Meninges and Blood Supply to the Brain

Question 1

Name the layers of the Meninges from deep to superfical

Answer 1

Pia mater
Arachnoid mater
Dura mater

Question 2

Describe the Pia mater

Answer 2

• a simple squamous epithelium Iying on the surface of the brain. The
  pia mater follows all of the gyri and sulci of the brain.

Question 3

Arachnoid mater
C. Dura mater - a tough, fibrous outermost layer of the meninges. It is not
connected to the arachnoid mater beneath it, but is normally in close apposition to it.
However, when bleeding occurs and blood accumulates beneath the dura mater, the
blood is said to occupy the “subdural space.” When bleeding occurs and blood
accumulates external to the dura mater (i.e., between the dura mater and
periosteum of the skull), the blood is said to occupy the ‘‘epidural space.”

Answer 3

• a filmy, opaque layer that follows all of the gyri and sulci of the brain.
  -Outer portion of the arachnoid mater is called the “membranous portion” and forms a sheet next to (but not attached to) the dura mater.
  -Inner portion of the arachnoid is called the “trabecular portion” and forms bridges to the
  pia mater. These trabecula serve to suspend the brain within the cranial vault.

Question 4

Describe the subarachnoid space:

Answer 4

between the membranous portion of the arachnoid and the pia mater

• normally filled with cerebrospinal fluid.
• contains superficial veins leading eventually to the dural sinuses. In the vicinity of the dural sinuses (especially the superior sagittal sinus), projections of arachnoid mater penetrate through the dura mater. These projections are called arachnoid granulations or villi, and serve as valves allowing the passage of cerebrospinal fluid back into the venous system.

Question 5

Subdural space

Answer 5

– btwn dura and arachnoid

Question 6

Epidural space

Answer 6

– btwn dura and periosteum

Question 7

Name the trigeminal nerve branches that innercate the dura mater of the anterior cranial fossa, middle cranial fossa and posterior cranial fossa.

Answer 7

Dura of lateral anterior cranial fossa innervated by the meningeal branch of the maxillary and mandibular nerve
Dura of medial anterior cranial fossa innervated by anterior and posterior branches of ophthalmic nerve
Dura of the middle cranial fossa innervated by the meningeal branch of the maxillary and mandibular nerves as well as tentorial n.
Dura of posterior cranial fossa innervated by the tentorial n. plus second and third cranial nerves hitchhiking.

Question 8

Describe the 4 projections of dura mater:

Answer 8

Falx cerebri
Falx cerebelli
Tentorium cerebelli
Diaphragma sella

Question 9

Falx cerebri – separates:

Answer 9

the R and L hemispheres of the cerebrum

is a sickle-shaped double layer of dura mater Iying in the median plane just superior to the corpus callosum of the brain. It is attached anteriorly to the crista galli, superiorly to the superior sagittal sinus and inferiorly to the tentorium cerebelli. Its superior surface splits to contain the superior sagittal sinus; its inferior surface splits to contain the inferior sagittal sinus

Question 10

Falx cerebell separtates the

Answer 10

R and L halves of the cerebellum

is a smaller sickle-shaped projection Iying in the median plane between the two cerebellar hemispheres. It is attached to the posterior and inferior parts of the tentorium cerebelli. Its posterior border splits to form the occipital sinus (analogous to the superior sagittal sinus of the falx cerebri).

Question 11

Tentorium cerebelli

Answer 11

supports occipital, contains transverse sinus at posteriolateral borders, anteriorly forms superior petrosal sinus

is a crescent-shaped fold of dura mater that
supports the occipital lobes of the cerebral hemispheres.

Posterior and lateral borders of the tentorium cerebelli split to contain the transverse sinus;

Anterior border of the tentorium (where is attaches to the ridge of petrous temporal bone) splits to contain the superior petrosal sinus.

Internal border of the tentorium cerebelli is free and attaches to the posterior clinoid processes. This free border (the “incisure of the tentorium cerebelli”) is clinically significant in cases of cerebral edema or other “mass lesions.” Under these circumstances the swollen brain presses against the oculomotor nerve as it passes along the incisure producing the symptoms of oculomotor nerve palsy.

