Final answer:
The erector spinae consists of three muscle groups: the iliocostalis, longissimus, and spinalis, each with segments associated with different regions of the back.
Step-by-step explanation:
The three muscles that make up the erector spinae group, which is the primary extensor of the vertebral column, include the following:
- Iliocostalis: This muscle group is laterally placed and has three segments - the iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis, each associated with the lumbar, thoracic, and cervical regions, respectively.
- Longissimus: Positioned intermediately, the longissimus group also has three parts - the longissimus capitis, longissimus cervicis, and longissimus thoracis, dedicated to the head, cervical, and thoracic regions.
- Spinalis: This group is medially placed and comprises the spinalis capitis, spinalis cervicis, and spinalis thoracis, relating to the head, cervical, and thoracic areas.