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13/10/2016
Anatomy 12
Muscles of the back
Nour Erekat
Salam Mustafa
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Quick revision of the previous lecture:
o What is the forward nodding movement of the head called?
Flexion.
o What results in this movement? Which joint?
The atlanto occipital joint.
o What is the anterior atlanto-occipital membrane?
It is the membrane that connects the anterior arch of the atlas to the anterior
margin of foramen magnum.
o What does ligamentum nuchae (nuchal membrane) connect?
It is the greatly thickened supraspinous and infraspinous ligament in the
cervical region that connects the spine of the 7th cervical vertebra to the
external occipital protuberance of the skull.
Do not be confused between the spine of the scapula and that of the vertebrae. Whenever it
is mentioned as spine alone, it is referred to the scapula. Whenever we refer to the vertebral
spine, we will mention it.
o What connects laminae of the vertebrae?
It is the ligamentum flavum which is similar to posterior atlanto occipital
membrane. Posterior atlanto occipital membrane which connects the
posterior arches of atlas to the posterior margin of foramen magnum is
similar to ligamentum flavum which connects the laminae of adjacent
vertebrae.
o How many articular fossae are in each individual vertebra?
4, 2 superior fossae and 2 inferior ones.
o How many foramina are in each vertebra?
3 in the cervical vertebrae (2 transverse that are unique for cervical vertebrae
and 1 vertebral foramen which is present in each vertebra in the vertebral
column), and 1 in the other vertebrae.
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o What movement does the atlanto-axial joint allow?
Rotation of the atlas and thus of the head around the odontoid process of the
axis.
Axis is called as such because it provides its odontoid process as an axis for rotation of the atlas
and the skull articulating with the atlas, around that process.
o What part does the mandibular fossa belong to?
The temporal bone.
Why is the fossa present in the temporal bone called the mandibular fossa? This is because it
articulates with a part of the mandible. Particularly, it articulates with the head of the
condylar process of the mandible forming the tempomandibular joint called TMJ.
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Objectives:
 Describe the superficial muscles of the back including the attachments.
 Describe the components of the deep muscles of the back including the
attachments.
 Describe the movements produced by each of the back muscles.
 Describe the innervation of each muscle of the back.
MUSCLES OF THE BACK
The muscles of the back are divided into 2 groups.
This is done so according to their location and association
(i.e where is it located and to what is it associated)
These are the Superficial, Intermediate, and Deep groups.
o Superficial Group
 These are connected with the shoulder girdle (clavicle and scapula).
 These include the Trapezius, Latissimus dorsi (the one on the opposite
side?), Levator scapulae, Rhomboid minor, and Rhomboid major.
 The last 3 muscles are all attached to the medial border of scapula.
 Rhomboid muscles can either be called rhomboid or rhomboidus.
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1. Trapezius:
The trapezius muscle arises from the occipital bone, ligamentum nuchae, spinous
process of the 7th cervical vertebra, and spinous process of all thoracic vertebrae
(all 12 thoracic vertebrae).
However, it inserts into 3 different sites and hence is divided into 3 parts; the
upper, middle and lower parts.
The upper part inserts into the lateral third of the clavicle, whereas the middle and
lower parts insert into acromnion and spine of the scapula.
Now, you can easily anticipate the movement each part causes. Upper fibers
elevate the scapula, whereas lower fibers do the opposite. They depress the
scapula. Middle fibers pull the scapula medially.
This muscle is innervated by the spinal part of accessory nerve.
Now have a look at the image next page. This is the posterior triangle of the neck
(the dashed triangle). You can see that the spinal accessory nerve has already
innervated the sternocleidomastoid muscle. It then continues backwards through
this triangle into the deep surface of the trapezius to innervate it. The landmark for
the spinal accessory nerve in the posterior triangle is Levator scapulae. The nerve
crosses backwards through the triangle, anterior to the levator scapulae.
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2. Latissimus dorsi:
It arises from the ileac crest, lumbar fascia, spinous process of the lower 6 thoracic
vertebrae, the 3rd and 4th ribs and finally the inferior angle of the scapula.
It inserts into the floor of bicipital groove of humerus (intertubercular sulcus).
