ArticlesAnatomySpine and backBack

ArticlesAnatomySpine and backBack

Back

Author: Edwin Ocran, MBChB, MSc • Reviewer: Alessio Gallina, PT, PhD
Last reviewed: April 03, 2025
Reading time: 7 minutes

The back (or dorsal trunk) refers to the region on the posterior surface of the trunk which extends from the inferior border of the neck to the gluteal region.

The upper back corresponds to the posterior thoracic wall, while the lower back refers to the lumbar region, posterior to the abdominal cavity.

The layers of the back comprise the skin, subcutaneous tissue, superficial (extrinsic) and deep (intrinsic) back muscles, the posterior portion of the ribs, and the vertebral column housing the spinal cord and surrounding meninges.

The back performs several important functions including:

housing and protecting the spinal cord
holding the body and head upright
bearing the weight of the upper body
facilitating the movements of the upper and lower limbs.

Key facts about the human back
Definition	The back is the posterior region of the trunk between the neck and the gluteal region
Main functions	To protect the spinal cord To hold the body and head upright To facilitate movements of the upper and lower limbs
Parts of the back	Upper back, lower back Regions: vertebral, scapular, interscapular, suprascapular, infrascapular, lumbar, sacral Triangles: auscultation, superior lumbar, inferior lumbar
Muscles of the back	Superficial: extend between the vertebral column and the pectoral girdle and arm, support and move the upper limb Deep: extend along the length of the vertebral column, maintain body posture and facilitate trunk movements
Vasculature of the back	Arteries: aorta, subclavian artery Veins: subclavian vein, brachiocephalic vein, azygos venous system, and inferior vena cava
Innervation of the back	Spinal nerves from all spinal levels, accessory nerve (CN XI)

Contents

Parts of the back
Vertebral column
Muscles of the back
Arteries, veins and innervation of the back
Sources
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Parts of the back

The posterior aspect of the trunk is divided into the back and the buttocks. The back can be further divided into these regions:

Vertebral region: over the vertebral column (thoracic and lumbar regions of the spine)
Scapular region: over the scapula
Interscapular region: between the medial borders of the scapulae
Suprascapular region: superior and medial to the spine of the scapula
Infrascapular region: inferior and medial to the scapular and lateral pectoral regions
Lumbar region: lateral to the lumbar vertebrae
Sacral region: over the sacrum

The region of the back lateral to the scapula is considered part of the lateral region of the thorax (or lateral pectoral area), which is a region of the anterior thoracic wall.

Three smaller regions of triangular shape are also of interest.

The triangle of auscultation is located between the trapezius, the latissimus dorsi and the rhomboid major (or the medial border of the scapula).

The superior lumbar triangle (of Grynfeltt-Lesshaft) is located between the twelfth rib, internal oblique and the quadratus lumborum muscle.

And the inferior lumbar triangle (Petit’s triangle) can be found between the iliac crest, the latissimus dorsi and the external oblique.

Take this quiz to test your knowledge about the regions of the back:

Vertebral column

The vertebral column (spine) is composed of 33-35 vertebrae, though this may vary between 33-35 due to rare anatomical differences. Of these, 24 are separated by intervertebral discs. The remaining vertebrae are usually fused to form two distinct bones: the sacrum and the coccyx.

The vertebral column is divided into five regions, from superior to inferior: cervical, thoracic, lumbar, sacral, and coccygeal.

The vertebrae articulate with each other by connecting their bodies and arches via intervertebral joints. These joints are present throughout the entire spine, while some regions have specific types of joints, such as the thoracic spine with the ribs.

Muscles of the back

The muscles of the back are organized into the superficial (extrinsic) muscles and the deep (intrinsic) muscles.

Understanding the anatomy of the muscles of the back is easier than you think. Check out these muscle anatomy charts!

The superficial muscles of the back are located beneath the skin and superficial fascia of the back and extend between the vertebral column and bones of the pectoral girdle and arm. These muscles can be further subdivided into superficial and intermediate layers. The principal function of the superficial muscles of the back is to support and move the upper limb through movement of the scapula and humerus.

The deep muscles of the back extend along the length of either side of the vertebral column, deep to the thoracolumbar fascia, all the way from the skull to the pelvis. These muscles can be further subdivided into superficial, intermediate, deep and deepest layers. Their main functions include maintaining the body posture as well as facilitating the movements of the vertebral column.

Learn more about the back muscles by diving into these study units:

Arteries, veins and innervation of the back

The main arterial supply for much of the posterior thorax and abdomen is the aorta. The subclavian arteries supply structures in the neck and scapular regions.

The veins of the back drain primarily into the azygos venous system, the inferior vena cava and the subclavian and brachiocephalic veins.

The structures of the back are innervated by spinal nerves that arise from all spinal levels and by the spinal accessory cranial nerve (CN XI).

Want to learn more about the neurovasculature of the back? Then work your way through the following study unit:

Sources

All content published on Kenhub is reviewed by medical and anatomy experts. The information we provide is grounded on academic literature and peer-reviewed research. Kenhub does not provide medical advice. You can learn more about our content creation and review standards by reading our content quality guidelines.

References:

Drake, R. L., Vogl, A. W., & Mitchell, A. W. M. (2015). Gray's Anatomy for Students (3rd ed.). Philadelphia, PA: Churchill Livingstone.
Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.
Standring, S. (2016). Gray's Anatomy (41st ed.). Edinburgh: Elsevier Churchill Livingstone.

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