The root of the neck

Junction between the thorax and neck

Boundaries

laterally: first pair of ribs and their costal cartilage

anteriorly: manubrium of the sternum

posteriorly: body of first thoracic vertebra

Blood vessels:

Arteries:

1. The brachiocephalic trunk

divides into right subclavian artery and right common carotid artery

2. subclavian artery

right: branch off from brachiocephalic trunk

left: from aorta

branches of subclavian artery

a. vertebral artery

        ascends through transverse foramen, goes into the cranial cavity

b. internal thoracic artery

c. thyrocervical trunk, branches into inferior thyroid artery (the largest, most important branch), suprascapular and transverse cervical arteries.

d. costocervical trunk

Veins:

internal jugular vein

subclavian vein

both drain into brachiocephalic vein

Nerves:

1. Vagus nerve: main parasympathetic nerve to thorax and abdomen

branch:

right recurrent laryngeal nerve: loops around subclavian artery

left recurrent laryngeal nerve: loops around aorta

2. Phrenic nerve, innervates thoracic diaphragm

3. Sympathetic trunks (more from neuro)

Muscles

1. scalenus anterior

O: anterior tubercles of transverse processes of thrid through sixth cervical vertebrae

I: scalene tubercle and cranial crest of the first rib

F: lateral flexes and rotates head

N: C3, 4, 5

2. Longus colli (cervicis)

O:

superior oblique portion: anterior tubercle of transverse processes of third, fourth, and fifth cervical vertebrae

interior oblique portion: anterior surface of bodies of first two or three thoracic vertebrae

vertical portion: anterior surface of bodies of first three thoracic and last three cervical vertebrae

I:

superior oblique portion: tubercle on anterior arch of atlas

interior oblique portion: anterior tubercle of transverse processes of fifth and sixth cervical vertebrae

vertical portion: anterior surface of bodies of second, third, and fourth cervical vertebrae.

F: lateral flexes and rotates head

N: C2, 3, 4

3. Logus Colli Capitis

      from anterior tubercles of C3 to C6 cervical transverse processes and attaches superiorly to base of the skull

 4. The rectus capitis anterior

      originates from anterior surface of the lateral mass of the atlas (C1) and inserts to the base of the skull

 5. Rectus capitis lateralis

    originates from transverse process of the atlas (C1), inserts to the jugular process of the occipital bone

Other structures in the neck

1. Thyroid gland

        two lobes connected by the isthmus, largest endocrine gland in the body

A. Blood supply

        highly vascular and extensive blood supply (surgical risk, especially in goiter). 

        Superior thyroid artery: branch of external carotid artery, 
        Inferior thyroid artery, branch of thyrocervical trunk (off subclavian artery)
        There is extensive anastomose with each other but seldom cross the midline

B. Venous drainage

        Usually three veins, superior thyroid, middle and inferior thyroid veins, may join together to join brachiocephalic vein or drain separately into internal jugular vein.

2. Parathyroid glands

        Four small glands embedded within thyroid gland. Usually get blood supply from inferior thyroid artery. Be careful not to remove parathyriod glands during thyriodecomy (damage of recurrent larygeal nerve). Tetany (generalized convulsion) could result from inadvertent removal of parathyroid glands.

3. Pharynx

        Shared by digestive and respiratory system, can be further divided into nasopharynx (posterior to the nose and superior to the soft palate, oropharynx (posterior to the mouth, and the laryngopharynx (posterior to the pharynx).

Muscles of the pharynx

Two layers, the external layer includes three constrictors (superior, middle and inferior )

Their general function is to constrict pharynx during swallowing.  They are innervated by branches from glossopharyngeal (CN 9) and vagus (CN 10) nerves.

Internal muscles of pharynx

        longitudinally arranged, elevate the larynx and pharynx during swallowing and speaking. These muscles include stylopharyngeus muscle, palatopharyngeus muscle and salpingopharyneus muscle. They are innervated by the CN 9.

Swallowing (Deglutition)

Involves three stages (mouth, pharynx and esophagus

1). Mouth:
        Voluntary, pushed b the tongue

2). Pharynx
        Involuntary, breathing and chewing stop, constriction of the three constrictors move the food through oral and laryngeal part of the pharynx, soft palate is elevated to prevent food from entering nasopharynx, (what if laughing or coughing during this stage). When food passes through oropharynx, the contraction of internal pharynx muscles elevate pharynx and larynx. Epiglottis also prevents food from entering the larynx.

3).  Esophagus
        Food passes through paryngopharynx into esophagus by the contraction of inferior constrictor of the pharynx.

        Injury of recurrent laryngeal nerve could cause the incompleteness of closing larynx, resulting food getting into larynx, choking is common.

4. Larynx

        In between pharynx and trachea, designed for phonation.

Skeleton:

        The thyroid cartilage, cricoid cartilage, arytenoid cartilage, corniculate and cuneiform cartilages, and epiglottic cartilage.

 

        These cartilages are inter connected by membrane and ligaments.

Muscles of the larynx

        Muscles of the larynx can be categorized into extrinsic and intrinsic Extrinsic muscles are infrahyoid and suprahyoid muscles that move larynx as a whole, stylopharyngeus muscle is also involved.

        Intrinsic larynx musclea are concerned with the movement of the laryngeal parts. All intrinsic muscles are innervated by recurrent laryngeal nerve except the cricothyroid muscle which is innervated by the external laryngeal nerve (both from CN 10).

Muscles of the inlet of the larynx

        Transverse arytenoid muscle, the oblique arytenoid muscle and the thyroepiglottic muscle. The general function of these muscles is to close the inlet of the larynx. 

Muscles of the vocal cord

Adductors of the vocal cord:

        lateral cricoarytenoid muscle

Abductors of the vocal cord

        posterior cricoarytenoid muscle

Tensor of the vocal cord

        cricothyroid muscle, increases the tension of the vocal cord 

Relaxer of the  vocal cord

        thyroarytenoid muscle