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SUPERFICIAL MUSCLES OF THE BACK
29. December.2011 Thursday
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.
There are two major groups of muscles in the back. The extrinsic back muscles include superficial and
intermediate muscles that produce and control limb and respiratory movements, respectively. The intrinsic
(deep) back muscles include muscles that specifically act on the vertebral column, producing its movements
and maintaining posture. Muscles in the superficial and intermediate groups are extrinsic muscles because they
originate embryologically from locations other than the back. They are innervated by anterior rami of spinal
nerves:
Muscles of the deep group are intrinsic muscles because they develop in the back.
 Superficial group consists of muscles related to and involved in movements of the upper limb;
 Intermediate group consists of muscles attached to the ribs and may serve as a respiratory function.
SUPERFICIAL GROUP OF BACK MUSCLES
The muscles in the superficial group are immediately deep to the skin and superficial fascia. They are
connected with the shoulder girdle. They attach the superior part of the appendicular skeleton (clavicle, scapula,
and humerus) to the axial skeleton (skull, ribs, and vertebral column). Because these muscles are primarily
involved with movements of this part of the appendicular skeleton, they are sometimes referred to as the
appendicular group. Accordingly, they are also referred as posterior axioappendicular muscles and produce and
control limb movements.
Muscles in the superficial group include:
 Trapezius
 Latissimus dorsi
 Rhomboid major
 Rhomboid minor
 Levator scapulae.
Rhomboid major, rhomboid minor, and levator scapulae are located deep to trapezius in the superior part of the
back. Although located in the back region, for the most part these muscles receive their nerve supply 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).
Trapezius
Each trapezius muscle is flat and triangular, with the base of the triangle situated along the vertebral
column (the muscle's origin) and the apex pointing toward the tip of the shoulder (the muscle's insertion).
The trapezius provides a direct attachment of the pectoral girdle to the trunk. This large, triangular
muscle covers the posterior aspect of the neck and the superior half of the trunk. It was given its name because
the muscles of the two sides form a trapezium (G. irregular four-sided figure). The muscles on both sides
together form a trapezoid.
The trapezius attaches the pectoral girdle to the cranium and vertebral column and assists in suspending
the upper limb. The fibers of the trapezius are divided into three parts, which have different actions at the
physiological scapulothoracic joint between the scapula and the thoracic wall:
 Descending (superior) fibers elevate the scapula (e.g., when squaring the shoulders).
 Middle fibers retract the scapula (i.e., pull it posteriorly).
 Ascending (inferior) fibers depress the scapula and lower the shoulder.
The superior fibers of trapezius, from the skull and upper portion of the vertebral column, descend to
attach to the lateral third of the clavicle and to the acromion of the scapula. The superior and inferior fibers
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work together to rotate the lateral aspect of the scapula upward, which needs to occur when raising the upper
limb above the head.
Descending and ascending trapezius fibers act together in rotating the scapula on the thoracic wall in
different directions, twisting it like a wing nut. The trapezius also braces the shoulders by pulling the scapulae
posteriorly and superiorly, fixing them in position on the thoracic wall with tonic contraction; consequently,
weakness of this muscle causes drooping of the shoulders.
Motor innervation of trapezius is by the accessory nerve [XI], which descends from the neck onto the
deep surface of the muscle. Proprioceptive fibers from trapezius pass in the branches of the cervical plexus and
enter the spinal cord at spinal cord levels C3 and C4.
http://content.answcdn.com/main/content/img/oxford/Oxford_Sports/0199210896.trapezius.1.jpg
Latissimus dorsi
The name latissimus dorsi (L. widest of back) was well chosen because the muscle covers a wide area
of the back. Latissimus dorsi is a large, flat triangular muscle that begins in the lower portion of the back and
tapers as it ascends to a narrow tendon that attaches to the humerus anteriorly. The posterior axillary fold is
formed by the tendon of latissimus dorsi as it passes around the lower border of the teres major muscle. It can
be easily palpated between the finger and thumb.
