BMB 1 - Vasculature to the Brain

Question 1

What percentage of blood flow (and O₂ and ATP) goes to the brain?

Answer 1

20%

Question 2

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)?

Answer 2

The internal carotid arteries (and circle of Willis);

the vertebrobasilar arteries

Question 3

True/False.

The circle of Willis is near entirely a product of the internal carotid arteries.

Answer 3

True.

Question 4

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).

Answer 4

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).

Question 5

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).

Answer 5

Question 6

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?

Answer 6

The internal carotid arteries;

the internal carotid arteries;

the internal carotid arteries

Question 7

The anterior communicating artery connects what vasculature?

Answer 7

The anterior cerebral arteries

Question 8

The posterior communicating arteries connects what vasculature?

Answer 8

The internal carotid arteries and the posterior cerebral arteries

Question 9

Aneurysm of the internal carotids / posterior communicating arteries are most likely to affect which cranial nerve(s)?

Answer 9

CN III

Question 10

60 - 70% of cranial aneurysms occur in which three arteries?

20% occur in which arteries?

Answer 10

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.)

Question 11

~__ 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.

Answer 11

~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.

Question 12

A patient presents with ptosis, mydriasis, and an eye that is depressed and abducted.

You suspect an aneurysm. Which arteries are most likely involved?

Answer 12

The internal carotid / posterior communicating arteries

(CN III palsy)

Question 13

Name some of the major S/Sy of CN III compression or disruption.

Answer 13

Unilateral ptosis, mydriasis, and an eye that is depressed and abducted.

Question 14

Why does CN III disruption result in an eye that is depressed and abducted?

Answer 14

Unopposed CN IV and CN VI activity

Question 15

Describe the portions of the brain supplied by the anterior cerebral arteries.

Answer 15

(Yellow area in image - anteromedial surfaces.)

Question 16

Describe the portions of the brain supplied by the middle cerebral arteries.

Answer 16

(Green area in image - lateral surfaces.)

Question 17

Describe the portions of the brain supplied by the posterior cerebral arteries.

Answer 17

(Blue area in image - posterior and inferior surfaces.)

Question 18

Most of the frontal lobe is supplied by which bilateral arteries?

Answer 18

Anterior cerebral

Question 19

Most of the parietal lobe is supplied by which bilateral arteries?

Answer 19

Anterior and middle cerebral arteries

Question 20

Most of the temporal lobe is supplied by which bilateral arteries?

Answer 20

Middle cerebral (some posterior cerebral)

Question 21

Most of the occipital lobe is supplied by which bilateral arteries?

Answer 21

Posterior cerebral

Question 22

A stroke affecting motor/sensory activity in the extremities is likely affecting which arteries in particular?

Answer 22

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.)

Question 23

The ophthalmic artery is a branch of which larger artery?

Answer 23

The internal carotid artery

Question 24

A patient with a stroke involving the posterior cerebral artery will have what visual complaints?

Answer 24

Complete blindness in half the visual field but with macular sparing!

Question 25

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)?

Answer 25

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.'*)

Question 26

Most of the visual cortex is supplied by the ____________ arteries, but the macular portion is supplied by the ___________ arteries.

Answer 26

Most of the visual cortex is supplied by the **_posterior cerebral_** arteries, but the macular portion is supplied by the **_middle cerebral_** arteries.

Question 27

A patient presents with a visual field matching the image below. What is this called and what artery may be occluded?

Answer 27

**Homonymous hemianopsia** with **macular sparing**; the right **posterior cerebral** **artery**

Question 28

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?

Answer 28

Watershed zones

Question 29

Name the two arterial overlaps that create watershed zones within the cerebral cortex.

Answer 29

**Anterior cerebral** and **middle cerebral** arteries; **posterior cerebral** and **middle cerebral** arteries

Question 30

Describe the watershed zone created by overlap (1) between the anterior and middle cerebral arteries and (2) between the posterior and middle cerebral arteries

Answer 30

(I.e., the MCA provides some redundancy.)

Question 31

The dural venous sinuses are composed of what type of tissue(s)?

Answer 31

Folds of **dura mater** (serving as channels)

Question 32

Describe the locations of the major dural sinuses (e.g. superior sagittal, straight, inferior sagittal, transverse, and sigmoid).

Answer 32

Question 33

Which sinuses drain into the confluence of sinuses? The confluence drains into what structure?

Answer 33

The **superior sagittal** sinus, **straight** sinus, and **occipital** sinus; the **transverse** and then **sigmoidal** sinuses

Question 34

The cavernous sinuses drain into the sigmoidal sinus via which two pathways?

Answer 34

The **superior** (leading to transverse) and **inferior** **petrosal** (leading to internal jugular) **sinuses**

Question 35

Which dural sinus runs along the top of the falx cerebri? Which dural sinus runs along the bottom of the falx cerebri?

Answer 35

The superior sagittal sinus; the inferior sagittal sinus

Question 36

Most cerebral veins run in what space?

Answer 36

The subarachnoid space

Question 37

What do bridging veins connect?

Answer 37

The **veins in the** **subarachnoid** **space** and the **superior** **sagittal** **sinus**

Question 38

Bridging veins exit the subarachnoid space to traverse what space?

Answer 38

The **subdural** space ## Footnote *(thus reaching the superior sagittal sinus)*

Question 39

What vein connects the middle cerebral vein and superior sagittal sinus?

