Cardiovascular System of the Head and Neck Home > Cardiovascular System > Cardiovascular System of the Head and Neck Cardiovascular System of the Head and Neck The cardiovascular system of the head and neck includes the vital arteries that provide oxygenated blood to the brain and organs of the head, including the mouth and eyes. It also includes the veins that return deoxygenated blood from these organs to the heart. Among these blood vessels are several unique and important structures that have evolved to help maintain the continuous flow of blood to the brain. The human brain is so powerful and metabolically active that it uses about 20% of all of the oxygen and glucose taken in by the body each day.... Move up/down/left/right: Click compass arrows Rotate image: Click and drag in any direction, anywhere in the frame Identify objects: Click on them in the image 2D Interactive 3D Rotate & Zoom Change Anatomical System Change View Angle Full Cardiovascular System of the Head and Neck Description [Continued from above] . . . Any interruption in the blood flow to the brain very quickly results in the decline of mental function, loss of consciousness, and eventually death if not corrected.

Oxygenated blood enters the neck from the trunk through four major arteries: the left and right vertebral arteries and the left and right common carotid arteries. The vertebral arteries travel through the transverse foramina of the cervical vertebrae before entering the skull at the foramen magnum and joining at the base of the brain to form the basilar artery. From there the basilar artery provides blood to the posterior structures of the brain, including the brain stem, cerebellum, and cerebrum. The left and right carotid arteries each divide in the neck to form the left and right internal carotid as well as the left and right external carotid arteries. The internal carotid arteries pass into the skull inferior to the brain through the left and right carotid foramina. At the base of the brain, the internal carotid arteries branch off into the left and right anterior cerebral arteries and the left and right middle cerebral arteries that supply blood to the middle and anterior regions of the brain. At the base of the brain several communicating arteries form anastomoses, or passages, between the left and right posterior cerebral, left and right internal carotid, and left and right anterior cerebral arteries.

These arteries collectively form a ring of blood vessels known as the Circle of Willis. The Circle of Willis provides insurance that the brain will continue to receive blood flow in the event that one of its major arteries is blocked by allowing blood flow between all of the major arteries to all of the regions of the brain. In the neck and head exterior to the skull, the external carotid artery provides blood flow to the skin, muscles, and organs. Several major arteries - including the facial, superficial temporal, and occipital arteries - branch off from the external carotid to provide blood to the many superficial structures of the head. Three pairs of major veins return deoxygenated blood from the tissues of the head and neck to the heart. The left and right vertebral veins descend through the transverse foramina of the cervical vertebrae to drain blood from the spinal cord, cervical vertebrae, and muscles of the neck. In the head, superficial structures on the exterior of the skull are drained by the pair of external jugular veins, which descend through the neck lateral to the vertebral veins. Most importantly, the brain is drained by a group of large cavities in the dura mater layer of the meninges known as dural venous sinuses.

Blood collected in these sinuses drains into the largest veins in the head and neck - the left and right internal jugular veins. The internal jugular veins collect blood from the brain as well as the superficial structures of the head and neck before descending through the neck towards the heart. Prepared by Tim Taylor, Anatomy and Physiology Instructor Carotid Arteries Carotid Arteries Sign Up for Our Free Newsletters Thanks, You're in! Health Tip of the Day Recipe of the Day There was an error. Please try again. Please select a newsletter. Please enter a valid email address. Did you mean ? What are the carotid arteries? - Heart & Circulatory System - Sharecare What are the carotid arteries? Topics | Heart and Circulatory System | What are the carotid arteries? A Answers (7) A SCAI answered The carotid arteries are two large blood vessels located toward the front of the neck that carry blood to the brain. Blood reaches the carotid arteries by traveling from the heart and passing through a large artery called the aorta. Then the blood moves through the carotid arteries to the brain.

Each of the carotid arteries splits into two separate arteries near the top of the neck to form the left and right internal and external carotid arteries. The larger of these two branched arteries, called the internal carotid artery, delivers oxygenated blood to portions of your brain responsible for cognition, speaking, and motor skills. As a result, stroke victims often suffer from deficits in these areas. A Dr. William D. Knopf, MD , Cardiology (Cardiovascular Disease), answered on behalf of Piedmont Heart Institute The carotid artery is a major artery that carries blood from the heart to the head. There is a carotid artery on each side of the neck, and each one splits into two branches. The interior branch carries blood to the brain and eyes, and the exterior branch carries blood to the face, tongue, and outside parts of the head. A American Academy of Ophthalmology's EyeSmart answered The carotid (pronounced ka-RAH-tid) arteries are located in your neck and are the main arteries supplying blood to the eyes and brain.

There are two carotid arteries: one on the right side of the neck (which supplies blood to the right side of the brain) and one on the left side of the neck (which supplies blood to the left side of the brain). When blood flowing through the carotid artery is reduced or blocked, the eyes and brain do not receive enough oxygen. As a result, brain function and vision can be greatly affected. A Brigham and Women's Hospital answered The carotid arteries are paired arteries in the neck that serve as the major blood supply to the brain. Carotid Artery Disease is when one or both arteries in your neck become narrowed due to accumulation of plaque. Blockages in these arteries can lead to stroke or other problems with brain circulation. A Dr. Mehmet Oz, MD , Cardiology (Cardiovascular Disease), answered The carotid arteries are the main arteries on either side of your neck that supply the head and neck with oxygenated blood. You have two carotid arteries, one on the left side of your neck and one on the right side. If you put your fingertips on the side of your neck, you will feel a pulse. That is your carotid artery.

The carotid arteries divide into internal and external carotid arteries. The job of the internal carotid arteries is to supply oxygen-rich blood to the brain. The external carotid arteries supply blood to the face, scalp, and neck. Helpful? 1 person found this helpful. A NewYork-Presbyterian Hospital answered The carotid arteries provide the brain with most of its blood supply and are located in the neck on either side of the windpipe. Head Arteries & Nerves Anatomy, Function & Diagram | Body Maps Facial: facial expression Vestibulocochlear: hearing and equilibrium of the inner ear, which affects balance Glossopharyngeal: back of tongue, including taste senses, and the sylopharyngeus muscle in the throat, which aids in swallowing Vagus: thoracic and abdominal cavities, as well as the larynx Accessory: larynx, neck, and lower neck muscles Hypoglossal: muscles of portions of the tongue The head’s blood supply comes mainly from the external and internal carotid arteries. These are the arteries you use to check your pulse in your neck. Damage to these arteries poses severe, immediate health risks, which can be fatal.

The internal carotid artery travels up from the aortic arch just outside the heart. It travels into the brain to provide oxygenated blood to the eyes, the front of the brain, and portions of the scalp. The external carotid artery helps supply part of the brain through its many branches, and it also gives blood to the thyroid gland in the neck. The thyroid gland is one of the largest endocrine glands in the body. Hormones from the thyroid gland control how quickly the body uses energy, when to make proteins, and how the body responds to other hormones. Inside the brain, important areas get blood from more than one source, which involves communication between two blood vessels. This is called anastomosis. This process also occurs in the hands, feet, and intestinal tract. In the brain, a circle consisting to of two carotid arteries and the basilar artery form the circle of Willis. This supplies blood in the center of the brain and branches to the cerebrum, pons, medulla oblongata, cerebellum, and the beginning of the spinal cord.

