Dominic Stone
Deep muscles, also known as intrinsic muscles, are a group of muscles that develop embryologically in the back. They are located underneath the erector spinae and are collectively called the transversospinales. The deepest layer of deep muscles is attached to the transverse and spinous processes of the vertebral column. The main functions of these muscles are flexion, extension, lateral flexion, and axial rotation of the vertebral column. They are also involved in maintaining the body's posture and producing movements of the head, neck, and trunk. The deep muscles of the back are further divided into three layers: superficial, intermediate, and deep.
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What You'll Learn
Deep muscles of the back
The deep muscles of the back, also called intrinsic or true back muscles, are a group of muscles that lie on each side of the vertebral column, deep to the thoracolumbar fascia. They are well-developed and collectively extend from the sacrum to the base of the skull. These muscles are associated with the movements of the vertebral column and the control of posture. The deep muscles of the back are covered by deep fascia, which plays a key role in their organisation.
The deep back muscles can be divided into four layers: superficial, intermediate, deep, and deepest layers. The superficial muscle layer is composed of the splenius muscles (spinotransversales muscles), which are the splenius capitis and splenius cervicis. These flat muscles are located on the posterolateral aspect of the neck and the posterior upper thorax, overlying the deep muscles of the neck. The splenius muscles produce extension of the neck when acting together and lateral flexion of the neck and rotation of the head to the same side when acting individually.
The intermediate layer contains the large erector spinae muscles, which are sometimes called the long muscles of the back. This muscle group is the largest of the deep back muscles and lies on either side of the vertebral column between the spinous processes of the vertebrae and the angles of the ribs. The muscles are composed of three vertical columns of muscle that lie side by side: the iliocostalis, longissimus, and spinalis muscles. Each muscle column is subdivided into regions (lumborum, thoracic, cervicis, capitis) based on which region of the axial skeleton it attaches to superiorly. The longissimus muscle is the longest and thickest muscle in this group. The spinalis muscle is the smallest of the three columns.
The semispinalis is the most superficial of the deep intrinsic muscles. It can be divided into thoracic, cervicis, and capitis segments, with fibres attaching to the spinous processes of vertebrae and the occipital bone of the skull. The semispinalis muscle group passes over the thoracic and cervical spines, running deep to the erector spinae muscle group. The multifidus muscle lies underneath the semispinalis and is most developed in the lumbar area. It traverses the entire spine from the sacrum to the cervical region and its primary action is proprioceptive in nature. The rotatores are the deepest muscles in this group, present along the entire length of the vertebral column and most prominent in the thoracic region.
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The anatomy of deep muscles
The superficial layer of deep muscles is primarily responsible for the movement of the cervical spine and is composed of the splenius muscles (also known as spinotransversales muscles), which are the splenius capitis and splenius cervicis. These flat muscles are located on the posterolateral aspect of the neck and the posterior upper thorax, overlying the deeper neck muscles. They originate from the spinous processes of cervical and thoracic vertebrae and produce extension of the neck when acting together.
The intermediate layer contains the large erector spinae muscles, also known as the long muscles of the back. The iliocostalis, longissimus, and spinalis muscles make up the erector spinae. The iliocostalis cervicis is vascularized by the occipital, deep cervical, and vertebral arteries, while the iliocostalis thoracis is supplied by the dorsal branches of posterior intercostal and subcostal arteries. The longissimus muscle is the longest and thickest in this group and is divided into three regions based on its attachments.
The deep intrinsic muscles, also known as the transversospinales, lie underneath the erector spinae. This group includes the semispinalis, multifidus, and rotatores muscles. The semispinalis is the most superficial of these deep intrinsic muscles and can be divided into thoracic, cervicis, and capitis segments. The multifidus muscle traverses the entire spine from the sacrum to the cervical region and has short, thick fibres that traverse each intervertebral space. The rotatores are the deepest muscles of the transversospinales group and contribute to the extension and rotation of the vertebral column.
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The function of deep muscles
Deep Back Muscles
The deep back muscles are the intrinsic muscles of the back, meaning they develop embryologically in the back. They are well-developed and collectively extend from the sacrum to the base of the skull. These muscles are associated with the movements of the vertebral column and the control of posture.
The deep back muscles can be divided into three layers: superficial, intermediate, and deep. The superficial layer is primarily responsible for the movement of the cervical spine and is composed of the splenius muscles, which are located on the posterolateral aspect of the neck and the posterior upper thorax, overlying the deep muscles of the neck. The splenius muscles produce extension of the neck when acting together and lateral flexion of the neck and rotation of the head to the same side when acting individually.
