M20: Brain 2 - Blood Supply, Meninges, Ventricles, and CSF

Question 1

internal carotid arteries

Answer 1

right and left internal carotid arteries branch from the common carotid artery on each
side and enter the cranium through the carotid canal in the temporal bone

Question 2

vertebral arteries

Answer 2

branch off of the subclavian arteries on each side, and they are protected as they
pass through the neck region by the transverse foramina of the cervical vertebrae

enter the cranium through the foramen magnum of the occipital bone

Question 3

Anterior cerebral artery

Answer 3

supplies blood to the anterior, medial, and very superior portions of the frontal lobe

Question 4

Middle cerebral artery

Answer 4

supplies blood to the posterior frontal lobe and most of the temporal and parietal lobes

Question 5

Posterior cerebral artery

Answer 5

supply blood to the occipital lobe and inferior aspect of the posterior temporal lobe

Question 6

What are the two primary routes for blood to reach the brain?

Answer 6

Vertebral arteries
Internal carotid arteries

Question 7

Cranial meninges structure and function

Answer 7

-Meninges are anchored to the skull, and the brain is suspended within the meninges

-The meninges extend around the spinal cord and are continuous throughout the CNS

-Three connective tissue layers surrounding the brain:
—-> Dura Mater: thick, outer covering
—–> Arachnoid Mater: thin, middle layer
—–> Pia Mater: very thin inner layer directly attached to the surface of the brain and spinal cord

-Functions:
—> Cover and protect the brain
—–> Protect against foreign substances, trauma, etc.
—–> Separate the soft tissue of the brain from the bones of the cranium

—> Enclose and protect blood vessels
——> Support vessels supplying the brain
——-> Form some of the veins (venous sinuses) draining blood from the brain

—> Stabilize the brain within the skull
—> Contain the CSF

Question 8

Dura mater

Answer 8

• Outer layer of the meninges
• Thickest layer of the meninges
  -Encloses the entire CNS and the major blood vessels that enter the cranium and vertebral cavity
  -2 fibrous layers
  —-> Periosteal layer: fused to the periosteum on the inner aspect of the skull
  ——> Meningeal layer: Next to the arachnoid mater
  —> Blood vessels located between the two layers in some locations

Contains dural venous sinuses and cranial dural reflections

Question 9

Dural venous sinuses

Answer 9

-Space between the periosteal & meningeal dura forms these large collecting veins
- Veins of the brain empty into these sinuses
- After supplying the brain with oxygen and nutrients, venules and veins merge and
eventually, send blood back toward the heart through a series of dural venous sinuses
and veins

Inferior sagittal sinus → straight sinus → superior sagittal sinus (absorbs CSF from the
meninges)→ confluence of sinuses → transverse sinuses → sigmoid sinuses → jugular veins → blood continues toward the heart to be pumped to the lungs for reoxygenation.

Question 10

Cranial Dural Reflections (Septa) structure and function

Answer 10

-infoldings of the dura that fit into large crevasses of the brain
—> Two infoldings go through the midline separations of the cerebrum and cerebellum

-Where the meningeal layer of dura extends deep into the cranial cavity between sections of
the brain

Contains falx cerebri, falx cerebelli, and tentorium cerebelli

Functions:
-Subdivide cranial cavity
-Support the brain
-Limit movement of the brain

Question 11

Falx cerebri

Answer 11

-located within the median longitudinal fissure between the cerebral hemispheres in the dura mater
- Contains inferior sagittal sinus and superior sagittal sinus

Question 12

Falx cerebelli

Answer 12

between the right and left cerebellar hemispheres in the dura mater

Question 13

Tentorium cerebelli

Answer 13

forms a shelf-like structure between the occipital lobes of the cerebrum and the cerebellum in the dura mater

Question 14

Arachnoid Mater

Answer 14

-Deep to the dura mater,middle layer of meninges
-Thin, avascular, semitransparent membrane visibly covering the brain

contains arachnoid trabeculae and arachnoid granulations

Question 15

Arachnoid Trabeculae

Answer 15

-Beneath the arachnoid is a thin, filamentous mesh which looks like a spider web, giving this layer its name
-Found in the subarachnoid space which is filled with circulating CSF

Question 16

Arachnoid granulations

Answer 16

-Send CSF from the subarachnoid space into the blood within the superior sagittal sinus
- CSF is filtered and drained back into the blood stream

