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Anatomy
Lec #15
29/3/2011
Muscular Triangle
it's called muscular because it's containing and surrounding by muscles.
Boundaries
Anterior  midline of the neck
Superior  superior belly of omohyoid M.
Posterior anterior border of the sternocleidomastoid M.
Contents
Muscles , Endocrine , Respiratory , Digestive
Muscles: 1-Omohyoid M.  posterior to it, is carotid triangle which contains
jugular vein and common carotid artery.
2- Sternohyoid M.  which extends from sternum to the hyoid bone
3- Sternothyroid M. which extends from sternum to the thyroid
4-Thyrohyoid M.  which extends from thyroid to the hyoid
"3+4" we can consider them as one muscle " sternum-thyroid-hyoid " ,,"1" from the
boundaries ,, so as a content we have only two muscles with different names !!
Endocrine : Thyroid gland and parathyroid glands
" parathyroid glands are located behind thyroid gland "
Respiratory: Larynx " Adam's apple "
Trachea
Digestive : Pharynx
Esophagus
MUSCULAR TRIANGLE " 3"
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Omohyoid M. "inferior belly and superior belly "
Origin  inferior belly : suprascapular notch and suprascapular ligament
Insertion  body of hyoid*
Nerve supple  ansa cervicalis
Action  depress hyoid bone .
*this is different from what mentioned in the slides , but this is what the doctor said at the lecture !!
Notes :
*Suprascapular notch is located on the superior border of the scapula and covered by
suprascapular ligament.
suprascapular nerve ,which arises from upper trunk of brachial plexus, passes below
the suprascapular ligament while the suprascapular artery travels superiorly to supra
scapular ligament.
*Omohyoid M. is a good land mark that divides spaces into subspaces .
Its inferior belly divides the posterior triangle into two parts and
Its superior belly divides the anterior triangle into carotid triangle and muscular
triangle.
Sternohyoid
Origin  clavical and posterior surface of the manubrium sterni
Insertion body of hyoid bone
Nerve supple  ansa cervicalis
Action depress hyoid bone during swallowing and speaking.
Sternothyroid
Origin  manubrium sterni
Insertion oblique line of the thyroid cartilage " thyroid cartilage is part of larynx
which has an oblique line for attachment of the muscles !! "
Nerve supple  ansa cervicalis
Action depress thyroid, hyoid "indirectly" and larynx
Thyrohyoid
Origin  oblique line of the thyroid cartilage
Insertion body of hyoid bone
Nerve supple C1 nerve via hypoglossal nerve
Action depress hyoid
Notes :
*C1 nerve supplies geniohyoid M. and thyrohyoid M. .
*All muscles in the muscular triangle supply by ansa cervicalis except thyrohyoid M.
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sternohyoid (sh)
superior belly of omohyoid (oh)
thyrohoid (th)
sternothyroid (st)
Thyroid gland
Butterfly-shaped Endocrine gland , located at the midline of the nick , inferior to the
larynx, embracing the trachea .
It has two capsules: " as the parotid and submandibular glands"
1-its own fibrous capsule " thin inner capsule"
2-outer capsule from pretracheal fascia which allows the thyroid to oscillate up and
down during swallowing and speaking.
Each thyroid consists of two lobes ; right and left .They are pear-shaped lobes ,each
has narrow "pointed" upper pole and broad "wide" lower pole .
The broad lobes are connected to each other at the midline anterior to the trachea by
bridge called isthmus which crossing the tracheal rings # 2 ,3 and 4 .
Tracheostomy is creating an opening through the neck into the trachea "under the level of the
tracheal ring #4 and above the level of sternum notch ". A tracheostomy provides an air passage to
help you breathe when the usual route for breathing is somehow obstructed or impaired.
Pyramidal lobe is a small part of the gland projects upward from isthmus , usually
shifted to the left of the midline ,representing the pathway of the thyroid.
"is an embryonic remnant of the caudal end of the thyroglossal tract".
Thyroid gland developes at the foramen cecum ,which is a shallow depression in the posterior dorsal
midline of the tongue behind the V-shaped teminalis sulcus, then descends and migrates down
through thyroglossal duct.
The descent of thyroid may be arrested at the base of the tongue to form a lingual thyroid which is
an incidental mass on the back of the tongue as a result the baby can't swallow well "huge
like"INCOMPLETE DESCENT OF THYROID
Ectopic thyroid tissue can :
1-remain above or below hyoid bone
2- migrate to thorax ,precisely to the superior mediastinum, with thymus gland.
" this results in pressure on the trachea and arch of the aorta in patients with pathological
enlargement !! ".
