Which muscles extend the back (vertebral column)?

The muscles that extend the back, or vertebral column, are primarily the erector spinae group, which is composed of the iliocostalis, longissimus, and spinalis muscles. These muscles run vertically along the length of the back, from the base of the skull to the pelvis.

Here are the steps to identify them:

1. The erector spinae muscles are located in the back, running vertically along the spine. They are deep muscles, located underneath the more superficial muscles of the back.

2. The erector spinae group is composed of three muscles: the iliocostalis, longissimus, and spinalis. Each of these muscles has several parts.

3. The iliocostalis is the most lateral (furthest from the midline) of the three muscles. It has three parts: iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis, which are located in the lower back, mid-back, and neck, respectively.

4. The longissimus is the intermediate muscle. It also has three parts: longissimus thoracis, longissimus cervicis, and longissimus capitis, which are located in the mid-back, neck, and base of the skull, respectively.

5. The spinalis is the most medial (closest to the midline) of the three muscles. It has three parts: spinalis thoracis, spinalis cervicis, and spinalis capitis, which are located in the mid-back, neck, and base of the skull, respectively.

6. These muscles work together to extend (straighten) the back and neck, and also assist with lateral flexion (bending to the side) and rotation of the spine.

7. Other muscles that assist with back extension include the semispinalis, multifidus, and rotatores muscles. These are smaller muscles located deeper in the back, closer to the spine.