Vessels+and+Nerves+of+the+Neck

toc =**Objectives**=

**Blood Vessels**

 * 1. Describe the "typical" venous drainage in the neck.**

Blood from the pterygoid plexus joins with the maxillary veins just deep to the mandible. The superficial temporal vein and maxillary veins combine into the retromandibular vein which runs posterior to the mandible. The facial and deep facial veins drain into the internal jugular vein. The posterior auricular vein drains into the external jugular vein.

The retromandibular vein drains both into the external and internal jugular veins. The external jugular vein receives tributaries from the transverse cervical, transverse scapular, and anterior jugular veins and sometimes the occipital vein. Meanwhile, the internal jugular vein drains the inferior petrosal sinus, occipital vein, pharyngeal vein, lingual vein, and superior and middle thyroid veins.

The external jugular vein then drains into the subclavian vein. As the subclavian vein courses medially, the internal jugular vein joins with it and the subclavian becomes the brachiocephalic vein and continues toward the superior vena cava. Just before it joins the subclavian vein, the internal jugular vein has a dilation called the inferior bulb, which contains a valve that keeps blood from backing up into the neck and head.


 * 2A. Where are the retromandibular, external and internal jugular veins found and what are their tributaries?**

The retromandibular vein is located along the posterior edge of the mandible and receives tributaries from the superficial temporal vein and maxillary veins. The retromandibular runs inferiorly and drains into the internal and external jugular veins.

The internal jugular vein runs down the side of the neck in a vertical direction, lying at first lateral to the internal carotid artery, and then lateral to the common carotid, and at the root of the neck unites with the subclavian vein to form the brachiocephalic vein (innominate vein). The internal jugular vein drains the brain, inferior petrosal sinus, occipital vein, pharyngeal vein, lingual vein, and superior and middle thyroid veins.

The external jugular vein crosses the SCM muscle obliquely, and in the subclavian triangle perforates the deep fascia, and ends in the subclavian vein, lateral to or in front of the anterior scalene muscle. After the external jugular joins, the subclavian vein joins with the internal jugular vein and becomes the brachiocephalic vein. The external jugular vein receives tributaries from the transverse cervical, transverse scapular, and anterior jugular veins and sometimes the occipital vein.


 * 2B. How is blood drained from the face?**

The frontal vein begins on the forehead in a venous plexus which communicates with the frontal branches of the superficial temporal vein. The veins converge to form a single trunk, which runs downward near the middle line of the forehead parallel with the vein of the opposite side. The supraorbital vein begins on the forehead where it communicates with the frontal branch of the superficial temporal vein. It runs downward superficial to the frontalis muscle, and joins the frontal vein at the medial angle of the orbit to form the angular vein. The angular vein formed by the junction of the frontal and supraorbital veins, runs obliquely downward, on the side of the root of the nose, to the level of the lower margin of the orbit, where it becomes the anterior facial vein.

The facial vein commences at the side of the root of the nose, and is a direct continuation of the angular vein. It runs obliquely downward and backward, descends along the anterior border and then on the superficial surface of the masseter, crosses over the body of the mandible, and passes obliquely backward, it unites with the deep facial vein to form the common facial vein, which crosses the external carotid artery and enters the internal jugular vein at a variable point below the hyoid bone.

The pterygoid plexus of veins lie along the lateral side of the face and communicate with the facial and deep facial veins and the maxillary vein.


 * 3. What are the branches of the external carotid artery?**

__Superior__ __Inferior__
 * S || Superficial temporal a. || supplies the parotid salivary gland and temporal regions ||
 * M || Maxillary a. || supplies tissues at the maxilla ||
 * A || Posterior auricular a. || supplies structures at the external ear ||
 * O || Occipital a. || supplies posterior scalp, SCM ||
 * F || Facial a. || supplies the face and ends at the angular artery at the corner of the eye ||
 * L || Lingual a. || supplies the tongue and floor of the mouth ||
 * A || Ascending pharyngeal a. || supplies the pharynx, SCM ||
 * S || Superior thyroid a. || supplies the thyroid gland, SCM, infrahyoid muscles, and part of the larynx ||


 * 4. Describe the carotid sinus and carotid body.**

The carotid sinus is a localized dilation of the internal carotid artery at its origin, the common carotid artery bifurcation (Note: While the carotid sinus may be found on the common carotid artery, it will not be found on the external carotid artery). The carotid body is an ovoid mass at the bifurcation. The sinus contains baroreceptors sensitive to arterial pressure and can act to decrease heart rate. The carotid body contains a small cluster of chemoreceptors and supporting cells responsible for sensing changes in blood gases, specifically low blood oxygen, and can increase the rate and depth of respiration, cardiac rate, and blood pressure accordingly. Both the carotid sinus and carotid body are innervated by glossopharyngeal nerve CNIX but can receive secondary innervation from vagus CNX and cervical sympathetics.

**Nerves and Plexuses**

 * 1. Describe the cervical plexus and its branches**

The cervical plexus is a plexus of the ventral rami of the first four cervical spinal nerves which are located from C1 to C4 cervical segment in the neck. It is located in the neck, deep to sternocleidomastoid. Nerves formed from the cervical plexus innervate the back of the head, as well as some neck muscles. The branches of the cervical plexus emerge from the posterior triangle at the nerve point, a point which lies midway on the posterior border of the Sternocleidomastoid.


