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SPH405

   SPH405 : The Class : Gross Anatomy : Central Nervous System II : Online Lesson 3
Neurological Foundations of Speech, Language and Hearing






  Online Lesson
Arterial Supply and Venous Drainage of the CNS

GOAL: To provide a general understanding of the arterial supply and venous drainage of the central nervous system.

OBJECTIVES: "After reading and study, graduate students in speech pathology will...

Name the major arteries of the brain and spinal cord and describe their distribution.

Relate cardiac outflow to the inputs to the Circle of Willis

Describe the role of the dura mater in the venous drainage of the brain.

Associate blockage of the middle cerebral artery with clinical presentations of communication disorders.

"...on the examination with 90% accuracy."

ARTERIAL SUPPLY AND VENOUS DRAINAGE

The ARTERIAL SUPPLY to the central nervous system is conveyed via the INTERNAL CAROTID arteries and the VERTEBRAL arteries.

  1. The internal carotid and the vertebral arteries supply the brain.


  2. The vertebral arteries supply the spinal cord.


  3. The internal carotid arteries branch from the common carotid arteries on either side of the neck.

    4. Internal Carotid Artery

  4. The vertebral arteries branch from the left and right subclavian arteries and travel along the cervical vertebrae before they supply the central nervous system.

FROM THE HEART

  1. The first artery from the heart is the aorta.


  2. The COMMON CAROTID arteries arise from DIFFERENT SOURCES depending upon whether they are located on the right or on the left sides of the thorax. Since the heart is located on the left side of the thorax, there is a difference between the anatomy of the circulatory system of the two sides of the thorax.
    1. The LEFT common carotid artery is a branch of the aorta. The aorta is the largest artery in the body, and the main trunk blood supply out of the heart. The aorta grows out of the top of the heart and curves over to the left, giving off the left common carotid artery as its second branch.


    2. The RIGHT common carotid artery is a branch of the brachiocephalic artery. The brachiocephalic artery is the first branch of the aorta as it leaves the heart. It divides into two branches, the subclavian and the common carotid arteries.

The VERTEBRAL ARTERIES are branches of the right and left subclavian arteries.
They ascend and insert into foramina in the transverse processes of the first six cervical vertebrae.

  1. As they run in the neck, the vertebral arteries branch off and form the anterior and posterior spinal arteries. These supply the spinal cord and the spinal meninges.


  2. Supply to the cord is via the anterior and posterior spinal arteries. These freely anastomose along the cord.

    3. The vertebral arteries continue their ascent into the skull through the foramen magnum.

    More about the carotid and vertebral arteries

SUMMARY:

  1. Left: aorta-common carotid; Aorta-subclavian-vertebral


  2. Right: Aorta-brachiocephalic-common carotid; Aorta-subclavian-vertebral

IN THE SKULL

The common carotid arteries pass upward to join the CIRCLE OF WILLIS in the area of the optic chiasm.

  1. They enter the skull through the carotid canals, just anterior and a little lateral to the foramen magnum.


  2. The circle of Willis is a roughly circular formation of arteries in the skull. the circular formation allows for collateral supply of blood in the event that one of the input conduits is blocked.

    3. Circle of Willis Images

The arteries that form the circle of Willis are:

  1. Internal carotid arteries


  2. Posterior cerebral arteries


  3. Posterior communicating arteries


  4. Anterior communicating artery

The internal carotid arteries enter the circle of Willis and divide.

Dissection showing Circle of Willis

They divide into large MIDDLE CEREBRAL arteries and smaller ANTERIOR CEREBRAL arteries.

  1. The large middle cerebral arteries supply the lateral surfaces of the hemispheres, the under surface of the temporal lobe, and the under surface of the frontal lobe.


  2. The smaller ANTERIOR cerebral arteries supply the medial surfaces of the frontal and parietal lobes, a narrow strip on the superior surfaces of each hemispheres, and the medial half of the inferior surfaces of each frontal lobe.

The two anterior cerebral arteries connect anteriorly with the anterior communicating artery.

The vertebral arteries enter the skull from the cervical vertebral column to supply the posterior part of the brain.

  1. They unite to form the BASILAR ARTERY (at the ventral aspect of the pons/medulla junction).


  2. The basilar artery bifurcates to form the two POSTERIOR CEREBRAL ARTERIES, forming the posterior part of the circle of Willis.


    1. They supply the under surface of the temporal lobes, a small strip on its lateral surface, and the occipital lobes.


    2. They connect to the middle cerebral arteries via the posterior communicating arteries.

There are many smaller branches off these that supply other brain structures.

