsistent fascicles arising from the semispinalis capitis muscle that extends to C7 – T1.
Motor innervation to this muscle group arises from the lateral branches of the posterior rami of adjacent spinal segments. When the bilateral spinalis muscles work in unison, they result in spine extension in the cervical and thoracic regions. However, unilateral contraction causes lateral flexion of the ipsilateral regions.
Moving away from the vertebral column, we meet the next erector spinae muscle, called longissimus. It is the central fasciculus of the intermediate intrinsic muscle group. Like the spinalis group, longissimus also has capitis, cervicis, and thoracis segments. Longissimus capitis has its insertion on the posterior part of the mastoid process of the temporal bone (beneath the splenius capitis). The flat, narrow band of muscle can be traced inferiorly to its origin at the transverse processes of C4 – T5 vertebrae. The thin, long fibers of longissimus cervicis, also called longissimus colli, arise from the transverse processes of T1 – T5. It continues cranially between capitis and thoracis until it inserts on the posterior tubercle of the transverse process from C2 – C6.
The most caudal part of this muscle group is the longissimus thoracis, which is also the largest erector spinae component. The name may be a bit misleading as this muscle group segment can be further subdivided into thoracic and lumbar segments. The thoracic part of this muscular column is made up of small, spindle-shaped muscles whose rostral tendons are much shorter than the caudal ones. The muscle fascicles insert on the tips of the transverse processes of T1 – T12 and the angles of the corresponding 5th to 12th ribs. The lumbar part of the muscle arises from the medial part of the transverse processes of the five lumbar vertebrae as well as the medial part of the iliac crest and the lateral sacral crest.
The lateral branches of the posterior rami of the associated spinal nerves provide motor innervation for this muscle group as well. When the longissimus muscles on both sides of the spine contract simultaneously, they extend the vertebral column. When only one of them contracts, the result is ipsilateral flexion of the spine. Longissimus capitis is slightly more special because it can also extend and laterally rotate the head.
Finally, iliocostalis is the most lateral part of the intermediate muscle group. Like the other parts of the erector spinae, iliocostalis also has cervical, thoracic, and lumbar components. Iliocostalis cervicis, also called iliocostalis colli, is made up of slender muscle bundles with long tendons. They are attached to their origin on the angles of the 3rd to 6th ribs. They eventually travel caudally over the posterior surface of the thorax to terminate at the posterior tubercle of the transverse process of C4 – C6 vertebrae.
The spindle-shaped fibers of the iliocostalis thoracis are situated laterally to the iliocostalis cervicis fibers. They arise from the upper border of the angles of the lower six ribs (7-12). In turn, their insertions are provided by the superior borders of the angles of the upper six ribs and the transverse processes of the seventh cervical vertebra. Finally, the iliocostalis lumborum has fleshy muscle bellies that have attachments to pelvic, thoracic and lumbar parts of the vertebrae. The muscle arises from the lateral crest of the sacrum, medial end of the iliac crest, and the thoracolumbar fascia. They eventually ascend in a laminar manner to insert at the angle of the 5th – 12th ribs and the transverse processes of L1 – L4.
Bilateral activation of the iliocostalis muscles via motor impulses from the lateral branches of the posterior rami of adjacent spinal nerves results in the extension of the vertebral column. However, unilateral contraction of the muscle group causes lateral flexion of the spine on the same side.It’s true. There are a lot of muscles to remember and it’s a lot to read. How about taking a break from reading and watching a video and doing a quiz instead?
A really easy way to remember the muscles in the intermediate layer is to learn the mnemonic 'I Like Standing'. It stands for:
(Lateral to medial)
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Continuing even deeper, one can locate the third layer of the intrinsic back muscles. These short, oblique muscles collectively form the transversospinales or the spinotransverse group. They mainly extend between the transverse processes of the vertebrae at their respective levels to the spinous processes. There are three subdivisions of this muscle group based on their layers. From superficial to deep, these include semispinalis, multifidus, and rotatores. Similar to the previous muscle groups, the transversospinales can be further subdivided according to the region of the vertebral column that they insert in (capitis, cervicis, thoracis, and lumborum). The rotatores are an exception, as their branches are described as short (brevis) and long (longus) fascicles.