Question 17

Pia mater

Answer 17

-Thin, delicate CT tightly attached to the brain
- Extends into every convolution of the CNS, lining the inside of the sulci in the cerebral and cerebellar cortices
—> Follows all contours of the gyri and sulci
-Supports large cerebral blood vessels

Question 18

Subarachnoid Space

Answer 18

-Between the arachnoid and pia mater
Arachnoid trabeculae
-Web like threads extending across the subarachnoid space from arachnoid mater to pia mater (Arachnoid trabeculae)
-Contains cerebrospinal fluid
-Blood vessels

Question 19

What is the Cerebrospinal Fluid (CSF)? How is it produced?

Answer 19

-Colorless fluid that circulates in the ventricles and subarachnoid space

-Produced by choroid plexus found within all of the ventricles of the brain (CSF is produced in
the ventricles by the filtering of blood in a specialized structure called the choroid plexus)
—-> Specialized ependymal cells and highly-permeable capillaries (Ependymal cells (a glial cell) surround blood capillaries in the choroid plexus and filter the blood to make CSF)

-Choroid plexus also removes waste from CSF and alters its composition as-needed
-CSF is constantly being produced

Question 20

CSF moves through and around the brain due to:

Answer 20

-Movement of cilia on the ependymal cells
-Movements of the vertebral column moving it around the spinal cord
-Pressure from the constant production forcing it out through the arachnoid granulations

Question 21

CSF Function

Answer 21

1. Buoyancy: Brain floats within CSF
2. Protection: Brain floats in the CSF and does not sit against the skull, provides cushioning
   for the brain
3. Environmental stability: Maintains the environment surrounding the brain
4. Transports hormones, nutrients, chemicals, wastes

Question 22

Circulation of CSF

Answer 22

1. Lateral ventricles → interventricular foramen of Monro → 3rd ventricle
2. 3rd Ventricle → cerebral aqueduct → 4th ventricle
3. 4th ventricle → one of these routes into the subarachnoid space:
   —-> Paired lateral apertures
   —-> Midline median aperture
   —-> Central canal of spinal cord
4. CSF enters the subarachnoid space
5. CSF flows into arachnoid granulations , which transport it into dural venous sinuses

Question 23

Brain Ventricles

Answer 23

-Two lateral ventricles
—> One in each hemisphere
—> Separated by the midline septum pellucidum
—> Has an anterior horn, body, posterior horn, and inferior horn that extends into the temporal lobes

-3rd ventricle
—>Midline, between the right thalamus and left thalamus
—>Interthalamicadhesion connecting right and left thalami forms the “hole” in the 3rd ventricle

-4th ventricle
—>Between the pons and cerebellum, extending into the superior portion of the medulla oblongata

-Interventricular Foramen (of Monro)
—>Two of these, each connecting one lateral ventricle to the 3rd ventricle

-Cerebral aqueduct
—>Connects the 3rd ventricle to the 4th ventricle

-CSF can leave the 4th ventricle through:
—>Lateral aperture on either side of the 4th ventricle
—>Median aperture at the midline, posterior aspect of the 4th ventricle
—>The central canal of the spinal cord

Question 24

Blood-Brain Barrier (BBB) function

Answer 24

Function:
- Tightly regulates what can leave the blood vessels and enter the space surrounding the brain tissue

Question 25

Regions with Blood-Brain Barrier (BBB) variation

Answer 25

-Increased permeability in parts of the hypothalamus allowing hormone diffusion

-Pituitary gland capillaries allow hormone diffusion

-High permeability in the pineal gland capillaries (sleep-wake cycle)

-Choroid plexus capillaries for the production of CSF

Question 26

Formation of the Blood-Brain Barrier (BBB)

Answer 26

-Continuous capillaries

-Extensive tight junctions prevent materials from diffusing between epithelial cells

-Astrocyte perivascular feet surround the capillaries

-Astrocytes restrict permeability of the capillary endothelial cells

Question 27

Subdural Hematoma

Answer 27

-Rapid acceleration or deceleration of head
-Tearing of a cerebral vein as it pierces the arachnoid mater to enter a dural sinus
-Some progress more quickly, other slower

Question 28

Epidural Hematoma

Answer 28

-Can occur with a skull fracture or other trauma that damages the meningeal artery
-Often fatal unless treated quickly