Blood Supply to the Brain Notes (NSCI 2101) PDF

Class 05: Blood supply to the brain Martin Wessendorf (he/him) Dept. Neuroscience, Univ. Minnesota  FYI If you would like to have more study questions, there are study questions at the end of each chapter in Nolte. These are often quite challenging and...

Class 05: Blood supply to the brain Martin Wessendorf (he/him) Dept. Neuroscience, Univ. Minnesota  FYI If you would like to have more study questions, there are study questions at the end of each chapter in Nolte. These are often quite challenging and can help you expand your understanding of the lecture material. If you have questions about Neuroscience or any branch of the biological sciences, the go-to source is Pub Med: https://pubmed.ncbi.nlm.nih.gov/. Let me know if you have difficulty making sense of the journal articles that you find— glad to try to help! I hold office hours Tuesdays 3-4 pm.  Brain & blood The whole body has ~5000 ml of blood; the brain holds ~150 ml (3%) of that blood. ~750-1000ml of blood flow through the brain per minute. The heart only pumps a total of about 5000 ml/min. The brain weighs about 3 lb. Therefore, in a 150- lb person the brain is ~2% of the total body mass, yet it uses ~20% of the total blood every minute. The brain is very metabolically active. The more metabolic activity, the more blood is needed.  What is blood? Water Ions & small molecules: levels are closely regulated – Sodium – Potassium – Glucose & other nutrients – Hormones Proteins – Serum albumen – Clotting factors – Antibodies Cells (~36-54% of blood, by volume—a measure called “hematocrit”) – Red blood cells (use hemoglobin to carry oxygen & CO2) – White blood cells (immune system) – Platelets (clotting)  Blood circulation simplified CO2 Right Left O2 to organs Lungs heart heart Body CO2 to blood O2 Heart (Drawn as if you are facing the person.) Blue = deoxygenated blood Red = oxygenated blood  Blood circulation Vena Pulmonary cava vein Right Left atrium atrium Lungs Body Right Left vent. ventricle Heart Pulmonary (Drawn as if you are artery Aorta facing the person.) Blue = deoxygenated blood Red = oxygenated blood  Definitions Artery: a high-pressure blood vessel carrying blood away from the heart Vein: a low-pressure blood vessel carrying blood toward the heart Note: Artery ≠ oxygenated blood Pulmonary Vein ≠ deoxygenated blood circulation  Blood circulation Vena cava Heart Pulmonary vein Arteries (.1-10s of mm) Right Left Arterioles (7-100 µm) atrium atrium Body Lungs (Brain) Capillaries (5-10 µm) Right Left vent. ventricle Venules (7-100 µm) Heart Veins (.1-10s of mm) Pulmonary artery Aorta Heart Blue = deoxygenated blood Red = oxygenated blood Internal carotid arteries  anterior brain Arch of aorta https://dbmmu5j6lxew.cloudfront.net/pe-carotidstenosis1.jpg  Vertebral arteries posterior brain (View is from the anterior/ventral side of the vertebral column.) http://examnnotes.com/images/vertebral%20artery%204.jpg  Blood supply to the brain Internal carotid a. Vertebral a. Circle of Willis Branches of Circle of Willis Anterior communicating a. Internal Anterior carotid a. cerebral a. Posterior communicating a. Middle cerebral a. Posterior cerebral a. Basilar a. Vertebral a. Regions supplied by brain arteries VB VB Lateral view Midsagittal view (A) Anterior cerebral artery: midline of cerebral cortex (M) Middle cerebral artery: lateral side of cerebral cortex (P) Posterior cerebral artery: posterior-inferior cerebral cortex (VB) Vertebral & Basilar arteries: brainstem & cerebellum Major arteries and veins run in subarachnoid space Calvaria http://biodrawing.com/Neurology_modules/NervousSystemSite/Neuroanatomy/figures/Meninges-004-02.png  Venous drainage of the brain Veins drain into the dural venous sinuses Dural venous sinuses drain into the internal jugular vein, which carries blood back toward the heart  Dural venous sinuses are formed by separations between two layers of dura (shown in gray, below). Dural venous sinus (Superior Veins sagittal sinus) Skull [Arachnoid granulation] 1 3 Cerebral cortex 2 Dura between cerebral hemispheres (falx cerebri)  Dural venous sinuses Falx Superior cerebri (Anterior) sagittal sinus Tentorium cerebelli top view midsagittal (side) view Transverse sinus Dural venous sinuses drain into internal jugular vein Dural venous sinuses on inside of skull Internal jugular vein emerging from bottom of skull https://i.pinimg.com/736x/e1/7c/7b/e17c7b10923fb44d7d27cde84c6d1a61.jpg Jugular foramen on underside of skull Anterior end of skull Jugular foramen https://i.pinimg.com/736x/e1/7c/7b/e17 c7b10923fb44d7d27cde84c6d1a61.jpg Foramen