The semispinalis group contains the longest and most superficial set of fascicles in the transversospinalis group. They are subdivided based on the region they occupy (i.e. subcapital, cervical, and thoracic). Semispinalis capitis overlies semispinalis cervicis. The muscle starts out as flat tendons arising from the superior articular processes of C4 – C7 as well as the transverse processes of T1 – T6. They travel superiorly, medially, and dorsally to insert at the medial aspect between the superior and inferior nuchal lines of the occipital bone. The semispinalis capitis muscle fibers are innervated by the descending fibers of the greater occipital nerve (C2-C3 nerve roots).
Semispinalis cervicis, also known as semispinalis colli, lies over the cervical and thoracic components of the multifidus muscle. Semispinalis cervicis originates from the transverse processes of T1 – T6 and inserts on the spinous processes of C2 – C5 vertebrae. The fascicle that inserts on the axis (C2) is the largest of the semispinalis cervicis group. Semispinalis thoracis overlies the thoracic component of multifidus and has thin fascicles with long tendons extending from either end. They arise from the transverse processes of T6 – T10 and insert on the spinous processes of C6 – T4 vertebrae. Both the semispinalis cervicis and thoracis groups are innervated by the medial branches of the posterior rami of the spinal nerves.
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The semispinalis muscles cause extension of the head, and cervical and thoracic vertebrae when they contract on both sides. Unilateral contraction of the muscle group causes lateral flexion of the head and cervical and thoracic spine on the same side, but rotation of these structures to the opposite side.
Multifidus is the second, bilateral muscle of the transversospinales group and it is located underneath semispinalis. It is made up of several fascicles that cover the laminae of the underlying vertebrae. They occupy the space lateral to the spinous processes of these vertebrae from the cervical to the lumbar regions. It also expands over the posterior surface of the sacrum. Multifidus cervicis, also called multifidus colli, arises from the superior articular processes around C4 – C7. They take a superomedial course to insert variably on the lateral aspect and the tips of the spinous processes of C2 – C5 vertebrae.
Multifidus thoracis originates from the transverse processes of the thoracic vertebrae. The fibers also take a superomedial course to insert variably on the spinous processes of the vertebrae 2 – 5 levels above their origin. Multifidus lumborum arises from the mammillary processes of the lumbar vertebrae and the posterior surface of the sacrum. Some fibers also arise from the posterior superior iliac spine of the ilium and the posterior sacroiliac ligament. They travel cranially to insert on the lateral surface and apices of the spinous processes about 2 to 5 levels above their origin. Motos supply to these muscle fibers come by way of the medial branches of the posterior rami of the nearby spinal nerves.
Bilateral activation of the multifidus muscles causes extension of the spine. However, unilateral contraction of the muscle cause lateral flexion of the vertebra ipsilaterally and rotation of the spine contralaterally.
The rotatores represent the third group of transversospinales muscles, situated underneath the multifidus muscles. They are located along the length of the entire spine, but they are most developed in the thoracic region. There are eleven pairs of rotatores muscles divided into short (breves) and long (longi) fascicles. Rotatores breves are responsible for connecting the upper posterior aspect of the transverse process of the vertebra with the lateral surface of the lamina and spinous process of the vertebra immediately above. Rotatores longi also connect the transverse processes of the thoracic vertebrae to the laminae and spinous processes, but in this case to two vertebral levels above.
The medial branches of the posterior rami of adjacent spinal nerves give motor supply to the rotatores muscles. These muscles are responsible for extension and contralateral rotation of the thoracic spine with bilateral and unilateral activation, respectively.
Beneath the transversospinal group of muscles is another set of much smaller muscles that form the deepest muscle layer. These minor back muscles are poorly developed in the thoracic region, but more prominent in the cervical and lumbar areas. The deepest layer of muscles is made up of the interspinales, intertransverse, and the levatores costarum. Each subgroup has functions unique to their location and attachments. Collectively, they contribute to the stability of the vertebrae.