Oxygen-depleted blood leaves the brain and goes back to the heart through veins such as the superficial temporal vein, frontal vein, occipital vein, the anterior facial vein, and others. The cranial venous sinuses also remove blood from the head. Unlike normal veins, these are large channels that drain blood. They run in various places in the brain, including along the back, through the middle, and through the outermost membrane, as well as behind the eyes. Debugging Tools Blood Vessel Distribution Blood Vessel Distribution Pulmonary Circuit The pulmonary circuit begins at the semilunar valve of the pulmonary trunk that carries deoxygenated blood to the lungs. The pulmonary trunk divides into left and right pulmonary arteries that go to each lung. Blood is oxygenated in capillaries that flow through the alveoli of the lungs. Oxygenated blood is then returned to the left atrium of the heart by four pulmonary veins. Systemic Circuit The systemic circuit begins at the aortic semilunar valve with the ascending aorta. As previously noted, the coronary arteries come off at base of the ascending aorta. The curving aortic arch connects the ascending aorta with the descending aorta.

Three elastic arteries come of aortic arch: 1. brachiocephalic trunk (a.k.a. innominate artery) divides into the right common carotid and right subclavian arteries. 2. left common carotid a. These arteries supply blood to the head, neck, shoulders and arms. The subclavian a. give off three major arteries before leaving the thoracic cavity: 1. Thyrocervical trunk 2. Internal thoracic a. 3. Vertebral a. After leaving the thoracic cavity and passing over the first rib, the subclavian a. becomes the axillary (axillary = armpit) a. After giving off branches that supply the shoulder and chest, the axillary a. enters the arm and becomes the brachial a. In the region of the elbow, the brachial a. divides into the arteries that supply the forearm, the radial a. that follows the radius, and the ulnar a. that follows the ulna. Both the radial and ulnar aa. extend to the wrist.

Systemic Veins The systemic veins return deoxygenated blood to the right atrium of the heart via the superior vena cava and inferior vena cava. Many systemic veins run alongside systemic arteries and have the same name as the accompanying artery. In the neck and limbs, in addition to the deep veins that run alongside deep arteries there are superficial veins that are much more variable. The superior vena cava receives blood from the head, neck, shoulder, chest and arms. Venous return from upper limb The superficial veins of the upper limb include the cephalic v. that ascends along radial side of forearm and stays on the lateral side of the arm until it fuses with the axillary v. The basilic v. ascends along the ulnar side of the forearm and stays on the medial side of the arm until it fuses with the brachial v and continues as the axillary v. The median cubital v. interconnects cephalic and basilic veins. The deep veins are alongside the arteries and have the same names. The radial and ulnar veins fuse to form brachial v. The brachial v. receives blood from basilic v and becomes axillary v.

and the axillary v. receives blood from the cephalic v. and becomes the subclavian v. Carotid Arteries and the Blood Supply to the Brain The common carotid a. ascends the neck and divides at the larynx into internal carotid a. and external carotid a. The external carotid a. supplies blood to the neck, pharynx, esophagus, larynx, lower jaw and face. The internal carotid a. enters the cranium through the carotid canal and divides into the: 3. Middle cerebral a. Blood is also supplied to the brain by the vertebral a. The vertebral a. comes off the subclavian a., ascends through the transverse foramina of the cervical vertebrae and enters cranium through foramen magnum. On the medulla oblongata it fuses to form the basilar a. At the pons the basilar a. divides into the posterior cerebral arteries. Although the internal carotid a. supplies the anterior brain and the vertebral a.

supplies the posterior brain, blood supply to the entire brain is ensured by anastomoses between the vessels from these two sources. This complex of anastomosing arteries is called the cerebral arterial circle (circle of Willis) and includes: Anterior cerebral arteries linked by anterior communicating artery Posterior cerebral arteries linked to internal carotids by the posterior communicating arteries Veins returning blood from cranium The superficial veins drain blood from cerebrum into dural sinuses. These dural sinuses form within the dura mater of the brain. The location of some of these sinuses can be easily seen by the impressions they leave on the inner surface of the skull. These include the superior sagittal sinus, transverse sinus and sigmoid sinus. The deep veins that drain blood from the brain, also ultimately drain into the dural sinuses. The blood collected from the brain drains into the sigmoid sinus which exits the cranium by the jugular foramen to become the internal jugular vein. The vertebral v. collects blood from the cervical spinal cord and rear of the skull. It travels alongside the vertebral a. through transverse foramina of cervical vertebrae.

Superficial veins of head and neck The facial, temporal and maxillary veins drain blood from the superficial tissues of the head. The temporal and maxillary veins drain into the external jugular v. and the facial vein drains into the internal jugular v. There is a broad anastomosis between the internal and external jugular veins at the angle of the mandible. The external jugular vein drains into the subclavian v. and the internal jugular v. joins the subclavian v. to form the brachiocephalic v. Veins within thorax In the thorax, the external and internal jugular veins fuse with the subclavian v. and become the brachiocephalic v. The right and left brachiocephalic veins fuse to form the superior vena cava. The azygos v. ascends from lumbar region on right side of vertebral column and drains into the superior vena cava at the level of the second thoracic vertebra. The smaller hemiazygos v. collects blood from the left side of the thorax and drains into the azygos v. The azygos v.

and hemiazygos v are the chief collecting vessels of the thorax. The inferior vena cava collects blood from organs inferior to diaphragm. Abdominal Aorta The descending aorta is divided into thoracic aorta and abdominal aorta by diaphragm. The thoracic aorta supplies blood to viscera of the thoracic cavity and the chest wall. The abdominal aorta gives off three unpaired arteries: 1. The celiac trunk divides into: a. Left gastric a. that supplies stomach and esophagus. b. Splenic a. that supplies spleen, stomach and pancreas. c. Common hepatic a. that supplies liver, stomach, gall bladder, duodenum and pancreas. 2. Superior mesenteric a. that supplies pancreas, duodenum, small intestines and most of large intestines. 3. Inferior mesenteric a. that supplies the terminal portions of colon and the rectum. Paired arteries come off the abdominal aorta and include: Suprarenal a. that supply the adrenal glands. Renal a. that supply adrenal glands and kidneys. Gonadal a. that supply ovaries and testes.

The abdominal aorta ends at the level of the fourth lumbar vertebra (L4) where it divides into right and left common iliac arteries. This region is called the terminal segment of the aorta. Veins draining abdomen The inferior vena cava drains blood from the lumbar wall, liver, kidneys, adrenal gland and the diaphragm. The following veins are involved: 1. Lumbar veins drain blood from the lumbar portion of the abdomen. 2. Gonadal veins drain blood from the testicles or ovaries. The left gonadal usually drains into the left renal vein. 3. Hepatic veins drain blood from the liver. 4. Renal veins drain blood from the kidneys. 5. Suprarenal veins drain blood from the adrenal glands. 6. Phrenic veins drain blood from the diaphragm. Hepatic Portal System Of the digestive organs, only blood draining from the liver goes directly to the inferior vena cava. Blood from the small intestines, large intestines, stomach, pancreas and spleen flows into the liver by the hepatic portal vein. The veins that drain into the hepatic portal vein include the superior mesenteric v., inferior mesenteric v.

and splenic v. This blood is nutrient-rich but oxygen-poor. Oxygen-rich blood is delivered to the liver by the hepatic artery proper. This arrangement allows the liver to perform its processing and storage functions. The blood from the hepatic portal vein flows through sinusoids in the liver and is collected by the hepatic veins. Arteries of Pelvis and Lower Limbs The common iliac a. supplies pelvis and lower limb. At the level of the lumbosacral joint it divides into: 1. Internal iliac a. that supplies urinary bladder, pelvis, external genitalia and medial side of thigh. 2. External iliac a. that supplies lower limb. The external iliac a. penetrates abdominal wall and becomes the femoral a. The deep femoral a. that supplies the muscles of the thigh branches off the femoral a. The femoral a. continues on the back side of the femur and becomes the popliteal a. after it pierces through the adductor magnus and crosses the popliteal fossa. The popliteal a. divides into the anterior tibial a. and the posterior tibial a.