magnum (spinal cord) http://classconnection.s3.amazonaws.com/339/flashcards/5 486339/jpg/jugular_foramen-14621CEADB043D8CCC1.jpg Jugular foramen on interior of skull Anterior end of skull Jugular foramen https://i.pinimg.com/736x/e1/7c/7b/e17 c7b10923fb44d7d27cde84c6d1a61.jpg https://classconnection.s3.amazonaws.com/524/flashc ards/1811524/jpg/jugular_foramen1354661911959.jpg  Regulation of blood flow in brain Hypoxia  vasodilation – Severe hypoxia can increase blood flow 400% Increased CO2  vasodilation Decreased CO2  vasoconstriction Changes in brain activity  changes in blood oxygenation Brain oxygenation can be mapped with “Functional MRI (fMRI)” (“Functional Magnetic Resonance Imaging”) Thus changes in brain activity can be mapped to specific brain regions  Experiment Present subject with a pungent but neutral odor (e.g. cheddar cheese), or with clean air Measure changes in brain activity as a function of the odorant by using the level of blood oxygenation  Increased oxygenated blood in olfactory (smell) cortex with presentation of odorant de Araujo et al 2005, Neuron. 46(4):671-9  Blood-brain barrier regulates access of chemicals to the brain https://proxy.duckduckgo.com/iu/?u=https%3A%2F%2Fi.pinimg.com%2Foriginals%2Fd1%2F76%2Fe8%2Fd176e8e9c9778f3f7ed1aa3e820d00e6.png&f=1&nofb=1  Blood-brain barrier Access to the brain is strictly regulated “Tight junctions” block diffusion between capillary endothelium Completely surrounded by astrocyte processes Water-soluble chemicals can pass through other capillaries but not those in the brain Nutrients enter and toxins exit via chemical pumps (“carriers”) https://proxy.duckduckgo.com/iu/?u=https%3A%2F%2Fi.pinimg.com%2Foriginals% 2Fd1%2F76%2Fe8%2Fd176e8e9c9778f3f7ed1aa3e820d00e6.png&f=1&nofb=1  Drugs and the blood-brain barrier Water-soluble drugs have difficulty passing into the brain – This can be good: not everything gets to the brain – Problematic if you need a drug to get into the brain Lipid-soluble (i.e. fat-soluble) drugs pass more easily – Heroin (faster-acting) vs. morphine (slower-acting) Blood brain barrier can slow removal of some drugs from the brain – Lack of a pump to remove a drug from the CNS may mean that it’s not eliminated from the brain There are a few places where the blood-brain barrier doesn’t exist: the circumventricular organs Posterior Anterior end end Mid-sagittal view of brain The circumventricular organs: the few places in the brain where the blood-brain barrier doesn’t exist A place where the brain senses how much salt is in the blood – “I’m thirsty!” A place where the brain releases hormones into the blood – “I need to stop making urine!” A place where the body senses toxins – “I need to puke!” All are in the diencephalon or brain stem All are sealed off from the rest of the brain – Substances can’t migrate out into the rest of the brain  Damage to brain vascular system: Trauma Skull fracture  tearing of dural arteries Head impact  tearing of veins supplying dural venous sinuses (--more serious threat in the elderly) Piercing injury (e.g. gun-shot)  tearing of dural or brain arteries and/or veins  Damage to brain vascular system: stroke Hemorrhagic stroke Ischemic stroke  Hemorrhagic stroke Due to aneurism (ballooning weak spot) in blood vessel Treatable if detected before bursting by clipping base of the “balloon” Often fatal if they burst Symptoms: Victim is suddenly overcome by extremely severe headache (“thunderclap https://med.nyu.edu/sites/default/files /radiology/Brain-Aneurysm-1.jpg headache”)—MEDICAL EMERGENCY!  Ischemic stroke Ischemia = lack of blood flow Ischemic stroke is due to an artery being blocked, usually by a blood clot Can sometimes be prevented by removing atherosclerotic plaque from arteries (“Carotid endarterectomy”) Can be treated with “clot-buster” drugs or by surgical removal of the clot, if treatment is begun quickly Symptoms: muscle weakness, difficulty speaking, drooping face, etc. depending on site of clot.  Risk factors for stroke High blood pressure (#1 by far) – Current guidelines: hypertension is >140 mm Hg systolic; pre-hypertension is >130 mm Hg systolic High cholesterol levels Diabetes Smoking Sickle-cell disease  How to prevent stroke: Get rid of your car and ride your bike There is a strong association between midlife cardiorespiratory fitness and decreased stroke risk in later life independent of other risk factors. Pandey et al, Stroke, 2016; 47: 1720-1726.  Bike commuting at the U https://pts.umn.edu/bike- scooter/bike-scooter Interested in winter biking? – Facebook’s “Winter Cycling” group – Or talk to Dr. Wessendorf Class 06: Cells Dr. Riedl