Blood Supply and Ventricles

Question 1

What are the 2 main supplies of blood to the brain?

Answer 1

Blood reaches the brain through posterior (vertebral arteries and the basilar artery) and anterior (internal carotid artery) pathways.
* One of the main sets of arteries supplying blood to the more anterior parts of the brain (cerebral cortex, thalamus, basal ganglia).
* Other source of blood is supplying to the caudal parts of the brain.

rostral part of brain = internal carotid artery
caudal part of brain = vertebral arteries

Question 2

Anatomy of blood vessels in the brain

Answer 2

Question 3

How is the blood circulating in the brain?

Answer 3

Anterior circulation of blood
* blood comes into the anterior part of the brain through 2 large arteries called the internal carotid arteries. These are connected to arteries that supply blood to the cerebral cortex and to other anterior structures. The blood coming into the internal carotid arteries flows anteriorly through the anterior cerebral artery.
* The anterior cerebral artery is going to go anteriorly and go in between the two cerebral hemispheres. It is going to course up on either side along the medial parts of the two hemisperes. Supplies blood to the medial part of both hemisperes of cortex.
* The middle cerebral artery is supplying blood to the insula and the lateral surface of cortex. If person has a stroke and has global aphasia where they are paralyzed on right side of body and cannot speak at all is typically caused by an oclusion of the MCA. Large artery that supplies lots of blood to many areas of brain.
* Circle of Willis: circle of connections, found on the ventral surface of the brain (surrounds the optic chiasm).

Posterior ciculation of blood:
* The vertebral arteries are the arteries flowing in along the ventral surface of the medulla. They meet right at the midline along the pons and flow right along the ventral surface of the pons as a single enourmous artery called Basilar artery.
* The posterior cerebral artery are supplying blood to the most posterior parts of the cerebral cortex (ie: occipital lobe). Occlusion/ blockage to these can cause damage to primary visual cortex.
* The internal carotid connected to the anterior cerebral artery and middle cerebral artery.
* Blood flowing up the vertebral arteries is supplying blood to the posterior cerebral artery which is supplying blood to the rest of the cerebral cortex.

Three other prominent arteries that emerge from the posterior parts of the blood supply:
* Posterior inferior cerebellar artery is supplying blood to posterior part of cerrebellum.
* Anterior inferior cerebellar artery is supplying blood to anterior part of cerebellum.

Question 4

Identify these areas

Answer 4

Question 5

Regions of Cortex Supplied by the Anterior, Middle and Posterior Cerebral Arteries.

Answer 5

• Occlusion or blockage to MCA would cause damage to large regions of primary motor cortex, primary somatic sensory cortex, wernicke’s and Broca;s area
  - occlusion of MCA on left side of brain would be aphasic (not able to speak) and paralyzed on right side of body.

Question 6

Ventricles and what is inside the ventricles

Answer 6

• The ventricles are filled with cerebrospinal fluid (CSF). CSF is a filtrate of the blood (the aqueous substance of the blood).
• There is tissue in the ventricles that extracts this CSF from blood and then secretes it.
• The brain floats in cerebrospinal fluid (CSF) and is encased by meninges.
• Human brain flattens and loses its shape if you rest it on a table. The human brain does not have enough internal structure to maintain its shape.
• This does not happen inside your skull because in your skull, your brain is floating in cerebral spinal fluid. CSF inside ventricles and outside of brain.
• The brain is covered by a kind of skin which has multiple layers called meninges.

Question 7

Meninges

Answer 7

The brain is surrounded by three meningial layers: 1) The dura is a tough collagenous membrane, firmly attached to the inner surface of the skull. The dura is not attached to the brain, it is attached to the skull and follows the inside of the skull. It is very tough (1/2mm thick), like leather (non-cellular layer).
2) The pia is a thin cell layer that follows the contours of the brain. The innermost layer, very thin layer of cells that follow all the contours of the brain. Follows the surface of the brain into the sulcus and out of the sulcus. Whole outer surface of the brain is covered with this thin layer of cells (pia - stuck right to the surface of the brain).
3) The arachnoid consists of a thin layer of cells attached to the dura. Thin cell layer attached to the dura so it is also following the contour of the skull.

