Erector Spinae
Back
Three columns of muscle (iliocostalis, longissimus, spinalis) running the length of your spine like cables.
Function
Extends and laterally flexes spine — keeps you upright
Origin
Sacrum, iliac crest, spinous processes of lumbar and lower thoracic vertebrae
Insertion
Ribs, transverse and spinous processes of vertebrae, mastoid process
Innervation
Dorsal rami of spinal nerves