Head And Neck Anatomy- Traingles of the Neck

					Histology Lecture 4: Triangles of the
Neck (posterior triangle & root of neck)
       Previously we mentioned that the Sternocleidomastoid muscle divides the neck into anterior
and posterior triangles, the region anterior to the Sternocleidomastoid muscle is the anterior triangle,
and the region posterior to it is the posterior triangle.




THE POSTERIOR TRIANGLE:

       Bound anteriorly by
        the posterior of the
        Sternocleidomastoid
        muscle.
       Bound posteriorly by
        the anterior border of
        the Trapezius
        Muscle.
       Bound inferiorly by
        the Clavicle.

THE ANTERIOR TRIANGLE:

       Bound anteriorly by
        the midline.
       Bound posteriorly by
        the anterior border
        of
        Sternocleidomastoid muscle.
       Bound superiorly by the inferior border of the mandible.




Posterior triangle (Structure/Components)
    Near the Sternocleidomastoid muscle this layer is the anterior/investing layer of the deep cervical
fascia (called investing because it invests/covers the superficial borders of the trapezius and
Sternocleidomastoid muscle), this layer is important because it forms the root of the posterior triangle
of the neck
       The Posterior Triangle (bound anteriorly by the Sternocleidomastoid muscle) is covered by the
        investing fascia/investing layer of deep cervical fascia at its roof.

