Posterior and Anterior Triangles Flashcards
Boundaries of posterior triangle
roof: cervical investing fascia
anterior: posterior border of SCM
posterior: anterior border of trapezius
inferior: superior margin of clavicle
floor: prevertebral fascia covering neck musculature (posterior, middle and anterior scalene), levator scapulae, splenius capitis and sometimes the semispinalis capitis
NOTE: the passage of the inferior belly of the omohyoid diides the posterior triangle into a larger, more superior OCCIPITAL TRIANGLE and a smaller, more inferior OMOCLAVICULAR (SUPRACLAVICULAR, SUBCLAVIAN TRIANGLE)
General contents of posterior triangle
external jugular vein and tributaries
cutaneous nerves of the cervical plexus: lesser occipital, great auricular, transverse cervical, supraclavicular
spinal accessory nerve
brachial plexus
inferior belly of the omohyoid muscle
third portion of the subclavian artery, transverse cervical, suprascapular, descending or dorsal scapular and occipital arteries
deep cervical lymph nodes (a portion of)
Spinal accessory nerve (CN XI); GSE in the posterior triangle
Spinal accessory nerve (CN XI); GSE
After exiting the jugular foramen between the internal carotid artery and internal jugular vein, the spinal accessory nerve passes posterior and lateral to the vein to enter the medial superior aspect of the SCM. After providing innervation to the SCM, the nerve exits the muscle on its medial posterior surface. It then crosses the floor of the posterior triangle obliquely and inferiorly in a posterior direction where it will eventually pass deep to the trapezius to participate in forming the SUBTRAPEZIAL PLEXUS (with branches of ventral rami of spinal nerves C3 and C4)
Brachial plexus in the posterior triangle in the neck
Composed of ventral rami of spinal nerves C5-T1
Roots of the plexus pass between the anterior and middle scalene muscles (SCALENE TRIANGLE) in the anterior inferior portion of the posterior triangle
CLINICAL NOTE: hypertrophy of these muscles can place undue pressure upon the root of brachial plexus resulting in Thoracic Outlet Syndrome
Axillary sheath
An extension of the prevertebral layer of fascia which covers the scalene muscles invests the roots of the brachial plexus along with the subclavian artery.
This is present in the posterior triangle of the neck.
cervicoaxillary canal
the axillary sheath, complete with trunks and cords of the brachial plexus and axillary artery, passes through the cervicoaxillary canal to enter the axilla.
Branches of the brachial plexus in the posterior triangle of the neck
a. Dorsal scapular n. (C5)- passes through the middle scalene to gain the ventral surface of the levator scapulae upon which it descends continuing along the medial border of the scapula ventral to the rhomboid muscles
b. Accessory phrenic n. - usually arises as a branch of C5 which descends parallel to the phrenic n. on the lateral surface of the anterior scalene muscle.
c. Nerve to subclavius- arises from the upper trunk (C5-C6), cescends anterior to the brachial plexus and the subclavian vessels and posterior to the clavicle to enter the deep surface of the muscle.
d. Suprascapular n. (C5,6)- arises from teh junction of C5 and C6 (upper trunk), parallels the course of the suprascapular vessels to the area of the scapular notch to innervate the supra and infraspinatus muscles.
e. Long thoracic n. (C5,6,7)- formed by twigs of C5,6,7 which join dorsal to the brachial plexus to descend into the axilla on the lateral surface of serratus anterior muscle which it innervates.
f. Direct branches to the scalene muscles supplied collectively by C5-C8
Arteries of the posterior triangle of the neck
Occipital a. - 5th branch of the external carotid artery passes from behind the SCM at the apex of the posterior triangle and ascends to supply the posterior scalp (in company with the greater occipital n.)
Transverse cervical and suprascapular aa. - branches of the thyrocervical trunk (from the 1st portion of the subclavian artery in the root of the neck), cross the posterior triangle inferiorly, medial (deep) to the inferior belly of the omohyoid muscle.
– Transverse cervical a.- eventually exits the posterior triangle by passing deep to the trapezius muscle which it supplies.
– Suprascapular a. - paralleled by its accompanying vein, it is joined by teh suprascapular n. as it passes out of the posterior triangle laterally to enter the scapular region.
Subclavian artery (3rd portion)- portion lateral to the anterior scalene located in the extreme anterior inferior extent of the posterio triangle. It passes from between the anterior and middle scalene muscles and accompanied by the trunks of the brachial plexus, is invested with prevertebral fascia (axillary sheath).
- possible branches: (inconsistent)
- —— transverse cervical a. can arise from this portion anomalously
- ——- suprascapular a. - can arise from this portion anomalously
- ——– dorsal scapular a. - passes dorsalward through the brachial plexus in the vicinity of the middle trunk to gain the ventral surface of the levator scapulae and descends parallel to the dorsal scapular n. ventral to the rhomboids along the medial border of the scapula.
Lymphatics of the posterior triangle
located DEEP to investing fascia
- composed of nodes of the deep cervical system which accompany the:
- spinal accessory n. (accessory nodes)
- transverse cervical a.- (transverse cervical nodes)
Accessory nodes
located along the path of CN XI, receive lymph from superficial lymph nodes of hte head (located SUPERFICIAL to the investing fascia) including:
- occipital nodes which drain the occipital area
- retroauricular nodes, which drain the posterior parietal area
Transverse cervical nodes
which receive lymph from the posterior thorax under the trapexius, the accessory chain of nodes, lateral areas of the neck, upper anterior thoracic wall including the mammary gland and sometimes drainage from the apical nodes of hte axillary system, drain to the INFERIOR DEEP CERVICAL NODES (along the internal jugular vein) to the jugular lymph trunk or directly into the internal jugular or subclavian vein.
Boundaries of the anterior triangle
roof: investing cervical fascia
anterior: line from symphysis menti to sternal notch
posterior: anterior border of SCM
superior: inferior margin of mandible
floor: structural components of the visceral compartment of the neck
Muscles of the anterior triangle
Digastric Sylohyoid Mylohyoid Sternoyoid Sternthyroid Thyrohyoid Omohyoid
Suprahyoid muscles
digastric, stylohyoid, mylohyoid
infrahyoid (strap) muscles
sternohyoid
sternothyroid
thyrohyoid
omohyoid
Digastric muscle
a two-bellied muscle with an intermediate tendon which passes through the attachment of the stylohyoid muscle and is tethered to the hyoid bone via a fascial sling
O: Anterior belly- digastric fossa of mandible
- - Posterior belly- mastoid notch of temporal bone
I: Hyoid bone via fascial sling from intermediate tnedon
A: elevates hyoid and base of tongue; with hyoid fixed via infrahyoid musculature, assists in opening the mouth
N: Anterior belly: mylohoid n (CN V3)
- - posterior belly: digastric branch of facial n. (CN VII)
Stylohyoid
O: Posterior base of styloid process
I: body of hyoid bone near lesser horn
A: elevates and retracts the hyoid and base of the tongue
N: digastric branch of facial n. (CN VII)
Mylohyoid
O: Mylohyoid line of both sides of mandible
I: Midline raphe from symphysis menti to body of hyoid bone
A: elevates hyoid and floor of mouth; when hyoid is fixed depresses mandible
N: Mylohyoid branch of trigeminal (CN V3)
