Lecture 7: The Cerebral Circulation & Neuronal Environment Flashcards
The blood supply of the brain and spinal cord arises from what structure?
- Two sets of branches from the dorsal aorta
1. Subclavian arteries
2. Common carotid arteries
Subclavian arteries gives rise to what?
Vertebral arteries
What artery branches off the common carotid arteries?
Internal carotid arteries and external carotid arteries
Loss of blood supply to the brain leads to?
Death of neurons within 3-5 mins (Neurons have high metabolic rate and high demand for oxygen)
Vertebral arteries that supply the spinal cord give rise to what arteries?
- Branches that merge into the anterior spinal artery (single artery in anterior/ventral surface)
- Gives rise to the paired posterior spinal artery (paired arteries in dorsal/posterior surface)
What are the supplementary arteries of the spinal cord?
- Medually arteries ( short 10-12 segmental arteries that join the anterior/posterior spinal artery)
- They arise from the segmented branches of the aorta
An obstruction/ damage (surgery) of the medullary artery could lead to loss of blood supply to the spinal cord. What function would be lost?
- Posterior blood supply -loss of sensory function
- Anterior blood supply- loss of motor function
What are the 2 major branches of the internal carotid artery (ICA)?
- Anterior cerebral artery (ACA)
- Middle cerebral artery (MCA)
Basilar artery is formed by what?
basilar a. (midline) is formed by right and left vertebral a
____ joins the blood supply from the internal carotids in an arterial ring structure called _____
basilar a, Circle of Willis
What does the circle of willis interconnect?
Interconnects the internal carotid and vertebral circulation
An anastomosis helps assure cortical circulation if one system slowly becomes occluded.
How does the Circle of Willis interconnect the internal carotid and vertebral circulation
Posterior cerebral a. < - > posterior communicating a. < - >middle cerebral/internal carotid a. < - > anterior cerebral a < - > anterior communicating a.
What branches are part of the Circle of Willis?
ACA and MCA (branches of the ICA) and PCA
ACA-Anterior Cerebral aa.
MCA-Middle Cerebral aa.
PCA- Posterior Cerebral aa. ( terminal of basilar a.)
If one of the major arteries becomes occluded, the Circle of Willis secures that all regions of the brain are still able to receive the blood by which structures?
Two small bridging communicating arteries:
1. Anterior (Ant) communicating a
2. Posterior (Post) communicating a
What is the blood supply to the cerebellum (3)?
Vertebral circulation
SCA – supplies the superior portion of the cerebellum
AICA – supplies the lateral portion of the cerebellum
PICA – supplies the inferior portion of the cerebellum
superior cerebellar artery
anterior inferior cerbellar artery-
post inferior cerebellar artery
What is the blood supply to the midbrain?
part of brainstem
- Posterior cerebral artery (terminal branches off vertebral artery)
- Superior cerebellar artery
What is the blood supply to the pons?
part of the brainstem
- Superior cerebellar artery
- Basilar artery
- Anterior inferior cerebellar artery (AICA)
AICA is a branch of the basilar artery to the brainstem
What is the blood supply to the medulla?
part of the brainstem
- Anterior inferior cerebellar artery (AICA)
- Posterior inferior cerebellar artery (PICA)
- Vertebral arteries
- Anterior and posterior spinal aa
AICA and PICA and branches of the basilar artery to the brainstem
Why is it important to discuss the blood supply to various regions of the brain?
A compromised blood supply to the brain results in the “Structure Damage/Deficit” in the brain (affects the Somatosensory System)
Anterior circulation to the forebrain is formed by what two arteries?
anterior cerebral (ACA)
middle cerebral (MCA)
braches off ICA
Posterior circulation to the posterior cerebral cortex, thalamus, and the brainstem is formed by what arteries?
- posterior cerebral (PCA )
- basilar
- vertebral
What are the deep penetration cerebral arteries?
lenticulostriate arteries
Branches of ____ and ____ supply blood to the cortex and to the deep structures.
ACA, MCA
Where do the lenticulostriate arteries branches off of and what does it supply?
The lenticulostriate arteries branches off MCA supply blood to the deep structures such as basal ganglia, internal capsule, and hippocampus.