        Once the layer of deep investing fascia is removed some nerves become visible, exposing the
        posterior/pre-vertebral layer of deep cervical fascia; this layer of the deep cervical fascia covers
        the muscular floor of the posterior triangle of the neck.

~~~Floor of Posterior triangle = Muscular (covered by pre-vertebral layer of deep cervical fascia)

Investing layer of deep cervical multiple structures pre-vertebral deep cervical fascia

Structures between Fascia layers (investing & pre-
vertebral):

The following are found between the deep investing cervical &
the COVERING OF THE FLOOR which is the pre-vertebral

*pre-vertebral = covering layer of the floor of the Posterior
Triangle.

        1- The cranial nerve #11 (spinal accessory nerve, called
           so because it has branches from CV2 & CV3), this
           nerve innervates the Trapezius &
           Sternocleidomastoid muscle. Emerges from beneath
           the midpoint of the posterior border of the
           Sternocleidomastoid muscle.
        2- Suprascapular artery, branch of the subclavian artery
        3- Inferior belly of OmoHyoid Muscle (Omo= Shoulder),
           this muscle has two bellies as well as an intermediate
           tendon; the intermediate tendon is located under the
           Sternocleidomastoid muscle.
        4- Transverse cervical vessels

Structures between Fascia layers (Pre -Vertebral
[carpet layer] & Floor of posterior triangle):

        1. Splenius Capitis Muscle.
        2. Levator Scapulae Muscle.
        3. Scalenus Posterior muscle (barely visible because
           of its posterior location), is the smallest of the
           Scalenus Muscles.
        4. Scalenus Medius Muscle.
        5. Scalenus Anterior Muscle.
            *All Scalenus muscles arise from the transverse process of the cervical vertebrae

         The Scalenus anterior muscles arises from the anterior tubercles of the transverse process CV3,
4, 5,6 and is inserted into the Scalene tubercle on the first rib (between the subclavian artery & nerve),
this muscle is innervated by the CV5, CV6 & CV7.

        The Scalenus Medius Muscle is the largest of the Scalenus muscles, arising from the posterior
tubercles of CV 2, 3, 4, 5, 6, 7, innervated by CV3 –CV8.

     The Scalenus posterior muscle (the smallest), arises from the transverse tubercles of
CV5CV7, and is inserted into the 2nd rib, this muscle is innervated by CV7 & CV8.

      **all 3 Scalenus muscles act upon vertebral column of the neck as inspirational
muscles.

       OmoHyoid muscle: Has an inferior belly and a superior belly. The inferior belly
        located at the intermediate tendon beneath Sternocleidomastoid muscle, the superior belly
        is located at the anterior triangle of the neck. The OmoHyoid Muscle (omo=shoulder/scapula –
        Hyoid =Hyoid Bone) originates from the superior border of the scapula inserting onto the
        inferior border of the Hyoid bone, innervated by ansa cervicalis a branch of the cervical plexus
        (will be discussed later), is a cervical loop that has CV2 & CV3 fibers at one end and the
        hypoglossal nerve (another name for CV 12) at the other end.


       Sternocleidomastoid muscle:            Has two heads of origin and one head of insertion:
                A- Clavicular head- emerging from the sternal end of the clavicle.
                B- Sternal head- emerges from the manubrium of the sternum.

        Is inserted onto the mastoid process of the temporal bone of the skull; it’s innervated by the
        spinal accessory nerve.

        Action: the contraction of a single Sternocleidomastoid muscle causes the head to rotate to the
        opposite side; contraction of both muscles causes flexion of the neck. The Sternocleidomastoid
        muscle also acts as an accessory muscle of respiration.

***the Scalenus Anterior muscle represents an important landmark in the posterior triangle of the neck,
lying anterior to this muscle (superficial to it) is the phrenic nerve. Between the Scalenus Anterior and
the Scalenus Medius lower parts of the brachial plexus are visible in addition to the third part of the
subclavian artery.
There are two nerves passing through the
Scalenus Medius Muscle, they are:

    A- The Dorsal Scapular Nerve the more
       superior of the two, is composed of
       fibers from C5, innervates Levator
       scapulae & Rhomboid Muscles.
    B- The Long Thoracic Nerve, (more
       inferior) is composed of fibers from
       CV5, CV6, and CV7; runs all the way
       down the body into thorax and
       supplies the Serratus Anterior
       Muscle.

                *these two nerves (Dorsal
                Scapular & Long Thoracic)
                innervate the muscles of the
                back.

        Running between the Scalenus
anterior and Scalenus Medius parts of the
Brachial Plexus are visible, inferior to that
the subclavian artery is visible (beneath the pre-vertebral fascia). The Phrenic Nerve is also visible
beneath the pre-vertebral fascia; this nerve arises from CV3, CV4, and CV5, the phrenic nerve
supplies/innervates the Diaphragm (C3, 4&5 keeps the diaphragm alive).

         The Brachial Plexus is composed
of the anterior primary (ventral) rami of
the spinal nerves from CV5 till T1 (CV5,
CV6, CV7, CV8, T1). CV5 & CV6 join
together to form the “Superior Trunk”,
CV7 forms the “Middle Trunk”, CV8 &
T1 join to form the “Inferior Trunk”.
Each of these trunks divides into
anterior and posterior division (3 Ant. &
3 Post.), the anterior division of the
superior and middle trunk join to form
the lateral cord, the anterior division of
the inferior trunk continues at the
Medial Cord, the three posterior
division of the three trunks join to form the posterior cord.
Brachial Plexus= 5 Anterior Rami  3 trunks  3 Ant. & 3 Post. Divisions  3 Cords  Terminal
Branches

      *Any and all plexuses are always formed by THE ANTERIOR RAMI OF THE NERVES NOT THE
