Anatomy of the Back Muscles

Compendium of origin, insertion, innervation, and action for the extrinsic and intrinsic muscles of the back based on Moore's Clinically Oriented Anatomy.

What are the components of the origin for the Trapezius muscle?

Medial Third of Superior Nuchal Line, External Occipital Protuberance, Nuchal Ligament, and SP of $C7-T12$

Which nerve provides motor innervation to the Trapezius?

Spinal Accessory N. ($CN XI$) & Anterior Rami ($C3-4$)

What are the specific actions of the upper, middle, and lower fibers of the Trapezius?

Upper: Elevation & Upward Rotation; Middle: Scapular Retraction; Lower: Depression & Upward Rotation

What is the nickname and humeral actions of the Latissimus Dorsi?

The "Pull up muscle"; Humeral Extension, Adduction, & IR

What is the insertion of the Latissimus Dorsi?

Intertubercular Groove of Humerus

Which nerve innervates the Latissimus Dorsi?

Thoracodorsal N. ($C6-8$)

What are the actions of the Levator Scapula?

Scapular Elevation & Downward Rotation, and Ipsilateral Cervical Sidebending

What is the innervation for the Rhomboid Minor and Rhomboid Major?

Dorsal Scapular N. ($C4-5$)

Where does the Rhomboid Minor insert in relation to the scapular spine?

Medial Border of Scapula, Superior to Scapular Spine

Where does the Rhomboid Major insert in relation to the scapular spine?

Medial Border of Scapula, Inferior to Scapular Spine

What are the bilateral and unilateral actions of the Splenius muscles?

Bil: Cervical Extension; Uni: Ipsilateral Cervical SB & ROT

What is the insertion for Splenius Cervicis?

TP of $C1-3$

List the three muscle groups that comprise the Erector Spinae.

Spinalis, Longissimus, and Iliocostalis

What are the general bilateral and unilateral actions of the Erector Spinae?

Bil: Spinal Extension; Uni: Ipsilateral SB

What are the general bilateral and unilateral actions of the Transversospinalis group?

Bil: Spinal Extension; Uni: Ipsilateral SB & Contralateral ROT

How many spinal levels does the Semispinalis span?

$4-6$ Spinal Levels

Which Transversospinalis muscle primarily functions to stabilize the spine and spans $2-4$ spinal levels?

Multifidus

What is the span and thoracic location of the Rotatores muscles?

They span $1-2$ spinal levels and run from the transverse to spinous processes of $T1-12$

What is the action of the Interspinalis muscles located between the SP of adjacent vertebrae from $C2-L5$?

Spinal Extension

What is the function of the Intertransversarii muscles located in the Cervical ($C2-7$) and Lumbar ($L1-5$) regions?

Ipsilateral SB & Stabilizes Spine

What are the bilateral actions of the Levator Costarum?

Rib Elevation & Thoracic Extension