Flashcards in Blood supply to the CNS Deck (39):
What percentages of the CO, 02 consumption and liver glucose does the brain take up?
02 consumption: 20%
Liver glucose: 2/3rds
What is the major blood supply to the brain?
Internal carotid artery supplies anterior part
Vertebral artery supplies posterior part
Describe the route of the vertebral arteries?
Branch of the subclavian artery
Ascends through the transverse foramina of the vertebrae
Enters the cranial cavity via the foramen magnum
Describe the circulation of blood for the posterior half of the brain
The two vertebral arteries join to form the basilar artery.
This then bifurcates into two posterior cerebral arteries
What is the benefit of the anastomotic circuit (circle of willis)?
Allows for compensation in case of artery occlusion preventing impairment of blood supply.
Describe the circulation of blood for the anterior half of the brain
The internal carotid artery splits laterally into the middle cerebral artery.
It also continues anteriorly as the anterior cerebral arteries travel in the medial longitudinal fissure of the brain and follow the corpus callosum backwards by 2/3rds (parieto-occipital sulcus).
It forms a circuit by the two posterior communicating arteries and one anterior comminicating artery.
Where do the middle cerebral arteries run?
Sylvian fissure (lateral sulcus)
At what level does the common carotid bifurcate?
C4; at the level of the thyroid cartilage/laryngeal prominence
When the common carotid bifurcates describe what happens next...
The external carotid goes on to supply the face, it branches outside the cranial cavity.
The internal carotid enters the skull via the carotid canal and supplies the anterior part of the brain.
What are the branches that the vertebral artery gives off before it turns into the basilar artery?
The anterior spinal artery -> supplies the spinal cord
The posterior inferior cerebellar artery (PICA)
Where is the basilar artery located?
On the anterior surface of the pons
What are the branches of the basilar artery?
Anterior inferior cerebellar artery
What is the order of venous drainage in the brain?
Internal jugular vein
What are dural venous sinuses?
Endothelial lined spaces between the periosteal and meningeal layer of dura mater.
How can infection enter the cranial cavity?
Through emissary veins which pass from outside the cranial cavity to the dural venous sinuses, they have no valves.
Describe the appearance of the dural venous sinuses?
The superior sagittal sinus runs along the superior border of the falx cerebri. This is how CSF is drained back into the ventricular system.
The inferior sagittal sinus runs along the inferior surface of the dural fold.
The confluence of sinuses is where the superior sagittal, straight and occipital sinuses join.
What lies in the carotid sheath?
The internal jugular vein, carotid and vagus nerve.
What is a stroke and what are they caused by?
Rapidly developing focal disturbance of brain function of presumed vascular origin, 24+ hours duration.
85% due to infarction, 15% haemorrhagic
What is a transient ischaemic attack?
Rapidly developing focal disturbance of brain function of presumed vascular origin that resolves within 24hrs.
What is a cerebral infarction?
Degenerative changes in a tissue following occlusion of an artery.
What is cerebral ischaemia?
Lack of sufficient blood supply to nervous tissue which can result in permanent damage if blood flow is not quickly restored (note that hypoxia/anoxia is a component of ischaemia)
What is a cerebral thrombus?
Formation of a blood clot
What is a cerebral 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]
What are risk factors for stroke, why this increases the risk and predominant it is in causing death?
3rd most common cause of death
Hypertension; congenital vessel weaknesses may lead to vessel rupture
Cardiac disease; turbulent flow may cause clots
Smoking; increase atherosclerosis
Diabetes mellitus; vascular efffects
Which areas of the brain does the middle cerebral artery supply?
Travels through the lateral fissure of the brain. It supplies the majority of the lateral parts of the brain and the anterior half of the temporal lobe.
Which areas of the brain does the anterior cerebral artery supply?
Supplies the medial surface of the brain as well as a strip of the anterosuperior part of the brain.
Travels from the frontal lobe to the parieto-occipital lobe.
Which areas of the brain does the posterior cerebral artery supply?
Supplies the occipital lobe and the lateral parts of the temporal lobe.
What will be the presentation of damage to the anterior cerebral artery?
Paralysis of contralateral leg
Disturbance of intellect and executive judgement
Loss of appropriate social behaviours due to disinhibition from damage to the frontal lobe e.g. aggressive behaviour
What will be the presentation of damage to the middle cerebral artery?
Contralateral hemiplegia (mostly arms), if damaged at the subcortical level, complete hemiparesis will occur as the projecting fibres below will have been affected
Hemisensory deficits (affects post central gyrus)
Aphasia (from lesion on the left side as this is where the language centres are located).
What will be the presentation of damage to the posterior cerebral artery?
What is Broca's and Wernicke's area?
Broca's: involved in speech
Wernicke's: involved in understanding language
What is a lacunar infarct?
Strokes can cause small holes/cavities to appear in the brain tissue called lacunae due to these parts of brain tissue dying.
Appear in deep structures (e.g. subcortical structures) due to small vessel occlusion.
May not be symptomatic depending on anatomical location.
Hypertension is another possible cause of lacunae.
What is arachnoid granulation?
Small burst of subarachnoid space that protrude into the superior sagittal sinus.
What is dysarthria?
Motor speech disorder; involved motor components that make up speech
Describe an extra/epidural haemorrhage
-Due to trauma, immediate effects
-Rupture of large arteries supplying the dura (meningeal arteries)
-High pressured arterial blood rips the dura from the skull
-Pressure is increased on the brain as there is no space (between the periosteal layer and skull is only a potential space) so cardiac and respiratory centres give up
-Unconscious patient, ipsilateral dilated pupil, contralateral hemiparesis
Describe an subdural haemorrhage
-Due to trauma, delayed effects
-More common in elderly patients and those on anticoagulants
-Headache, drowsiness -> hemiparesis and sensory deficits develop
Describe an subarachnoid haemorrhage
Quick arterial bleeds
Ruptured aneurysms of the basal vessels
(beri aneurysms are usually found in vessels of the circle of willis)
Describe an intracerebral haemorrhage
Spontaneous hypertensive rupture of arteries in the deep cerebrum