Download Muscles of the Back

Muscles of the Back
The muscles of the back may be divided into three groups:



The superficial muscles connected with the shoulder girdle.
The intermediate muscles involved with movements of the thoracic cage.
The deep muscles or postvertebral muscles belonging to the vertebral column
The superficial muscles of the back - Muscles Connecting the Upper Limb to the Vertebral Column
Muscle
Origin
Trapezius Occipital bone, ligamentum
nuchae, spine of seventh
cervical vertebra, spines of
all thoracic vertebrae
Insertion
Nerve Supply
Upper fibers into lateral Spinal part of
third of clavicle; middle accessory nerve
and lower fibers into
(motor) and C3 and 4
acromion and spine of (sensory)
scapula
Floor of bicipital groove Thoracodorsal nerve
of humerus
Latissimus Iliac crest, lumbar fascia,
dorsi
spines of lower six thoracic
vertebrae, lower three or four
ribs, and inferior angle of
scapula
Levator
Transverse processes of first Medial border of
scapulae four cervical vertebrae
scapula
Rhomboid Ligamentum nuchae and
Medial border of
minor
spines of seventh cervical
scapula
and first thoracic vertebrae
Rhomboid Second to fifth thoracic
Medial border of
major
spines
scapula
a
Nerve
Rootsa
Action
XI cranial Upper fibers elevate the
scapula; middle fibers pull
nerve
(spinal
scapula medially; lower
part)
fibers pull medial border of
scapula downward
C6, 7, 8, Extends, adducts, and
medially rotates the arm
C3 and 4 and dorsal C3, 4, 5
scapular nerve
Dorsal scapular nerve C4, 5
Dorsal scapular nerve C4, 5
Raises medial border of
scapula
Raises medial border of
scapula upward and
medially
Raises medial border of
scapula upward and
medially
The predominant nerve root supply is indicated by boldface type.
The intermediate muscles of the back
Muscle
Origin
Insertion
Action
Innervation
Artery
Notes
serratus
posterior
superior
ligamentum nuchae, ribs 2-5,
spines of vertebrae lateral to
C7 and T1-T3
the angles
elevates branches of the
the upper ventral primary
ribs
rami of spinal
nerves T1-T4
posterior
a respiratory muscle, it
intercostal aa. 1- receives ventral ramus
4
innervation; embryonically
related to the intercostal
muscles, not the deep back
mm.
serratus
posterior
inferior
thoracolumbar
fascia, spines of
vertebrae T11-T12
and L1-L2
pulls
down
lower
ribs
lowest posterior
intercostal a.,
subcostal a.,
first two lumbar
aa.
ribs 9-12,
lateral to
the angles
branches of the
ventral primary
rami of spinal
nerves T9-T12
a respiratory muscle, it
receives ventral ramus
innervation; embryonically
related to the intercostal
muscles, not the deep back
mm.
Deep Muscles of the Back (Postvertebral Muscles)
In the standing position, the line of gravity passes through the odontoid process of the axis, behind the
centers of the hip joints, and in front of the knee and ankle joints. It follows that when the body is in this
position, the greater part of its weight falls in front of the vertebral column. It is, therefore, not surprising
to find that the postvertebral muscles of the back are well developed in humans. The postural tone of these
muscles is the major factor responsible for the maintenance of the normal curves of the vertebral column.
The deep muscles of the back form a broad, thick column of muscle tissue, which occupies the hollow on
each side of the spinous processes of the vertebral column. They extend from the sacrum to the skull. It
must be realized that this complicated muscle mass is composed of many separate muscles of varying
length. Each individual muscle may be regarded as a string, which, when pulled on, causes one or several
vertebrae to be extended or rotated on the vertebra below. Because the origins and insertions of the
different groups of muscles overlap, entire regions of the vertebral column can be made to move smoothly.
The spines and transverse processes of the vertebrae serve as levers that facilitate the muscle actions. The
muscles of longest length lie superficially and run vertically from the sacrum to the rib angles, the
transverse processes, and the upper vertebral spines. The muscles of intermediate length run obliquely
from the transverse processes to the spines. The shortest and deepest muscle fibers run between the spines
and between the transverse processes of adjacent vertebrae.
The deep muscles of the back may be classified as follows:
Superficial Vertically Running Muscles
Intermediate Oblique Running
Muscles
Deepest Muscles
 Interspinales
 Intertransversarii
Knowledge
of
the
detailed
attachments of the various muscles
of the back has no practical value to
a clinical professional, and the
attachments are therefore omitted in
this text.
Splenius
The splenius is a detached part of the
deep muscles of the back. It consists
of two parts. The splenius capitis
arises from the lower part of the
ligamentum nuchae and the upper
four thoracic spines and is inserted
into the superior nuchal line of the
occipital bone and the mastoid
process of the temporal bone.
The splenius cervicis has a similar
origin but is inserted into the
transverse processes of the upper
cervical vertebrae.
Nerve Supply - All the deep muscles of the back are innervated by the posterior rami of the spinal nerves.
Muscular Triangles of the Back
Auscultatory Triangle
The auscultatory triangle is the site on the back where breath sounds may be most easily heard with a
stethoscope. The boundaries are the latissimus dorsi, the trapezius, and the medial border of the scapula.
Lumbar Triangle
The lumbar triangle can refer to either the inferior lumbar (Petit) triangle, which lies superficially, or the
superior lumbar (Grynfeltt) triangle, which is deep
and superior to the inferior triangle. Of the two, the
superior triangle is the more consistently found in
cadavers, and is more commonly the site of
herniation*; however, the inferior lumbar triangle
is often simply called the lumbar triangle, perhaps
owing to its more superficial location and ease in
demonstration.
Deep Fascia of the Back (Thoracolumbar Fascia)
The lumbar part of the deep fascia is situated in the
interval between the iliac crest and the 12th rib. It
forms a strong aponeurosis and laterally gives
origin to the middle fibers of the transversus and
the upper fibers of the internal oblique muscles of
the abdominal wall.
Medially, the lumbar part of the deep fascia splits
into three lamellae. The posterior lamella covers
the deep muscles of the back and is attached to the lumbar spines. The middle lamella passes medially, to
be attached to the tips of the transverse processes of the lumbar vertebrae; it lies in front of the deep
muscles of the back and behind the quadratus lumborum. The anterior lamella passes medially and is
attached to the anterior surface of the transverse processes of the lumbar vertebrae; it lies in front of the
quadratus lumborum muscle.
Arrangement of the deep muscles of the back. B. Lateral view of the skeleton showing the line
of gravity. Because the greater part of the body weight lies anterior to the vertebral column,
the deep muscles of the back are important in maintaining the normal postural curves of the
vertebral column in the standing position.
The intrinsic back muscles
The intrinsic back muscles are part of the trunk musculature. It comprises a system of deep back muscles at
the vertebral column ranging from the pelvis up to the head. They are located in an osteofibrous canal,
bounded by the vertebrae, the ribs and the thoracolumbar fascia. All intrinsic back muscles are innervated
by the posterior branches of the spinal nerves. Embryologically they derive from the dorsal part of the
myotomes (epimere) which reside locally during the entire development for which reason they are also
referred to as true or autochthonous back muscles. In contrast the back muscles deriving from the ventral
part of the myotomes (hypomere), e.g. latissimus dorsi muscle and trapezius muscle, migrate into the trunk
musculature subsequently (secondary back muscles).
The intrinsic back musculature is subdivided into a medial and lateral tract and the deep neck muscles.
Medial tract
The medial tract extends between the spinal and transverse processes of the vertebrae. It is innervated by
the medial branches of the posterior branches of the spinal nerves. One differentiates between the spinal
and transversospinal system.


