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The erector spinae muscles are a group of deep muscles in the back that play a crucial role in spinal stability and movement. These muscles, including the iliocostalis, longissimus, and spinalis, work together to extend and laterally flex the spine, neck, and trunk. The innervation of these muscles is a complex process, involving various spinal nerves and their branches. The specific innervation patterns vary across the different sections and individuals, but the overall function of these muscles is to provide stability and facilitate movement in the spinal region.
| Characteristics | Values |
|---|---|
| Erector Spinae Muscle Groups | Iliocostalis, Longissimus, Spinalis, Semispinalis Thoracis |
| Spinalis Muscle Groups | Spinalis Capitis, Spinalis Cervicis, Spinalis Thoracis |
| Longissimus Muscle Groups | Longissimus Capitis, Longissimus Cervicis, Longissimus Thoracis |
| Iliocostalis Muscle Groups | Iliocostalis Lumborum, Iliocostalis Thoracis, Iliocostalis Cervicis |
| Function | Extend and laterally flex the spine |
| Innervation | Lateral branches of the posterior rami of the cervical, thoracic and lumbar spinal nerves |
| Blood Supply | Vertebral, Deep Cervical, Occipital, Intercostal, Lumbar, Transverse Cervical, Subcostal, Lateral Sacral Arteries |
| Pathology | Pain |
| Related Conditions | Low Back Pain (LBP) |
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What You'll Learn
Iliocostalis Lumborum
The erector spinae muscles are a group of three deep muscles of the back that extend and laterally flex the spine. They are divided into three regional groups: spinalis muscles, longissimus muscles, and iliocostalis muscles.
The iliocostalis lumborum is the lower (lumbar) portion of the iliocostalis muscle. The word "iliocostalis" comes from the Latin "ilium," meaning "flank or groin," and "costa," meaning "rib." "Lumborum" comes from the Latin "limbus," meaning "loin." Together, iliocostalis lumborum translates to "the muscle between the groin, or flank, and the ribs in the loin region."
The muscle bulk formed by the erector spinae group, including the iliocostalis lumborum, can be felt running parallel to the spine. These muscles are vital for allowing free movement of the spine. Specifically, you would not be able to straighten your back after bending or rotating if there was significant dysfunction to the erector spinae muscle group, including the iliocostalis lumborum.
The lumbar part of the iliocostalis lumborum originates from the sacrum or iliac crest, or spinous processes of the lower lumbar or thoracic vertebrae. It courses superiorly and inserts into the transverse processes of vertebrae L1-L5 and the adjacent part of the middle layer of thoracolumbar fascia. The muscle fibres are laminated so that those attaching to L1 are the most superficial and medial, while those inserting to L4 are the deepest and most lateral.
The thoracic part of the iliocostalis lumborum originates from the same site as the lumbar part, in the form of an aponeurotic sheath covering the lumbar part. Fibres course superiorly over the back and insert into the angle of ribs 5-12, laterally to the iliocostalis thoracis. The muscle fibres of the thoracic part are serially aligned, so that those attaching to the fifth rib are the most medial and inferior, while those inserting to the twelfth rib are the most lateral and superior.
Injury to the iliocostalis lumborum may be indicated by pain concentrated in the lower back or pain in the buttocks. Very rarely, injury to this muscle will manifest as lower abdominal pain. Common daily activities that may cause injury to the muscle include lifting a heavy object, rotating while lifting, or even sitting immobile for extended periods.
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Longissimus Capitis
The longissimus muscle is the central, thickest, and longest erector spinae muscle. It is divided into three parts: capitis, cervicis, and thoracis, based on their superior attachments and locations. The longissimus capitis is the most cranially positioned of the three.
The longissimus capitis is the longest muscle of the head and neck. It originates from the transverse processes of the fourth cervical to fourth/fifth thoracic vertebrae (C4-T5) and ascends across the lateral surface of the semispinalis capitis muscle. It then attaches to the transverse processes of the last three/four cervical vertebrae (C4-C7). Finally, it inserts at the lateral surface of the mastoid process of the temporal bone, near the attachments of the sternocleidomastoid and splenius capitis muscles.
The longissimus capitis and cervicis are innervated by the lateral branches of the posterior/dorsal rami of cervical spinal nerves. The longissimus capitis receives arterial blood from the vertebral artery, deep cervical artery, superficial and deep descending branches of the occipital artery, and the deep branch of the transverse cervical artery.