Veins draining lower limbs The deep veins of the lower limbs are again alongside the arteries of the same name. The anterior tibial v. and posterior tibial v. drain blood from lower leg and fuse to form the popliteal v. The ascends alongside the femur and becomes the femoral v. The deep femoral v. that collects blood from the inner thigh drains into the femoral v. When the femoral v. penetrates the abdominal wall it is called the internal iliac v. The superficial veins of the lower limb include the great saphenous v. that ascend along the medial aspect of the leg and thigh and drains into the femoral v. and the small saphenous v. that ascends along the posterior and lateral side of the leg and joins the popliteal v. Veins draining pelvis Inside the pelvis external iliac v. merges with internal iliac v. to form common iliac v. The common iliac veins fuse at the 5th lumbar vertebra to form the inferior vena cava. Fetal Circulation Differences between the adult and fetal circulation reflect differences in the nutritional and respiratory support.

The fetus depends upon the maternal circulation for oxygen, nutrients and waste removal. Exchange takes place at the placenta. In the fetus, two umbilical arteries branch off internal iliac arteries and go to the placenta and a single umbilical vein drains the placenta. The umbilical vein drains oxygenated and nutrient-rich blood into ductus venosus in liver. The ductus venosus also receives deoxygenated blood from the liver and drains into the inferior vena cava. The fetal pulmonary circuit is not as important to the fetus as the lung is collapsed. Some of the blood that enters the right atrium bypasses the pulmonary circuit by going through an opening in the interatrial septum called the foramen ovale. As blood leaves the right ventricle another major portion of blood bypasses the pulmonary circuit by going through a short muscular artery that connects the pulmonary trunk with the aorta called the ductus arteriosus. At birth, the lungs open and receive air and the pulmonary circuit becomes important. The ductus arteriosus undergoes vasoconstriction that is strong enough to stop the flow of blood. The ductus arteriosus then undergoes fibrosis to become the ligamentum arteriosum.

As blood pressure rises in the left atrium a one way valve closes the foramen ovale and it adheres to the wall and undergoes fibrosis. It leaves a remnant in the interatrial septum called the fossa ovalis. At birth, the neonate also begins to rely on its own digestive system. The ductus venosus vasoconstricts and undergoes fibrosis to become the ligamentum venosum. Blood ceases to flow to the placenta by the umbilical arteries that collapse and become the median umbilical ligaments. The umbilical vein also collapses and becomes the round ligament or ligamentum teres. The following summarizes the changes: Arterial Supply Anatomy: Overview, Gross Anatomy, Microscopic Anatomy Arterial Supply Anatomy Author: María-Teresa González-López, MD; Chief Editor: Thomas R Gest, PhD more... Share Overview Overview Arteries are the large vessels that carry oxygenated blood away from the heart (except for the pulmonary circuit, in which the arterial blood is deoxygenated).

The distribution of the systemic arteries is like a ramified tree, the common trunk of which, formed by the aorta, commences at the left ventricle, while the smallest ramifications extend to the peripheral parts of the body and the contained organs (see the image below). Arterial supply, anterior view. The arteries, in their distribution, communicate with one another (forming what are called anastomoses) and end in minute vessels, called arterioles, which in their turn open into a close-meshed network of microscopic vessels, termed capillaries, the true deliverers of oxygen and nutrients to the cells. Arteries are found in all parts of the body, except in the hairs , nails , epidermis , cartilages, and cornea. The larger trunks usually occupy the most protected situations; in the limbs, they run along the flexor surface, where they are less exposed to injury. Next: Gross Anatomy Aorta The aorta commences at the upper part of the left ventricle.

After ascending for a short distance, it arches backward and to the left side; it then descends within the thorax on the left side of the vertebral column, passes into the abdominal cavity through the aortic hiatus in the diaphragm, and ends opposite the lower border of the fourth lumbar vertebra by dividing into the right and left common iliac arteries. Ascending aorta The ascending aorta commences at the upper part of the base of the left ventricle. At its origin, it presents (opposite the segments of the aortic valve) 3 small dilatations called the aortic sinuses. At the union of the ascending aorta with the aortic arch, the caliber of the vessel is increased. This dilatation is termed the bulb of the aorta. The only branches of the ascending aorta are the 2 coronary arteries, which supply the heart; they arise near the commencement of the aorta immediately above the attached margins of the semilunar valves. Aortic arch The aortic arch forms 2 curvatures, one with its convexity upward and the other with its convexity forward and to the left.

As the vessel runs backward, its left side is in contact with the left lung and pleura. Three branches are given off from the arch of the aorta: the brachiocephalic trunk, the left common carotid artery, and the left subclavian artery. The brachiocephalic trunk is the largest branch of the arch of the aorta and divides into the right common carotid and right subclavian arteries. Descending thoracic aorta The descending thoracic aorta is contained in the posterior mediastinum. At its commencement, it is situated on the left of the vertebral column. As it descends, it approaches the median line; at its termination, it lies directly in front of the column. The branches of this segment are divided into 2 sets, visceral (pericardial, bronchial, esophageal, and mediastinal) and parietal (subcostal, superior phrenic, and posterior intercostal). Usually, 9 pairs of posterior intercostal arteries arise from the aorta.

Abdominal aorta The abdominal aorta begins at the aortic hiatus of the diaphragm, in front of the lower border of the body of the last thoracic vertebra. It descends in front of the vertebral column and ends on the body of the fourth lumbar vertebra, commonly a little to the left of the midline, by dividing into the 2 common iliac arteries. The branches may be divided into 2 sets, visceral (celiac, superior mesenteric, inferior mesenteric, middle suprarenal, renal, testicular, and ovarian) and parietal (inferior phrenic, lumbar, middle sacral, terminal branches, and common iliac). Arteries of trunk Celiac trunk The celiac trunk is a short thick trunk that arises from the front of the aorta, just below the aortic hiatus of the diaphragm. It passes forward nearly horizontally and divides into 3 large branches: the left gastric, the common hepatic (gastroduodenal and proper hepatic), and the splenic (pancreatic branches, short gastric branches, and left gastro-omental).