This large, fan-shaped muscle passes from the trunk to the humerus and acts directly on the
glenohumeral joint and indirectly on the pectoral girdle (scapulothoracic joint). The latissimus dorsi extends,
retracts, and rotates the humerus medially (e.g., when folding the arms behind the back or scratching the skin
over the opposite scapula). As a result, movements associated with this muscle include extension, adduction,
and medial rotation of the upper limb. Latissimus dorsi can also depress the shoulder, preventing its upward
movement.
In combination with the pectoralis major, the latissimus dorsi is a powerful adductor of the humerus and
plays a major role in downward rotation of the scapula in association with this movement. It is also useful in
restoring the upper limb from abduction superior to the shoulder; hence the latissimus dorsi is important in
climbing. In conjunction with the pectoralis major, the latissimus dorsi raises the trunk to the arm, which occurs
when performing chin-ups (hoisting oneself so the chin touches an overhead bar) or climbing a tree, for
example. These movements are also used when chopping wood, paddling a canoe, and swimming (particularly
during the crawl stroke).
The thoracodorsal nerve of the brachial plexus innervates the latissimus dorsi muscle.
Levator scapulae
The superior third of the strap-like levator scapulae lies deep to the sternocleidomastoid; the inferior
third is deep to the trapezius. From the transverse processes of the upper cervical vertebrae, the fibers of the
levator of the scapula pass inferiorly to the superomedial border of the scapula. True to its name, the levator
scapulae acts with the descending part of the trapezius to elevate the scapula, or fix it (resists forces that would
depress it, as when carrying a load.
With the rhomboids and pectoralis minor, the levator scapulae rotates the scapula, depressing the
glenoid cavity (rotating the lateral aspect of scapula inferiorly). Acting bilaterally (also with the trapezius), the
levators extend the neck; acting unilaterally, the muscle may contribute to lateral flexion of the neck (toward
the side of the active muscle). Levator scapulae is innervated by branches from the anterior rami of spinal
nerves C3 and C4 and the dorsal scapular nerve.
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Rhomboid minor and rhomboid major
The rhomboids (major and minor), which are not always clearly separated from each other, have a
rhomboid appearance—that is, they form an oblique equilateral parallelogram. The two rhomboid muscles lie
deep to the trapezius, inferior to levator scapulae and form broad parallel bands that pass inferolaterally from
the vertebrae to the medial border of the scapulae. Rhomboid minor is superior to rhomboid major, and is a
small, cylindrical muscle that arises from the ligamentum nuchae of the neck and the spinous processes of
vertebrae CVII and TI and attaches to the medial scapular border opposite the root of the spine of the scapula.
The larger rhomboid major originates from the spinous processes of the upper thoracic vertebrae and
attaches to the medial scapular border inferior to rhomboid minor.
The rhomboids retract and rotate the scapula, depressing its glenoid cavity. They also assist the serratus anterior
in holding the scapula against the thoracic wall and fixing the scapula during movements of the upper limb. The
rhomboids are used when forcibly lowering the raised upper limbs (e.g., when driving a stake with a sledge
hammer). The dorsal scapular nerve, a branch of the brachial plexus, innervates both rhomboid muscles.
INTERMEDIATE GROUP OF BACK MUSCLES
The muscles in the intermediate group of back muscles consist of two thin muscular sheets in the
superior and inferior regions of the back, immediately deep to the muscles in the superficial group. These
muscles are related to the movements ofthe thoracic cage, as the superficial muscles are related to the
movements of the shoulder (girdle).
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 (Fibers from
these two serratus posterior muscles pass obliquely outward from the vertebral column to attach to the ribs.
This positioning suggests a respiratory function, and at times, these muscles have been referred to as the
respiratory group).
They are described with muscles of the thoracic wall. The serratus
posterior superior lies deep to the rhomboids, and the serratus posterior
inferior lies deep to the latissimus dorsi.
Both serratus posterior muscles are attached to the vertebral column and
associated structures medially, and either descend (the fibers of serratus
posterior superior) or ascend (the fibers of serratus posterior inferior) to attach
to the ribs. These two muscles therefore elevate and depress the ribs.
Both serratus muscles are innervated by intercostal nerves, the superior
by the first four intercostals and the inferior by the last four.