The longissimus capitis is involved in the lateral rotation and extension of the neck. It also rotates the head. A strain in the longissimus capitis can cause tenderness in the back of the head and neck, scalp numbness, and neck stiffness. It can be caused by a blow to the head or neck, a vehicle crash, or prolonged overhead activities.
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Spinalis Cervicis
The erector spinae are a group of deep back muscles that extend and laterally flex the spine. They are divided into three muscle groups: spinalis, longissimus, and iliocostalis. The spinalis muscles are the most medial of the three groups. They are divided into three regional groups, from superior to inferior: spinalis capitis, spinalis colli, and spinalis thoracis.
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Spinalis Thoracis
The erector spinae muscles are a group of deep back muscles that extend and laterally flex the spine. They play an important role in spinal stability and low back pain (LBP). The erector spinae muscle group is formed by three muscles: the iliocostalis, longissimus, and spinalis muscles.
The spinalis muscles are the most medial of the three erector spinae muscles. They are divided into three regional groups: spinalis capitis, spinalis colli, and spinalis thoracis. The focus of this discussion will be on the spinalis thoracis muscle.
The spinalis thoracis muscle is the most prominent and well-organized part of the spinalis muscle group. These muscle fibres originate from the spinous processes of T11-L2 vertebrae and travel superiorly to attach along the spinous processes of T2-T8 vertebrae. There can be variations between individuals regarding the origin and insertion sites of the spinalis thoracis muscle. The fibres of the spinalis thoracis muscle travel superiorly along the upper back region, forming the intrinsic muscles of the back and posterior neck regions.
The spinalis thoracis muscle is innervated by the lateral branches of the posterior rami of the adjacent spinal nerves, specifically the thoracic and upper lumbar nerves. The blood supply to this muscle comes from the dorsal branches of the superior and posterior intercostal arteries, as well as branches of the lumbar arteries.
The spinalis muscles, including spinalis thoracis, work together with the other muscles in the erector spinae group to produce major movements of the spine. The unilateral contraction of the erector spinae muscles results in lateral flexion and rotation of the cervical, thoracic, and lumbar spines.
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Dorsal Rami
The erector spinae muscles are a group of deep muscles in the back that extend and laterally flex the spine. They play an important role in spinal stability and low back pain (LBP). The erector spinae muscles are formed of three muscles: iliocostalis, longissimus, and spinalis.
The dorsal rami of spinal nerves provide motor and sensory innervation to the deep muscles of the back, skin of the posterior head, neck, and back, and the zygapophyseal joints and periosteum of the vertebral column. The dorsal rami divide into medial, intermediate, and lateral branches. The lateral branch supplies innervation to the iliocostalis muscle, the most lateral part of the erector spinae muscles, which attaches to the ribs. The intermediate branch supplies innervation to the spinalis and longissimus muscles, the central and medial muscles of the erector spinae, respectively.
The spinalis muscles are the most medial erector spinae muscles and are divided into three regional groups: spinalis capitis, spinalis colli, and spinalis thoracis. The spinalis muscles are innervated by the lateral branches of the posterior rami of the cervical, thoracic, and lumbar spinal nerves.
The longissimus muscles are the central and thickest erector spinae muscles. Similar to the spinalis muscles, they are divided into three regional groups: longissimus capitis, longissimus colli, and longissimus thoracis. The longissimus muscles have identical innervation to the spinalis muscles; from the lateral branches of the posterior rami of the adjacent spinal nerves.
The iliocostalis muscles are the most lateral part of the erector spinae muscles and are innervated by the lateral branches of the posterior rami of the cervical, thoracic, and lumbar spinal nerves. The iliocostalis has three different insertions: iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis.
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Frequently asked questions
The erector spinae are a group of muscles that include the spinalis, longissimus, and iliocostalis muscles. They are deep muscles of the back that extend and laterally flex the spine.
The spinalis muscles are innervated by the lateral branches of the posterior rami of the cervical, thoracic, and lumbar spinal nerves.
The longissimus muscles have an identical innervation to the spinalis muscles, with branches from the adjacent spinal nerves.
The iliocostalis muscles are innervated by the lateral branches of the posterior rami of the cervical, thoracic, and lumbar spinal nerves.
