Vascular & Ventricular Systems of the CNS

Key questions

1. Q1What makes up the blood–brain barrier, and what does it block?

   Brain endothelial cells joined by tight junction proteins that mostly lack fenestrations. It blocks high-molecular-weight and charged substances.
2. Q2What gets through the BBB?

   Small or lipophilic substances (e.g., L-dopa, estrogen) and molecules moved by specific transporters.
3. Q3How do hydrophilic molecules like glucose cross the BBB?

   By facilitated transport through endothelial transporters (e.g., GLUT1); the barrier itself blocks hydrophilic molecules.
4. Q4What must a CNS drug be, and where can it act despite the BBB?

   Lipophilic or attached to a sequence that is actively transported. Drugs can also reach areas where the BBB is disrupted, such as sites of trauma.
5. Q5How can the BBB be useful for drug design?

   Drugs made not to cross it avoid CNS side effects — e.g., the non-drowsy antihistamine Allegra (fexofenadine); many chemotherapy drugs are also designed to stay out.
6. Q6How can a large biologic drug be delivered past the BBB?

   By engaging the transferrin receptor for transport by endocytosis — used for a drug for Hunter syndrome (a lysosomal storage disease of complex polysaccharides, mostly in young boys).
7. Q7What are circumventricular organs, and which ones sense blood directly?

   Areas with an incomplete barrier. Sensing: area postrema (vomiting in response to toxins); subfornical organ and organum vasculosum (water and ion balance; immune signals → fever, warmth-seeking, loss of appetite).
8. Q8Which circumventricular organs release substances into blood?

   Hypothalamus–pituitary (growth, homeostasis, reproduction) and the pineal gland (melatonin, circadian rhythm).

Key questions

1. Q9How much energy does the brain use?

   20% of the body's oxygen and calories, while being only 2% of body weight.
2. Q10How fast does lack of blood harm the brain?

   Consciousness is lost in ~10 seconds; after ~6 minutes damage is irreversible or death follows. With mild hypothermia, patients can survive 10–20 minutes with little damage.
3. Q11How is oxygen released to active brain tissue?

   Hemoglobin releases O₂ in regions of low pH.
4. Q12What is the brain's fuel?

   Glucose is the main ATP source; lactate and ketone bodies can supplement it.
5. Q13How does blood flow match demand?

   Vasodilation where ATP is low (high neural activity or hypoxia); overall flow is held constant by autoregulation across a range of arterial pressures.
6. Q14What does chronic high blood pressure do?

   Alters vessel structure → higher risk of stroke and dementia.

Key questions

1. Q15Where do the internal and external carotids go?

   Common carotid → internal carotid (through the carotid canal to the Circle of Willis) and external carotid (neck, face, scalp).
2. Q16Trace the posterior circulation.

   Vertebral arteries (branches of the subclavians) run through the transverse foramina of the cervical vertebrae, enter via the foramen magnum and join to form the basilar artery.
3. Q17What feeds the anterior vs posterior parts of the Circle of Willis?

   Anterior: internal carotids. Posterior: vertebral (basilar) arteries.
4. Q18Besides the cerebral arteries, which branches of the internal carotid did the lecture name?

   Ophthalmic artery (eye) and anterior choroidal artery (deeper brain structures and choroid plexus).
5. Q19Which deep structures do the MCA and PCA also feed?

   MCA: the striatum (lenticulostriate branches). PCA: the thalamus.
6. Q20Name the cerebral and cerebellar arteries.

   Cerebral: anterior (ACA), middle (MCA), posterior (PCA). Cerebellar: superior (SCA), anterior inferior (AICA), posterior inferior (PICA).
7. Q21What supplies the pons?

   Short circumferential branches of the basilar artery — the source of pontine infarctions.
8. Q22How is the spinal cord supplied?

   Anterior spinal artery and posterior spinal arteries branch from the vertebrals (or PICA) and run down the cord, reinforced by radicular arteries.
9. Q23What are watershed areas?

   Border zones between the territories of two cerebral arteries, most vulnerable to low perfusion.
10. Q24How can the vertebral arteries be damaged?

    Vertebrobasilar occlusion (atherosclerosis) or vertebral artery dissection (trauma, neck distortion).

Key questions

1. Q25Embolism vs thrombosis?

   Embolism: a traveling clot obstructs a cerebral vessel → ischemia (ischemic stroke). Thrombosis: clot forms in place, in large or small brain vessels.
2. Q26What is an aneurysm, where does it form, and how is it treated?

   A dilation of the vessel wall, often at branch points; usually asymptomatic until it ruptures. Treated by clipping its stalk.
3. Q27What is a hemorrhagic stroke?

   Breakage of a blood vessel with bleeding into or around the brain.
4. Q28What is an arteriovenous malformation (AVM)?

