BMB 1 - Vasculature to the Brain Flashcards
What percentage of blood flow (and O2 and ATP) goes to the brain?
20%
The anterior vascular input to the brain comes from what arteries (80% of cerebral blood flow)?
The posterior vascular input to the circle of Willis comes from what arteries (20% of cerebral blood flow)?
The internal carotid arteries (and circle of Willis);
the vertebrobasilar arteries
True/False.
The circle of Willis is near entirely a product of the internal carotid arteries.
True.
True/False.
The brain has an anterior blood supply (from the internal carotids) and a posterior blood supply (from the vertebral arteries) to provide redundancy in case one set is occluded (i.e., the mixing between these two supplies in the circle of Willis allows for resistance to stroke damage).
False.
The brain has an anterior blood supply (from the internal carotids) and a posterior blood supply (from the vertebral arteries) but they remain largely separate (NOTE: the circle of Willis is entirely supplied by the ICAs).
Describe the differences in portions of the brain covered by anterior circulatory input (i.e. the ICAs and circle of Willis) vs. the posterior circulatory input (i.e. the vertebral and basilar arteries).
The anterior cerebral arteries are a branch of what other arteries?
The middle cerebral arteries are a continuation of what other arteries?
The posterior communicating arteries are a branch of what other arteries?
The internal carotid arteries;
the internal carotid arteries;
the internal carotid arteries
The anterior communicating artery connects what vasculature?
The anterior cerebral arteries
The posterior communicating arteries connects what vasculature?
The internal carotid arteries and the posterior cerebral arteries
Aneurysm of the internal carotids / posterior communicating arteries are most likely to affect which cranial nerve(s)?
CN III
60 - 70% of cranial aneurysms occur in which three arteries?
20% occur in which arteries?
The anterior communicating,internal carotid, andposteriorcommunicating arteries;
the middle cerebral arteries
(See image for the smattering of other arteries that may be involved in rare cases.)
~__ of brain aneurysms occur in the anterior communicating arteries.
~__ of brain aneurysms occur in the internal carotid / posterior communicating arteries.
~__ of brain aneurysms occur in the middle cerebral arteries.
~__ of brain aneurysms occur in smaller arteries like the basilar apex, superior cerebellar, posterior inferior cerebellar, and vertebrobasilar junction arteries.
~35 of brain aneurysms occur in the anterior communicating arteries.
~35 of brain aneurysms occur in the internal carotid / posterior communicating arteries.
~20 of brain aneurysms occur in the middle cerebral arteries.
~10 of brain aneurysms occur in smaller arteries like the basilar apex, superior cerebellar, posterior inferior cerebellar, and vertebrobasilar junction arteries.
A patient presents with ptosis, mydriasis, and an eye that is depressed and abducted.
You suspect an aneurysm. Which arteries are most likely involved?
The internal carotid / posterior communicating arteries
(CN III palsy)
Name some of the major S/Sy of CN III compression or disruption.
Unilateral ptosis, mydriasis, and an eye that is depressed and abducted.
Why does CN III disruption result in an eye that is depressed and abducted?
Unopposed CN IV and CN VI activity
Describe the portions of the brain supplied by the anterior cerebral arteries.
(Yellow area in image - anteromedial surfaces.)
Describe the portions of the brain supplied by the middle cerebral arteries.
(Green area in image - lateral surfaces.)
Describe the portions of the brain supplied by the posterior cerebral arteries.
(Blue area in image - posterior and inferior surfaces.)
Most of the frontal lobe is supplied by which bilateral arteries?
Anterior cerebral
Most of the parietal lobe is supplied by which bilateral arteries?
Anterior and middle cerebral arteries
Most of the temporal lobe is supplied by which bilateral arteries?
Middle cerebral (some posterior cerebral)
Most of the occipital lobe is supplied by which bilateral arteries?
Posterior cerebral
A stroke affecting motor/sensory activity in the extremities is likely affecting which arteries in particular?
