Cranium, meninges and brain part 3

Question 1

Describe the arteria supply to the dura mater

Answer 1

Travels in the outer periosteal layer
anterior meningeal arteries- anterior cranial fossa
middle meningeal arteries- middle cranial fossa
posterior meningeal arteries and other meningeal branches in the posterior cranial fossa

All are small arteries except for the middle meningeal artery, which is much larger and supplies the greatest part of the dura

Question 2

What are the anterior meningeal arteries branches of

Answer 2

Ethmoidal arteries

Question 3

Describe the middle meningeal arteries

Answer 3

Branch of maxillary artery- enters the middle cranial fossa through the foramen spinosum and divides into anterior and posterior branches:

anterior branch- passes in an almost vertical direction to reach the vertex of the skull, crossing the pterion during its course

posterior- passes in posterosuperior direction supplying the region of the middle cranial fossa.

Question 4

Describe the accessory meningeal artery

Answer 4

Usually a small branch of the maxillary artery that enters the middle cranial fossa through the foramen ovale and supplies areas medial to the foramen.

Question 5

Describe the posterior meningeal artery

Answer 5

Branches come from several sources:

posterior meningeal artery- terminal branch of the ascending pharyngeal artery, enters posterior cranial fossa through the jugular foramen

meningeal branch- from ascending pharyngeal artery enters posterior cranial fossa through the hypoglossal canal

meningeal arteries from the occipital artery enter the posterior cranial fossa through the jugular foramen and the mastoid foramen

meningeal branch from the vertebral artery- arises as the vertebral artery enters the posterior cranial fossa through the foramen magnum

Question 6

Summarise the blood supply to the brain

Answer 6

The brain receives its arterial supply from two pairs of vessels:
vertebral and internal carotid arteries, which are interconnected in the cranial cavity to produce a cerebral arterial circle (of Willis)

The two vertebral arteries enter the cranial cavity through the foramen magnum and just inferior pons to form the bailar artery
The two internal carotid arteries enter the cranial cavity through the carotid canals on each side.

Question 7

Summarise the vertebral arteries

Answer 7

Arises from the first part of each subclavian artery in the lower part of the neck, and passes superiorly through the transverse foramina of the upper six cervical vertebrae. On entering the cranial cavity through the foramen magnum each vertebral artery gives off a small meningeal branch
Continuing forward, the vertebral artery gives rise to three additional branches before joining with its accompanying vessel to form the bailar artery.

Question 8

Describe the branches of the vertebral arteries

Answer 8

one branch joins with its companion from the other side to form the single anterior spinal artery- which then descends in the anterior median fissure of the spinal cord

second branch is the posterior spinal artery, which passes posteriorly around the medulla and then descends on the posterior surface of the spinal cord in the area of the attachment of the posterior roots- there are two posterior spinal arteries, one on each side (although the posterior spinal arteries can originate directly from the vertebral arteries, they more commonly branch from the posterior inferior cerebellar arteries).

just before the two vertebral arteries join, each gives off a posterior inferior cerebellar artery.

Question 9

Describe the basliar artery

Answer 9

Travels in a rostral direction along the anterior aspect of the pons. Its branches in a caudal to rostral direction include anterior inferior cerebellar arteries, several small pontine arteries, and the superior cerebellar arteries. The basilar artery ends at a bifurcation- giving rise to two posterior cerebral arteries

Question 10

Describe the internal carotid arteries

Answer 10

The two internal carotid arteries arise as one of the terminal branches of the common carotid arteries. They proceed superiorly to the base of the skull where they enter the carotid canal.
Entering the cranial cavity each internal carotid artery gives off the opthalamic artery, the posterior communicating artery, the middle cerebral artery, and the anterior cerebral artery.

Question 11

Describe the cerebral arterial circle

Answer 11

The cerebral arterial circle (of Willis) is formed at the base of the brain by the interconnecting vertebrobasilar and internal carotid systems of vessels. This anastomotic interconnection is accomplished by:

an anterior communicating artery connecting the left and right anterior cerebral arteries to each other, and
two posterior communicating arteries, one on each side, connecting the internal carotid artery with the posterior cerebral artery

Question 12

Summarise venous drainage

Answer 12

Venous drainage of the brain begins internally as networks of small venous channels lead to large cerebral veins, cerebellar veins, and veins draining the brainstem, which eventually empty into the dural venous sinuses. The dural venous sinuses are endothelial-lined spaces between the outer periosteal and the inner meningeal layers of the dura mater, and eventually lead to the internal jugular veins

Question 13

What else drains into the dural venous sinuses

Answer 13

Diploic veins, which run between the internal and external tables of compact bone in the roof of the cranial cavity, and emissary veins, which pass from outside the cranial cavity to the dural venous sinuses

Question 14

Why are the emissary veins important clinically

Answer 14

Because they can be a conduit through which infections can enter the cranial cavity because they have no valves.

Question 15

Summarise the dural venous sinuses

Answer 15

Include the superior sagittal, inferior sagittal, straight, transverse, sigmoid and occipital sinuses, and the cavernous, sphenoparietal, superior petrosal, inferior petrosal, and basilar sinuses.

