Welcome to this lecture on “Back Muscles”.
This slide identifies the objectives that
you should be able to answer at the conclusion
of this presentation. First, list the structures
of the back.
Categorize back muscles into groups.
List the suboccipital muscles and define the
Describe the attachments, innervations and
actions of the above muscles.
Identify the relevant neurovascular structures.
And then we will summarize the key take-home
And lastly, provide attribution for the images
that were used throughout this presentation.
This represents the body map in our focus
of today, we will be on the region defined
in through here, we will go pretty low onto
the back and we will come very high outwards
to the shoulder and even to the anterolateral
clavicle and then we will work our way also
to the back, the neck and up to the skull.
This list just provides you an idea of the
structures that are associated with the back.
Moving from superficial to deep, we would
have the skin, underlying the skin we would
have superficial fascia and then deep to the
superficial fascia, deep fascia, we would
have our muscles.
Also, in this area, we’d have relevant neurovascular
structures. In the midline of the back, we
would have our vertebral column and its associated
ligaments. We would also have within the vertebral
canal, the spinal cord and its associated
meninges. And we would also have the posterior
aspects of the ribs
in these particular regions here.
When we look at the muscles of the back they
are going to be arranged in three layers.
We have a superficial layer which is visualized
here. Here is one of the superficial muscles,
here is a second superficial muscle.
We will also have three more that fall within
this layered category.
Deep to the superficial muscles, we have intermediate
muscles. Both the superficial and the intermediate
layers are known as extrinsic muscles and
then the deepest layer is the deep layer and
these are known as the intrinsic or true back
Here is a listing of the five muscles that
make up the superficial layer. We have the
trapezius muscle and the latissimus dorsi
muscle, both of those are seen in this particular
illustration. Here is our trapezius. It occurs
on the opposite side as well and when we follow
the contours of the trapezius, it does form
a trapezoid shape.
Below is the extensive latissimus dorsi muscle
on this side and we see the latissimus dorsi
on the opposite side as well. The next three
superficial muscles are the rhomboid major,
the rhomboid minor and the levator scapulae.
These are seen in this particular illustration
and we will focus on the right side of the
Here is your rhomboid major, this slender
strap like muscle represents your rhomboid
minor. And then this muscle that we see running
up into the neck represents the levator scapulae
muscle. Now, let’s take a look at each one
of these superficial muscles and we will wanna
understand the attachments, innervation as
well as associated actions.
We are looking at the trapezius, it has multiple
points of origin. It’s going to attach to
a prominent projection on the occipital bone
called the external occipital protuberance.
It will then proceed laterally to that protuberance
and attached to the superior nuchal line.
It will also originate along the ligamentum
nuchae and then the spinous processes of C7
and then T1 all the way down normally to the
level of the spinous process of T12. It has
three points of insertion, one of those would
be to the spine of the scapula, in this general
vicinity. It then extends laterally and will
insert onto the acromion of the scapula and
then will wrap around to the anterior portion
and also insert on the lateral one third of the
clavicle. Motor innervation to your trapezius
is going to be supplied by a cranial nerve
and this is the accessory nerve.
The actions of the trapezius will depend on
the orientation of the fibers that are contracting
principally. For example, if you have these
fibers of the trapezius contracting, these
middle fibers, they are oriented horizontally,
they will then pull the scapula towards the
midline of the posterior back that is referred
to as adduction or retrusion. If the superior
fibers are primarily contracting, they will
elevate or pull the scapula upwards. If the
lower fibers are contracting and note their
orientation down and in these lower fibers
will depress, pull down the scapula.
And there is one more action that can be produced.
If the superior and the inferior fibers are
working in unison, they will rotate the glenoid
cavity of the scapula or the humerus articulates,
it will rotate that cavity superiorly and
then that will allow for abduction of the
humerus above the horizontal. This is done
in association with the serratus anterior.
The latissimus dorsi has multiple points of
origin. It’s going to attach or originate
from the spinous processes of T7 through T12
and also, the spinous processes of all five
lumbar vertebrae. It has a partial attachment
to the iliac crest and the sacrum and will
partially originate from the inferior three
to even inferior four of ribs.
These points of origin are very wide or broad
and you look as these fibers cross laterally
and upwards towards the humerus, they all
converge into a narrow band and the latissimus
is going to insert into the floor of the inner
tubercular groove or the sulcus of the humerus.
The nerve that innervates your latissimus dorsi
is your thorcodorsal nerve and the actions
produced by the latissimus would be several.
One action would be to extend the humerus,
pull it posteriorly.
It’s also a very powerful adductor of the
humerus, so it pull it toward the midline
and action shared with the pectoralis major,
for example. It will also medially rotate
your humerus turning it inwards toward your
body and if you have your hands and arms extended
above your body, the latissimus would help
pull your trunk up towards your upper limbs
and again, this function is shared with the
Here we are looking at the rhomboids and levator
scapulae. Our focus here, first, is with the
rhomboid major which we see running right
in through here, the rhomboid major has points
of origin from spinous processes and we can
see those points of origin along and through
here. These particular points will be the
spinous processes of T2 all the way down to
T5, the insertion is on the medial border
of the scapula at the level of the spine down
toward the inferior angle.
The innervation of the rhomboid major is the
dorsal scapular nerve and the action or actions
of this muscle would be adduction. It would
pull the scapula in toward the midline, also
known as retrusion and because of the oblique
course of these fibers, it can help to elevate
or pull the scapula upwards.
The rhomboid minor is shown here, it is a
slender band of muscle fibers. It’s going
to attach to the inferior aspects of your
ligamentum nuchae running right along in through
here. It also has attachments for its points
of origin, to the spinous processes of C7,
the vertebra prominens as well as the first
It will attach to the medial aspect of the
scapula, add in slightly above the spine of
the scapula. It’s innervated by the same
nerve as the rhomboid major, dorsal scapular
and also will share the same actions in producing
adduction of the scapula as well as elevate
Your levator scapulae is shown here as this
band of muscle fibers. The levator scapulae
is originating from the transverse processes
of C1 through C4, that is better seen on the
opposite side where you see those tendinous
slips representing the points of origin from
those transverse processes.
The insertion of your levator scapulae, as
the name suggests, will be to the scapula
and specifically it’s going to be along
the superior border on the medial side of
the scapula. The levator scapulae is innervated
by the dorsal scapular nerve, it also receives
contributions from anterior rami of the 3rd
and 4th cervical nerves. For its action, the
name tells you exactly what it does, it’s
going to lift or elevate, pull the scapula
Now, we want to shift our attention to the
intermediate muscle group and there are only