Erector spinae

Origin: On the spines of the last four thoracic vertebrae

Insertion: Both the spines of the most cranial thoracic vertebrae and the cervical vertebrae

Artery: Lateral sacral artery

Nerve: Posterior branch of spinal nerve

Action: Extends the vertebral column

Antagonist: Rectus abdominis muscle

Description:

The erector spinae muscle is a large muscle group that runs longitudinally along the spine and is primarily responsible for extending and stabilizing the vertebral column. It is composed of three main columns: the iliocostalis, longissimus, and spinalis muscles.

1. Iliocostalis muscle: This is the most lateral column and is divided into three parts: iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis. The iliocostalis lumborum originates from the iliac crest and sacrum and inserts into the lower ribs. The iliocostalis thoracis extends from the lower ribs to the upper ribs, and the iliocostalis cervicis extends from the upper ribs to the cervical vertebrae.

2. Longissimus muscle: This is the intermediate column and is also divided into three parts: longissimus thoracis, longissimus cervicis, and longissimus capitis. The longissimus thoracis originates from the lumbar vertebrae and inserts into the thoracic vertebrae and ribs. The longissimus cervicis extends from the thoracic vertebrae to the cervical vertebrae, and the longissimus capitis extends from the cervical vertebrae to the mastoid process of the temporal bone.

3. Spinalis muscle: This is the most medial column and is divided into three parts: spinalis thoracis, spinalis cervicis, and spinalis capitis. The spinalis thoracis originates from the lower thoracic and upper lumbar vertebrae and inserts into the upper thoracic vertebrae. The spinalis cervicis extends from the lower cervical vertebrae to the upper cervical vertebrae, and the spinalis capitis extends from the cervical vertebrae to the occipital bone.

The erector spinae aponeurosis is a common aponeurosis that blends with the thoracolumbar fascia, with a proximal attachment on the sacrum an the spinous processes of the lumbar vertebrae, for the three erector spinae muscles (iliocostalis, longissimus, and spinalis) and overlying the inferior portion of the erector spinae muscles. It provides critical attachment points for the erector spinae muscles and contributes to the biomechanical integrity of the lumbar spine

The erector spinae muscles are innervated by the dorsal rami of the spinal nerves and play a crucial role in maintaining posture and enabling movements such as bending and rotating the spine