Anatomy of the Back

• The back extends from the cranium to the apex of the coccyx.
• It includes the posterior aspects of the trunk, from the neck to the sacrum.

Bony Structure of the Back

• The skeleton of the back includes the cranium, vertebral column, ribs, and pelvic girdle.
• The vertebral column consists of 33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused into the sacrum), and 4 coccygeal (fused into the coccyx).
• Vertebrae articulate with each other via intervertebral discs and zygapophyseal joints.
• The ribs articulate with the thoracic vertebrae and connect to the sternum via costal cartilages, forming the rib cage.

Muscles of the Back

• Back muscles are divided into extrinsic (superficial and intermediate) and intrinsic (deep) muscles.
• Extrinsic muscles mainly act on the movements of the upper limbs and respiration.
• Intrinsic muscles mainly act on the movements of the vertebral column and maintaining posture.

Extrinsic Muscles (Superficial)

• Trapezius: Extends from the cranium and cervical vertebrae to the scapula and clavicle; elevates, retracts, and rotates the scapula.
• Latissimus dorsi: Extends from the lower thoracic vertebrae, lumbar vertebrae, sacrum, lower ribs, and iliac crest to the humerus; adducts, internally rotates, and extends the arm.
• Levator scapulae: Extends from the upper cervical vertebrae to the scapula; elevates the scapula.
• Rhomboid major and minor: Extend from the upper thoracic vertebrae to the scapula; retract and rotate the scapula.

Extrinsic Muscles (Intermediate)

• Serratus posterior superior: Extends from the lower cervical and upper thoracic vertebrae to the upper ribs; elevates the ribs.
• Serratus posterior inferior: Extends from the lower thoracic and upper lumbar vertebrae to the lower ribs; depresses the ribs.

Intrinsic Muscles (Deep)

• Splenius capitis and splenius cervicis: Extend from the upper thoracic and lower cervical vertebrae to the cranium and upper cervical vertebrae; extend and rotate the head and neck.
• Erector spinae (iliocostalis, longissimus, and spinalis): Extends from the sacrum, iliac crest, and lumbar vertebrae to the ribs and thoracic and cervical vertebrae; extends the vertebral column and controls flexion; also laterally flexes the column.
• Transversospinalis (semispinalis, multifidus, and rotatores): Extends from the thoracic and lumbar vertebrae to the upper thoracic and cervical vertebrae; stabilize and extend the vertebral column, rotate the vertebral column to the opposite side.
• Interspinales and intertransversarii: Extend between the spinous and transverse processes of the vertebrae; stabilize the vertebral column and assist in extension and rotation.
• Levatores costarum: Extend from the thoracic vertebrae to the ribs; elevate the ribs and assist in respiration.

Vasculature of the Back

• Vertebral and ascending cervical arteries supply the deep muscles of the neck.
• Segmental arteries (posterior intercostal and lumbar) supply the muscles of the back.
• Vertebral and segmental veins drain blood from the back.

Innervation of the Back

• Posterior rami of the spinal nerves (dorsal nerves) innervate the intrinsic muscles of the back, the skin of the back, and the joints of the vertebral column.
• Anterior rami of the spinal nerves innervate the extrinsic muscles of the back (trapezius, latissimus dorsi, levator scapulae, and rhomboids).
• The greater occipital nerve (posterior ramus of C2) innervates the skin of the occipital region.
• The third occipital nerve (posterior ramus of C3) innervates the skin of the suboccipital region.

Suboccipital Region

• The suboccipital region is located in the posterior neck, below the occipital bone.
• It contains the suboccipital muscles (rectus capitis posterior major, rectus capitis posterior minor, obliquus capitis superior, and obliquus capitis inferior).
• These muscles act in the extension, lateral flexion, and rotation of the head.
• The suboccipital triangle is bordered by the rectus capitis posterior major, obliquus capitis superior, and obliquus capitis inferior.
• The vertebral artery and suboccipital nerve (posterior ramus of C1) are located in the suboccipital triangle.

Nerves of the Back

• Spinal nerves: 31 pairs of spinal nerves emerge from the spinal cord and innervate the muscles, skin, and joints of the back.
• Dorsal nerves (posterior rami of the spinal nerves): innervate the intrinsic muscles of the back, the skin of the back, and the joints of the vertebral column.
• Ventral nerves (anterior rami of the spinal nerves): Innervate the extrinsic muscles of the back.
• Suboccipital nerve (posterior ramus of C1): Innervates the suboccipital muscles.
• Greater occipital nerve (posterior ramus of C2): Innervates the skin of the occipital region.
• Third occipital nerve (posterior ramus of C3): Innervates the skin of the suboccipital region.