Extrinsic back muscles:
- Superficial and intermediate muscles
- Connect the axial skeleton with the appendicular skeleton
- Innervated by ventral rami of spinal nerves
Intrinsic back muscles:
- Deep muscles (subdivided further into superficial, intermediate, and deep layers)
- Confined to the axial skeleton
- Innervated by dorsal rami of spinal nerves
|Extrinsic muscles of the back||Superficial layer:|
|Intermediate layer:||Synergistic muscles of respiration|
|Intrinsic or deep (or primary) muscles of the back||Superficial or spinotransversales group:||Extensors of the cervical spine|
|Intermediate layer or erector spinae group:|
|Deep group:||Rotation and extension of the vertebral column|
Extrinsic Back Muscles: Superficial Muscles
Superficial extrinsic back muscles are primarily associated with the movement of the shoulder/arm.
|Trapezius||Accessory nerve (CN XI) and the cervical plexus (C2–C4)|
|Latissimus dorsi||Spinous processes of T7–L5, dorsal sacrum, medial ⅓ of iliac crest, and 9th‒12th ribs||Crest of lesser tubercle of the humerus||Thoracodorsal nerve (C6–C8)|
|Rhomboid major||Spinous processes of T2–T5||Medial border of the scapula||Dorsal scapular nerve (C5)||Fixes and moves the scapula cranially and medially|
|Rhomboid minor||Spinous processes of C7‒T1||Medial border of the scapula|
|Levator scapulae||Transverse processes and posterior tubercles of C1–C4||Superior angle of the scapula||Dorsal scapular nerve (C5) and ventral rami C3–C4|
Extrinsic Back Muscles: Intermediate Muscles
Intermediate extrinsic back muscles are primarily involved with rib/thoracic cage motion.
|Serratus posterior superior||Spinous processes of C6–T2||Costal angle of ribs 2–5||Ventral rami of spinal nerves T1–T4 (intercostal nerves)|
|Serratus posterior inferior||Spinous processes T11–L2||Lower edge of ribs 9–12||Ventral rami of spinal nerves T9–T12 (intercostal nerves)|
Intrinsic Back Muscles: Superficial layer
The intrinsic, or deep, back muscles are grouped into 3 layers: superficial, intermediate, and deep; they are primarily involved in moving the vertebral column. The superficial layer is primarily responsible for the movement of the cervical spine.
|Splenius capitis||Spinous processes of C7–T3 and the supraspinal ligament||Lateral half of superior nuchal line and the mastoid process||Dorsal rami of C1–C6||Extensor and lateral bending of the cervical spine and the head|
|Splenius cervicis||Spinous processes of T3–T6 and the supraspinal ligament||Posterior tubercle of the transverse processes of C1–C3|
Intrinsic Back Muscles: Intermediate Layer
Intermediate layer (intrinsic muscles): The 3 muscles of the intermediate layer make up the erector spinae group.
|Spinalis||Thoracis: spinous process of upper lumbar and lower thoracic vertebrae||Spinous process of upper thoracic vertebrae||Dorsal rami of spinal nerves|
|Cervicis: nuchal ligament and C7 spinous process||Spinous process of C2–C7|
|Capitis: transverse processes of C4–T6||Superior and inferior nuchal lines|
|Longissimus||Thoracic: dorsal sacrum, spinous processes of lumbar/inferior thoracic spine||Accessory processes of the lumbar spine, transverse processes of thoracic spine, and costal angle of ribs 2–12||Dorsal rami T3–T5|
|Cervical: transverse processes of T1–T6||Cervical: posterior tubercle of transverse processes of C2–C5||Cervical: dorsal rami C3–T2|
|Capitis: transverse processes of C3–T3||Capitis: mastoid process of the temporal bone||Capitis: dorsal rami C1–C3|
|Iliocostalis||Lumbar: iliac crest, dorsal sacrum, and the thoracolumbar fascia||Costal angle of ribs 7–12||Dorsal rami T9–L1|
|Thoracic: costal angle of ribs 7–12||Costal angle of ribs 1–6||Dorsal rami T2–T9|
|Cervical: costal angle of ribs 3–6||Posterior tubercle of transverse processes of C3–C6||Dorsal rami T1–T2|
Intrinsic Back Muscles: Deep Layer
The deepest layer of the deep back muscles is attached to the transverse and spinous processes of the vertebral column and facilitates movement of the spine.
|Semispinalis||Capitis: articular processes of C4–C6 and the transverse processes of C7–T6||Between the superior and inferior nuchal lines||Dorsal rami of the spinal nerves||Extension and contralateral rotation of the head and vertebral column|
|Cervicis: posterior surfaces of the transverse processes of T1–T6||Spines of C2–C5|
|Thoracis: transverse processes of T6–T10||Spines of C6–T4|
|Multifidus||Dorsal sacrum, iliac crest, posterior sacroiliac ligaments, mammillary processes, transverse processes of T1–T12, and the articular processes C4–C7||Spinous processes of C2–L5||Dorsal rami C3–S3||Extend the complete vertebral column|
|Rotatores||Transverse processes of the cervical, thoracic, and lumbar spine||Spinous processes of adjoining superior vertebra||Dorsal rami of the spinal nerves||Stabilize the vertebral column|
|Interspinales||Spinous processes of C3–T1, T2–L1, and L2–S1||Spinous processes of C2–C7, T1–T12, and L1–L5||Extend the complete vertebral column|
|Intertransversarii||Medial lumbar: mammillary and accessory processes of all lumbar vertebrae||Adjoining osseous structures of the lumbar spine||Lateral flexion of the spine|
|Thoracic: transverse processes of T10–T12||Transverse processes of T11–12 and at the accessory processes of L1|
|Posterior cervical: C1–C7, posterior tubercle of the transverse processes||Posterior tubercles of the respective adjoining vertebra|
|Levatores costarum||Transverse processes of C7–T11||Extension of the thoracic spine|
- Lumbago (low back pain): Low back pain is 1 of the most common reasons for visits to medical providers. The pain is most commonly related to the musculoskeletal system and increases with age. Common causes include improper lifting, poor posture, lack of regular exercise, skeletal fracture, discogenic disease, or degenerative arthritis. Intrinsic back muscle wasting and increased fatigability are common in patients with chronic low back pain.
- Triangle of auscultation: The triangle of auscultation is an area over the posterior thorax where the breathing sounds are most audible due to the relative thinning of the musculature. The borders of the triangle are defined by:
- Superiorly: inferior border of trapezius
- Inferiorly: latissimus dorsi muscle
- Laterally: medial border of the scapula
- Suboccipital triangle: The suboccipital triangle is a pyramid-shaped anatomical area that contains the vertebral artery and suboccipital nerve. The triangle is located at the posterolateral occipital scalp. The suboccipital nerve may play a role in cervicogenic headaches and occipital neuralgia.
- Drake, R.L., Vogl, A.W., & Mitchell, A.W.M. (2014). Gray’s Anatomy for Students (3rd ed.). Philadelphia, PA: Churchill Livingstone.
- Jenkins D.B. (2009). Chapter 13. Elsevier Health Sciences. Hollinshead’s Functional Anatomy of the Limbs and Back (9th ed.pp 219-228).