Triangles of Neck: Learning Objectives

Question 1

What are the boundaries of the anterior/posterior triangle of the neck? What muscle separates the
anterior from the posterior triangle?

Answer 1

Boundaries of Anterior Triangle:
Superior - inferior margin of mandible
Inferior- Jugular Notch
Medial- anteriomedian line of the neck
Lateral- anterior margin of sternocleidomastoid
Anterior- platysma m. and investing layer of fascia

Boundaries of Posterior Triangle:
Anterior- posterior margin of sternocleidomastoid m.
Posterior- anterior margin of trapezius
Inferior- middle 1/3 of clavicle
Roof- platysma m. and deep investing cervical fascia
Floor- splenius capitus m., levator scapulae m., scalenuis m.

The muscles that separates the two triangles is the sternocleidomastoid m.

Question 2

What muscles form the floor of the posterior triangle?

Answer 2

The splenius capitus m.,levator scapulae m., and scalenuis m.

Question 3

List the suprahyoid/infrahyoid muscles and their innervation.

Answer 3

Suprahyoid Muscles:
Digastric m.
-Ant. belly -n. to mylohyoid from trigeminal (CN V)
-Post. belly -facial nerve (CN VII)
Mylohyoid m.
-n. to mylohyoid from trigeminal (CN V)
Stylohyoid m.
-facial n. (CN VII)
Geniohyoid m.
-C1 via Hypoglossal n. (CN XII)

Infrahyoid Muscles:
Sternohyoid m. 
     -ansa cervicalis
Sternothyroid
     -ansa cervicalis
Thryohyoid
     -C1 via hypoglossal n. (CN XII) 
Omohyoid 
     -ansa cervicalis

Question 4

What are the functions/actions of the suprahyoid and infrahyoid mm.?

Answer 4

The suprahyoid mm. stabalize the hyoid bone and elevate it. They also depress the mandible.
The infrahyoid mm. stabalize the hyoid bone and larynx and thyroid and depress all three.

Question 5

Which spinal cord levels are involved in the cervical plexus?

Answer 5

Ventral primary rami of C1-C4.

Question 6

Where is a cervical block administered? Why?

Answer 6

The cervical nerve block is administered at the nerve point of the neck, which is along the posterior margin of the sternocleidomastoid m. at the superior and middle 1/3 of the muscle.

Question 7

What forms the superior and inferior roots of ansa cervicalis?

Answer 7

The superior root is formed by C1 and/or C2. Inferior root is C2 and C3.

Question 8

What vessel is often the point of entry to the venous system for central line placement?

Answer 8

Internal jugular vein

Question 9

What are the branches of the external carotid artery in the neck? What does each supply?

Answer 9

Superior Thyroid a. - thyroid
Lingual a. - tongue and mouth
Facial a. - supplies superficial muscles of facial expression
below the nose.
Ascending pharyngeal a. - pharynx
Occipital a.- back of scalp and sternomastoid mm.
Posterior auricular a.- scalp post. to auricle and auricle itself
Maxillary a.- deep structures of the face (maxillary teeth,
gums, and palate)
Superficial temporal a. -temple, scalp

Question 10

Where is the carotid pulse taken?

Answer 10

Carotid Triangle (a subdivision of the anterior cervical triangle)

Question 11

List the 10 mm of the Anterior Triangle

Answer 11

• (2) Cerivcal mm = Platysma and SCM
• (4) Suprahyoid mm = Diagastric (Ant and Post bellies), Mylohyoid, Stylohyoid, and Geniohyoid
• (4)Infrahyoid mm = Thyrohyoid, Omohyoid (Superior belly only!), Sternohyoid, and Sternothyroid

Question 12

List the 6 mm of the Posterior Triangle

Answer 12

• Splenius capitus
• Levator scapulae
• Anterior, Middle, and Posterior Scalenes
• Inferior belly of Omohyoid

Question 13

Be able to label a diagram indicating the various subdivisions of the anterior triangle. What are the boundaries of each triangle?

