Intrinsic Back Muscles (groups)

Splenius Group Muscles

-Includes splenius capitis and splenius cervicis

-attach to skull and spine

-oblique (lateral to medial muscle fibers)

Splenius Group actions and innervations

Actions: Ipsilateral rotation, lateral flexion, extension of head and neck

Innervation: Dorsal rami of spinal nerves C3/4-C8

Erector Spinae Group Muscles

-Includes spinalis, longissimus, and illiocostalis

-attach to skull, spine, ribs, and illiac crest

-fibers run vertically

-muscles are stacked laterally

Erector Spinae group actions and innervation

Actions:

Bilateral contraction- extension of vertebral column

Unilateral contraction- lateral flexion of trunk, ipsilateral rotation of trunk

Innervation: Dorsal rami of spinal nerves

transversospinalis group muscles

-Includes semispinalis, multifidus, rotatores

-attach to spine, sacrum, illiac crest, skull

-columns stack on top of each other

-christmas tree-like fibers

transversospinalis group action and innervation

Action: Stability and posture, extend and contralaterally rotate head, neck and trunk, intersegmental motion

Innervation: Dorsal rami of spinal nerves

segmental group muscles

-Includes interspinalis and intertransversarii

-attach on SPs/TVPs of vertebrae to SPs/TVPs of superior vertebrae respectively

Segmental group actions and innervation

Actions: Proprioception, extension, lateral flexion

Innervation: Dorsal rami of spinal nerves

*Intertransversarii are also innervated by ventral rami

Suboccipital group muscles

Includes rectus capitus major/minor and oblique capitus superior/inferior

-forms Suboccipital triangle

-attach to skull and vertebrae

Suboccipital group actions and innervation

Actions: stabilize head, small precise head movements(lateral flexion, extension)

High density of spindle fibres- important in proprioception of the head

Innervation: Suboccipital nerve (dorsal ramus of C1)