The intermediate layer contains the large erector spinae muscles, which are sometimes called the long muscles of the back. The erector spinae muscles are the primary postural and antigravity muscles of the spine.
The deepest layer of the deep back muscles is attached to the transverse and spinous processes of the vertebral column. This layer includes the transversospinales group, which is composed of three major muscles: the semispinalis, multifidus, and rotatores. The semispinalis is the most superficial of the deep intrinsic muscles and is associated with the extension and rotation of the head and vertebral column. The multifidus is located underneath the semispinalis muscle and traverses the entire spine from the sacrum to the cervical region. The rotatores are the deepest muscles of the transversospinales group and are most prominent in the thoracic region. They contribute to the extension and rotation of the vertebral column and also stabilize the vertebrae.
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The blood supply to deep muscles
Deep muscles are those that lie beneath other muscles. They are responsible for maintaining the body's posture and producing movements of the head, neck, and trunk. The blood supply to deep muscles is critical for their functioning and is facilitated by various arteries and blood vessels in the body.
The deep muscles of the lower back, such as the iliocostalis and longissimus, have more varied blood supplies. The iliocostalis cervicis is vascularized by the occipital, deep cervical, and vertebral arteries, while the iliocostalis thoracis is supplied by the posterior intercostal and subcostal arteries. The longissimus, which is the longest and thickest muscle in the erector spinae group, is supplied by branches of the posterior rami of the corresponding regional spinal nerves.
In the lower limbs, the gluteal region is supplied by the superior and inferior gluteal arteries, which arise from the internal iliac artery. The posterior tibial artery supplies the deep posterior leg muscles, such as the tibialis posterior, and continues down the surface of the leg into the foot. The fibular artery supplies muscles in the lateral compartment of the leg, while the anterior tibial artery becomes the dorsalis pedis artery in the foot, supplying the tarsal bones and the dorsal aspect of the metatarsals.
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The innervation of deep muscles
Deep back muscles work together to support and maintain the body's posture and produce movements of the head, neck, and trunk. The main functions of these muscles are flexion, extension, lateral flexion, and axial rotation of the vertebral column. All of these muscles are innervated by the segmental branches of the posterior rami of spinal nerves. The nerve and the group of muscle fibres that are simultaneously innervated by it are called a motor unit. Motor units vary in size.
The splenius muscles are innervated by the posterior rami of the middle and lower cervical spinal nerves. The blood supply for both muscles comes from the vertebral, occipital, superior intercostal, deep cervical, and transverse cervical arteries. When acting together, both muscles produce extension of the neck. However, when acting individually, each muscle causes lateral flexion of the neck and rotation of the head to the same side.
The erector spinae muscles are the primary postural and antigravity muscles of the spine. They derive their innervation from the deeper cerebral tracts such as the reticulospinal and vestibulospinal tracts. The iliocostalis muscle forms the lateral column of the erector spinae muscle group. The muscle is divided into three regions according to its attachments. The iliocostalis is innervated by lateral branches of the posterior rami of cervical, thoracic, and lumbar spinal nerves. Each region of the iliocostalis muscle has a specific blood supply.
The longissimus muscle forms the central column of the erector spinae muscle group and is the longest and thickest of this group. It is divided into three regions based on their attachments. The nerve supply to the various parts of the longissimus muscle is by branches of the posterior rami of the corresponding regional spinal nerves. The longissimus capitis and cervicis are vascularized by the vertebral artery, deep cervical artery, superficial and deep descending branches of the occipital artery, and deep branch of the transverse cervical artery. The longissimus thoracis, on the other hand, is supplied by the dorsal branches of the superior intercostal, posterior intercostal, lateral sacral, and median sacral arteries.
The semispinalis muscle group passes over the thoracic and cervical spines, running deep to the erector spinae muscle group. The fibres of semispinalis capitis and cervicis course superomedially from the transverse processes as a long, thin muscle. Acting unilaterally, the semispinalis capitis acts in ipsilateral lateral flexion and rotation. Bilaterally, it assists in the extension of the spine. Semispinalis capitis is supplied by the greater occipital nerve. There is no specific artery that supplies the semispinalis group, but they derive supply largely from the occipital artery.
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Frequently asked questions
Deep muscles are the intrinsic muscles that develop embryologically in the back. They are further divided into three layers: superficial, intermediate, and deep.
The deep muscles are associated with the movements of the vertebral column and the control of posture. The main functions of these muscles are flexion, extension, lateral flexion, and axial rotation of the vertebral column.
The deep back muscles include the semispinalis, multifidus, and rotatores. The semispinalis is the most superficial of the deep intrinsic muscles, while the multifidus lies underneath it. The rotatores are the deepest muscles of the transversospinales group.
