Back muscles

Summary

The back comprises the dorsal part of the neck and the torso (dorsal body cavity) from the occipital bone to the top of the tailbone. The muscles of the back can be divided in three main groups according to their anatomical position and function. The superficial muscles participate in the movements of the upper limb, the intermediate muscles support the respiratory function, and the deep muscles are involved in the posture and rotation of the vertebral column. The first two groups include the extrinsic muscles, which are innervated by the anterior branches of the spinal nerves, while intrinsic muscles of the latter group are innervated by the posterior branches. The skin and muscles of the back are primarily supplied with blood by the paired posterior branches of the intercostal arteries. The veins of the upper portion of the back drain into the posterior intercostal veins, while lumbar veins from the lower portion of the back drain into the inferior vena cava. Similarly, the intercostal lymph nodes receive drainage from the thoracic portion of the back, while the inguinal lymph nodes drain from the lumbar back.

The organs, blood vessels, lymphatic vessels, and nerve pathways of the neck (see overview of head and neck region), the spinal cord, and the vertebral column (the spine) are covered in their own learning cards.

Overview of the muscles of the spine

Intrinsic muscles Extrinsic muscles
Development
  • Local (primary) development
  • Secondary development
Examples
  • Deep muscles of the back
Innervation
Function
  • Involved in posture and rotation of vertebral column, head, and neck
  • Dynamic function: The muscles enable movement of the torso around three axes.
  • Stabilizing function: Ligament and muscles connect the vertebrae with one another.
  • Superficial muscles: involved in movements of the upper limb
  • Intermediate muscles: involved in respiratory function

Intrinsic suboccipital muscles

Extrinsic suboccipital muscles

The extrinsic suboccipital muscles include rectus capitis lateralis and rectus capitis anterior muscles, which are prevertebral muscles of the neck. See prevertebral muscles in the learning card “Overview of the head and neck region” for more details.

Superficial back muscles

Superficial back muscles are the first layer of muscles below the skin and superficial fascia. These muscles connect the clavicula, scapula, and humerus to the axial skeleton, and the main function is related to the movement of the upper limb. They are also covered in relation to the shoulder and shoulder girdle in the learning card “Shoulder, axilla, and brachial plexus.” The latissimus dorsi is covered in the learning card on the “Chest wall” as well.

Muscle Origin Insertion Function Innervation

Trapezius

Descending (upper) portion
Transverse portion
Ascending (lower) portion
Levator scapulae
  • Scapula: elevation (shrugging)
  • In conjunction with the rhomboid muscles: returns the elevated arm to its neutral position.
Latissimus dorsi
Rhomboid major
Rhomboid minor

Intermediate back muscles

Two muscles (the serratus posterior superior and inferior) belong to the intermediate group of back muscles. They are immediately deep to the muscles in the superficial group and pass obliquely outward from the vertebral column to attach to the ribs. These muscles support the respiratory function and are also covered under chest wall muscles in the “Chest” learning card.

Muscle Origin Insertion Function Innervation
Serratus posterior superior
Serratus posterior inferior

Deep back muscles

The intrinsic back muscles are divided based on their function in four groups.

Spinotransverse system

Muscle Origin Insertion

Function

Innervation

Splenius capitis

Splenius cervicis

Erector spinae (sacrospinal system)

Muscle Origin Insertion

Function

Innervation
Iliocostalis Cervicis (cervicalis ascendens)
  • Unilateral: ipsilateral flexion of the torso
  • Bilateral: dorsal extension of the torso
Dorsi (thoracis)
Lumborum (iliocostalis muscle; sacrolumbalis muscle)
Longissimus Capitis (trachelomastoid muscle)
  • Unilateral
  • Bilateral: dorsal extension of the torso
Cervicis (transversalis cervicis)
Thoracis and lumborum
Spinalis Capitis
Cervicis
Dorsi
  • T1–T8
  • T10–L3

Transversospinal system

Muscle Origin Insertion

Function

Innervation
Rotatores Short
  • Contralateral rotation of the spine
Long
Multifidus Cervical
  • Unilateral: ipsilateral flexion of the torso
  • Bilateral: dorsal extension of the torso
Thoracic
Lumbar and sacral
  • Mammillary processes L3–L5
  • S1–S4
  • Iliac crest
Semispinalis Thoracis
Cervicis
Capitis
  • Unilateral: ipsilateral rotation of the head
  • Bilateral: dorsal extension of the head

Segmental muscles

Muscle Origin Insertion

Function

Innervation
Levatores costarum
Interspinales Cervical
  • C2–T1
  • Segmental dorsal extension in the cervical, thoracic, and lumbar spine
Thoracic
  • T2–T3
  • T11–L1
Lumbar
  • L2–L5
Intertransversarii muscles Anterior intertransversarii (cervical)
  • Unilateral: ipsilateral flexion of the neck and torso
  • Bilateral: stabilization of the spine
Lateral lumbar intertransversarii
  • Costal processes L2–L5
  • Costal processes (of the neighboring vertebra)
Posterior intertransversarii
Thoracic intertransversarii
Medial lumbar intertransversarii
  • Accessory and mamillary processes L2–L5
  • Accessory and mamillary processes (of the neighboring vertebra)

The interspinales muscles skip one vertebral segment, the spinalis muscles skip multiple segments!

Vasculature and lymphatics

Vascular supply

Neck

Structure Characteristics
Arterial
Venous Superficial
Deep
  • Deep cervical vein

Back

Vessels Characteristics
Arterial
Venous

Vertebral body

Lymphatics

Cross through Drain into
Thoracic spine (cranial)
Lumbar spine (caudal)
last updated 01/24/2020
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