Superior mesenteric artery The superior mesenteric artery is a large vessel that arises below the celiac artery and supplies the whole length of the small intestine, except the superior part of the duodenum; it also supplies the cecum, the ascending part of the colon, and the proximal two-thirds of the transverse colon. Its branches are the inferior pancreaticoduodenal, intestinal, middle colic, ileocolic, and right colic arteries. Inferior mesenteric artery The inferior mesenteric artery supplies the distal third of the transverse colon, the whole of the descending colon, the sigmoid colon, and the greater part of the rectum. Its branches are the left colic, sigmoid, and superior rectal arteries. Renal arteries The renal arteries arise from the side of the aorta, immediately below the superior mesenteric artery. The right is longer than the left and passes behind the inferior vena cava, the right renal vein, the head of the pancreas, and the descending part of the duodenum. The left is higher than the right.

Each vessel gives off some small inferior suprarenal branches to the suprarenal gland, the ureter, and the surrounding cellular tissue and muscles. Iliac arteries On the left side of the body of the fourth lumbar vertebra, the abdominal aorta divides into the 2 common iliac arteries. They diverge from the termination of the aorta, pass downward and laterally, and divide into 2 branches, the external iliac and internal iliac arteries. The former branch supplies the lower extremity; the latter supplies the viscera and muscles of the pelvis. The common iliac arteries give off small branches to the peritoneum, the psoas major, the ureters, and the surrounding areolar tissue; occasionally, they give rise to the iliolumbar or supernumerary renal arteries. The internal iliac artery (hypogastric artery) supplies the muscles and viscera of the pelvis, the buttock, the external genitalia, and the medial side of the thigh.

Its branches are from the anterior trunk (umbilical, obturator, uterine, vaginal, inferior vesical, middle rectal, internal pudendal, and inferior gluteal) and from the posterior trunk (iliolumbar, lateral sacral, and superior gluteal). The external iliac artery is larger than the internal iliac, and it gives off 2 branches, the inferior epigastric (immediately above the inguinal ligament) and the deep iliac circumflex, before passing beneath the inguinal ligament to become the femoral artery. Arteries of head and neck The principal arteries supplying the head and neck are the 2 common carotid arteries. These vessels ascend in the neck, where each divides into 2 branches, the external carotid (supplying the exterior of the head, the face, and the greater part of the neck) and the internal carotid (supplying to a great extent the parts within the cranial and orbital cavities). The common carotid arteries differ in their mode of origin. The right begins at the bifurcation of the brachiocephalic trunk behind the sternoclavicular joint and is confined to the neck.

The left springs from the highest part of the arch of the aorta to the left of, and on a plane posterior to, the brachiocephalic trunk. Each vessel passes obliquely upward, from behind the sternoclavicular articulation to the level of the upper border of the thyroid cartilage, where it divides into the external and internal carotid arteries. Behind the angle of bifurcation of the common carotid artery is a reddish-brown oval body known as the carotid body (glomus caroticum). External carotid artery The external carotid artery begins opposite the upper border of the thyroid cartilage. Taking a slightly curved course, it passes upward and forward, then inclines backward to the space behind the neck of the mandible. The branches of external carotid artery may be divided into 4 sets: anterior (superior thyroid, lingual, and facial), posterior (occipital and posterior auricular), ascending (ascending pharyngeal), and terminal (superficial temporal and maxillary).

The maxillary artery is the larger of the 2 terminal branches of the external carotid; it supplies the deep structures of the face and may be divided into mandibular, pterygoid, and pterygopalatine portions. Internal carotid artery The internal carotid artery supplies the anterior part of the brain, as well as the eye and its appendages, and sends branches to the forehead and nose. In view of its course and relations, this vessel may be divided into 4 portions: cervical, petrous, cavernous, and cerebral. The cervical portion of the internal carotid gives off no branches. The petrous portion gives off the caroticotympanic and the artery of the pterygoid canal; the cavernous portion gives off the cavernous, hypophyseal, semilunar, and anterior meningeal; and the cerebral portion gives off the ophthalmic, anterior cerebral, middle cerebral, posterior communicating, and choroidal. The cerebral arteries are derived from the internal carotid and vertebral, which form a remarkable anastomosis known as the cerebral arterial circle (of Willis ) at the base of the brain.

In front, this anastomosis is formed by the anterior cerebral arteries, branches of the internal carotid that are connected together by the anterior communicating artery. Behind, it is formed by the 2 posterior cerebral arteries, branches of the basilar that are connected on either side with the internal carotid by the posterior communicating artery. Anterior cerebral artery The anterior cerebral artery arises from the internal carotid at the medial extremity of the lateral cerebral fissure. It passes forward and medially across the anterior perforated substance, above the optic nerve, to the commencement of the longitudinal fissure. Here, it comes into close relationship with the opposite artery, to which it is connected by a short trunk, the anterior communicating artery. From this point, the 2 vessels run side by side in the longitudinal fissure, curve around the genu of the corpus callosum, and, turning backward, continue along the upper surface of the corpus callosum to its posterior part, where they end by anastomosing with the posterior cerebral arteries.

Middle cerebral artery The middle cerebral artery, the largest branch of the internal carotid, runs at first laterally in the lateral cerebral or Sylvian fissure and then backward and upward on the surface of the insula, where it divides into a number of branches that are distributed to the lateral surface of the cerebral hemisphere. The branches of this vessel are the anterolateral ganglionic, inferior lateral frontal, ascending frontal, ascending parietal, parietotemporal, and temporal arteries. Posterior cerebral artery and posterior communicating artery The posterior communicating artery runs backward from the internal carotid and anastomoses with the posterior cerebral, a branch of the basilar. A number of small branches are given off from its posterior half--the posteromedial ganglionic branches, which, with similar vessels from the posterior cerebral, pierce the posterior perforated substance and supply the medial surface of the thalami and the walls of the third ventricle. Anterior choroidal artery The anterior choroidal artery is a small but constant branch that arises from the internal carotid, near the posterior communicating artery.

It is distributed to the hippocampus, fimbria, tela choroidea of the third ventricle, and choroid plexus. Arteries of upper limbs The vessel that extends from its origin to the outer border of the first rib is termed the subclavian artery. From this point to the lower border of the axilla, it is named the axillary artery. From the lower margin of the axillary space to the bend of the elbow, it is termed the brachial artery; here, the trunk ends by dividing into 2 branches, the radial and ulnar arteries. Subclavian artery On the right side, the subclavian artery arises from the brachiocephalic trunk behind the right sternoclavicular articulation; on the left side, it springs from the arch of the aorta, behind the left common carotid.

The branches of the subclavian artery are the vertebral artery (entering the skull through the foramen magnum, uniting with the vessel of the opposite side to form the basilar artery), the thyrocervical trunk, the internal thoracic artery (dividing at the level of the sixth intercostal space into the musculophrenic and superior epigastric arteries), the costocervical trunk, and the dorsal scapular artery. Axillary artery The axillary artery is the continuation of the subclavian, which commences at the outer border of the first rib. The branches of these vessels are, from the first part, the highest thoracic; from the second part, the thoracoacromial and lateral thoracic; and from the third part, the subscapular, posterior humeral circumflex, and anterior humeral circumflex. Brachial artery The brachial artery commences at the lower margin of the tendon of the teres major. Passing down the arm, it ends about 1 cm below the bend of the elbow, where it branches into the radial and ulnar arteries.