Question 12

Diaphragma sella is the

Answer 12

– roof above hypophyseal fossa, covers pituitary gland

is a circular, horizontal fold of dura that forms a roof
above the hypophyseal fossa of the sella turcica, covering the pituitary gland. It contains a central aperture, through which the hypophysial stalk
passes.

Question 13

Superior Sagittal Sinus

Answer 13

lies in the midline along the convex border of the
falx cerebri.

Recieves Venous blood from the cerebral, diploic,
meningeal, and parietal emissary veins.

Question 14

Inferior Sagittal Sinus

Answer 14

lies in the free edge of the falx cerebri.

It is joined by the great cerebral vein (the great vein of Galen) to form the straight sinus.

Question 15

Straight Sinus

Answer 15

runs along the line of attachment of the falx cerebri to the tentorium cerebelli.

Question 16

Transverse Sinus

Answer 16

runs laterally from the confluence along the edge of

the tentorium cerebelli.

Question 17

Sigmoid Sinus

Answer 17

is a continuation of the transverse sinus and arches
downward and medially in an S-shaped groove on the mastoid part of the temporal bone. They enter the superior bulb of the internal jugular vein.

Question 18

Cavernous Sinuses

Answer 18

Located on each side of the sella turcica and the
body of the sphenoid bone.

• internal carotid artery and the abducens nerve pass through these sinuses,
• oculomotor, trochlear and maxillary nerves pass through the lateral wall of these sinuses.

-communicate with the superior ophthalmic vein, as
well as the pterygoid plexus of veins via emissary veins.

Question 19

Superior Petrosal Sinus

Answer 19

lies in the margin of the tentorium cerebelli.

Runs from the posterior end of the cavernous sinus to the transverse sinus.

Question 20

Inferior Petrosal Sinus

Answer 20

Drains the cavernous sinus into the bulb of the
internal jugular vein.

Runs in a groove between the petrous part of the
temporal bone and the basilar part of the occipital bone.

Question 21

Occipital Sinus

Answer 21

lies in the falx cerebelli.

Drains into the confluence of sinuses.

Question 22

Describe the route of the posterior ciculation of the brain:

Answer 22

(i.e., branches of the vertebral A.).

Vertebral arteries are branches of the aorta and subclavian arteries -> ascend through the transverse foramina of the upper six cervical vertebrae, and then curve posteriorly behind the lateral mass of the atlas to pierce the dura mater,
entering the posterior cranial fossa through the foramen magnum -> connect with the anterior and posterior spinal arteries and actually provide
most of the blood for the cervical spinal cord.

Right and left vertebral arteries fuse to form the basilar artery at the junction of the medulla and pons, and then split to form the right and left posterior cerebral arteries at the junction of the pons and midbrain.

Question 23

What does the posterior circulation of the brain subserve?

Answer 23

brain stem, cerebellum, and portions of the cerebrum – namely, the posterior-medial cerebrum and inferior cerebrum.

Question 24

Describe the Anterior circulation of the brain:

Answer 24

Internal carotid enters the carotid canal within the petrous portion of the temporal bone near the middle ear. -> cavernous sinus and gives rise to the inferior hypophyseal artery and small arterioles subserving the trigeminal ganglion. Then pierces the dural roof of the cavernous sinus, giving rise along the way to the superior hypophyseal, ophthalmic, and anterior choroidal arteries, as well as to three of the arteries associated with the Arterial Circle of Willis - the anterior cerebral, the middle cerebral, and the posterior communicating arteries. It is this
last artery which interconnects the anterior and posterior circulations.

Question 25

What does the anterior circulation of the brain subserve?

Answer 25

rest of the cerebral - namely, the lateral cerebrum and anterior-medial portions of the cerebrum.

Question 26

Describe the Arterial Circle of Willis and it’s function:

Answer 26

Consists of anterior cerebral, middle cerebral,
posterior communicating, anterior communicating (connects the anterior cerebral artery), and posterior cerebral arteries (connects the middle and posterior cerebral artery), as well as to a small portion of the internal carotid artery. In some individuals, the size of the posterior communicating artery is very small. In these individuals, it is
believed that the function of the Arterial Circle of Willis is to balance pressure differences between the anterior and posterior circulations, as well as between the right and left sides of the cerebrum.