 * **Branch** || **Innervation** ||
 * __Cutaneous__ ||  ||
 * Lesser occipital nerve || lateral part of occipital region (C2, C3) ||
 * Greater auricular nerve || skin near concha auricle and external acoustic meatus (C2, C3) ||
 * Transverse cervical nerve || anterior region of neck (C2, C3) ||
 * Supraclavicular nerves || region of suprascapularis,shoulder, and upper thoracic region (C3,C4) ||
 * __Muscular__ ||  ||
 * Ansa cervicalis || omohyoid (superior belly C1; inferior belly C2, C3), sternothyroid (C2, C3), sternohyoid (C2, C3) ||
 * Nerve to geniohyoid muscle || geniohyoid muscle (C1) ||
 * Nerve to thyrohyoid muscle || thyrohyoid muscle (C1) ||
 * __Mixed__ ||  ||
 * Phrenic nerve || diaphragm (C3-C5) ||


 * 2A. Describe the location and relationships for each nerve plexus or named nerve.**

See above.

The four cutaneous nerves emerge from the nerve point of the neck. Lesser occipital nerve goes to the posterior head; greater auricular nerve goes to the ear; transverse cervical nerve goes to the anterior triangle; supraclavicular nerve goes to the top of the shoulder.

The root from C1 hitchhikes with the hypoglossal nerve XII before giving off the superior root for ansa cervicalis and splitting into nerves to the geniohyoid and thyrohyoid muscles.

The phrenic nerve recieves contributions from C3-C5. The accessory nerve CNXI recieves some contributions from C2-C4.


 * 2B. What is the ansa cervicalis and what does it supply?**

The ansa cervicalis is a loop of nerves that are part of the cervical plexus. Branches from the ansa cervicalis innervate the sternohyoid muscle, sternothyroid muscle, and superior and inferior bellies of the omohyoid muscle. The superior root of the ansa cervicalis is formed by a branch of spinal nerve C1. These nerve fibers hitchhike with the hypoglossal nerve CNXII before leaving to form the superior root. The superior root goes around the occipital artery and then descends in the carotid sheath. It sends a branch off to the superior belly of the omohyoid muscle and is then joined by the inferior root. The inferior root is formed by fibers from spinal nerves C2 and C3 and sends branches to sternothyroid muscle, sternohyoid muscle, and the inferior belly of omohyoid muscle. The ansa cervicalis is either on or imbedded in the carotid sheath but is //not// part of the contents of the carotid sheath.

Ansa cervicalis is latin for "goose neck."


 * 2C. What spinal levels contribute to the phrenic nerve?**

Spinal roots C3, C4 form the cervical plexus and a contribution from C5 by the brachial plexus contribute to the phrenic nerve


 * 3. Describe the vagus nerve (CNX) and its branches in the neck (e.g. recurrent, inferior, and superior laryngeal nerves.)**

The vagus nerve (CN X) starts in the brainstem (within the medulla oblongata) and extends, through the superior vagal ganglion into the jugular foramen, through the inferior vagal ganlgion, down through the carotid sheath, below the head, and to the abdomen.

The vagus n. gives rise to several branches: The superior laryngeal n. arises from the inferior vagal ganglion and descends by the side of the pharynx, behind the internal carotid artery, and divides into two branches: external laryngeal nerve and internal laryngeal nerve, innervating the larynx.

The external laryngeal nerve has motor innervation to cricothyroid and inferior pharyngeal constricter muscles. The internal laryngeal nerve has sensory innervation to the laryngeal mucosa superior to the vocal cords and visceral motor (parasympathetic) innervation to the glands of laryngeal mucosa.

The right recurrent laryngeal nerve passes under the right subclavian a. while the left recurrent laryngeal nerve passes under the arch of the aorta to ascend up as inferior laryngeal nerves to innervate the larynx. The inferior laryngeal nerves provide motor innervation to intrinsic laryngeal mucles except cricothyroid, visceral motor (parasympathetic) innervation to glands in the laryngeal mucosa, and sensory innervation to the laryngeal mucosa inferior to the vocal cords.


 * 4. What is the accessory nerve (CNXI) and what are its components?**

The accessory nerve (or Spinal accessory nerve) is the eleventh of twelve cranial nerves. It leaves the cranium through the jugular foramen along with the glossopharyngeal nerve (IX) and vagus nerve (X). There are two parts to the accessory nerve: A spinal part, that innervates the muscles around the neck (sternocleidomastoid muscle and trapezius muscle on the ipsilateral side. A cranial part, made of rootlets that quickly combine with the vagus nerve.


 * 5. What is the location of the hypoglossal nerve (CNXII) and what is its relationship to the cervical plexus?**

The hypoglossal nerve is the twelfth cranial nerve (XII). It passes through the hypoglossal canal. On emerging from the hypoglossal canal, the nerve picks up a branch from the anterior ramus of C1 (hitchhiker). It spirals behind the vagus nerve and passes between the internal carotid artery and internal jugular vein lying on the carotid sheath. After passing deep to the posterior belly of the digastric muscle, it passes to the tongue. It supplies motor fibers to all of the intrinsic and extrinsic muscles of the tongue, except the palatoglossus muscle which is innervated by the vagus nerve (X) and the accessory nerve (XI).


 * 6. What parts of the brachial plexus are in the neck.**

The C5-C8 nerve roots as well as a portion of the superior middle and inferior trunks. The brachial plexus passes in between anterior and middle scalene muscles of the neck.


 * 7. Describe the cervical part of the sympathetic trunk.**

The cervical portion of the sympathetic trunk contains three ganglion: Superior cervical, Middle cervical, and Inferior cervical. The inferior cervical (C7) and first thoracic (T1) ganglia usually fuse to form the stellate ganglia. The superior cervical ganglion is found arond the C1,C2 vertebral level, middle cervical ganglion at C6 vertebral level, and the stellate ganglion at the C7-T1 vertebral level.

The superior cervical ganglion supplies structures to the head.