Forms medial boundary of suboccipital triangle. Fibers course superomedially.

origin:  spinous process of C2 (axis)

insertion:  lateral inferior nuchal line

innervation:  C1 posterior ramus

action:

    bilteral- extend head

    unilateral- ipsilateral rotation of head

Fibers course superiorly.

insertion: medial inferior nuchal line

innervation: C1 posterior ramus

action: extend head

Forms lateral boundary of suboccipital triangle. Fibers course superiorly.

origin: transverse process of C1 (atlas)

insertion: lateral skull between nuchal lines

innervation: C1 posterior ramus

action:

bilateral- extend head

unilateral- ipsilateral bending of head

Deep to the semispinalis captitis follow greater occipital nerve to obliquus capitis inferior. Inferior boundary of suboccipital triangle. Fibers course laterally.

origin: spinous process C2 (axis)

insertion: transverse process C1 (atlas)

innervation: C1 posterior ramus

action: ipsilateral rotation of head

Lies deep to the splenius, fibers course vertically, parallel to the long axis of the neck. Greater occipital nerve passes through this muscle.

origin: transverse processes of thoracic to lower cervical vertebrae

insertion: occipital bone between the superior and inferior nuchal lines

innervation: posterior rami of spinal nerves

action:

bilateral- extend back and head

unilateral- contralateral rotation of vertebral column, ipsilateral rotation of head

Located deep to the erector spinae, fibers course superomedially

origin: transverse processes of cervical vertebrae

insertion: inserts on spinous processes 4-6 vertebrae superior to origination

innervation: posterior rami of spinal nerves

action:

bilateral- extend back and head

unilateral- contralateral rotation of the vertebral column, ipsilateral rotation of the head

Rhomboid major

(shaped like a kite)

Plane of separation between major and minor may not be obvious

origin: spinous processes of upper thoracic vertebrae

insertion: medial border of scapula inferior to base of spine

innervation: dorsal scapular nerve

action: retract and downward rotation of scapula

Plane of separation between major and minor may not be obvious

origin: spinous processes of lower cervical to 1st thoracic vertebrae

insertion: medial border of scapla superior to base of spine

innervation: dorsal scapular nerve

action: retract and downward rotation of scapula

Located deep to the erector spinae. Only muscles with fibers that lie across the posterior surface of the sacrum.

origin: common tendon of erector spinae/arch of vertebrae

insertion: spinous processes of vertebrae 2-4 levels superior

innervation: posterior rami of spinal nerves

action:

bilateral- extend back

unilateral- contralateral rotation of vertebral column

Lie deep to the multifidus

origin: transverse processes of lumbar through cervical vertebrae

insertion: spinous processes of vertebrae 1-2 levels supeior

innervation: posterior rami of spinal nerves

action:

bilateral- extend back

unilateral- contralateral rotation of vertebral column

origin: transverse processes thoracic vertebrae

insertion: rib inferior to origin

innervation: C1 posterior ramus

action: elevate ribs

Lateral column of erector spinae group. Long tendons extend laterally beneath the scapula. Lies deep to the posterior serratus muscles.

origin: common tendon and ribs

insertion: ribs

innervation: posterior rami of spinal nerves

action:

bilateral- extend bac

unilateral- lateral bending

Longest muscle in the body. Intermediate muscle of the erector spinae. Lies deep to the posterior serratus muscles.

origin: common tendon and upper transverse processes

insertion: ribs, transverse processes of thoracic and cervical vertebrae, mastoid process

innervation: posterior rami of spinal nerves

action:

bilateral- extend back

unilateral- ipsilateral head rotation, lateral bending

Medial column of erector spinae, lies deep to the serratus posterior muscles. Lies close to the spine in the lamina groove.

origin: common tendon, inferior thoracic to inferior cervical spinous processes, blends semispinalis capitis

insertion: spinous processes, semispinalis capitis

innervation: posterior ramus of spinal nerves

action:

bilateral- extend back

unilateral- ipsilateral head rotation, lateral bending

Lies deep to the trapezius, its fibers course obliquely acrosss neck toward the mastiod process.

origin: ligamentum nuchae, cervical spinous processes

insertion: mastoid process, lateral superior nuchal line

innervation: posterior rami of spinal nerves

action:

bilateral- extend head and neck

unilateral-ipsilateral head rotation

Lies deep to the capitis, not easliy isolated. General location can be outlined in the lamina groove of the upper thoracic and cervical spine.

origin: mid-thoracic spinous processes

insertion: transverse processes C1-C3

innervation: posterior rami of spinal nerves

action:

bilateral- extend neck (and head

unilateral- ipsilateral head rotation

origin: superior nuchal line, nuchal ligament, thoracic spinous processes

insertion: lateral clavicle, acromion, spine of scapula

innervation: CN XI (upper cervical anterior rami for proprioception)

action: elevate, retract, depress scapula

Broadest muscle of the back

origin: lower thoracic and lumbar spinous processes, thoracolumbar fascia, iliac crest

insertion: intertubercular sulcus of humerus

innervation: thoracodorsal nerve

action: adduct, medially rotate, extend arm

origin: superior cervical transverse processes

insertion: superior angle scapula

innervation: upper cervical anterior rami

action: elevates the scapula

Intermediate muscle, very thin

origin: ligamentum nuchae, upper spinous processes

insertion: ribs 2-5

innervation: anterior rami of spinal nerves

action: elevate ribs 2-5

Intermediate muscle, very thin

origin: inferior thoracic to superior lumbar spinous processes

insertion: ribs 9-12

innervation: anterior rami of spinal nerves

action: depress ribs 9-12

Within the triangle of auscultation, intercostal space 6 has no overlying muscle making it ideal for auscultation.

bounded by: latissimus dorsi, trapezius, and rhomboid major