A high incidence of damage of deep penetrating cerebral arteries in patients with what?
chronic hypertension and in the elderly: rupture (intracerebral hemorrhage) or occlusion (lacunar infarct).
Deep Penetrating Cerebral arteries can also be called what?
End arteries which supply regions without significant collateral blood supply. Therefore, their occlusion results in stroke syndromes.
True or False: The size of the infarct ranges from small, (lacunes) to large areas in brain
True
note that lacuna strokes can go unoticed but can cause death
Lacunae strokes are occlusions of what?
Lenticulostrate arteries
What happens to the brain cells after a lacunar stroke?
Within a few months of the infarction, the necrotic brain cells are reabsorbed by macrophages, leaving a small cavity a “lake” or “lacune.” The cells distal to the occlusion die.
The brain uses ____ of normal cardiac output and ____ of body’s O2 consumption
15%, 25%
The overall cereberal blood flow rate is ____ but due to neural activity blood flow ____ in active areas of the brain during various mental activities.
constant, increases
The ratio of ____ in particular regions of the brain increases due to increased regional demand for oxygen.
hemoglobin to deoxyhemoglobin
What is an aneurysm?
balloon-like swelling of arterial wall near bifurcation
can break can cause bleeding and cause obstruction in blood flow
The venous drainage exits the skull through what vessel(s)?
Venous blood drains from the brain through superficial and deep veins into the dural sinuses (Superior Sagittal Sinus), which then drain into the internal jugular (IJ) vein.
What makes up the cerebral microvasculature?
Microvasculature: Deep Penetrating Cerebral Arteries and Capillaries
- basal lamina of blood vessels: borderlines b/w blood vessels and what’s outside
- blood-brain barrier (BBB) of capillaries: connection b/w cells w/in BBB
What is the Virchow-Robin Space (perivascular space)?
It’s a Perivascular subpial space around large blood vessels in the brain. NOT around capillaries
Where does the Virchow-Robin Space (perivascular space) end?
Space stops at the capillary level (stops where capillary starts)
They surround and follow the path of penetrating cortical arterioles e.g. Lenticulostriate aa. (not around capillaries).
What is the clinical significance of VRS?
VRS has a tendency to dilate so you can identify enlarged VRS which have been associated with age, dementia and incidental inflammatory white matter lesions e.g., in multiple sclerosis.
What are VRS “Vascular cuffs” ?
the places of leukocyte aggregation during viral encephalitis.
What is the glymphatic system?
a macroscopic waste clearance system that utilizes a unique system of perivascular tunnels, formed by astroglial cells, to promote efficient elimination of soluble proteins and metabolites from the central nervous system.
The glymphatic system facilitates the brain-wide distribution of whichcompounds?
glucose, lipids, amino acids, growth factors, and neuromodulators
When does the glymphatic system function?
mainly during sleep and is largely disengaged during wakefulness.
What are the 3 types of barriers included in the CNS barrier system?
- Choroid plexus CSF-Blood barrier: tight junctions in the choroid epithelium
- Blood- Brain Barrier(BBB): tight junctions in the endothelial cells
- Arachnoid-CSF-Blood Barrier: (separates CSF from EC fluids and blood of the dura) tight junctions in the arachnoid cells
Once you reach the ____ you are at the blood brain barrier
intracerebral capillary
What is the BBB composed of?
Small capillary surrounded by glial feet processes of astrocytes, containing tight junctions between the endothelial cells coming together to form the BBB
True or False: Astrocytes participate in the formation of the BBB
True
____ is formed by endothelial cells with tight junctions and glial feet processes of astrocytes
BBB
Function of BBB
BBB limits and restricts diffusion of solutes in blood such as bacteria, and large or hydrophilic molecules. It separates and protects the brain from blood-borne pathogens
What is a region within the brain with no BBB?
Circumventricular organs (CVOs)
Circumventricular organs (CVOs) are known as what?
Functional “gates” in the BBB
Name 4 characterizations of the Circumventricular organs (CVOs)
- Have higher capillary density compared to other areas in the brain
- No BBB
- There are fenestrations and pericapillary space in the endothelial cells of the brain capillaries in CVOs.