The anterior cerebral arteries
(Remember, the homunculi end with legs and feet in the medial aspects of the frontal lobe - i.e. within the longitudinal fissure.)
The ophthalmic artery is a branch of which larger artery?
The internal carotid artery
A patient with a stroke involving the posterior cerebral artery will have what visual complaints?
Complete blindness in half the visual field but with macular sparing!
Why would a patient with complete occlusion of the posterior cerebral artery present keep their central (macular) vision even as the half of their visual field is impaired (see image)?
The middle cerebral artery branches back to the visual cortex to supply the macular portions of the visual cortex
(From lecture: ‘The MCA provides a branch that extends to the optic radiations. As a result, central fibers are not knocked out by lack of blood.’)
Most of the visual cortex is supplied by the ____________ arteries, but the macular portion is supplied by the ___________ arteries.
Most of the visual cortex is supplied by the posterior cerebral arteries, but the macular portion is supplied by the middle cerebral arteries.
A patient presents with a visual field matching the image below.
What is this called and what artery may be occluded?
Homonymous hemianopsia with macular sparing;
the right posterior cerebral artery
What is the name for zones of tissue that are slightly protected from stroke through redundancy but are at increased risk of infarct in cases of more global hypotension?
Watershed zones
Name the two arterial overlaps that create watershed zones within the cerebral cortex.
Anterior cerebral and middle cerebral arteries;
posterior cerebral and middle cerebral arteries
Describe the watershed zone created by overlap (1) between the anterior and middle cerebral arteries and (2) between the posterior and middle cerebral arteries
(I.e., the MCA provides some redundancy.)
The dural venous sinuses are composed of what type of tissue(s)?
Folds of dura mater (serving as channels)
Describe the locations of the major dural sinuses (e.g. superior sagittal, straight, inferior sagittal, transverse, and sigmoid).
Which sinuses drain into the confluence of sinuses?
The confluence drains into what structure?
The superior sagittal sinus, straight sinus, and occipital sinus;
the transverse and then sigmoidal sinuses
The cavernous sinuses drain into the sigmoidal sinus via which two pathways?
The superior (leading to transverse) and inferior petrosal (leading to internal jugular) sinuses
Which dural sinus runs along the top of the falx cerebri?
Which dural sinus runs along the bottom of the falx cerebri?
The superior sagittal sinus;
the inferior sagittal sinus
Most cerebral veins run in what space?
The subarachnoid space
What do bridging veins connect?
The veins in the subarachnoid space and the superior sagittal sinus
Bridging veins exit the subarachnoid space to traverse what space?
The subdural space
(thus reaching the superior sagittal sinus)
What vein connects the middle cerebral vein and superior sagittal sinus?
The anastomotic vein of Trolard
What structures run through the cavernous sinuses?
The internal carotid a.; CNs III, IV, and V (V1 and V2 opthlamic and maxillary portions), and VI
Describe the locations of the structures that pass through the cavernous sinuses as they pass through.
O Tom Cat
Oculomotor n.
Trochlear n.
Ophthalmic branch of V1
Maxillary branch of V2
Carotid artery (internal)
Abducens n.
t
True/False.
The brain has virtually no lymphatic drainage, relying instead on the dural sinus system.
False.
The brain has lymphatic drainage, often running alongside the dural sinus system (clears extracellular proteins, excess fluid, and metabolic waste products -including soluble beta-amyloid- from the brain).
When are cranial lymphatics active?
During sleep only
(similar to certain CSF pulses)
What cell types control the activation and inactivation of lymphatic connections to the CSF?
Glial cells (especially astrocytes)
Does any of the brainstem arterial supply come from the anterior brain circulation (i.e. from the ICA and circle of Willis)?
No.
It is all posterior (from the vertebral arteries).
The medulla receives most of its blood supply from which artery(ies)?
The vertebral,
anterior spinal,
and posterior inferior cerebellar arteries
The pons receives most of its blood supply from which artery(ies)?