At first, the brachial artery lies medial to the humerus, but as it runs down the arm, it gradually gets in front of the bone; at the bend of the elbow, it lies midway between its 2 epicondyles. The branches of this artery are the deep brachial (profunda brachii), the superior ulnar collateral, the nutrient, the inferior ulnar collateral, and the muscular branches. Radial artery The radial artery commences at the bifurcation of the brachial, just below the bend of the elbow, and passes along the radial side of the forearm to the wrist. The branches of the radial artery may be divided into 3 groups, corresponding with the 3 regions in which the vessel is situated: a forearm group (radial recurrent, muscular, palmar carpal, and superficial palmar), a wrist group (dorsal carpal and first dorsal metacarpal), and a hand group (princeps pollicis, radialis indicis, and deep palmar arch). Ulnar artery The ulnar artery is the larger of the 2 terminal branches of the brachial and begins a little below the bend of the elbow.

The branches may be arranged in the following groups: a forearm group (anterior ulnar recurrent, posterior ulnar recurrent, common interosseous, and muscular), a wrist group (palmar carpal and dorsal carpal), and a hand group (superficial palmar arch and a contribution to the deep palmar arch). Arteries of lower limbs The artery that supplies the greater part of the lower extremity is the direct continuation of the external iliac. It runs as a single trunk from the inguinal ligament to the lower border of the popliteal fossa, where it divides into 2 branches, the anterior and posterior tibial arteries. The upper part of the main trunk is named the femoral artery, the lower part the popliteal artery. Femoral artery The femoral artery begins immediately behind the inguinal ligament and ends at the junction of the middle and lower thirds of the thigh, where it passes through an opening in the adductor magnus to become the popliteal artery.

In the upper third of the thigh, the femoral artery is contained in the femoral triangle (Scarpa's triangle); in the middle third of the thigh, it is contained in the adductor canal (Hunter’s canal). The branches of the femoral artery are the superficial epigastric (arising from the front of the femoral artery about 1 cm below the inguinal ligament), superficial iliac circumflex, superficial external pudendal, highest genicular, deep external pudendal, muscular, and profunda femoris arteries. Profunda femoris artery The profunda femoris is a large vessel arising from the lateral and back part of the femoral artery that gives off the following branches: lateral femoral circumflex, medial femoral circumflex, perforating, and muscular. The terminal part of the profunda is sometimes named the fourth perforating artery. Popliteal artery The popliteal artery is the continuation of the femoral and courses through the popliteal fossa. It extends from the opening in the adductor magnus and vertically downward to the lower border of the popliteus, where it divides into the anterior and posterior tibial arteries.

The branches of the popliteal artery are the muscular, cutaneous, and geniculars. Around and above the patella and on the contiguous ends of the femur and tibia is an intricate network of vessels forming a superficial and a deep plexus. Anterior tibial artery The anterior tibial artery commences at the bifurcation of the popliteal, at the lower border of the popliteus. It becomes the dorsalis pedis artery at the level of the anterior aspect of the ankle, where it is most superficial. The branches of the anterior tibial artery are the posterior tibial recurrent, anterior tibial recurrent, anterior lateral malleolar, muscular, and anterior medial malleolar arteries. Dorsalis pedis The dorsalis pedis is the continuation of the anterior tibial. It passes forward from the ankle joint along the tibial side of the dorsum of the foot to the proximal part of the first intermetatarsal space, where it divides into 2 branches, the first dorsal metatarsal and the deep plantar. Posterior tibial artery The posterior tibial artery begins at the lower border of the popliteus.

The branches are the fibular, posterior medial malleolar, nutrient, communicating, muscular, medial calcaneal, and lateral and medial plantar arteries. Fibular artery The fibular artery arises from the posterior tibial artery and passes obliquely toward the fibula. It then runs behind the tibiofibular syndesmosis and divides into lateral calcaneal branches, which ramify on the lateral and posterior surfaces of the calcaneus. Pulmonary trunk The pulmonary trunk conveys the venous blood from the right ventricle of the heart to the lungs. It is a short, wide vessel, arising from the conus arteriosus of the right ventricle. The whole of this vessel is contained within the pericardium. It is enclosed with the ascending aorta in a single tube of the visceral layer of the serous pericardium, which is continued upward upon them from the base of the heart. On either side of its origin is the auricle of the corresponding atrium and a coronary artery, with the left coronary artery passing in the first part of its course behind the vessel.

The right branch of the pulmonary trunk, the right pulmonary artery, is longer and larger than the left and runs horizontally to the right, behind the ascending aorta and the superior vena cava and in front of the right bronchus within the root of the right lung, to the hilum, where it divides into 2 branches. The left branch of the pulmonary trunk, the left pulmonary artery, is shorter and somewhat smaller than the right and passes horizontally in front of the descending aorta and left bronchus within the root of the left lung to the hilum, where it divides into 2 branches, 1 for each lobe of the lung. Previous Next: Microscopic Anatomy Arteries are composed of three coats: an internal or endothelial coat (tunica intima), a middle or muscular coat (tunica media), and an external or connective tissue coat (tunica adventitia). The 2 inner coats together are very easily separated from the external coat. The arteries, in their distribution throughout the body, are included in thin fibroareolar investments, which form their sheaths.

The vessel is loosely connected with its sheath by delicate areolar tissue, and the sheath usually encloses the accompanying veins, and sometimes a nerve. All the larger arteries, like the other organs of the body, are supplied with blood vessels. These nutrient vessels, called the vasa vasorum, arise from a branch of the artery or from a neighboring vessel and are distributed to the external coat. [ 1 ] Arteries are also supplied with nerves, which are derived from the sympathetic nervous system. These nerves form intricate plexuses upon the surfaces of the larger trunks and run along the smaller arteries as single filaments. The branches derived from these plexuses penetrate the external coat and are distributed principally to the muscular tissue of the middle coat; by causing the contraction and relaxation of this tissue, these branches regulate the amount of blood sent to any part. Previous Pathophysiologic Variants Atherosclerosis Atherosclerosis is a condition in which fatty material collects along the walls of medium and large arteries. This fatty material thickens, forms calcium deposits, and may eventually block the arteries. Pieces of plaque can break off and move through the affected artery to smaller blood vessels, blocking them and causing tissue damage or death (embolization).

Blood clots can also form around a tear (fissure) in the plaque, leading to blocked blood flow. Atherosclerosis can affect many different organ systems (eg, heart, lungs , brain , intestines, kidneys , and extremities), and it has been proposed as the primary etiology of descending thoracic and abdominal aortic aneurysms and the second most common cause of ascending aortic aneurysms. If the clot moves into an artery, it can cause a stroke or heart attack. Risk factors for atherosclerosis include diabetes, high blood pressure, smoking, high blood cholesterol levels, increasing age, high-fat diet, obesity, and personal or family history of heart disease. Aortic aneurysm An aortic aneurysm is a permanent localized dilation whose diameter is at least 1.5 times larger than the expected normal diameter of that artery.

The diagnosis of an aneurysm in the thoracic or abdominal aorta requires knowledge of its normal diameter: at the level of the mid-descending thoracic aorta, the average aortic diameter is 28 mm for men and 26 mm for women; at the level of the celiac axis, it is 23 mm for men and 20 mm for women; and at the infrarenal aorta, it is 19.5 mm for men and 15.5 mm for women. Aortic aneurysms are the 13th leading cause of mortality in the United States, and the mean age at the time of diagnosis ranges from 59 to 69 years. Men are typically diagnosed at a younger age, and a 2:1 to 4:1 male predominance exists. Traditional risk factors have included atherosclerosis, smoking, hypertension, and genetic disorders such as Marfan syndrome and Ehlers-Danlos syndrome . According to the law of Laplace, wall tension increases as the radius of an aneurysm increases (tension = pressure × radius).

