The Spine 87FIGURE 3.17 The erector spinae (posterior view).Erector Spinae
The erector spinae (L. erector, to raise or make erect
+ spina, spine) is a paired massive muscle that is
the most powerful extensor of the spine. It lies in
the trough on each side of the vertebral column. The
muscle begins inferiorly as a large mass but soon
divides into three approximately vertical columns of
muscle. The medial column is called the spinalis
(spina, vertebral column, spine); the intermediate
column is called the longissimus (longissimus, lon-
gest); and the lateral column is called the iliocostalis
(ilio, ilium + cost, rib). Each column can be further
divided into three parts in accordance with its superior
attachments as shown in figure 3.17. As can be seen
from viewing the attachments of these muscles, they
span different regions of the spine and are composed
of slips that generally span six to eight vertebral seg-
ments. Both the iliocostalis (thoracis and lumborum)
and longissimus (thoracis) have attachments onto
the ribs in the thoracic region, while the spinalis is
more centrally located and spans between vertebrae
and associated ligaments only.
Although different components and regions of
the erector spinae have slightly different actions,
their combined bilateral contraction can produce
extension of the spine, the head, or both such as
is used when raising the trunk back to vertical from
a forward-bent position. When one side contracts,
they all can produce lateral flexion to the same side, especially when used in combination with the
abdominal muscles. In addition, the longissimus and iliocostalis can produce rotation to the same
side for the spine or head such as is used to help twist the torso so that the shoulders face front in
an arabesque. The erector spinae also contribute to stability and protection of the spine.
Palpation: While standing, place your fingers flat against the low back with your right fingers just to
the right of the low lumbar spinous processes and your left fingers just to the left of the same spinous
processes. Slowly flex the trunk forward about 40° and then slowly raise the torso back to vertical. The
tension you feel under your fingers when the torso rises is due to contraction of the erector spinae. You
can also feel the erector spinae contracting on alternate sides when you walk slowly with your hands
in the same position as just described.Attachments and Primary Actions of Semispinalis
Muscle Inferior attachment(s) Superior attachment(s) Primary action(s)
Semispinalis (sem-ee-spi-NA-lis)
Semispinalis capitas
(kah-PIT-us)Transverse processes of
C7-T7
Articular processes
of C4-6Occipital bone of skull
Spinous processes 4-6
Segments above in cervical
and upper thoracic regionsExtension of head and C spine
Lateral flexion of head and C spine (same)
Rotation of head and C spine (opposite)Semispinalis cervicis
(ser-VIS-us)Transverse processes
of T1-6Spinous processes of C2-5 C and upper T spinal extension
C and upper T spinal lateral flexion (same)
C and upper T spinal rotation (opposite)
Semispinalis thoracis
(tho-RA-sis)Transverse processes
of T6-10Spinous processes of C6-
T4C and T spinal extension
C and T spinal lateral flexion (same)
C and T spinal rotation (opposite)