The interspinales muscle group extends from the cervical to the thoracic regions. They are located on either side of the interspinous ligament, spanning the space between the tips of the spinous processes of successive vertebrae. In the cervical region, interspinales cervicis (interspinales colli) consists of six pairs of muscles. They extend from the spinous processes of C2-C7 vertebrae to C1-C6. The thoracic group (interspinales thoracis) occupy the space between the spinous processes of T2, T11, T12 and those of T1, T10, and T11 vertebrae. Interspinales lumborum consists of four pairs of muscles between the five lumbar vertebrae. Occasionally, there is an interspinales muscle between T12 – L1 and L5 – S1.
Motor supply to the interspinales muscles arrives by way of the posterior rami of spinal nerves along the length of the muscle. Contraction of the interspinales muscles causes extension of both the cervical and lumbar vertebrae.
As the name suggests, the intertransversarii muscles are small fascicles that span between the transverse processes of adjacent vertebrae. These muscles are present (with some degree of variability) at all levels of the vertebral column, but they are most developed in the cervical region. They assist with lateral flexion and stabilizing the spinal column.
There are seven pairs of well-defined muscles (intertransversarii cervicis/colli) in the cervical region. Each of them can be separated by the ventral rami of the spinal nerve into anterior and posterior components. The posterior component is further subdivided into medial and lateral slips. The medial slip of the posterior component is known as the intertransverse muscle ‘proper’. It can be divided even further by the dorsal ramus of the spinal nerve into medial and lateral components. The first pair of muscles is found between C1 – C2 and the last pair exists between C7 – T1. The thoracic component of the intertransversarii (intertransversarii thoracis) is made up of single fascicles from T10 – L1.
The lumbar intertransversarii (intertransversarii lumborum) are more similar to the cervical counterparts in that there are two sets of muscles: medial (mediales) and lateral (laterales). The intertransversarii mediales runs between the mammillary processes of one vertebra to the accessory process of the other. On the other hand, intertransversarii laterales is separated into ventral and dorsal components. The dorsal component connects the transverse and accessory processes of adjacent vertebrae, while the ventral division connects the transverse process of the lumbar vertebrae.
Both anterior and posterior rami of the spinal nerves emerge along the length of the muscle to initiate motor activity. As a result, the intertransversarii muscles stabilize the spine (bilateral activation) and lateral flexion of the spine (unilateral contraction).
The levatores costarum muscles are minor deep back muscles that are not well developed. When present, they are responsible for elevating the ribs and rotating the thoracic spine.
These muscles arise from the transverse processes from C7 – T11 and insert along the superior border of the external surface of the rib one level below its origin.
They are innervated by the posterior rami of the spinal nerves arising along the thoracic vertebrae.
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After learning about all the deep back muscles, it’s time to understand how they are kept viable. The blood supply of the intrinsic back muscles varies at different levels of the vertebral column. The dorsal branches of the posterior intercostal arteries and the lumbar arteries supply oxygenated, nutrient-rich blood to these muscle bands.
The erector spinae has a unique arrangement of blood supply. Essentially, blood vessels travel between the grooves created between the muscle columns and give off branches at varying levels. Below is a list of additional blood vessels that also supply the deep back muscles.
- Occipital artery
- Vertebral artery
- Deep cervical artery
- Transverse cervical artery
- Superior intercostal artery
- Subcostal arteries
- Lateral sacral arteries
Knowing the blood supply of the deep back muscles is just as important as knowing the muscles themselves. The links below can help you to become more familiar with these anatomy terms.
You can enumerate the attachments and innervation of all the intrinsic back muscles, but what do they actually do? The deep back musculature is essential for maintaining posture and controlling the movement of the vertebral column. Bilateral contraction of the muscles stretches the body (dorsal extension).
On the other hand, unilateral contraction bends the body to one side (lateral flexion). Unilateral contraction of intrinsic back muscles can also result in head and neck rotation. Rotation of the trunk is executed with the assistance of the oblique abdominal muscles. Overall, the deep back muscles work synergistically with the superficial back muscles, and antagonistically with the anterior abdominal muscles.