POSTERIOR.

        All 5 structures mentioned: Dorsal scapular Nerve, Long Thoracic Nerve, brachial plexus,
         Phrenic nerve& Subclavian Artery, are found between the muscular floor of the posterior
         triangle of the neck and its covering (the pre-vertebra cervical fascia).

******Cervical dorsal trunk = transverse cervical artery

The subclavian artery (visible below the brachial plexus in the image above) can be divided into three
parts:

    1- From its origin to the medial border of the Scalenus Anterior muscle.
    2- Behind the Scalenus anterior muscle.
    3- From the lateral border of the Scalenus Anterior extending to the lateral end of the first rib
       where it continues as the axillary artery.



The pre-vertebral fascia that covers the brachial plexus and the subclavian artery as they pass between
Scalenus anterior and Scalenus Medius, in the lower part of the posterior triangle of the neck continues
as the “axillary fascia/sheath”.

         ** Axillary Fascia originates/arises from the pre-vertebral fascia covering the brachial plexus and
         subclavian artery.
The Root of the Neck:
The root of the neck is the region of the neck that is superior to the Superior thoracic Aperture and the
Axillary (Nerve???). There are multiple structures in the root of the neck:


ARTERIES:
        On the right side we have the Brachiocephalic artery giving off the Common Carotid artery and
then the Subclavian Artery (sections/parts of Subclavian discussed above). There four branches
emerging from the first part of the subclavian artery:

                A- Artery arising from the anterior inferior aspect of the Subclavian, the Internal
                   Thoracic Artery, which passes downwards behind the clavicle to enter the thorax;
                   this artery accompanies the long thoracic nerve to the Serratus Anterior muscle.
                B- Thyro-Cervical Trunk, a short trunk that arises from the superior surface of the
                   subclavian and quickly divides into three branches:
                                  i. Inferior Thyroid artery
                                 ii. Transverse Cervical artery
                                iii. Suprascapular artery
                                     o *Both the Transverse Cervical and the Suprascapular pass
                                         between the Scalenus anterior and the sternocleidomastoid
                                         Muscle.
                                     o The Inferior Thyroid Artery ascends along the medial border of
                                         the Scalenus Anterior until it reaches the level of CV6 and then
                                         it gives off the Ascending Cervical Artery (on the anterior
                                         surface of the Scalenus anterior) which parallels the phrenic
                                         nerve. It also gives the Inferior Laryngeal Artery.


         When Explaining the Artery Above (Inferior Thyroid) the Doc. Referred to it as the “Transverse Cervical”
          but according to the slides the Transverse gives off a different set of branches. However I’m not sure
                              about which artery runs along the Scalenus Anterior till CV6

                                    o   The Transverse Cervical Artery usually gives two branches a
                                        Superficial Branch and a Deep branch. The Superficial branch
                                        accompanies the accessory nerve to the deep surface of the
                                        trapezius; it may arise from the thyrocervical artery as the
                                        superficial cervical artery. The deep branch accompanies the
                                        dorsal scapular nerve on the deep surfaces of the Levator
                                        Scapulae and Rhomboid Muscles, sometimes it arises as a
                                        separate branch from the third part of the subclavian.
                   o   The Suprascapular branch goes to the region of the scapular
                       notch so that it crosses above the transverse scapular ligament.

C- Vertebral Artery- enters through the transverse foramen of CV 6, and then ascends
   through the transverse foramen of the succeeding vertebrae to reach the superior
   aspect of the lamina where there is a group for it, after which it enters the
   subocciptal triangle after which it passes in the foramen magnum to reach the
   surface of the brainstem.
D- CostoCervical Artery- from the second part of the Subclavian divides to give Deep
   Cervical Artery which runs superiorly to supply the deep muscles of the back, and
   the Highest/Superior/Supreme Intercostal Artery which supplies the first two
   intercostal spaces.
OTHER STRUCTURES:
      Vagus Nerve
      Recurrent Laryngeal (a branch of the Vagus)
      Phrenic Nerve
      Internal Jugular Vein
      Subclavian Vein (anterior to Scalenus Anterior)
      Subclavian Artery (Poterior to Scalenus Anterior)
      VEINS ARE ALWAYS SUPERFICIAL TO ARTERIES (RUN INFRONT OF THEM)




What's the point of wearing your favorite rocketship underpants if nobody ever asks to
see 'em?

Susie: You'd get a good grade without doing any work.
Calvin: So?
Susie: It's wrong to get rewards you haven't earned.
Calvin: I've never heard of anyone who couldn't live with that.

"Mom's not feeling well. So I'm making her a get well card."
"That's thoughtful of you."
"See, on the front it says, 'Get Well Soon' ... and on the inside it says,'Because me bed
isn't made, my clothes need to be put away and I'm hungry. Love Calvin.' Want to sign it?"
"Sure, I'm hungry too"   ~~~~CALVIN

                              Done By: Ali Hassan Al-Qudsi

				
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