- Examples are the Neurohypohysis and Pineal gland
have a neuroendocrine function: have no tight junctions b/w endothelial cells and can send products quickly to the bloodstream
What is another example of a CVO seen in a monkey w/ the use of horseradish peroxide?
CVO=Circumventricular organs
Median Eminence(ME) area of the hypothalamus
ME has NO BBB
What is the Arachnoid-CSF Blood Barrier?
- Separates CSF from extracellular fluids
- Blood of the dura and has meningothelial cells with tight junctions in the arachnoid cell
What are meninges?
3 CT layers that protect brain, brainstem, and the spinal cord
Review: 3 layers of Meninges
- Dura mater (outermost, thick layer)
- Arachnoid mater (spiderlike projections that bridge overfolds and tissues of cortex)
- Pia mater (inner, delicate layer closely adhering to the cerebral cortex)
pia mater travels with perivascular space and “hugs: the brain tissue
What is the subarachnoid space filled with?
Cerebral Spinal Fluid (CSF)
What does the Arachnoid-CSF-Blood Barrier contain?
- Contains Arteries and veins that supply and drain the CNS.
- Transversed by meningothelial (modified CT)
prevents things from the skull and dura from getting into the Subarchoid space (SAS)
What is the subdural space, and what can occur here?
has a star
Subdural space is b/w the dura matter and arachnoid and it is an artifact. An epidural and subdural hematoma can occur here
What are the cerebral ventricles?
Interconected spaces filled with serevral spinal fluid (CSF) and lined by ependymal cells
Where do the Lateral (or First and Second) ventricles (the largest) , Third and Fourth ventricles lie?
Lie in the core of the forebrain and brainstem
Where is CSF produced?
A modified vascular structure-choroid plexus (CP)
Modified ependymal cells where there is active secretion of CSF
Choroid plexus
What lines the CSF filled ventricles?
epithelial-like cells of ependyma (cuboidal to columnar)
What is the epithelial –like cells of ependyma involved in
- Involved in absorbing CSF
- May be modified w/in the ventricles to produce CSF: part of the choroid plexus (CP) present in each of the ventricles
No external lamina (unlike epithelium), cilia and microvili on the apical surface of the cell.
Review: Ependymal cells
- Lines inner surface of the brain surface
- ciliated
- may be modified w/in ventricles to produce CSF: part of choroid plexus
Review: What are 2 fxns of the ependymal cells?
- Movement of CSF
- bidirectional transport of materials b/w CSF and neuropil
What ventricle is the Choroid plexus (CP) located at?
in each of the ventricles
could be a place of a potential communication between the blood and CSF
For the CP CSF-blood barrier, do the CP epithelial cells have tight junctions?
YES
CP endothelial cells of the capillaries are fenestrated
Explain the circulation of the CSF
review
CSF from ventricles flows from ependymal cells of the lateral ventricle, 3rd, and perforarations of the 4th ventricles into the subarachnoid space, then through arachnoid villi, and finally drains into the venous sinuses in arachnoid villi.
What is the choroid plexus villi?
Protruding structure w/ folded regions covered by ependymal cells with tight jxn
Choroid epithelium almost completely surrounds what?
Choroidal capillaries
What is formed by the ependymal epithelial cells of the choroid plexus connected by tight junctions?
Choroid plexus and Blood CSF barrier
What do ependymal cells receive?
Some plasma components from leaky blood capillaries, so there is no jxn there so those components can penetrate within the ependynmal cells. Then the ependymal cells makes the components into CSF
What are the 3 layers choroid plexus?
- Fenestrated capillary
- Scatter pial cells and collagen
- Choroid epithelial-like ependymal cells with tight jxns
Pia faces subarachnoid space with blood supply,
ependyma faces ventricles
CSF is produced by what type of secrection?
Active secretion by CP into ventricles and not passive diffision from blood
What is the composition of CSF and what controls the composition?
- Clear and colorless, low in protein, and similar (but not identical) to serum in ionic composition.
- The Choroid plexus controls the composition
Blood- CSF Barriers: Summary
- The ____ is a vascular tissue found in all cerebral ventricles.
- The choroid plexus is a vascular tissue found in all cerebral ventricles
Blood- CSF Barriers: Summary
What is the functional unit of the CP?
a capillary enveloped by a layer of differentiated ependymal epithelium.
