A09 Blood Supply of The Brain

Question 1

What proportion of the weight of the body is represented by the brain?

At rest:

What proportion of the body’s cardiac output is received by the brain?

What proportion of the body’s supply of oxygen is received by the brain?

Answer 1

• The brain represents 2% of the body’s weight.
• The brain receives 20% of the body’s cardiac output.
• The brain receives 21% of the body’s supply of oxygen.

Question 2

What is the primary cause of disorders of the nervous system?

Answer 2

Hypoxic injury due to vascular insufficiency.

Question 3

Through which space do the arteries supplying the nervous system travel?

What surrounds the arteries in this space?

Answer 3

• The arteries travel in the subarachnoid space.

- They are surrounded by CSF.

Question 4

How do the arteries supplying the nervous system differ histologically from arteries found elsewhere in the body?

Answer 4

• Arteries supplying the nervous system have thinner walls.
• Arteries supplying the nervous system have no external elastic laminae.
• Arteries supplying the nervous system are surrounded by astrocytic processes.

Question 5

How do capillaries in the nervous system differ from capillaries found elsewhere in the body?

Answer 5

They are similar to capillaries in other regions of the body, but they are surrounded by astrocytic processes forming the blood-brain barrier.

Question 6

Which arteries supply the spinal cord?

Answer 6

Longitudinally-oriented spinal arteries:

• 1 anterior spinal artery.
• 2 posterior spinal arteries.

Question 7

List the sources of the spinal arteries.

Answer 7

1 - Vertebral arteries.

2 - Spinal branches of the abdominal aorta.

Question 8

List the arteries that supply structures in the neurocranium.

Answer 8

1 - The paired internal carotid arteries.

2 - Vertebral arteries.

Question 9

What is the source of the vertebral arteries?

Answer 9

The subclavian arteries.

Question 10

Describe the course of the two vertebral arteries as they ascend the neck.

Answer 10

1 - They initially ascend the neck in the transverse foramen of C6 - C1.

2 - They then wrap around the superior articulating facet of C1.

3 - They then pass medially and pierce the dura and arachnoid at the foramen magnum.

4 - They then enter the subarachnoid space in the cranial cavity.

5 - They unite at the pontomedullary border to form the basilar artery.

6 - The basilar artery bifurcates to form the two posterior cerebral arteries.

Question 11

List the areas of the CNS supplied by the vertebral arteries.

Answer 11

• All but the most rostral parts of the hindbrain.

- The occipital lobe.

Question 12

Describe the course of the internal carotid artery across the skull.

Answer 12

1 - It enters the skull at the carotid canal.

2 - It the passes through the petrous part of the temporal bone.

3 - It then enters the cavernous sinus.

4 - It then enters the cranial cavity proper at the anterior clinoid process of the sphenoid bone.

5 - It then bifurcates to form the middle and anterior cerebral arteries.

6 - The anterior communicating arteries connect the left and right anterior cerebral arteries.

Question 13

List 4 structures supplied by branches of the internal carotid artery as it passes through the petrous part of the temporal bone and the cavernous sinus.

Answer 13

1 - The middle ear.

2 - The dura of the cavernous sinus.

3 - The pituitary gland.

4 - The trigeminal ganglion.

Question 14

Where, and from which artery, does the opthalmic artery arise?

Answer 14

The ophthalmic artery arises from the internal carotid artery medial to the anterior clinoid process of the sphenoid bone.

Question 15

Which arteries connect the anterior and posterior cerebral arteries?

Answer 15

The posterior communicating arteries.

Question 16

Which structures drain the intracranial structures?

Where are these structures located?

Answer 16

• The intracranial venous sinuses.

- They lie between the outer and inner layers of dura mater.

Question 17

What is the relevance of the astrocytic processes to the transport of substances to / from the blood and nervous tissue?

Answer 17

• Astrocytes relay chemical messages to endothelial cells that cause them to form tight junctions.
• There is therefore a degree of neural control of the permeability of the blood-brain barrier.

Question 18

Describe the course of the middle meningeal artery.

List the structures it supplies.

Answer 18

• It originates from the maxillary artery at the neck of the mandible.
• It passes through the foramen spinosum of the sphenoid bone to enter the cranial cavity.
• WIthin the cranial cavity, the middle meningeal artery travels within the periosteal layer of dura mater.
• It then passes superiorly between the sphenomandibular ligament medially and the lateral pterygoid muscle laterally to pass up the walls of the cranial cavity.
• It supplies much of the dura mater, bone and bone marrow of the cranial cavity.