The basilar artery
The midbrain receives most of its blood supply from which artery(ies)?
The posterior cerebral
and superior cerebellar arteries
Which arteries wrap around the midbrain, supplying blood in a circumferential manner?
The superior cerebellar arteries
Which arteries don’t wrap as much around the midbrain, supplying blood to the paramedian and lateral tegmental regions?
The posterior cerebral arteries
Describe the paramedian, short circumferential, and long circumferential branches of the basilar artery as they extend into the pons.
(Also: which hits most of the medial lemniscus and corticospinal tracts?)
(Paramedian branches)
Describe the contributions of the anterior spinal, vertebral, and posterior inferior cerebellar arteries in supplying the medulla.
4 - Posterior inferior cerebellar a.
5 - Vertebral a.
6 - Anterior spinal a.
(wedge-shaped distributions)
Disruption of the anterior spinal artery to the medulla results in what S/Sy?
Interruption of the medial lemniscus and corticospinal tract
(upper motor neuron and/or sensory deficits)
Disruption of the vertebral artery to the medulla results in what S/Sy?
Interruption of the spinothalamic tract
(contralateral loss of pain and temperature)
Disruption of the posterior inferior cerebellar artery to the medulla results in what S/Sy?
Lateral medullary syndrome
(Wallenberg syndrome!)
Describe the S/Sy of late medullary syndrome (Wallenberg syndrome).
Contralateral sensory deficits of the trunk and extremities;
ipsilateral sensory deficits of the cranial nerves
(the cross body finding is the chief symptom from which a diagnosis can be made)
A patient presents with ataxia (he walks on a slight slant) and loss of temperature and discriminative sensation on one side of his body; the patient’s speech is slurred and you learn he has difficulty swallowing; he also seems to have some sensory deficits on the side of his face opposite the sensory deficits on his body.
What is the likely diagnosis?
Lateral medullary syndrome
(Wallenberg syndrome)
Lateral medullary syndrome (Wallenberg syndrome) results due to infarction of one of which vessels?
The posterior inferior cerebellar arteries
True/False.
Autoregulation of brain blood flow is impaired following stroke.
True.
True/False.
Cerebral metabolism and blood flow increase with age.
False.
Cerebral metabolism and blood flow decrease with age.
The brain has very little glycogen and energy reserves – as a result, certain parts of the brain can survive only for a few _________ if blood flow ceases.
The brain has very little glycogen and energy reserves – as a result, certain parts of the brain can survive only for a few minutes if blood flow ceases.
Name the major metabolite regulating cerebral blood flow.
CO2
(O2 at very low levels)
True/False.
Cerebral blood flow drives cerebral metabolism.
False.
Metabolism drives cerebral blood flow.
Name three factors regulating autoregulation of cerebral blood flow.
1. Myogenic
2. Long-term changes in MAP
3. CO2 levels
Either a(n) ____________ in blood pressure or a(n) ____________ in intracranial pressure will lead to a decrease in cerebral perfusion pressure.
Either a decrease** in blood pressure or an **increase in intracranial pressure will lead to a decrease in cerebral perfusion pressure.
Cerebral perfusion pressure = __________ - __________
Cerebral perfusion pressure = MAP - ICP
Hypoxemia increases cerebral perfusion pressure only if O2 is < _____ mmHg.
Cerebral perfusion pressure is directly proportional to CO2 until CO2 reaches _____ mmHg.
Hypoxemia increases cerebral perfusion pressure only if O2 is < 50 mmHg.
Cerebral perfusion pressure is directly proportional to CO2 until CO2 reaches 90 mmHg.
A decrease in CO2 leads to cerebral vaso___________, ___creasing cerebral blood flow.
A decrease in CO2 leads to cerebral vasoconstriction, decreasing cerebral blood flow.
True/False.
Brain veins have no valves (to allow bidirectional flow of blood) and no muscular layer.
True.
