Makindo Medical Notes

Anatomy

Muscles of the Back Region - Listed Alphabetically:

Erector Spinae

Origin: Iliac crest, sacrum, transverse and spinous processes of vertebrae, supraspinal ligament
Insertion: Angles of the ribs, transverse and spinous processes of vertebrae, posterior aspect of the skull
Action: Extends and laterally bends the trunk, neck, and head
Innervation: Segmentally innervated by dorsal primary rami of spinal nerves C1-S5
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa., subcostal aa., lumbar aa.
Notes: The erector spinae muscle is separated into 3 columns: iliocostalis (laterally), longissimus (intermediate), and spinalis (medially). Each column has multiple named parts.

Iliocostalis

Origin: Iliac crest and sacrum
Insertion: Angles of the ribs
Action: Extends and laterally bends the trunk and neck
Innervation: Dorsal primary rami of spinal nerves C4-S5
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa., subcostal aa., lumbar aa.
Notes: The most lateral part of the erector spinae, subdivided into lumborum, thoracis, and cervicis portions.

Interspinales

Origin: Upper border of spinous process
Insertion: Lower border of spinous process above
Action: Extends trunk and neck
Innervation: Dorsal primary rami of spinal nerves C1-L5
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa., subcostal aa., lumbar aa.
Notes: Small and fairly insignificant muscles.

Intertransversarii

Origin: Upper border of transverse process
Insertion: Lower border of transverse process above
Action: Laterally bends trunk and neck
Innervation: Dorsal primary rami of spinal nerves C1-L5
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa., subcostal aa., lumbar aa.
Notes: Small and fairly insignificant muscles.

Longissimus

Origin: Transverse process at inferior vertebral levels
Insertion: Transverse process at superior vertebral levels and mastoid process
Action: Extends and laterally bends the trunk, neck, and head
Innervation: Dorsal primary rami of spinal nerves C1-S1
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa., subcostal aa., lumbar aa.
Notes: The intermediate part of the erector spinae, subdivided into thoracis, cervicis, and capitis portions.

Multifidus

Origin: Sacrum, transverse processes of C3-L5
Insertion: Spinous processes 2-4 vertebral levels superior to their origin
Action: Extends and laterally bends trunk and neck, rotates to opposite side
Innervation: Dorsal primary rami of spinal nerves C1-L5
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa., subcostal aa., lumbar aa.
Notes: Semispinalis, multifidus, and rotatores make up the transversospinal muscle group.

Obliquus Capitis Inferior

Origin: Spinous process of the axis
Insertion: Transverse process of atlas
Action: Rotates the head to the same side
Innervation: Suboccipital nerve (DPR of C1)
Artery: Occipital a.
Notes: Greater occipital nerve (DPR of C2) passes superiorly around the inferior margin of the obliquus capitis inferior.

Obliquus Capitis Superior

Origin: Transverse process of atlas
Insertion: Occipital bone above inferior nuchal line
Action: Extends the head, rotates the head to the same side
Innervation: Suboccipital nerve (DPR of C1)
Artery: Occipital a.
Notes: The suboccipital triangle is formed by obliquus capitis superior, obliquus capitis inferior, and rectus capitis posterior major.

Rectus Capitis Posterior Major

Origin: Spinous process of axis
Insertion: Inferior nuchal line
Action: Extends the head, rotates to the same side
Innervation: Suboccipital nerve (DPR of C1)
Artery: Occipital a.
Notes: None

Rectus Capitis Posterior Minor

Origin: Posterior tubercle of atlas
Insertion: Inferior nuchal line medially
Action: Extends the head
Innervation: Suboccipital nerve (DPR of C1)
Artery: Occipital a.
Notes: Rectus capitis posterior minor is deeper and inserts more medial than rectus capitis posterior major.

Rotatores

Origin: Transverse processes
Insertion: Long rotatores: spines 2 vertebrae above origin; short rotatores: spines 1 vertebra above origin
Action: Rotates the vertebral column to the opposite side
Innervation: Dorsal primary rami of spinal nerves C1-L5
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa., subcostal aa., lumbar aa.
Notes: Semispinalis, multifidus, and rotatores make up the transversospinal muscle group.

Semispinalis

Origin: Transverse processes of C7-T12
Insertion: Capitis: back of skull between nuchal lines; cervicis & thoracis: spines 4-6 vertebrae above origin
Action: Extends the trunk and laterally bends the trunk, rotates the trunk to the opposite side
Innervation: Dorsal primary rami of spinal nerves C1-T12
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa., subcostal aa., lumbar aa.
Notes: Semispinalis, multifidus, and rotatores make up the transversospinal muscle group.

Spinalis

Origin: Spinous processes at inferior vertebral levels
Insertion: Spinous processes at superior vertebral levels and base of the skull
Action: Extends and laterally bends trunk and neck
Innervation: Dorsal primary rami of spinal nerves C2-L3
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa., subcostal aa., lumbar aa.
Notes: Most medial part of the erector spinae; subdivided into thoracis, cervicis, and capitis portions.

Splenius

Origin: Ligamentum nuchae and spines C7-T6
Insertion: Capitis: mastoid process & superior nuchal line laterally; Cervicis: posterior tubercles of C1-C3 vertebrae
Action: Extends and laterally bends neck and head; rotates head to same side
Innervation: Dorsal primary rami of spinal nerves C2-C6
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa.
Notes: Splenius means bandage; named for its broad, flat shape.

Splenius Capitis

Origin: Ligamentum nuchae and spines of C7-T6 vertebrae
Insertion: Mastoid process and lateral end of the superior nuchal line
Action: Extends and laterally bends the neck and head, rotates head to the same side
Innervation: Dorsal primary rami of spinal nerves C2-C6
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa.
Notes: Splenius means bandage and capitis refers to the insertion of this portion of the muscle.

Splenius Cervicis

Origin: Ligamentum nuchae and spines of C7-T6 vertebrae
Insertion: Posterior tubercles of the transverse processes of C1-C3 vertebrae
Action: Extends and laterally bends neck and head, rotates head to the same side
Innervation: Dorsal primary rami of spinal nerves C2-C6
Artery: Supplied segmentally by deep cervical a., posterior intercostal aa.
Notes: Splenius means bandage and cervicis refers to the insertion of this portion of the muscle.