Blood- CSF Barriers: Summary
Unlike the capillaries that form the blood-brain barrier, what do the choroid plexus capillaries contain?
Choroid plexus capillaries are fenestrated and have no tight junctions (the endothelium, does not form a barrier to the movement of small molecules).
Blood- CSF Barriers: Summary
What is the The Blood-CSF barrier at the CP formed by?
Epithelial-like ependymal cells with the tight junctions
Blood- CSF Barriers: Summary
Envelops the brain is the other barrier with connective tissue (CT) meningiothelial cells of this membrane also linked by tight junctions.
Blood-CSF barrier in the arachnoid membrane
Serves as a “sink” for some subtances from the brain
CSF system
What is a route for neurohormones?
CSF
How does the CSF drain?
Into venous sinuses from arachnoid villi
What is hydrocephalus?
when there is no proper CSF flow with an excess of CSF in the intracranial cavity leading to enlargement of the ventricles and compression of the brain.
problem with CSF transport
What is hydrocephalus?
when there is no proper CSF flow with an excess of CSF in the intracranial cavity leading to enlargement of the ventricles and compression of the brain.
problem with CSF transport
What are 3 causes of hydrocephalus?
- excess production of CSF (from a tumor)
- a deficiency in CSF reabsorption.
- blockage of CSF circulation (the most common- reason-obstructive hydrocephalus)
What is obstructuve hydrocephalus?
- Circulation of CSF can be obstructed at any point in the pathway of CSF, e.g., tumor can occlude path of CSF.
- The severity of the occlusion would depend on the stage of tumor progression/tumor growth.
Give an example of Obstructive Hydrocephalus
- Obstruction can occur at the cerebral aqueduct resulting in the decreased passage of CSF from the 3rd ventricle to the 4th ventricle.
- For example, the presence of a colloid cyst of the third ventricle could obstruct the foramina of Monro and result in obstructive hydrocephalus.
Explain how CSF can act as a diagnostic tool (reflection of a disease)
- in fungal infections, lymphocyte count is elevated
- in bacterial infection (meningitis), the neutrophils are 90% of the CSF cell count
the normal leukocyte count in the CSF is 5-10 cells/ml,
- The posterior cerebral artery (PCA) is a branch of which of the following blood vessels?
A. Anterior spinal artery
B. Internal carotid artery
C. Basilar artery
D. Posterior spinal artery
C. Basilar artery
- An MSP3 student presents to the ED following the gradual onset of memory loss, mood changes, confusion, and overall cognitive decline. Laboratory findings suggest a large buildup of toxic metabolites within cerebral circulation. Given these results, which of the following may be the cause of their symptoms?
A. Overstimulation of the brain leading to a meningeal tear
B. Lack of sleep leading to dysfunction of the glymphatic system
C. Viral encephalitis leading to leukocyte aggregation in perivascular cuffs.
D. Genetic malformation of the cerebral aqueduct resulting in decreased CSF drainage
B. Lack of sleep leading to dysfunction of the glymphatic system
- Which of the following blood vessels provide vascularization to the posterior cerebral cortex?
I. Anterior cerebral artery (ACA)
II. Middle cerebral artery (MCA)
III. Posterior cerebral artery (PCA)
IV. Basilar artery
V. Vertebral artery
A. II, III, & IV
B. I, II, III, & IV
C. I, III, & V
D. III, IV, & V
D. III, IV, & V
- The blood brain barrier is formed by which of the following combinations of cells?
A. Fenestrated endothelial cells + microglia
B. Non-fenestrated endothelial cells + astrocytes
C. Non-fenestrated endothelial cells + microglia
D. Fenestrated endothelial cells + astrocytes
B. Non-fenestrated endothelial cells + astrocytes
- All of the following accurately describe cerebrospinal fluid (CSF) EXCEPT:
A. Contains low concentrations of protein and high concentrations of Na+/K+
B. Flows from the lateral ventricle to the 3rd ventricle via the foramen of monro
C. Passes through the arachnoid villi in order to drain into the venous sinuses
D. Secreted into the ventricles from epithelial like ependymal cells of the Choroid Plexus
A. Contains low concentrations of protein and high concentrations of Na+/K+
