Session 2 - Blood supply an' shiz of the brain thingy

Question 1

What are the two main arteries of the brain?

Answer 1

Internal carotid and vertebral arteries

Question 2

What is the course of the internal carotid from arch of the aorta

Answer 2

Arch -> Brachiocephalic/common carotid -> Internal Carotid

Question 3

What is the course of the vertebral arteries from arch of aorta?

Answer 3

Arch -> Brachiocephalic/left subclavian ->

Question 4

Where do internal carotid arteries enter the skull?

Answer 4

Carotid canal

Question 5

Give four branches of the internal carotid artery

Answer 5

o Ophthalmic Arteries
o Posterior Communicating Arteries
o Middle Cerebral Arteries
 Lateral surfaces of the cerebral cortex
o Anterior Cerebral Arteries
 Supplies medial surfaces of the frontal and parietal lobes

Question 6

Through what do the vertebral arteries enter the skull?

Answer 6

The foramen magnum

Question 7

What does the vertebral artery become?

Answer 7

Basilar artery -> Posterior cerebral arteries

Question 8

What do the 
Anterior Cerebral Artery
Middle Cerebral Artery
Posterior Cerebral Artery
supply?

Answer 8

Anterior Cerebral Artery Medial surfaces of the frontal and parietal lobes
Middle Cerebral Artery Lateral surfaces of cerebral cortex
Posterior Cerebral Artery Inferior surface of the Brain
Occipital lobes

Question 9

What is the circle of willis made up of?

Answer 9

The Anterior and Posterior Cerebral Arteries are joined together through communicating branches to form the Circle of Willis at the base of the brain.

Question 10

Why is the circle of willis important?

Answer 10

. This anastomosis may provide a collateral circulation should one of the arteries become progressively blocked, but is usually inadequate following sudden occlusion (e.g. cerebral thrombosis, cerebral haemorrhage, cerebral embolism) and vascular stroke is a common result.

Question 11

What are the dural venous sinuses?

Answer 11

The Dural Venous Sinuses are endothelium lined spaces between the periosteal and meningeal layers of the Dura Mater. These sinuses link the venous drainage of the brain into the Internal Jugular Veins.

Question 12

Name 7 dural venous sinuses

Answer 12

o	Superior Sagittal Sinus
o	Inferior Sagittal Sinus
o	Straight Sinus
o	Transverse Sinus
o	Occipital Sinus
o	Cavernous Sinus
o	Sigmoid Sinus
	Continue as the Internal Jugular Veins
	Exit the skull through the jugular foramen

Question 13

Outline the ventricular system of the brain

Answer 13

The ventricular system of the brain consists of four ventricles, connected by the Cerebral Aqueduct:
o	Two Lateral Ventricles 
	1st & 2nd Ventricles
o	Two Midline Ventricles
	3rd & 4th Ventricles

Question 14

Where is the 3rd ventricle situated?

Answer 14

The 3rd ventricle is a slit-like cavity between the right and left halves of the diencephalon, and is continuous posteroinferiorly with the Cerebral Aqueduct.

Question 15

What is the cerebral aqueduct=?

Answer 15

The cerebral aqueduct is a narrow channel in the midbrain connecting the 3rd and 4th ventricles.

Question 16

Where is the 4th situated?

Answer 16

The pyramid-shaped 4th ventricle in the posterior part of the pons and medulla extends inferoposteriorly. Inferiorly it tapers into a narrow channels that continuous into the cervical region of the spinal cord as the central canal.

Question 17

How does CSF get from 4th ventricle to sub-arachnoid space?

Answer 17

CSF drains into the subarachnoid space from the 4th ventricle through a single Median Aperture and Paired Lateral Apertures.

Question 18

What is the significance of the median and paired lateral apetures clinically?

Answer 18

These apertures are the only means by which CSF enters the subarachnoid space. If they are blocked, CSF accumulates and the ventricles distend, producing compression of the substance of the cerebral hemispheres.

Question 19

At what rate is CSF secreted, and where is it secreted from?

Answer 19

400-500ml/day by Choroid Epithelial Cells of the Choroid Plexuses, found in the floors of the bodies and inferior horns of the 1st and 2nd Ventricles and in the roofs of the 3rd and 4th ventricles.

Question 20

What does the choroid plexus consist of?

Answer 20

The choroid plexuses consist of vascular fringes of Pia Mater covered by Cuboidal Epithelial Cells.

Question 21

Outline the circulation of CSF

Answer 21

CSF leaves the lateral vertricles through the Interventricular foramina and enters the 3rd ventricle. From there CSF passes through the cerebral aqueduct into the 4th ventricle.

CSF leaves the 4th ventricle via the median and lateral apparatus and enters the Subarachnoid space, which is continuous around the spinal cord and posterosuperiorly over the cerebellum.
CSF also passes into the extensions of the subarachnoid space around the Spinal Cord and Cranial Nerves, the most important of which are those surrounding the optic nerves (papilloedema).

Question 22

How is CSF absorbed?

Answer 22

CSF is absorbed into the venous system through the Arachnoid Granulations, especially those that protrude into the superior sagittal sinus.

The subarachnoid space, containing CSF, extends into the cores of the arachnoid granulations.
CSF enters the venous system both by transport through and around the cells of the arachnoid granulations into the dural venous sinus.

Question 23

What are the three main functions of CSF?

Answer 23

o Protects the brain by providing a cushion against blows to the head
 Along with the skull and meninges
o Provides buoyancy that prevents the weight of the brain from compression cranial nerve roots and blood vessels against the internal surface of the cranium.
o Provides Chemical Stability, rinsing the metabolic waste from the CNS through the blood brain barrier, e.g. maintaining low K+ concentration for synaptic transmission