Anatomy of back muscles

Erector spinae

 Erector spinae group of muscles 

Spinalis 

Origin - Spinous process of L2 to T 11 

Insertion - Occipital bone 

Function - Spine Extension | Maintain neutral spine | Spine lateral flexion. 

Longissimus

Origin - Blends with the iliocostalis muscle in the lumbar region

insertion - Mastoid process on the skull

Function - Spine Extension | Maintain neutral spine | Spine lateral flexion. 

Iliocostalis

Origin - Iliac crest, sacrum, spinous process of L-5 to T-11

Insertion - Transverse processes of C-4 to C-6

Function - Spine Extension | Maintain neutral spine | Spine lateral flexion.

Upper Fiber of Trapezius

Origin - Occipital protuberance

Insertion - Lateral 3rd of posterior aspect of clavicle

Function - Shoulder gridle elevation | Neck extension

Middle Fiber of Trapezius

Origin - T-1 to T-4

insertion - Acromion process, spine of scapula

Function - Scapular retraction

Lower Fiber of Trapezius

Origin - T-5 to T-12

Insertion - Medial end of spine of scapula

Function - Shoulder depression

Levator Scapulae

Origin - Transverse process of C1-C4

Insertion - Medial border of Scapula-superior to Spine of Scapula

Function - Shoulder gridle elevation 

Rhomboid Minor 

Origin - Spinous process of C-7 to T-1

insertion - Medial border of Scapula - in the line of Spine of Scapula

Function - Scapular retraction

Rhomboids Major

Origin - Spinous process of T-2 to T-5

Insertion - Medial border of Scapula-inferior to Spine of Scapula

Function - Shoulder retraction