Therefore, it is intuitively apparent that larger aneurysms have a greater risk of rupture is intuitive, and for this reason, the ultimate disease process is the same for all: progressive aortic dilatation and eventual rupture. Aortic aneurysms may be classified into 3 groups according to their location: ascending aorta, descending thoracic aorta (any portion of the aorta between the left subclavian artery and the diaphragm), or thoracoabdominal aorta (which may involve the entire thoracoabdominal aorta from the origin of the left subclavian artery to the aortic bifurcation) They are standardized according to the Crawford classification, which shows the extent of aortic involvement. Although aortic aneurysms remain asymptomatic for long periods, most ultimately produce various symptoms before they rupture. When the aneurysm is large in the region of the aortic hiatus, pressure on adjacent structures may cause midback and epigastric pain. Other potential signs and symptoms related to compression or erosion of adjacent organs include stridor, wheezing, cough, hemoptysis, dysphagia, and gastrointestinal obstruction or bleeding.

The pain (located in abdomen or back between scapulae) may be acute in onset, signifying impending rupture; in that case, the patient presents in extremis. A significant number of aortic aneurysms are asymptomatic when diagnosed, being incidentally noted on chest radiography (the enlarged ascending aorta produces a convex contour of the right superior mediastinum) or another imaging study, such as echocardiography or computed tomography (CT). CT scanning provides precise evaluation of the aorta in regard to size, extent, and location of the disease process. Once an aortic aneurysm has been discovered, precise determination of its extent and diameter is the next step toward determining the appropriate treatment and, when repair is indicated, planning the appropriate intervention. Because the diameter of an aneurysm strongly correlates with the risk of rupture or dissection, size has long been used as the criterion for elective surgical intervention. Emergent operation is indicated in the setting of a rupture aortic aneurysm. Open repair or endovascular treatment can be considered.

Aortic dissection Aortic dissection is a potentially life-threatening condition in which a progressive separation of the aortic wall layers occurs, usually after a tear forms in the intima and inner media. Propagation of the separation within the layers of the media creates a new channel (the false lumen, in which blood remains still) that is separated from the original (the true lumen, in which blood continues to travel) by the dissecting membrane. As the aortic dissection grows bigger, the channel with immotile blood can get bigger and push on other branches of the aorta. This usually occurs in the thoracic portion of the artery but may also occur in the abdominal portion. The acute form of aortic dissection is often rapidly lethal (50% of patients suffering acute type A aortic dissection are dead within 48 hours), whereas those surviving the initial event go on to develop a chronic dissection with more protean manifestations. Aortic dissection occurs in approximately 2 out of every 10,000 people and is most often seen in men aged 40-70.

It is classified as type A or B (Stanford classification), depending on where it begins and ends: type A begins in the first (ascending) part of the aorta, and type B begins in the descending part of the aorta. It may be also classified as type I, II, and III according to the De Bakey system: type I include dissections that involve the proximal aorta, arch, and descending thoracic aorta; type II only involves the ascending aorta; and type III include dissections that originate in the descending thoracic and thoracoabdominal aorta. Several risk factors have been identified that can damage the aortic wall and lead to dissection, including atherosclerosis, high blood pressure, aging, bicuspid aortic valve, connective tissue disorders, and traumatic injury. Hypertension is the mechanical force most often associated with dissection and is associated in more than 75% of cases. The symptoms usually begin abruptly. Pain may be described as sharp, stabbing, or tearing, and it is usually located in the midsternum for ascending aortic dissection and in the interscapular region for descending thoracic aortic dissection.

The pain changes position and typically moves to the arms and legs as the dissection worsens (migratory pain). Patients may also present with signs or symptoms related to malperfusion of the brain (involvement of the brachiocephalic vessels), limbs, or visceral organs. Chronic aortic dissection is usually asymptomatic, and presenting patients often experience intermittent dull chest pain or even severe skeletal pain from erosion into the bony thorax with large or rapidly expanding aneurysms. Diagnostic imaging--CT or echocardiography (transthoracic or transesophageal)--is essential to clarify the anatomy of an aortic dissection. CT scanning is widely available and is now the most frequently used test to diagnose acute aortic dissection. It requires an intravenous (IV) contrast medium and can be performed quickly. Hospitalization is mandatory, and drugs that lower blood pressure must be given through a vein (IV). Strong pain relievers are usually needed, and heart medications such as beta-blockers may reduce some of the symptoms. Furthermore, type A aortic dissections require immediate surgery to repair the aorta, whereas type B aortic dissections may be treated with medication first.

If the aortic valve is damaged, valve replacement is necessary. If the heart arteries are involved, a coronary bypass is also performed. Previous Vascular Concepts - State of the art Endovascular Devices The Heart | Cardiac Cycle | The Blood | Types of Arteries | Blood Circulation | Blood Pressure | ECG Systemic Circulation The carotid artery is a major artery of the head and neck. There are two carotid arteries, one on the left and one on the right. From their origins and for about half their length, the carotid arteries are known as common carotid arteries . The left carotid arises from the arch of the aorta, while the right carotid arises as one of the branches of the bifurcation of the brachiocephalic artery (trunk) into the carotid and right subclavian artery. The carotids then continue along similar paths within their respective sides of the neck and skull. In the systemic circulation, which serves the body except for the lungs, oxygenated blood from the lungs returns to the heart from two pairs of pulmonary veins, a pair from each lung.

It enters the left atrium, which contracts when filled, sending blood into the left ventricle (a large percentage of blood also enters the ventricle passively, without atrial contraction). The bicuspid, or mitral, valve controls blood flow into the ventricle. Contraction of the powerful ventricle forces the blood under great pressure into the aortic arch and on into the aorta. The coronary arteries stem from the aortic root and nourish the heart muscle itself. Three major arteries originate from the aortic arch, supplying blood to the head, neck, and arms. The other major arteries originating from the aorta are the renal arteries, which supply the kidneys; the celiac axis and superior and inferior mesenteric arteries, which supply the intestines, spleen, and liver; and the iliac arteries, which branch out to the lower trunk and become the femoral and popliteal arteries of the thighs and legs, respectively. The arterial walls are partially composed of fibromuscular tissue, which help to regulate blood pressure and flow. In addition, a system of shunts allows blood to bypass the capillary beds and helps to regulate body temperature.

At the far end of the network, the capillaries converge to form venules, which in turn form veins. The inferior vena cava returns blood to the heart from the legs and trunk; it is supplied by the iliac veins from the legs, the hepatic veins from the liver, and the renal veins from the kidneys. The subclavian veins, draining the arms, and the jugular veins, draining the head and neck, join to form the superior vena cava. The two vena cavae, together with the coronary veins, return blood low in oxygen and high in carbon dioxide to the right atrium of the heart. Pulmonary Circulation The pulmonary circulation carries the blood to and from the lungs. In the heart, the blood flows from the right atrium into the right ventricle; the tricuspid valve prevents backflow from ventricles to atria. The right ventricle contracts to force blood into the lungs through the pulmonary arteries. In the lungs oxygen is picked up and carbon dioxide eliminated, and the oxygenated blood returns to the heart via the pulmonary veins, thus completing the circuit. In pulmonary circulation, the arteries carry oxygen-poor blood, and the veins bear oxygen-rich blood.

