Corpus: Interspinal muscle

The interspinal muscle are short, paired skeletal muscles of the back that are part of the medial tract of the erector spinae muscle.

The interspinal muscle are primarily found in the cervical and lumbar regions, where they connect the spinous processes of adjacent vertebrae. In the cervical region, known as the interspinales colli muscles, the muscles originate from the lower surfaces of the spinous processes of the cervical vertebrae C2 to C7. They insert on the upper surfaces of the spinous processes of the cervical vertebrae C3 to T1.

In the lumbar region, termed the interspinales lumborum muscles, the muscles originate from the spinous processes of the lumbar vertebrae L1 to L5, with insertions on the spinous processes of the vertebrae immediately above, extending to the first sacral vertebra.

In the thoracic spine, known as the interspinales thoracis muscles, these muscles are rudimentary and often absent. However, when present, they are most commonly found between the spinous processes of T1-T2, T2-T3, and further caudally between T11-T12 and T12-L1.

The interspinal muscles are innervated by the medial branches of the posterior rami of the segmental spinal nerves.

The primary function of the interspinal muscles is to assist in extending the spinal column. They also play a supportive role in maintaining an upright posture.