There is a bit of space between the pia matter and the arachnoid + dura which is called the subarachoid space.
* In some regions this space is very narrow and in other places it is quite thick. This space is very narrow near the cerebral cortex but much wider when you get to the more caudal parts of the brain (ie; cerebellum).
* In the subarachnoid space, strands of collagen connective tissue called trabeculae extend into pia forming a scaffolding that holds the brain in place. This subarachnoid space contains cerebrospinal fluid as well as arteries that supply blood to the brain.
* Brain is floating in the CSF that is in the subarachnoid space.
* All the arteries are also in this subarachnoid space.

• The dura is comprised of an external periosteal leaflet and an internal meningeal leaflet. In most regions of the brain the two leaflets are fused; however, at the longitudinal fissure they separate. The meningeal leaflets dive into the longitudinal fissure to form the falx cerebri. The separation of the two leaflets forms a triangular tube, called the superior sagittal sinus, which runs along the dorsal midline.
• The superior sagittal sinus is a major pathway for blood to flow out of the brain.
• The superior sagittal sinus is the main outflow for blood (just a tube that runs right along the midline). All the blood that is flowing in from all these arteries has to flow out, and the main way it flows out is through this sinus and from here it flows out.
• CSF is also flowing in the superior sagittal sinus through these little openings called arachnoid villus

Question 8

How does Venous blood flow?

Answer 8

Venous blood flows caudally in the superior sagittal sinus, which converges with the straight sinus (draining blood from deep brain structures) at the confluence of the sinuses at the back of the brain and ultimately leaves the skull through the internal jugular vein.

Question 9

CSF

Answer 9

• The brain contains a network of fluid-filled spaces called ventricles.
• The subarachnoid space is filled with CSF and it gets there by flowing into the subarachnoid space from the ventricles
• Cerebrospinal fluid (CSF) is produced in the ventricles by specialized tissue called choroid plexus and flows through the ventricular system. Chlorois plexus is filtering the blood, it is extracting the bloodfluid (CSF) and secreting it inside the ventricles.

Entire network of ventricles: 4 ventricles:
* the two lateral ventricles
* the 3rd ventricle: very narrow space between the two thalamus
* the 4th ventricle: space between the cerebellum and the brainstem.
The ventricles form a system inside the brain, they are all connected together so the CSF can flow from one ventricle to another.

Question 10

The ventricles in the brain.

Answer 10

• The lateral ventricles comprise anterior (frontal), posterior (occipital) and inferior (ventral) horns. The lateral ventricle extends throughout all the lobes of the brain.
• Lateral ventricle is connected to the 3rd ventricle through the foramen of Monro (interventricular foramen).
• The 3rd ventricle lies between the thalami. It is connected to the 4th ventricle by the aquaduct of Sylvius (the cerebral aquaduct).
• The 4th ventricle is formed by the space between the cerebellum and the brainstem. CSF flows out of the 4th ventricle through lateral and caudal openings called, respectively the foramen of
  Lushka and the foramen of Magendie (flowing out of brain through foramen of Magendie and from there is flows around the brain and into the superior sagittal sinus).

Question 11

Anterior cross section of brain

Answer 11

Only see lateral ventricles

Question 12

Answer 12

Lateral ventricles and 3rd ventricle

Question 13

Answer 13

Can see thalamus and 4th ventricle

Question 14

Answer 14

little bit of lateral ventricle left.

Question 15

Mid saggital section of ventricles

Answer 15

Question 16

Cisterns

Answer 16

• The CSF that flows out of the 4th ventricle fills the subarachnoid space surrounding the brain.
• CSF accumulates in cisterns at various sites surrounding the brain.
• The cistern are enlargements in the space between the dura/arachnoid (which adheres to the skull) and the pia (which follows the contours of the brain). These are repositories for CSF.
• From the cisterns, CSF is flowing around the brain and then into the superior saggital sinus.

Question 17

Arachnoid Villi

Answer 17

• CSF flows into the superior sagittal sinus though valve-like structures called arachnoid villi.
• These villi cluster to form macroscopically visible structures called arachnoid granulations.
• If you take the dura off and you are left with just the arachnoid and pia (stuck together by all the trabechuli). You cannot really see the brain.
• Running right along the midline is the SSS, which is running through the Dura. And there are all these little holes where the subarachnoid space is connected to the SSS. Those holes/one-way valves are called villi and this is how the CSF is flowing from subarachnoid space to SSS.
• All the villi together form a macrascopic structure called arachnoid granulations.