Coronary Circulation The coronary circulation consists of the blood vessels that supply blood to, and remove blood from, the heart. The vessels that supply blood high in oxygen to the heart are known as coronary arteries. The vessels that remove the deoxygenated blood from the heart are known as cardiac veins. The coronary arteries that run on the surface of the heart are called epicardial coronary arteries. These arteries, when healthy, are capable of autoregulation to maintain coronary blood flow at levels appropriate to the needs of the heart muscle. These relatively narrow vessels are commonly affected by atherosclerosis and can become blocked, causing angina or a heart attack. The major vessels of the coronary circulation are: The left main coronary artery divides into left anterior descending (LAD) and circumflex branches (LCX) The right main coronary artery divides into aciute marginal artery and posterior descending artery. The left and right coronary arteries originate at the base of the aorta. The major coronary vessels lie on the epicardial surface of the heart and function as low resistance, distribution vessels. These epicardial arteries branch into smaller arteries that dive into the myocardium and become the micro vascular resistance vessels that regulate coronary blood flow.

Arterioles give rise to a dense capillary network so that each cardiac myocyte has several capillaries running parallel to the muscle fiber. The high capillary-to-fiber density ensures short diffusion distances to maximize oxygen transport into the cells and removal of metabolic waste products from the cells (e.g., CO 2 , H + ). Carotid Artery Carotid Artery Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy ) Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy ) advertisement Images: Related links to external sites (from Google) These images are a real-time random sampling from a Google search on the term "Carotid Artery." Click on the image (or right click) to open the source website in a new browser window.

Search Google for all related images Ontology: Carotid Arteries Una de las arterias carótidas primitivas, internas o externas Definition (SNOMEDCT_US) One of the common carotid, internal carotid, or external carotid arteries Definition (NCI_CDISC) One of two arteries that supply oxygenated blood to the head and neck; the left common carotid branches from the aorta and the right common carotid from the innominate (brachiocephalic artery). (NCI) Definition (NCI) One of two arteries that supply oxygenated blood to the head and neck; the left common carotid branches from the aorta and the right common carotid from the innominate (brachiocephalic artery). Definition (NCI_NCI-GLOSS) A major artery that carries blood from the heart to the head. There is a carotid artery on each side of the neck, and each one splits into two branches. The interior branch carries blood to the brain and eyes, and the exterior branch carries blood to the face, tongue, and outside parts of the head.

Definition (MSH) Either of the two principal arteries on both sides of the neck that supply blood to the head and neck; each divides into two branches, the internal carotid artery and the external carotid artery. Definition (CSP) key artery located in the front of the neck that carries blood from the heart to the brain; cholesterol plaques on the inner wall of the carotid artery can lead to stroke. Concepts Body Part, Organ, or Organ Component (T023) MSH Medical Aspects: Blood Supply The Neuroscience on the Web Series: SPPA 636 Neuropathologies of Language and Cognition CSU, Chico, Patrick McCaffrey, Ph.D. Chapter 4. Medical Aspects: Blood Supply to the Brain Blood Supply to the Brain The consequences of stroke depend upon which areas of the brain are affected by ischemia, hemorrhage, hematoma or aneurysm. Therefore, it is important to understand the organization of the cerebral blood supply system. Two arterial systems supply the brain with blood: the internal carotid and basilar.

The internal carotids and basilar arteries are connected via the circle of Willis , which allows blood to pass from one system to another in the event of blockage. The Internal Carotid Arteries There are two internal carotid arteries. They ascend from the aortic arch toward the brain along each side of the neck. They pass behind the ear into the temporal lobe and enter the subarachnoid space. They then go to the circle of Willis where each bifurcates to form two main branches: the anterior cerebral artery and the middle cerebral artery. The course of the internal carotid arteries and their branches is tortuous. Because of their many twists and turns these arteries are all subject to blockages caused by cholesterol build-up. For this reason, the internal carotids, and the middle and anterior cerebral arteries are more vulnerable to ischemic rather than hemorrhagic stroke. According to FitzGerald, 1996, the contralateral internal carotid may use the circle of Willis/anterior communicating artery to supply blood to both pairs of anterior and middle cerebral arteries.

Complete interruption of blood flow in the anterior cerebral artery is not very likely because the opposite anterior cerebral can use the anterior communicating artery to make up for the deficiency. Even the facial artery (external carotid) can shunt blood to the anterior and middle cerebral arteries via the ophthalmic artery. The Anterior Cerebral Arteries The anterior cerebral arteries supply blood to the medial cortex, including the medial aspects of the motor and sensory strips. Due to the upside-down representation of the homunculus in both of these area, a blockage in an anterior cerebral artery could cause paralysis or sensory deficits which affect the opposite side of the body from the hips on down. For example, a patient who has suffered such a blockage might have a paralyzed leg or be incontinent of bowel and/or bladder. Since the parts of the motor and sensory strips connected to the arm receive some blood from the anterior cerebral artery, the arm may also be somewhat affected by this kind of blockage. Finally, apraxia of gait may also occur if an anterior cerebral artery fails to supply an adequate amount of blood to the medial part of the motor strip. The anterior cerebral arteries also supply blood to the anterior aspects of the frontal lobes.

As these areas are involved in higher level cognition such as reasoning and judgment, a condition called cerebral dementia may result from anterior cerebral artery blockages. Confused language , or a language indicative of cognitive impairment, may also occur. The Middle Cerebral Arteries These large arteries have tree-like branches that bring blood to most of the lateral cortex of each cerebral hemisphere. This means that the middle cerebral arteries supply blood to the cortical areas involved in speech, language and swallowing. The left middle cerebral artery provides Broca's area , Wernicke's area , Heschl's gyrus, and the angular gyrus with blood. Also, the "head" and "neck" areas of the motor and sensory strips in both hemispheres receive their blood supply from the middle cerebral arteries. Damage to these cortical areas on either side of the brain can impair motor speech and swallowing functions. In addition, the middle cerebral arteries provide most of the blood supply to the corpus striatum . The striatas, which are arterial branches of the middle cerebral arteries, are known as the arteries of stroke as they are the main source of blood for the internal capsule.

A rupture of the lenticulo-striate artery results in bleeding usually in the region of the internal capsule (Steadman, 1997). When one of these arteries is damaged, the bottleneck of fibers within the internal capsule , including the pyramidal tract, can be affected, causing many disabilities. The striatas have relatively thin walls and pressure within them is high. For this reason, they are more vulnerable to hemorrhages than to blockages. Because the middle cerebral arteries supply blood to so many areas of the brain, blockages in this part of the circulatory system can cause numerous types of disorders. If the left middle cerebral artery is blocked, aphasia and apraxia may occur. Blockages of the right middle cerebral artery can cause left side neglect, which is an impairment in the ability to recognize and respond to stimuli on the left side of the body, prosopagnosia or the inability to recognize faces, and various cognitive problems, including agnosia. All of these are part of the right hemisphere syndrome. Blockages of either middle cerebral artery can cause contralateral hemiplegia or hemiparesis as well as contralateral hyposthesia.