Answer 13

(4) subtriangle pairs of Anterior cervical triangle (see ppt slide 5):
- Muscular Triangles–superior belly of omohyoid (lateral); inframedial edge of SCM (inferiolateral), anterior median line of neck (medial) and hyoid bone (superior)
- Carotid Triangles–posterior belly of Diagastric (superior); superior belly of omohyoid (medial); and medial border of SCM (lateral)
- Submandibular (Digastric!) Triangles–bounded by both bellies of Digastric m and by mandible (superior)
- Submental (suprahyoid) Triangles–anterior median line of neck (medial); anterior belly of Digastric (lateral); and hyoid bone (inferior)

Question 14

List the contents of the Muscular subtriangle

Answer 14

All 4 infrahyoid strap mm (sternohyoid, sternothyroid, thryohyoid, and superior belly of omohyoid) and the Thyroid gland. Contains NO vessels!

Question 15

List the contents of the Carotid subtriangle

Answer 15

Common Carotid A
Carotid Sinus
Internal Jugular Vein
CN X and CN XII

Question 16

List the contents of the Submandibular (digastric) subtriangle

Answer 16

Submandibular gland

Facial artery and Facial vein

Question 17

List the contents of the Submental subtriangle

Answer 17

Only lymph nodes

Question 18

Identify the superficial and deep groups of the infrahyoid mm

Answer 18

• the 2 most superficial mm are the Sternohyoid and Omohyoid (Superior belly)
• the Thyrohyoid originates deep to the Sternohyoid and Omohyoid, but arises lateral to Omohyoid’s superior belly to insert on the hyoid bone
• the Sternothyroid is deep to the Sternohyoid

Question 19

The carotid triangle provides surgical access to what anatomical structure

Answer 19

• the Carotid system of arteries
• IVJ
• Vagus and hypoglossal nn
• and the cervical sympathetic trunk

Question 20

What are the (4) sensory branches of the cervical plexus? Be able to identify the regions on the neck they would innervate on a diagram.

Answer 20

• Great Auricular n (C2-C3): around inferior aspect of ear; parotid sheath
• Transverse cervical n (C2-C3): anterior skin of neck
• Supraclavicular n (C3-C4): skin over clavicle and shoulder
• Lesser occipital n (C2): scalp behind ear

Question 21

How is the ansa cervicalis formed? Over what structure is the ansa formed? What does the ansa do?

Answer 21

[Remember: Cervical Plexus is formed by the ventral primary rami of C1-C4.} It’s motor branches come together anteriorly to form Ansa cervicalis– loop of superior root (C1 and/or C2) + inferior root (C2 and C3). Formed on top of IJV. It gives off 4 branches of motor inn to sternothyroid, sternohyoid, and omohyoid (BOTH sup and inf bellies)

Question 22

What is congenital torticollis?

Answer 22

Congenital torticollis refers to SCM fibrosis (a fibrous tissue tumor) resulting in no lengthening of the SCM during embryological development. It presents like a normal unilateral SCM contraction with head tilted towards and face turned away from the affected side.

Question 23

Where can the spinal accessory nerve be damaged? How does this present clinically?

Answer 23

CN XI is the most common iatrogenic (caused by physician) nerve injury. Can be damaged during extensive cervical dissections in posterior cervical triangle. For ex, during removal of cancerous lymph nodes.
Presentation: Shouler droop is most obvious sign of CN XI injury. Also, weakness in turning head to opposite side against resistance.

Question 24

Does the internal carotid artery have any branches in the neck? How does the internal carotid artery enter the base of the skull–through what opening?

Answer 24

The internal carotid artery sends NO branches into the neck. It supplies the brain (along w/ vertebral aa). It enters the cranial cavity through the carotid canal in the petrous part of the temporal bone.