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CLINICAL NOTES
Testing the superficial muscles of the back
To test the trapezius (or the function of the spinal accessory nerve [CN XI] that supplies it), the
shoulder is shruggedx against resistance (the person attempts to raise the shoulders as the examiner presses
down on them). If the muscle is acting normally, the superior border of the muscle can be easily seen and
palpated.
To test the latissimus dorsi (or the function of the thoracodorsal nerve that supplies it), the arm is
abducted 90° and then adducted against resistance provided by the examiner. If the muscle is normal, the
anterior border of the muscle can be seen and easily palpated in the posterior axillary fold.
To test the rhomboids (or the function of the dorsal scapular nerve that supplies them), the individual
places his or her hands posteriorly on the hips and pushes the elbows posteriorly against resistance provided by
the examiner. If the rhomboids are acting normally, they can be palpated along the medial borders of the
scapulae; because they lie deep to the trapezius, they are unlikely to be visible during testing.
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.
Stiff Neck
Levator scapulae
The muscle most often involved with a stiff neck is the levator scapula which connects the neck and
shoulder.
The most usual complaint of a "stiff neck" is pain when trying to turn the head to the side where it hurts,
often turning the body instead of the neck to look behind. It is often associated with a headache but not always.
The most common causes for developing this kind of stiff neck are; turning the head to one side while
typing, long phone calls without a headset, sleeping without proper pillow support with the neck tilted or
rotated, sitting in a chair with armrests too high and exposure of the neck to a cold draft. There are other causes
basically from shortening of this muscle as illustrated with using a cane that is too long.
Activities such as vigorous tennis, swimming the crawl stroke and watching a tennis match rotating the
head back and forth can also cause a stiff neck.
xShrugged:To
raise (the shoulders), especially as a gesture of doubt, disdain, or indifference. Omuz silkmek
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Table. Extrinsic back muscles [Superficial (appendicular) group & intermediate (respiratory) group of back muscles]
Muscle
Origin
Insertion
Innervation
Function
Trapezius
Superior nuchal line,
Lateral one-third of
Motor-accessory
Assists in rotating the
external occipital
clavicle, acromion,
nerve [XI];
scapula during
protuberance,
spine of scapula
proprioception-C3
abduction of
ligamentum nuchae,
and C4
humerus above
spinous processes of
horizontal; upper
CVII to TXII
fibers elevate, middle
fibers adduct, and
lower fibers depress
scapula
Latissimus dorsi
Spinous processes of
Floor of intertubercular Thoracodorsal nerve
Extends, adducts, and
TVII to LV and sacrum,
sulcus of humerus
(C6 to C8)
medially rotates
iliac crest, ribs X to XII
humerus
Levator scapulae Transverse processes of Upper portion medial
C3 to C4 and dorsal
Elevates scapula
CI to CIV
border of scapula
scapular nerve (C4,
C5)
Rhomboid major Spinous processes of TII Medial border of
Dorsal scapular nerve Retracts (adducts)
to TV
scapula between spine (C4, C5)
and elevates scapula
and inferior angle
Rhomboid minor Lower portion of
Medial border of
Dorsal scapular nerve Retracts (adducts)
ligamentum nuchae,
scapula at the spine of (C4, C5)
and elevates scapula
spinous processes of
scapula
CVII and TI
Serratus
Lower portion of
Upper border of ribs II
Anterior rami of
Elevates ribs II to V
posterior
ligamentum nuchae,
to V just lateral to their upper thoracic nerves
superior
spinous processes of
angles
(T2 to T5)
CVII to TIII and
supraspinous ligaments
Serratus
Spinous processes of TXI Lower border of ribs IX Anterior rami of
Depresses ribs IX to
posterior inferior to LIII and supraspinous to XII just lateral to
lower thoracic nerves XII and may prevent
ligaments
their angles
(T9 to T12)
lower ribs from being
elevated when the
diaphragm contracts
SUPERFICIAL MUSCLES OF THE BACK
ETYMOLOGY/DICTIONARY
Rhomboid L. rhombus, from Gk. rhombos "rhombus, spinning top," from rhembesthai "to spin, whirl,"
Rhombus or rhomb is a convex quadrilateral whose four sides all have the same length.
Serratus L. serratus “notched like a saw,” from serra “saw,”
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