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Arterial supply:" It is a Highly vascular endocrine gland , receives ~40-120 ml of blood/minute"
By 3 branches :
1-Superior thyroid artery, which is the first branch of external carotid artery, going
to upper pole and it's accompanied with external laryngeal nerve .
2-Inferior thyroid artery ,which is branch from thyrocervical trunk, going to lower
pole and it's accompanied by recurrent laryngeal nerve .
3- Thyroda ima artery ,which is branch either from brachiocephalic trunk or arch of
aorta, going to the lower part of isthmus . present in 3% .
Notes:*The main arterial supplies of the thyroid "1+2" are accompanied with nerve.
*External laryngeal nerve ,which is branch from superior laryngeal nerve, supplies
cricothyroid M..
*Thyrocervical trunk is branch from the first division of subclavian artery.
*Arteries anastomose freely over surface of the gland .
*The risk of thyroid gland during surgry appears as it's a highly vascular
gland"bleeding" , and the role of the surgeon is to minimize the bleeding.
Vanous drainage:By 3 pairs of valveless veins
1-Superior thyroid vein, from upper pole, going to internal jugular vein, accompanies
with superior thyroid artery .
2-Middle thyroid vein, from middle of the lobe to internal jugular vein .
3-Inferior thyroid veins ,, 2 from isthmus ,, usually united to end into left
brachiocephalic vein .
Notes:*Bleed profusely if injured .
*Superior thyroid artery , superior thyroid vein and external laryngeal nerve are
located close to each other .
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Relations :- "check the picture, page 12, in the slides"
Anterolateral : Sternocleidomastoid
" muscles "
Omohyoid superior
Sternothyroid
Sternohyoid
Posteriorly : Carotid sheath and its contents. " common carotid artery , internal
jugular vein and vagus nerve ".
Medial:
Respitatory:larynx
trachea
Digestive : pharynx
esophagus
Others: cricothyroid M.
recurrent laryngeal nerve " between the esophagus and trachea".
Lymphatics :
Follow the arteries to deep cervical lymph nodes.
Sympathetic innervation :
most from the middle sympathetic ganglion through the inferior thyroid artery .They
act as vasoconstrictors .
Functions :
the entire functional conrol of thyroid is hormonal ,it produces thyroxine and
thyrocalcitonin hormones.
Thyroxine" T3,T4": secreted by follicular cells.
increase metabolic rate of the most body cells.
increase O2 consumption.
maintenance of body temperature.
Thyrocalcitonin : secreted by parafollicular cells
lowers blood calcium level by inhibiting osteoclasts .
*The most common thyroid problems involve abnormal production of thyroid hormones. Too much
thyroid hormone results in a condition known as hyperthyroidism
*All types of thyroid problems in women are much more common than thyroid problems in men.
*Symptoms of hyperthyroidism in adults include: Nervousness and feeling excessively hot
in normal or cold temperatures.
*Symptoms of hypothyroidism in adults include : exhaustion and poor appetite
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parathyroid glands
*four small ovoid endocrine glands, located behind lateral lobes of thyroid gland .
*all lie on or within thyroid gland, inside pretracheal fascia .
*2 superior at the upper pole, more constant in position, usually at the middle of its
posterior border . also called Parathyroid IV "in embryology".
*2 inferior at the lower pole , variable in position , may exist in thorax.also called
Parathyroid III
*Supplied mainly by the inferior thyroid artery
*Parathyroid hormone ,which is secreted by chief cells, stimulating osteoclasts
activity to increase calcium level in blood .
DEEP FASCIA OF THE NECK
*Start from the posterior aspect of vertebral column , extending from the posterior
aspect of the skull" occiput " to C2 and this is called ligamentum nuchae
{nuchae means neck}.
*It's divided into 3 layers ; investing layer ,prevertebral layer and pretraclear layer .
Investing layer {fascia}:the outer one ,called investing because it was one then divided to two then return
back as one , it's investing structures like ; trapezius posteriorly, sternocleidomastoid
M., then fused anteriorly at the midline of the neck.
REMEMBER !! The roof of posterior triangle contains investing layer .
Prevertebral fascia :surrounding prevertebral muscles " bundle of muscles anterior to the vertebrae".
Pretrachlear fascia:It's mobile , Surrounding the trachea , esophagus and the structures between them
such as thyroid gland.
Facsial spaces :Located between the layers of deep fascia " investing and pretrachlear ", " pretrachlear
and prevertebral", these spaces are important in infection and surgery.
Infection in one space will not reach the other but it will pass up and down
"so the function of these spaces is protection ".
If you want to remove the thyroid gland you should know how to remove the fascia
first.
GOOD LUCK !!  
EMAN GHALEB
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