Question 16

Describe the superior sagittal sinus

Answer 16

The superior sagittal sinus is in the superior border of the falx cerebri. It begins anteriorly at the foramen cecum, where it may receive a small emissary vein from the nasal cavity, and ends posteriorly in the confluence of sinuses, usually bending to the right to empty into the right transverse sinus. The superior sagittal sinus communicates with lateral extensions (lateral lacunae) of the sinus containing numerous arachnoid granulations
The superior sagittal sinus usually receives cerebral veins from the superior surface of the cerebral hemispheres, diploic and emissary veins and veins from the falx cerebri- and also CSF

Question 17

Describe the inferior sagittal sinus

Answer 17

is in the inferior margin of the falx cerebri. It receives a few cerebral veins and veins from the falx cerebri, and ends posteriorly at the anterior ridge of the tentorium cerebelli, where it is joined by the great cerebral vein and together with the great cerebral vein forms the straight sinus

Question 18

Describe the straight sinus

Answer 18

Continues posteriorly along the junction of the falx cerebri and the tentorium cerebelli and ends in the confluence of sinuses, usually bending to the left to empty into the left transverse sinus
the straight sinus usually receives blood from the inferior sagittal sinus, cerebral veins (from the posterior part of the cerebral hemispheres), the great cerebral vein (draining deep areas of the cerebral hemispheres), superior cerebellar veins, and veins from the falx cerebri.

Question 19

What is meant by the confluence of sinuses

Answer 19

The superior and sagittal sinuses, and the occipital sinus (in the falx cerebelli) empty into the confluence of sinuses, which is a dilated space at the internal occipital protuberance and is drained by the right and left transverse sinus

Question 20

Describe the paired transverse sinuses

Answer 20

The paired transverse sinuses extend in horizontal directions from the confluence of sinuses where the tentorium cerebelli joins the lateral and posterior walls of the cranial cavity.

Question 21

Compare the right and left transverse sinuses

Answer 21

Right- receives blood from the superior sagittal sinus

left- receives blood from the straight sinus

Question 22

Where else do the transverse sinuses also receive blood from

Answer 22

From the superior petrosal sinus, veins from the inferior parts of the cerebral hemispheres and the cerebellum, and diploic and emissary veins.

Question 23

Outline the path of the transverse sinuses

Answer 23

As the transverse sinuses leave the surface of the occipital bone, they become the sigmoid sinuses, which turn inferiorly, grooving the parietal, temporal and occipital bones, before ending at the beginning of the internal jugular veins. The sigmoid sinuses also receive blood from the cerebral, cerebellar, diploic, and emissary veins

Question 24

Where are the cavernous sinuses found

Answer 24

The paired cavernous sinuses are against the lateral aspect of the body of the sphenoid bone on either side of the sella turcica. They are of great clinical importance because of their connections and the structures that pass through them

Question 25

Where do the cavernous sinuses receive blood from

Answer 25

Not only from the cerebral veins but also from the opthalamic veins (from the orbit) and emissary veins ( from the pterygoid plexus of veins in the infratemporal fossa). These connections provide pathways for infections to pass from extracranial sites into intracranial locations. In addition, because structures pass through the cavernous sinuses are located in the walls of these sinuses they are vulnerable to injury due to inflammation

ALSO RECIEVE BLOOD FROM SPHENOPARIETAL SINUSES and emissary vein from pterygoid plexus of veins

Question 26

Which structures pass through the cavernous sinus

Answer 26

internal carotid artery

abducent nerve

Question 27

List the structures in the lateral wall of each cavernous sinus from superior to inferior:

Answer 27

oculomotor nerve
trochlear nerve
opthalamic nerve
maxillary nerve

Question 28

What connects the right and left cavernous sinuses

Answer 28

Intercavernous sinuses on the anterior and posterior sides of the pituitary stalks

Question 29

Describe the sphenoparietal sinuses

Answer 29

Drain into the anterior ends of each cavernous sinus. These small sinuses are along the inferior surface of the lesser wings of the sphenoid and receive blood from the diploic and meningeal veins

Question 30

Describe the superior petrosal sinuses

Answer 30

Drain the cavernous sinuses into the transverse sinus. Begins at the posterior end of the cavernous sinus, passes posterolaterally along the superior margin of the petrous part of each temporal bone, and connects the transverse sinus. The superior petrosal sinuses also receive cerebral and cerebellar veins.

Question 31

Describe the inferior petrosal sinuses

Answer 31

Begin at the posterior part of the cavernous sinuses. These bilateral sinuses pass posteroinferiorly in a groove between the petrous part of the temporal bone and the basal part of the occipital bone, ending in the internal jugular veins. They assist in draining the cavernous sinuses and also receive blood from cerebellar veins and veins from the internal ear and brainstem.

Question 32

Describe the basilar sinuses

Answer 32

Connect the inferior petrosal sinuses to each other and to the vertebral plexus of veins. they are of the clivus, just posterior to the sella turcica of the sphenoid bone.