MUSCLES OF THE BACK
Most body weight lies anterior to the vertebral column,
especially in obese people; consequently,
the many strong muscles attached to
the spinous and transverse processes of
the vertebrae are necessary to support
and move the column.
MAJOR GROUPS:
Extrinsic muscles = control the limb and respiratory movements.
Superficial muscles
Intermediate muscles
Intrinsic muscles (deep) = acts on the vertebral column producing its
movement and maintaining posture.
Extrinsic Back Muscles
The superficial extrinsic back muscles
Trapezius,
Latissimus dorsi,
Levator scapulae,
Rhomboids
are posterior axio-appendicular muscles that
connect the axial skeleton (vertebral column) with the
superior appendicular skeleton (pectoral girdle and
humerus)
and produce and control limb movements.
Their nerve supply is from the anterior rami of cervical nerves
and act on the upper limb.
The trapezius receives its motor fibers from a cranial nerve, the spinal
accessory nerve (CN XI).
The intermediate extrinsic back muscles
(serratus posterior)
are thin muscles, commonly designated as superficial respiratory
muscles, but are more likely proprioceptive rather than motor in
function (Vilensky et al., 2001).
The serratus posterior superior lies deep to the rhomboid muscles,
and the serratus posterior inferior lies deep to
the latissimus dorsi.
Both serratus muscles are innervated by intercostal nerves, the
superior by the first four intercostals and the inferior by the last four.
Intrinsic Back Muscles
The intrinsic back muscles (muscles of back proper, deep back muscles)
are innervated by the posterior rami of spinal nerves and
act to maintain posture and
control movements of the vertebral column.
These muscles, which extend from the pelvis to the cranium, are
enclosed by deep fascia that attaches:
Medially to
the nuchal ligament,
the tips of the spinous processes of the vertebrae,
the supraspinous ligament, and
the median crest of the sacrum.
Laterally to
the cervical and lumbar transverse processes
the angles of the ribs.
The thoracic and lumbar parts of the deep fascia constitute the
thoracolumbar fascia.
It extends laterally from the spinous processes and forms a thin covering over
the intrinsic back muscles in the thoracic region and a strong thick covering for
muscles in the lumbar region.
The intrinsic back muscles are grouped into
superficial,
intermediate,
and deep layers
according to their relationship to the surface.
SUPERFICIAL LAYER of Intrinsic muscles
The splenius muscles (L. musculi splenii) are thick and flat and lie on the lateral
and posterior aspects of the neck, covering the vertical muscles somewhat like
a bandage, which explains their name (L. splenion, bandage). The splenius
muscles arise from the midline and extend superolaterally to the
cervical vertebrae (splenius cervicis) and
cranium (splenius capitis).
The splenius muscles cover and hold the deep neck muscles in position
INTERMEDIATE LAYER of Intrinsic muscles
The massive erector spinae muscles
lie in a “groove” on each side of the vertebral column between the
spinous processes centrally and the angles of the ribs laterally.
are the chief extensors of the vertebral column and
are divided into three columns:
o The iliocostalis forms the lateral column,
o the longissimus forms the intermediate column, and
o the spinalis forms the medial column.
Each column is divided regionally into three parts according to the superior
attachments (e.g., iliocostalis lumborum, iliocostalis thoracis, and iliocostalis
cervicis).
The common origin of the three erector spinae columns is through a broad
tendon that attaches inferiorly to
the posterior part of the iliac crest,
the posterior aspect of the sacrum,
the sacro-iliac ligaments, and
the sacral and inferior lumbar spinous processes.
The erector spinae are often referred to as the “long muscles” of the back.
In general, they are dynamic (motionproducing) muscles, acting bilaterally
to extend (straighten)
the flexed trunk.
DEEP LAYER of Intrinsic muscles
Deep to the erector spinae is an obliquely disposed group of much shorter
muscles, the transversospinalis muscle group consisting of the
semispinalis,
multifidus, and
rotatores.
These muscles originate from transverse processes of vertebrae and pass to
spinous processes of more superior vertebrae. They occupy the “gutter”
between the transverse and the spinous processes and are attached to these
processes, the laminae between them, and the ligaments linking them
together.
The semispinalis is
the superficial member of the group.
it arises from approximately half of the
vertebral column.
It is divided into three parts according
to the superior attachments :
o Semispinalis capitis,
o semispinalis thoracis, and
o semispinalis cervicis.
Semispinalis capitis forms the longitudinal bulge in
the back of the neck near the median plane.
The multifidus
is the middle layer of the group and
consists of short, triangular muscular
bundles that are thickest in the
lumbar region.
The rotatores, or rotator muscles, are the
deepest of the three layers of
transversospinal muscles and are best
developed in the thoracic region.
