Back Muscles

What are the superficial extrinsic muscles of the back?

Trapezius, latissimus dorsi, rhomboids, and levator scapulae

What does it mean to be an extrinsic back muscle?

A muscle that doesn’t contribute to spinal movement

What nerve innervates the trapezius?

Accessory nerve CN XI (motor); C3/C4 (sensory)

What is the action of the Trapezius?

Upper: elevates the scapula

Middle: retract the scapula

Lower: depresses the scapula

What is the origin of the trapezius?

Medial 1/3 of superior nuchal line

External occipital protuberance (EOP)

Nuchal ligament

SP (spinous process) C7-T12 to lateral 1/3 clavicle

Acromion

Spine of scapula

What nerve innervates the latissimus dorsi?

Thoracodorsal nerve C6/C7/C8 (motor)

What is the action of the lats?

Extends, adducts, medially rotates humerus

Pulls body toward arms when hanging/ climbing

What is the origin of the Lats?

SP T6-12

Thoracolumbar (TL) fascia

Iliac crest to floor of intertubercular sulcus of humerus

What nerve innervates the rhomboid?

Dorsal scapular nerve (DSN) C4/C5 (motor)

What is the action of the rhomboid?

Retract, rotate inferiorly, fix scapula to thoracic wall

What is the origin of the rhomboid?

Minor: Nuchal ligament, SP C7-T1 to base of spine of scapula

Major: SP T2-5 to medial border of scapula (from level of spine to inferior angle)

What nerve innervates the levator scapulae?

DSN C4/C5 (motor)

What is the action of the levator scapulae?

Elevates scapula & rotates it inferiorly

What is the origin of the levator scapulae?

TP (transverse process) of C1-4 to medial border scapula superior to root of scapular spine

What are the intermediate extrinsic back muscles?

Serratus Posterior Superior (SPS) and Serratus Posterior Inferior (SPI)

What nerve innervates the SPS muscle?

Anterior rami of upper intercostal nerves T2-5

What is the action of the SPS muscle?

Elevate ribs

(accessory muscle for deep inhalation)

What is the origin of the SPS muscle?

Nuchal ligament

SP of C7-T3 to superior borders of 2nd-4th ribs

What is notable about the SPS muscle?

It is thin and consists of mainly fascia

What nerve innervates the SPI muscle?

Anterior rami of lower intercostal nerves T9-12

What is the action of the SPI muscle?

Depresses ribs/draws them backwards

(accessory muscle for forced exhalation)

What is the origin of the SPI muscle?

SP of T11-L2 to inferior borders of 8th -12th ribs

What are the superficial intrinsic muscles of the back?

Splenius (capitis/cervicis)

What does it mean to be an intrinsic muscle?

Muscles that attach to the spine and contribute to spinal movement

What nerve innervates the splenius muscle?

Posterior rami of spinal nerves

What is the action of the splenius?

Ipsilateral rotation, unilateral bend (side bend), extension of the neck

What are the 2 segments of the splenius and how do they differ?

Splenius capitis attaches to mastoid process of cranium

Splenius cervicis muscle attaches to cervical vertebrae

What is the origin of the splenius?

Capitis: nuchal ligament, SP C7-T6 to mastoid process and lateral 1/3 superior nuchal line and to…

Cervicis: tubercles of TP C1-4 vertebrae

What are the intermediate intrinsic muscles of the back?

Erector spinae

What muscles make up the erector spinae?

Spinalis, longissimus, iliocostalis

What nerve innervates the erector spinae?

Posterior rami of spinal nerve

What is the (main) action of the erector spinae?

Unilateral side bending and ipsilateral rotate

Where do the 3 segments of the erector spinae originate ?

Broad tendon from posterior part of iliac crest, posterior part of sacrum, SI ligaments, sacral and inferior lumbar/sacral SPs, and supraspinous ligament

Where does the iliocostalis muscle run to?

Ribs

Where does the longissimus run to?

TPs from C4-T5 (??)

Where does the spinalis run to?

Cervical and Thoracic SPs

What are the deep intrinsic layer of the back?

Semispinalis, multifidus, rotatores

What is the primary function of the deep intrinsic back?

Stabilization

What nerve innervates the semispinalis?

Posterior rami of spinal nerve

What is the origin of the semispinalis?

TPs of C4-T12 to occipital bone

SPs in thoracic spine and cervical spine (mainly in C/S)

What is the action of the semispinalis?

Extends head; cervical and thoracic spine and rotates contralaterally

What nerve innervates the multifidus?

Posterior rami of spinal nerves

What is the origin of the multifidus?

Posterior sacrum, PSIS, aponeurosis or erector spinae, sacroiliac ligaments, mammillary processes of lumbar spine vertebrae, TPs of T1-3, articular processes of C4-7 to entire length of SPs, 2-4 segments higher to proximal attachment

What is the action of the multifidus?

Stabilizes vertebrae during local movements of vertebral column

Rotates contralaterally

What nerve innervates the rotatores?

Posterior rami of spinal nerves

What is the action of the rotatores?

Stabilize vertebrae

Assist with local extension and contralateral rotation

What is the origin of the multifidus?

TPs of vertebrae to junction of lamina and TP or SP of 1-2 segments superior

What is the action of the multifidus?

Stabilize vertebrae; assists with local extension and contralateral rotation

What nerve innervates the multifidus?

Posterior rami of spinal nerves

Where is the suboccipital triangle?

Deep to the trapezius and semispinalis capitis; between occipital bone and posterior aspects of C1 and C2

What muscles make up the suboccipital triangle?

(lateral) Obliquus capitis superior, (inferior) obliquus capitis inferior, (medial) rectus capitis posterior major, rectus capitis posterior minor

What nerve innervates the muscles of the suboccipital triangle?

Suboccipital nerve (dorsal ramus C1-motor)

What is the origin of the RCPMa?

SP of C2 to lateral part inferior nuchal line of occiput

What is the action of the RCPMa and RCPMi?

Extension of the OA (atlanto-occipital) joint

Ipsilateral rotation of AA (atlanto-axial) joint

What is the origin of the RCPMi?

Posterior tubercle of posterior arch of C1 to medial part of inferior nuchal line of occiput

What is the action of the OCS?

Extension of OA joint

What is the origin of the OCS?

TP of C1 to occiput between superior and inferior nuchal lines

What is the origin of the OCI?

SP of C2 to TP of C1

What is the action of the OCI?

Ipsilateral rotation; side bending of AA

What are some characteristics of the greater occipital nerve?

Dorsal ramus of C2

Exits below OCI and pierces semispinalis muscle

Where does the vertebral artery travel?

From subclavian artery through transverse foramina of C1-C6

What are some clinical symptoms of vertebral artery compromise?

Dizziness, blurred vision, and/or nystagmus

What is a action of the erector spinae muscles when they contract unilaterally?

Lateral flexion of the vertebral column to the right

What is the main action of the splenius muscles when they contract unilaterally?

Left sidebending of the head and neck

How many segments does the multifidi span?

2-4 segments

How many segments does the semispinalis span?

4-6 segments

How many segments do the rotatores span?

1-2 segments