  1. Superior cerebellar, pontine and anterior inferior cerebellar arteries branch from the basilar artery.


  2. The anteromedial and posteromedial communicating arteries branch from the circle of Willis.

SUMMARY:
Blood flows into the Circle of Willis through the internal carotid arteries and the basilar artery.

Blood flows out of the circle of Willis through the middle cerebral arteries and posterior cerebral arteries

Other parts of the brain are supplied through other, smaller branches.

Head Angiogram showing Blood Vessels of the Brain

VENOUS DRAINAGE

The brain drains are mainly the tributaries of the DURAL VENOUS SINUSES, which, in turn, drain into the INTERNAL JUGULAR VEINS.

  1. VENOUS SINUSES are spaces within the dura mater through which blood flows on the way back to the heart.


  2. The SUPERIOR SAGITTAL SINUS is located in the midline along the superior border of the falx cerebri.


  3. The INFERIOR SAGITTAL SINUS lies on the midline along the inferior margin of the falx cerebri.


  4. STRAIGHT SINUS lies in the midline at the junction of the falx cerebri and the tentorium cerebelli, extending from the posterior inferior sagittal sinus to the CONFLUENCE OF THE SINUSES.


  5. LEFT and RIGHT LATERAL SINUSES are oriented laterally along the periphery of the tentorium cerebelli and convey blood from the confluences of the sinuses to the SIGMOID SINUSES, and on to the INTERNAL JUGULAR veins.


  6. The CAVERNOUS SINUSES lie anterior to most of this, along the lateral aspects of the sphenoid b., and receive blood from or communicate with the orbits, face and other structures within the skull.

    7. Veins and Sinuses of the Brain

The sinuses and veins of the skull, thus communicate with one another, providing a pathway for the spread of infections or drugs.

The location of the cavernous sinus also contains several important structures, inc. the cavernous sympathetic n. plexus, cranial nerves III, IV VI., The ophthalmic and maxillary branches of V, and the internal carotid artery

VASCULAR DISEASE of the central nervous system is a major cause of speech (and other) communicative disorders.

Arteriosclerosis is primarily a disease of old age, manifested by headache, vertigo, tinnitus, memory loss, changes in personality and impaired judgement in the early stages, with increasingly severe symptoms as the disease progresses.

Arterial Disease

Atherosclerosis

Hypertensive encephalopathy is frequently encountered in essential hypertension.

Cerebralvascular accidents (CVA's) (apoplexy) are associated with disease of the intracranial vascular tree, or of the blood, itself, or is due to trauma. There are three types.

CEREBRAL THROMBOSIS, caused by occlusion of an artery, possibly by clotting of the blood at a site where sclerotic plaque impedes the flow of blood.

  1. RECURRENT CEREBRAL ISCHEMIA ("Transient Ischemic Attacks" or TIA's) are recurrent episodes of cerebral circulation impairment closely related to atherosclerosis or thrombosis.


  2. PROGRESSIVE CEREBRAL ISCHEMIA, narrowing of the cerebral arteries, particularly of the carotid artery in the neck, is common in 40% of patients over 50.

CEREBRAL HEMORRHAGE, caused by the rupture of a cerebral blood vessel.

  1. Hemorrhage, or bleeding, can occur when a weak area in the wall of an artery ruptures.


  2. Intracranial aneurysm is large dilatation ("bubble") of the cerebral blood vessels. These can rupture. Mortality rate is high.


  3. SUBARACHNOID HEMORRHAGES are primarily due to congenital weaknesses in the vessels of the subarachnoid space.


  4. SUBDURAL HEMORRHAGES are common results of blows to the skull. Blood builds up in the subdural space and can create pressure on the brain. The space-occupying blood must be evacuated by surgery.

CEREBRAL EMBOLISM, brought about when a particle called an embolus, formed by a piece of fat, blood clot, tumor, air, clump of bacteria, etc., flows in the bloodstream to a vascular site narrow enough to trap it and allow it to stop or greatly impede the flow of blood.

To learn more about the causes of stroke, click on the link below for an audio on the causes of stroke and heart attack. Click on the "listen here" link at the top of the page to start the audio.

Causes of Stroke

For more in-depth information, read this online article about stroke and cerebral ischemia:

Stroke and Cerebral Ischemia

Once you have finished you should:

Go on to Assignment 1
or
Go back to Central Nervous System Part II

 
 

E-mail Bill Culbertson at bill.culbertson@nau.edu
Call Bill Culbertson at (520) 523-7440

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