Paralysis and sensory deficits will affect the head and neck most. Because the "hand" and "arm" areas are superior to the "head" and "neck" areas of the pre and postcentral gyri, they receive some blood supply from the anterior cerebral arteries. For this reason, they may not suffer as much after a middle cerebral artery blockage. Damage to the internal capsule caused by blockage or hemorrhage of the striata (branch of middle cerebral) can cause upper motor neuron dysarthria and dysphagia. In addition, damage to either middle cerebral artery can cause hemianopsia or the loss of sight in one half of the visual field. This blindness affects the contralateral aspect of both visual fields. For example, a blockage in the right middle cerebral artery will cause left hemianopsia or blindness in the left visual field of both eyes. The Vertebro-Basilar System Both of the vertebral arteries ascend through the spinal column and enter the brain through the magnum foramen. Once in the brain, they continue to ascend, traveling beside the brain stem. At the lower border of the pons the two vertebral arteries join together to form the basilar artery or vertebro-basilar artery.

The vertebral arteries and the basilar are straight arteries and therefore not as subject to blockages due to the build up of cholesterol as are the internal carotids. The posterior inferior cerebellar not only supply the cerebellum but take blood to the lateral medulla. Anterior and posterior spinal arteries supply the ventral and dorsal medulla, respectively (FitzGerald 1996). The three arteries are branches of the vertebral. The side of the pons and the cerebellum receive blood from the anterior inferior cerebellar artery and the superior cerebellar artery. These arteries are branches of the basilar. The anterior inferior cerebellar artery also has a branch, the labyrinthine artery, that supplies the inner ear. The basilar also gives off about twelve pontine arteries that supply the medial pons (FitzGerald, 1996). At the superior border of the pons, the basilar artery divides to form the two posterior cerebral arteries. Before the basilar artery divides, several other arteries arise from it. These include the anterior, inferior, and posterior cerebellar arteries as well as pontine branches.

So, the cerebellum and pons are mainly supplied by branches of the basilar. The Posterior Cerebral Arteries At the superior border of the pons, the basilar artery divides to form the two posterior cerebral arteries. These arteries supply blood to the part of the brain that lies in the posterior fossa of the skull, including the medial aspects of the occipital lobes , the inferior portions of the temporal lobes , the brainstem, and the cerebellum . They also deliver blood to the thalamus and some other subcortical structures. A vascular lesion may result in Thalamic Aphasia or Thalamic Syndrome where the posterior thalamic nucleus is disconnected from the sensory cortex. This rare syndrome causes complete contralateral sensory loss alternating with bouts of severe pain (FitzGerald, 1997). As the vertebral and basilar are somewhat wide arteries and their course is relatively straight, they are not as subject to blockages caused by the build-up of cholesterol as the internal carotids. This means that, overall, cerebrovascular accidents effect the basilar system less frequently than the internal carotid system.

However, the basilar and posterior cerebral arteries may hemorrhage due to shearing injuries caused by accidents or pressure due to edema of the brain. Since they provide blood to the occipital lobes, damage to these arteries can cause a variety of visual problems, including cortical blindness and alexia, which is an inability to read and visual agnosia, or the inability to recognize stimuli presented visually. Because these arteries supply blood to the cerebellum and to the brain stem, blockages or hemorrhaging there can cause either ataxic (cerebellar) or flaccid (lower motor neuron) dysarthria . . It is important to note that the effects of ischemic stroke are almost always contralateral and therefore unilateral. On the other hand, hemorrhagic strokes may damage both hemispheres, depending upon the size and location of the resulting hematoma. One exception to this pattern is alternating hemiplegia. This is a paralysis that can be caused by ischemic stroke and affects different structures on each side of the body. It results from a brain stem lesion that damages cranial nerve nuclei and one side of the pyramidal tract in the same area.

Lesions of cranial nerve nuclei will cause a paralysis of the structures served by that nerve on the same side of the body as the injury. Because the pyramidal tract provides only contralateral innervation to the spinal nerves, damage to these fibers will cause a paralysis of different structures on the other side of the body. For example, a lesion that affects the right nucleus of the trigeminal nerve and the right half of the pyramidal tract will cause paralysis of the right side of the jaw and of the skeletal muscles on the left side of the body. The Circle of Willis The Circle of Willis or the Circulus Arteriosus is the main arterial anastomatic trunk of the brain. According to Bhatnagar and Andy (1995), anastomosis occurs when vessels bring blood to one spot and then redistribute it. The two internal carotid arteries and the basilar arteries feed into the Circle of Willis. The blood is then redistributed by the anterior, middle and posterior cerebral arteries. Thus, the ends of the internal carotids and the basilar artery enter the Circle while the three cerebral arteries arise and exit from it.

(Neither the internal carotids nor the basilar arteries can be considered "cerebral" arteries since they do not begin within the brain). In the Circle of Willis the two internal carotids are joined together by the anterior communicating artery while the posterior communicating artery links the internal carotid system with the basilar artery. These connections make collateral circulation, which Love and Webb (1992, p. 40) define as "the flow of blood through an alternate route," possible. This is a safety mechanism, allowing brain areas to continue receiving adequate blood supply even when there is a blockage somewhere in an arterial system. When all arteries are functioning normally, their blood supplies will not mix where they meet in the Circle because the pressure of their streams will be equal. As long as the Circle of Willis can maintain blood pressure at fifty percent of its normal level, no infarction or death of tissue will occur in an area where a blockage exists. If collateral circulation is good, sometimes a blockage will have no permanent effects. Sometimes, an adjustment time is required before collateral circulation can reach a level that supports normal functioning; the communicating arteries will enlarge as blood flow through them increases.

In such cases, a transient ischemic attack may occur, meaning that parts of the brain are temporarily deprived of oxygen. Collateral circulation is not always sufficient to prevent a stroke. Some people lack one or more of the communicating arteries in the Circle of Willis. This means that, if a blockage develops, blood cannot be redistributed from another arterial system and stroke will occur. FitzGerald (1996), writes that 25% of people get blood to their posterior cerebral arteries from the internal carotids, rather than from the vertebro-basilar system. Also, even when all the communicating arteries exist, the influence of several extraneural factors including abnormal blood pressure, cerebrovascular resistance, and arteriosclerosis may impede collateral circulation. Low blood pressure, which can result from surgical shock, may prevent blood from traveling through the smaller diameter arteries. Pressure or hypertension can cause stenosis of the arteries by pushing plaque up against their walls. Cerebrovascular resistance makes it more difficult for blood to flow from one area to another. It can be caused by arterial spasm, a high level of tri-glycerides in the blood which increases its viscosity, or by elevated levels of cerebral spinal fluid.

Arteriosclerosis or the formation of "plaque" consisting of muscle cells and blood cells, as well as fats on arterial walls also makes it more difficult for blood to flow through communicating arteries. Watershed Areas Parts of the brain located at the ends of the distribution areas of the vascular systems are called the watershed areas. According to Bhatnager and Andy (1995, p.345), a watershed area is a "tertiary brain area located peripheral to primary distribution areas for anterior, posterior, and middle cerebral arteries; it derives blood via the branches of all three cortical arteries." Because they are at the extreme ends of arterial distribution they are particularly vulnerable to ischemia and infarction in those who have circulation problems. Lesions in the watershed areas may cause transcortical sensory aphasia.

Question: Which arteries supply the head and neck with oxygenated blood?
Answer: Carotid