Blood flow

Question 1

What are the two sources of blood supply to the brain?

Answer 1

Internal carotid artery and vertebral arteries

gives rise to a network of arteries called circle of willis

Question 2

What do the carotid arteries arteries supply?

Answer 2

External Carotid - supplies the face
Internal Carotid - makes its way up into the skull to supply the cerebral hemispheres
The vertebral arteries branch off the subclavian arteries and make their way through transverse foramina in the cervical vertebrae and through the foramen magnum into the brain

Question 3

Explain the circle of willis (easier to label picture)

Answer 3

The two arteries are the bottom are the vertebral arteries
The vertebral arteries join together to form the basilar artery
The basilar artery bifurcates to form the posterior cerebral arteries
The vertebral arteries and basilar artery start moving anteriorly before they bifurcate into posterior cerebral arteries
The internal carotid arteries travel superiorly and then head outwards (laterally) to form the middle cerebral arteries that emerge through the fissure between the frontal, parietal and temporal lobes
The internal carotids also branch to form the anterior cerebral arteries that go up in between the two medial surfaces of the hemispheres and they follow the corpus callosum backwards about 2/3 of the way
This arrangement of arteries is made into a circle by TWO posterior communicating arteries and ONE anterior communicating artery
It is a circle so that if one side gets occluded there is still another route for blood to travel

Question 4

Exlpain the venous drainage of the brain

Answer 4

there is a huge system of large veins that drain the cerebral hemispheres via the jugular system: cerebral veins, venous sinuses, dura mater, internal jugular veins

Question 5

Describe the dura venous sinuses

Answer 5

Running along the top is the superior sagittal sinus, which is housed between the two folds of dura
This is also the point at which the CSF is drained back into the venous system
Running along the bottom of the dural fold is the inferior sagittal sinus
These sinuses run backwards to form a big space filled with blood called the CONFLUENCE OF THE SINUSES (where all the sinuses come together)

Question 6

Define a stroke

Answer 6

Cerebrovascular accident
Definition:
Rapidly developing focal disturbance of brain function of presumed vascular origin lasting more than 24 hours
These are 85% due to infarction and 15% due to haemorrhage

Question 7

Define a Transient Ischaemic Attack

Answer 7

Rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours

Question 8

Define an Infarction

Answer 8

Degenerative changes that occur in tissue following occlusion of an artery
In this case, it is the death of brain tissue following the occlusion of an artery

Question 9

Cerebral ischaemia

Answer 9

Lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not restored quickly
Thrombosis

Formation of a blood clot (thrombus)

Embolism

Plugging of small vessel by material carried from larger vessel e.g. thrombi from the heart or atherosclerotic debris from the internal carotid

The more proximal the occlusion is in the artery, the more devastating the result
Due to hypoxia/anoxia