Answer 39

The anastomotic vein of Trolard

Question 40

What structures run through the cavernous sinuses?

Answer 40

The **internal carotid** a.; CNs **III**, **IV**, and **V** *(V1 and V2 opthlamic and maxillary portions)*, and **VI**

Question 41

Describe the locations of the structures that pass through the cavernous sinuses as they pass through.

Answer 41

**_O Tom Ca_**_t_ **O**culomotor n. **T**rochlear n. **O**phthalmic branch of V1 **M**axillary branch of V2 **C**arotid artery (internal) **A**bducens n. t

Question 42

**True/False**. The brain has virtually no lymphatic drainage, relying instead on the dural sinus system.

Answer 42

**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***).

Question 43

When are cranial lymphatics active?

Answer 43

During sleep _only_ | (similar to certain CSF pulses)

Question 44

What cell types control the activation and inactivation of lymphatic connections to the CSF?

Answer 44

Glial cells (especially astrocytes)

Question 45

Does any of the brainstem arterial supply come from the anterior brain circulation (i.e. from the ICA and circle of Willis)?

Answer 45

**No**. It is all posterior (from the vertebral arteries).

Question 46

The medulla receives most of its blood supply from which artery(ies)?

Answer 46

The **v****ertebral**, **anterior** **spinal**, and **posterior** **inferior** **cerebellar** arteries

Question 47

The pons receives most of its blood supply from which artery(ies)?

Answer 47

The **basilar** artery

Question 48

The midbrain receives most of its blood supply from which artery(ies)?

Answer 48

The **_posterior cerebral_** and **superior cerebellar** arteries

Question 49

Which arteries wrap around the midbrain, supplying blood in a circumferential manner?

Answer 49

The superior cerebellar arteries

Question 50

Which arteries don't wrap as much around the midbrain, supplying blood to the paramedian and lateral tegmental regions?

Answer 50

The posterior cerebral arteries

Question 51

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?)

Answer 51

(Paramedian branches)

Question 52

Describe the contributions of the anterior spinal, vertebral, and posterior inferior cerebellar arteries in supplying the medulla.

Answer 52

**4** - Posterior inferior cerebellar a. **5** - Vertebral a. **6** - Anterior spinal a. (wedge-shaped distributions)

Question 53

Disruption of the anterior spinal artery to the medulla results in what S/Sy?

Answer 53

Interruption of the **medial** **lemniscus** and **corticospinal** **tract** (upper motor neuron and/or sensory deficits)

Question 54

Disruption of the vertebral artery to the medulla results in what S/Sy?

Answer 54

Interruption of the **spinothalamic** **tract** (contralateral loss of pain and temperature)

Question 55

Disruption of the posterior inferior cerebellar artery to the medulla results in what S/Sy?

Answer 55

**Lateral medullary syndrome** | (Wallenberg syndrome!)

Question 56

Describe the S/Sy of late medullary syndrome (Wallenberg syndrome).

Answer 56

**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*)

Question 57

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?

Answer 57

Lateral medullary syndrome (Wallenberg syndrome)

Question 58

Lateral medullary syndrome (Wallenberg syndrome) results due to infarction of one of which vessels?

Answer 58

The posterior inferior cerebellar arteries

Question 59

**True/False**. Autoregulation of brain blood flow is impaired following stroke.

Answer 59

True.

Question 60

**True/False**. Cerebral metabolism and blood flow increase with age.

Answer 60

**False**. Cerebral metabolism and blood flow ***decrease*** with age.

Question 61

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.

Answer 61

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.

Question 62

Name the major metabolite regulating cerebral blood flow.

Answer 62

**CO₂** | (O₂ at very low levels)

Question 63

**True/False**. Cerebral blood flow drives cerebral metabolism.

Answer 63

**False**. ***Metabolism*** drives ***cerebral blood flow***.

Question 64

Name three factors regulating autoregulation of cerebral blood flow.

Answer 64

**1.** Myogenic **2.** Long-term changes in MAP **3.** CO₂ levels

Question 65

Either a(n) ____________ in blood pressure or a(n) ____________ in intracranial pressure will lead to a ***decrease in cerebral perfusion pressure***.

Answer 65

Either a **_decrease**_ in blood pressure or an _**increase_** in intracranial pressure will lead to a ***decrease in cerebral perfusion pressure***.

Question 66

Cerebral perfusion pressure = __________ - \_\_\_\_\_\_\_\_\_\_

Answer 66

Cerebral perfusion pressure = **_MAP_** - **_ICP_**

Question 67

Hypoxemia increases cerebral perfusion pressure only if O₂ is \< _____ mmHg. Cerebral perfusion pressure is directly proportional to CO₂ until CO₂ reaches _____ mmHg.

Answer 67

Hypoxemia increases cerebral perfusion pressure only if O₂ is \< **_50_** mmHg. Cerebral perfusion pressure is directly proportional to CO₂ until CO₂ reaches **_90_** mmHg.

Question 68

A ***decrease*** in CO₂ leads to cerebral vaso\_\_\_\_\_\_\_\_\_\_\_, \_\_\_creasing cerebral blood flow.

Answer 68

A ***decrease*** in CO₂ leads to cerebral vaso**_constriction_**, **_de_**creasing cerebral blood flow.

Question 69

**True/False**. Brain veins have no valves (to allow bidirectional flow of blood) and no muscular layer.

Answer 69

True.