TRIANGLES OF NECK. Part I.

I. OVERVIEW OF NECK

A. Neck can be thought of as compartmentalized (Snell Fig. 11-4; Atlas Fig. 8.1)

1. Posterior compartment contains

a. Vertebrae of neck = cervical vertebrae

b. Many muscles which move cervical vertebrae and neck; in general ‑ posterior to vertebrae, muscles are continuations of muscles of back and suboccipital region; laterally, muscles are called Scalenes; anteriorly muscles are called Prevertebral muscles; Prevertebral muscles are located directly anterior to vertebrae.

2. Anterior compartment contains

a. Viscera ‑ in lower part of neck, trachea, thyroid gland and esophagus.

b. Pharynx ‑ in upper part of neck; pharynx is a tube composed of muscles and fascia; the esophagus and the larynx open into the pharynx; the pharynx is continuous anteriorly with the oral and nasal cavities; the esophagus is part of the upper end of the GI tract; the larynx contains structures that make sounds in speech; the larynx is the upper end of the respiratory system.

c. Hyoid bone ‑ bone in anterior part of neck; attached to skull and skeleton only by muscles and ligaments; attachments also go to larynx, tongue and skull; muscles which move hyoid bone produce movement of larynx and tongue (which occurs during swallowing and talking)

3. Lateral compartment (lateral and posterior to pharynx) contains blood vessels (Carotid arteries and Internal Jugular veins) and Vagus nerve.

II. MUSCLES OF NECK - see attached chart

A. Muscles not attached to hyoid bone

1. Sternocleidomastoid muscle

2. Scalenus anterior and medius

B. Infrahyoid muscles ‑ all muscles act to depress hyoid bone

Note: Hyoid bone has parts: body (central part), greater and lesser horns (cornu) (lateral parts) (Atlas Figure page 740); all infrahyoid and suprahyoid muscles (except sternothyroid) attach to body of hyoid; greater horns can be palpated in neck above thyroid cartilage and used as landmarks to locate surrounding structures.

1. Omohyoid

2. Sternohyoid

3. Sternothyroid

4. Thyrohyoid

C. Suprahyoid muscles ‑ all act to elevate the hyoid bone.

1. Digastric - also opens mouth

2. Stylohyoid - note: splits to surround digastric tendon

3. Mylohyoid - forms muscular floor of mouth

4. Geniohyoid

III. NERVES OF NECK

A. Cervical plexus ‑ formed from ventral primary rami of spinal nerves C2‑C4, which emerge from posterior border of sternocleidomastoid (near its mid‑point); most branches are cutaneous: (Atlas Fig. 8.3A, Snell Fig. 11-1)

1. Lesser Occipital nerve (C2) ‑ innervates skin behind ear and skin of upper lateral neck

2. Great Auricular nerve (C2,C3) ‑ innervates skin over parotid gland and skin located inferior to ear.

3. Transverse Cervical nerve (C2,C3) ‑ innervates skin of anterior neck.

4. Supraclavicular nerves (C3,C4) ‑ innervate skin of lower lateral neck and shoulder

5. Phrenic nerve ‑ (C3,4,5) provides motor innervation to the diaphragm, crosses anterior to Scalenus Anterior muscle. (Atlas Fig. 8.3C)

B. Ansa cervicalis ‑ fibers from anterior ramus of C1 do something devious; they join the Hypoglossal nerve (cranial nerve XII) as "hitchhiking fibers"; some of these fibers leave the Hypoglossal nerve in the neck and descend down and join other nerves of anterior rami of C2 and C3; all of this forms a loop known as the Ansa Cervicalis; some fibers leave the Ansa Cervicalis and innervate neck muscles (that are described above); other fibers of C1 travel further with the Hypoglossal nerve; those fibers then leave the Hypoglossal nerve to innervate the Thyrohyoid and Geniohyoid muscles; the result is that the Hypoglossal nerve has branches that look like they innervate neck muscles; they don't; only fibers from C1‑C3 actually innervate those muscles. (Atlas Figs. 8.9, 8.10A)

IV. ARTERIES OF HEAD AND NECK

A. Subclavian artery ‑ at root of neck; artery passes laterally toward arm, posterior to Scalenus Anterior muscle (Atlas Figs. 8.6A, 8.7A); Scalenus Anterior muscle is used as a landmark to divide the artery into three parts:

1. Part I (medial to scalenus anterior) ‑ three branches: (1) Vertebral artery, which ascends into neck and enters foramina transversaria of vertebra C1‑C6; (2) Internal Thoracic artery which descends into thorax posterior to sternum; (3) Thyrocervical trunk ‑ branches into Inferior Thyroid, Transverse (or Superficial) Cervical, and Suprascapular arteries.

