‫بسم هللا الرحمن الرحيم‬
Lecture # 6
Date: Feb. 27th, 2011
Subject: the accessory nerve and the posterior triangle.
The accessory nerve:
Slide #13: we can see from up to down; pons
spinal nerves (C1, C2, C3, C4, C5, C6 & C7).
medulla
foramen magnum
spinal cord
Posterior cranial fossa has jugular foramen { which is transmitting glossopharyngeal nerve(),
vagus nerve() and accessory nerve()}.
The accessory nerve has two roots:
1) Cranial root: originates from the cranial part of medulla oblongata (Specifically from nucleus
ambigios) in the posterior cranial fossa.
2) Spinal root: originates from C1, C2, C3, C4 & C5, then ascending up within the vertebral canal,
then within foramen magnum, then it will reach the posterior cranial fossa where it will find its
brother(cranial root). They will meet each other to unite and pass through jugular foramen. After
they leave the jugular foramen, they will be separated; the cranial root will join the vagus n. to
descend down to the thorax to give RECURRENT LARYNGEAL N. that supplies all internal muscles of
the larynx except cricothyroid muscle. The spinal root supplies two muscles; trapezius &
sternocleidomastoid.
The posterior triangle:
Slide #2: We should know the sternocleidomastoid (SCM) muscle which has a key position in the
neck, and it divides the neck into two triangle;


Anterior triangle= anterior to it.
Posterior triangle= posterior to it.
The sternocleidomastoid muscle (Slide #3):
Origin: manubrium sterni & medial 1/3rd of the clavicle
Insertion: mastoid process & occipital bone.
Nerve supply: spinal accessory nerve.
Action:

 Bilateral (on both sides): flex the neck to the anterior.
 Unilateral (on one side): flex the neck to one side, so the ear touches shoulder.
Rotating the neck to see other side.
Note:
Sternocleidomastoid m.
Mastoid: related to
mastoid process
(insertion).
Sterno: related to the
sternum (origin).
Cleido: related to the
clavicle (origin).
Torticollis (‫)مرض أبو لوي‬, is a stiff neck associated with SCM m. spasm, classically causing lateral
flexion contracture of the cervical spine musculature (a condition in which the head is tilted to one
side). The muscles affected are principally those supplied by the spinal accessory nerve.
Posterior Triangle of Neck :
Boundaries (slide #4):




Anteriorly by posterior boarder of SCM m.
Posteriorly by anterior boarder of Trapezius.
Inferiorly by middle part of clavicle.
Superiorly where SCM m. overlaps trapezius.
Roof (slide #5):
Skin
superficial fascia
investing (surrounding) layer of cervical fascia.
Floor (slides #5, #6 & #7):
Consist of no. of muscles covered by prevertebral cervical fascia:
12345-
Semispinalis capitis (similar to spinalis muscle in back region).
Splenius capitis.
Levator scapulae; to elevate the scapula.
Scalenus medius.
Scalenus anterior.
Note: capitis means head.
Remember, when we talked about the thorax, we talked about scalenus tubercle crossed by
subclavian vein, artery & brachial plexus.
Scalenus anterior inserted into 1st rib, pass anterior to it is subclavian vein, behind it is subclavian
a. & lower trunk of brachial plexus.(so it will be VAN from anterior to posterior, or vein/
scalenus ant./ artery/ lower trunk of brachial plexus [n.])
Note: we can't see the scalenus post. because it was hidden by muscles above.
Divisions (slide #8):
The inferior belly of omohyoid muscle divides the posterior triangle into:


Supraclvicular triangle (inferior): contains subclavian vessels
Occipital triangle.
The contents (slides #8,#9, #10, #11 & #12):


Inferior belly of omohyoid (omo=scapula)
3 veins (slide #9):
1- External jugular vein:
Retromandibular vein divides into anterior division which will unite with the facial vein to
drain into internal jugular vein. And the posterior division of the retromandibular vein will
unite with posterior auricular vein to form external jugular vein which will descend on the
external surface of SCM then within posterior triangle, finally it drains in subclavian vein.
2- Transverse cervical vein.
3- Suprascapular vein.
Note: (2+3) are horizontal and they drain into external jugular vein. And all these veins (1+2+3)
drain into subclavian vein.

3 arteries(slide #10):
1- 3rd part of subclavian artery: as we know the subclavian a. divides into 3 divisions by
scalenus ant. (D in slides) medial to it 1st part, posterior to it 2nd part & lateral to it 3rd
part(which will go to the upper limb).
The 1st part gives internal thoracic a. & thyrocervical trunk/artery. Thyrocervical trunk gives
3 branches, e.g inferior thyroid artery.
Note: the superior thyroid come from external carotid artery.
2- Transverse cervical artery: accompanied with its vein & it originates from thyrocervical trunk
which is a branch from 1st division of subclavian artery.
3- Suprascapular artery: which originates from thyrocervical trunk, passing deep to
sternocleidomastoid then hidden by clavicle, then it’s accompanied with its vein & nerve they
will go to scapula to supply it. So the suprascapular a. is targeted to scapula.
Suprascapular notch has bridge (suprascapular ligament), and we said in upper limb air force
(suprascapular artery) above the bridge (ligament), and the navy (suprascapular nerve) below the
bridge (within the notch).
Note: (2+3) = branches from thyrocervical trunk (from 1st part of subclavian artery).

4 nerves (slide #12):
1- Accessory nerve: emerging through jugular foramen, then deep to SCM m. and supplying it.
The region above is called "care free region", & below it "careful region" because many
structure are present there.
2- Brachial plexus (figure 1): which originate from C5,C6, C7, C8 & T1. But sometimes
originate from C4 and called "prefixed", or "postfixed" from T2.
Roots of the brachial plexus emerge between scalenus anterior & scalenus medius, then unite
to form upper, middle & lower trunks, then divide.
3- Cervical plexus (figure 2): originate from ant. Divisions of C2, C3 & C4 (Note: C1 doesn’t
give cutaneous branch). It emerges behind midpoint of SCM m. at a site called nerve point.
And it gives the following branches:

Great occipital n. (from dorsal ramus of C2, then go to the central part of the post. aspect
of the scalp.
When this nerve is exposed to pressure, it will cause migraine.

Lesser occipital n. ( also from C2, passes parallel to post. boarder of the SCM m.)
Extra information: it supplies the medial surface of the skin of the auricle, then extending up
to supply the scalp.
Note: great & lesser occipital nerve supply the scalp.

Great auricular n. (originate from C2 & C3, directed toward angle of mandible supplying
the skin over the angle of mandible and the skin over the parotid gland and ear pinna).


Transverse cervical n. (originates from C2 & C3, supplies skin of ant. triangle of neck)
Suprascapular nerves (originate from C3 & C4, they are 3 divisions supplying skin
anterior, lateral & posterior of shoulder).
4- Phrenic nerve: originate from C3, C4 & C5 ( mainly C4).
(Figure 1)
(Figure 2(
Done by:
Rai7anah 5aled