The spinalis muscle and the interspinales muscles belong to the spinal system. They connect the
spinal processes of neighboring vertebrae. The spinalis muscle originates slightly laterally from the
interspinales muscles.
The transversospinal system comprises the short and long rotatores muscles, multifidus muscle
and the semispinalis muscle. They all run diagonally from the transverse to the spinal processes. The
short rotatores muscles insert at the next higher vertebrae, the long rotatores muscles at the second
higher vertebrae. The multifidus muscle skips 2-4 vertebrae, the semispinalis muscle even 4-7
vertebrae. Furthermore the semispinalis muscle has a robust insertion at the occipital bone.
Lateral tract
The lateral tract is a system of long longitudinal muscles. It lies more superficially than the medial tract
and inserts more laterally. It is innervated by the lateral branches of the posterior branches of the spinal
nerves. One differentiates between the sacrospinal, intertransverse and spinotransverse system.



The sacrospinal system consists of the longissimus muscle and iliocostalis muscle. Both share an
origin tendon at the thoracolumbar fascia. They have numerous origins and insertions at the ribs and
transverse processes. In addition the longissimus capitis muscle inserts at the mastoid process of the
temporal bone.
The splenius muscle builds the spinotransverse system. It originates at the spinal processes of the
upper thoracic and cervical vertebrae and runs laterocranially.
The intertransverse system comprises the intertransversarii muscles and levatores costarum
muscles. They extend between two neighboring transverse processes. The levatores costarum muscles
are innervated by both the anterior and posterior branches of the spinal nerves (double innervation).
Part of the intertransversarii muscles are even innervated only by anterior branches of the spinal nerves
for which reason they do not count as intrinsic back muscles.
Deep neck muscles
The deep neck muscles (suboccipital muscles) are innervated by the posterior branch of the first spinal
nerve (C1), the suboccipital nerve, and are therefore considered as intrinsic back muscles. They consist of
four paired muscles:

Rectus capitis posterior major muscle (spinal process of axis → inferior nuchal line)

Rectus capitis posterior minor muscle (posterior tubercle of atlas → inferior nuchal line)

Obliquus capitis superior muscle (transverse process of atlas → inferior nuchal line)

Obliquus capitis inferior muscle (spinal process of axis → transverse process of atlas)
Function
The intrinsic back musculature is essential for the stabilization and movement of the vertebral column.
Bilateral contraction stretches the body (dorsal extension), unilateral contraction bends the body to one
side (lateral flexion). The rotation is effected with the assistance of the oblique abdominal muscles. The
deep neck muscles support the movement of the atlanto-occipital joint. They have particularly many
muscle spindles contributing to the proprioception of the head.
The contents of the suboccipital triangle are the suboccipital nerve and the vertebral artery. Note that the
suboccipital nerve (dorsal ramus of C1) emerges between the occipital bone and vertebra C1. The
suboccipital nerve supplies motor innervation to the muscles of the suboccipital region. The suboccipital
nerve is the only dorsal ramus that has no cutaneous distribution. Identify the vertebral artery. Use an
illustration to study the course of the vertebral artery through the neck and into the skull.
* hernia - A hernia is the protrusion of an organ or the fascia of an organ through the wall of the cavity
that normally contains it. There are different kinds of hernia, each requiring a specific management or
treatment.