2. Part II (post. to scalenus ant.) ‑ one branch: Costocervical trunk ‑ which branches into a. Superior Intercostal artery to supply first two intercostal spaces with Posterior Intercostal arteries and b. Deep Cervical Artery to deep neck muscles.

3. Part III (lat. to scalenus ant.) ‑ no branches.

B. External Carotid artery ‑ Common carotid artery arises from aorta on left, brachiocephalic artery on right; it ascends into neck and divides at level of upper border of thyroid cartilage into Internal and External Carotid arteries; Internal Carotid artery ascends to skull without branching; External Carotid branches supply face and scalp (Atlas Fig. 8.6A); branches are (from inferior to superior):

1. Superior Thyroid artery ‑ descends to thyroid gland ‑ gives off Superior Laryngeal artery which courses to larynx.

2. Ascending Pharyngeal artery ‑ small branch which ascends to pharynx.

3. Lingual artery ‑ ascends to supply tongue.

4. Facial artery ‑ arises below mandible, crosses over surface of mandible to supply face, lips and nose.

5. Occipital artery ‑ small branch which arises on posterior side of ext. carotid (opposite Facial artery) and supplies posterior scalp.

6. Posterior Auricular artery ‑ small branch from posterior side of ext. carotid which supplies posterior ear and adjacent scalp.

7. Superficial Temporal artery ‑ large terminal branch of External Carotid; arises opposite external auditory meatus; ascends to supply scalp and Temporalis muscle.

8. Maxillary artery ‑ second large terminal branch of External Carotid; many branches (considered in lecture on Infratemporal region).

V. VEINS OF HEAD AND NECK

A. Overview ‑ most arterial branches have accompanying veins (venae comitantes); branching pattern is variable; normally (Atlas Figs. 8.4, 8.5A):

1. Superficial Temporal and Maxillary veins unite to form Retromandibular vein.

2. Retromandibular vein divides at angle of mandible into Anterior and Posterior divisions.

3. Anterior division joins Facial Vein to form Common Facial vein which drains into Internal Jugular vein.

4. Posterior division joins Posterior Auricular vein to form External Jugular vein.

5. External Jugular vein descends across Sternocleidomastoid muscle to drain into Subclavian vein.

6. Anterior Jugular vein forms from small veins below mandible; descends to join Ext. Jugular vein above clavicle.

VI. FASCIA OF NECK

A. Superficial fascia ‑ loose connective tissue below dermis; in neck generally thin and hard to demonstrate; contains platysma muscle and superficial veins.

B. Deep cervical fascia ‑ layers of connective tissue; one layer completely surrounds neck; other layers form tubes contained within that layer; names of some layers poorly chosen and confusing (Snell Fig. 11‑4; Atlas Fig. 8.1)

1. Investing layer of Deep cervical fascia ‑ completely surrounds neck; splits into 2 layers to enclose trapezius and sternocleidomastoid muscles and suprahyoid and infrahyoid muscles.

2. "Prevertebral" layer of deep cervical fascia ‑ forms a tube which completely surrounds vertebral column, muscles of back of neck, prevertebral, lateral vertebral and suboccipital muscles (not trapezius).

3. "Pretracheal" (visceral) layer of deep cervical fascia ‑ actually completely surrounds cervical viscera, including thyroid gland, trachea, and esophagus; inferiorly it enters mediastinum.

Note: Retropharyngeal space ‑ potential space between "prevertebral" and "pretracheal" layers; infection can spread from head (as in tonsillitis) and neck via retropharyngeal space into mediastinum; George Washington may have died from this.

4. Carotid sheath ‑ paired; on each side surrounds Common and Internal Carotid arteries, Internal Jugular vein, Vagus nerve, and Deep Cervical lymph nodes (sympathetic chain is posterior to carotid sheath); infections tend to remain localized within the sheath.

VII. LYMPHATICS OF HEAD AND NECK ‑ described as three groups of lymphatics and nodes: Superficial and Deep Rings of nodes and Deep Cervical chain (Snell Fig. 11‑25)

A. Superficial Ring of nodes ‑ drain areas adjacent to their location: consist of Submental, Submandibular, Buccal, Parotid, Retroauricular and Occipital nodes.

B. Deep Ring of nodes ‑ consist of Retropharyngeal and Pretracheal nodes.

C. Deep Cervical Chain of lymph nodes (Atlas Fig. 7.88; Snell Fig. 11‑25) ‑ chain of nodes along Internal Jugular vein; receive lymph vessels from all nodes of head and neck.

D. Jugular lymph trunk ‑ efferent lymph vessels from deep cervical nodes drain into Thoracic Duct (on left), Right Lymphatic Duct (on right); these drain into Brachiocephalic veins (at junction of Internal Jugular and Subclavian Veins).