This muscle adducts, extends and medially rotates the arm. It acts as an antagonist
to the pectoralis major muscle. This muscle is innervated by thoracodorsal nerve
which arises from the posterior cord of brachial plexus and its fibers are derived
from the 6th, 7th, and 8th cervical
nerves.
In these 2 pictures you
can see the
thoracodorsal nerve
innervating latissimus
dorsi.
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3. Levator scapulae, 4.Rhomboid minor, 5.Rhomboid major:
These 3 muscles insert onto the medial border of the scapula but at different parts
of it of course. However, they have different origins. They are all innervated by the
dorsal scapular nerve which arises from the brachial plexus.
 Levator scapulae: It originates from the
transverse process of the upper 4 cervical
vertebrae. As the name indicates, its function
is to elevate the scapula upwards. In addition
to being innervated by dorsal scapular nerve
like the other 2 muscles, it is also innervated
by branches from the anterior ramus of spinal
nerve C5*.
Spinal nerve C5 is a nerve
that originates from the
spinal column from above
the cervical vertebra 5.
This nerve then
contributes to dorsal
scapular nerve. So, dorsal
scapular is actually part of
spinal nerve c5.
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 Rhomboid minor: It originates from the inferior part of ligamentum nuchae
and the spinous process of 7th cervical vertebra and 1st thoracic vertebra.
Since it is inserted into the medial border of scapula, it pulls the border of
the scapula upwards and medially.
 Rhomboid major: It arises from spinous processes of 2nd thoracic vertebra
until 5th thoracic vertebra. It has the same action as rhomboid minor, it pulls
the border of scapula upward and medially.
*The doctor specifically said spinal nerve C5 and then said that snell mentions C3 and C4 instead. But
you need to know it as C5 I guess.
Levator scapulae, rhomboid
minor and major being
innervated by dorsal scapular
nerve.
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Everything that has been said so far is summarized in this table. You need to know
every single detail. But everything has been mentioned so this shouldn’t be a
problem to you (supposedly though :3).
o Intermediate Group:
 These are involved in the movement of the thoracic cage.
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And now we move on to the last group of muscles:
o Deep Group:
 These are also referred to as postvertebral muscles.
 This is because they are located right behind the vertebral column.
 They are divided into 3 groups according to their location and orientation of
their fibers.
 First, the Superficial vertically running muscles.
 Next, the Intermediate oblique running muscles.
 Last, the Deepest muscles.
 They are innervated by dorsal or the posterior rami of the spinal nerves.
 Each individual muscle causes one or several vertebrae to be extended or
rotated on the vertebra below.
1. Superficial Vertically Running Muscles:
These are the long muscles. They are the longest out of all the deep muscles. They
are the most superficial of this group of course and their fibers run in a straight line
vertically.
They run from the sacrum to the rib angles, the transverse processes, and the upper
vertical spines.
These muscles are Iliocostalis, Erector spinae longissimus, and Spinalis.
Clarification
Erector spinae is the 3 muscles together; Iliocostalis, Longissimus, and Spinalis.
Each of these muscles is a group of 3.
For example, there are 3 muscles that make up the Iliocostalis group. The same
thing applies to the 2 other groups.
Check the picture next page.
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2. Intermediate Oblique Running Muscles:
These muscles are deeper than the previous group
we just talked about, but more superficial in
comparison to the Deepest group (like that’s a
surprise). The deepest group is the shortest of all.
They are intermediate in length and run obliquely
from the transverse processes to the spines of the
vertebrae.
These muscles are Semispinalis,
Transversospinalis multifidus, and Rotatores.
3. Deepest Muscles:
These are the shortest,
the deepest and run
between the spines and
between the transverse
processes of adjacent
vertebrae.
The ones that run
between the spines are
called Interspinales,
whereas the ones the
run between transverse
processes are called
Intertransversarii.
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4. Splenius:
One last deep muscle that is detached from all the other muscles is the Splenius.
The splenius has 2 parts that originate from the same location but differ in their
insertion.
They both originate from the lower part of the ligamentum nuchae and the upper
four thoracic spines.
 Splenius capitis: It inserts into the
scalp. More specifically, into the
superior nuchal of the occipital
bone and the mastoid process of the
temporal bone.
 Splenius cervicis: It inserts onto
the transverse processes of the
upper 4 cervical vertebrae.
Edited by: Sajda Drine
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