   A tangle of abnormal vessels connecting arteries directly to veins, most common in the CNS. It reduces tissue oxygen and puts arterial pressure on weak veins/sinuses → hemorrhage. Early signs: seizures, headaches, weakness; sometimes only a pulsatile "whooshing" bruit. Treated by surgical removal.
5. Q29What is a dural fistula?

   An AVM in which meningeal arteries connect directly to a dural sinus; years of arterial pressure raise hemorrhage risk. Treated by neuroradiology and surgery.
6. Q30Name the five types of intracranial hemorrhage.

   Intraparenchymal, intraventricular, subarachnoid, subdural and epidural.
7. Q31How is an intracranial hemorrhage managed?

   Control blood pressure, reduce intracranial pressure, and surgically evacuate the hematoma.
8. Q32Which imaging is used for vascular problems?

   CT identifies hemorrhage types; MRI rules out tumors; MRA and angiography show the vertebrals, basilar, internal and external carotids, Circle of Willis and cerebral arteries (angiography diagnosed the lecture's dural fistula).

Key questions

1. Q33Name the external (superficial) veins.

   Superficial cerebral veins (superior, middle, inferior) and superficial cerebellar veins (superior, inferior).
2. Q34Where do the internal veins drain?

   Veins of the striatum, thalamus, choroid plexus and hippocampus → internal cerebral veins → great cerebral vein (of Galen) → straight sinus.
3. Q35What are dural venous sinuses, and how do they differ from veins?

   Spaces between the outer and inner layers of dura. No endothelial lining, no valves, so flow is not strictly one-way.
4. Q36Name the major sinuses.

   Superior sagittal, inferior sagittal, straight, occipital, transverse, superior petrosal, inferior petrosal, sigmoid.
5. Q37Where does all this blood end up?

   Sinuses → sigmoid sinus → internal jugular vein. Emissary veins also connect scalp veins to the sinuses.

Key questions

1. Q38What does CSF do?

   Often called the brain's lymphatic system: it cushions the brain and gives buoyancy (including to the ventral arteries), removes waste, and transports hormones and ions.
2. Q39What are the normal CSF volume, production and pressure?

   About 150 mL total; 400–500 mL made per day; normal pressure 70–180 mm H₂O.
3. Q40Where and how is CSF made?

   By the choroid plexus — tufts of specialized ependymal cells folded into villi in the lateral, third and fourth ventricles — which filters arterial blood and actively transports some molecules (choroidal artery and vein).
4. Q41Compare CSF with plasma.

   CSF: K⁺ 2.8 mM (plasma 4.5), Ca²⁺ 1.0 mM (2.4), protein 34 mg/dL (6500), 0–5 WBCs and no RBCs.
5. Q42How does CSF flow and leave?

   Choroid plexus → through the ventricles → into the subarachnoid space around brain and cord → through arachnoid granulations into the superior sagittal sinus.
6. Q43What are arachnoid granulations, and why is flow one-way?

   Protrusions of arachnoid through the dura, only in the superior sagittal sinus. CSF pressure exceeds venous pressure, so CSF flows one way into the sinus.
7. Q44What CSF findings point to which disease?

   Neutrophils + cloudy: bacterial meningitis. Lymphocytes (IgG): active multiple sclerosis. RBCs: subarachnoid hemorrhage. Malignant cells: metastatic cancer.
8. Q45When is a lumbar puncture justified?

   Signs such as severe headache, stiff neck, confusion, seizures, persistent flu-like symptoms, fatigue, altered consciousness, severe nausea, fever or rash, light sensitivity, poor coordination.

Key questions

1. Q46What is hydrocephalus, and what causes it?

   Increased CSF volume and pressure with enlarged ventricles, from blocked CSF movement or failed absorption.
2. Q47What is obstructive (non-communicating) hydrocephalus?

   A block inside the ventricular system — e.g., at the interventricular foramen or cerebral aqueduct.
3. Q48What is communicating hydrocephalus, and what causes it?

   CSF flows freely through the ventricles and subarachnoid space, but can't get into the venous system: congenital absence of arachnoid villi, or villi blocked by RBCs after hemorrhage or protein after infection.
4. Q49What is normal pressure hydrocephalus?

   A misnomer — CSF pressure is elevated across repeated measurements. Usually elderly. Triad: urinary problems, dementia, impaired gait ("wet, wacky and wobbly").
5. Q50How is hydrocephalus treated?

   Shunting, removing the blockage, or supportive care.
6. Q51How does a CSF shunt work?

   An inflow catheter in a ventricle, a one-way valve and an outflow catheter; it drains CSF when pressure rises, through subcutaneous tubing, usually to the peritoneum. About a 1-hour surgery, adjustable to CSF pressure, 50–80% success.