1.2 Step 11. Carotid sheath and its contents скачать в хорошем качестве

1.2 Step 11. Carotid sheath and its contents

These videos have been excerpted from Netter’s Video Dissection Modules on Student Consult.  http://bit.ly/2oEt9CO Step 11 Now, on the left side, carefully pick away the carotid sheath being careful to preserve the ansa cervicalis. Within the sheath, identify the internal jugular vein, common carotid artery, and vagus nerve, which descends between them. Note where the internal jugular vein joins the subclavian vein. At this junction on the left, the jugular lymphatic trunk joins the thoracic duct, which then drains into the venous system. Clean and identify the left brachiocephalic vein and the right brachiocephalic vein, which drain to the superior vena cava. Note the extensive collection of lymph nodes around these vessels. Key Terms • Carotid sheath: the fibrous sheath that surrounds the internal carotid artery in the neck N34. It extends from the base of the skull to the level of the first rib and in addition to the common carotid artery. It contains the deep cervical lymph nodes, the internal jugular vein and the vagus nerve. The latter descends in the posterior part of the sheath, between the artery and vein. The upper most part of the sheath also contains parts of the glossopharyngeal, accessory and hypoglossal nerves. The sheath is formed by contribution from adjacent layers of muscle fascia. • Ansa cervicalis: a loop of nerve fibers associated with the cervical plexus. The loop is formed by fibers from C1, C2 and C3. It descends about half way down the neck in close association with the common carotid artery and internal jugular vein, and it has branches to the omohyoid, sternohyoid, and sternothyroid muscles N31. The C1 contribution travels with the hypoglossal nerve for a short distance and then some of the fibers leave as the superior root of the ansa. This makes it appear like the superior root is a branch of the hypoglossal nerve; C1 fibers that remain with XII become branches to the thyrohyoid and geniohyoid muscles. Contributions from C2 and C3 rami form the inferior root of the ansa, which is incorporated into the carotid sheath where it lies along the lateral side of the jugular vein N30 N31. • Internal jugular veins: the two main venous channels in the neck N28. Each vein begins at the base of the skull as a direct continuation of the sigmoid sinus via the jugular foramen. At its origin, it has a dilation called the jugular bulb, which occupies the jugular fossa of the skull N10. In addition to receiving the venous drainage from the brain, it has retromandibular, facial and lingual, laryngeal and superior and middle thyroid tributaries N70. Each vein descends lateral to ipsilateral internal carotid artery N74 within the carotid sheath, and joins the subclavian vein to form a brachiocephalic vein. • Common carotid artery: a paired artery that supplies the head and neck with oxygenated blood via its two branches, the internal and external carotid arteries. The left and right common carotid arteries follow the same course, but have different origins: the right common carotid originates in the neck from the brachiocephalic trunk, while the left arises from the aortic arch in the thoracic region N75. Each vessel passes obliquely upward, from behind the sternoclavicular joint to the level of the upper border of the thyroid cartilage, within the carotid sheath, which is derived from the deep cervical fascia. Within the sheath are also found the internal jugular vein, lateral to the artery, and the vagus nerve, posterior to both vessels N30 N31. At approximately the level of the fourth cervical vertebra, the common carotid artery bifurcates into an internal carotid artery and an external carotid artery N76. ABOUT: The project was made possible by several very dedicated faculty and staff at University of North Carolina, Chapel Hill--especially O.W. Henson and Noelle A. Granger--and partner schools, and by a grant from the Fund for the Improvement of Post-Secondary Education of the US Department of Education. This channel includes over 400 short videos highlighting the steps in a full-body human dissection in the gross anatomy lab. Each step is narrated and key structures labeled.