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Thinking questions

Ventricular System, Meninges, and CSF Study suggestion: Read the selected pages from Chapter 2 first, then read Chapter 8. Thinking questions. How to pack something very fragile that has to be shipped cross-country

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Thinking questions

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  1. Ventricular System, Meninges, and CSFStudy suggestion: Read the selected pages from Chapter 2 first, then read Chapter 8

  2. Thinking questions • How to pack something very fragile that has to be shipped cross-country • How to make a person who is heavy into a person who can be lifted with one hand

  3. Overview of this lecture, so you see the big picture • CNS is very fragile and vulnerable, and it is constantly being transported around • Cushion from ___________ and ___________ • Encase the whole thing in _______________ • CNS would collapse under its own weight if placed on a table. Brain’s weight is reduced from 1500g (3.3 lbs)  75 g (1/10 of a lb.) because it is ___________ in __________

  4. Introduction to CSF • Cerebrospinal Fluid (CSF) • Colorless • Continuously produced deep within internal brain spaces called ___________, and cushions around whole CNS ______________ • Functions • Mechanical cushion around CNS • Removal of harmful substances & waste

  5. CSF CIRCULATION: Where does it start? Produced in ventricles*, and flows caudally through ventricular system • Two lateral ventricles • Interventricularforamen • One third ventricle • Cerebral aqueduct • One fourth ventricle • Two foramina of Luschka • One foramen of Magendie * CSF produced by choroid plexus in the ventricular cavities

  6. Can you find the structures mentioned in the previous slide on these figures?

  7. So, CSF exits the ventricular system • Exits from 4th ventricle through • Two foramina on lateral sides of fourth ventricle = __________________ • One foramen in posterior part of fourth ventricle = foramen of ___________________ • Enters into a space called _____________ that encircles/covers whole CNS!

  8. More about subarachnoid space • Net-line structure within the SAS is called arachnoid trabeculae • Large pockets/enlargements of SAS are called _______________________ • Do you see the arachnoid trabeculae? Do you see any cisterns? • Lumbar puncture (spinal tap) from lumbar cistern

  9. Subarachnoid space is sandwiched between two of the three covering layers over the CNS • These three layers are called the MENINGES. • ??? How is this related to meningitis?

  10. Outer covering of brain:Where are the meninges? • (Scalp) • (Muscles and surface arteries) • (Bone: Skull) • Meninges • Cover brain and spinal cord • 3 layers • Between two of the layers is a cushioning layer of fluid called cerebrospinal fluid

  11. Meninges • Three-layer covering of CNS, from outermost to innermost • Dura mater (outermost, tough, DURable) • has 2 fused, closely united sub-layers • One next to bone • One next to arachnoid mater • 2 layers separate in spots to form venous sinuses • Arachnoid mater + subarachnoid space (below it): • Pia mater (innermost, “tender” fragile) • Three layers continuous: brain & spinal cord

  12. Meninges cover all of the CNS, including spinal cord

  13. Dura mater: More details • In certain places, the two layers separate to form dural venous sinuses (system of cavities and channels to drain venous blood) • Rigid sheets of dura mater extend into cranial vault (Fig. 3-11 in W&A) • Falxcerebri • flat, crescent-shaped • separates two cerebral hemispheres • Tentoriumcerebelli • dome-shaped • separates cerebral hemispheres from cerebellum • Diagphragmasella (not pictured) • Roof of structure that encloses pituitary gland

  14. Do you see where the dural venous sinuses are?

  15. Coronal section: More details on dura mater • Look at falxcerebri and tentoriumcerebelli • Folds of dura mater • Brace brain from displacement • Receive blood from brain’s cerebral veins • Receive cerebrospinal fluid from subarachnoid space

  16. Subarachnoid space (SAS): More details • Sub-arachnoid space filled with cerebrospinal fluid (CSF) • Extends into sulci (p. 63 of W) • Larger portions of this space called cisterns (Figure 3-9) • Arachnoid protrudes into dural venous sinuses • Protrusions = arachnoidvilli • CSF absorbed into blood + removed from SAS

  17. Pia mater: More details • Adheres tightly to surface of brain • Outer surface has many blood vessels • Many blood vessels cross the space between the pia and the arachnoid maters

  18. Circulation of CSF: Lateral view

  19. Clinical applications related to CSF • Blockage of CSF movement or failure of resorbtion mechanism  accumulation of fluid in ventricles or around brain tissue  hydrocephalus • Treated by shunting CSF from ventricle to body peritoneal or pleural cavities • Medical diagnostics on CSF • CSF pressure (high pressure associated with tumor, hemorrhage, hydrocephalus, meningitis or encephalitis) • CSF chemical and cell studies

  20. Clinical application related to meninges Extracerebral hemorrhages • Hemorrhages from the blood vessels in the meninges or on the surface of the brain, from: • Weakness of vessel wall • Traumatic injury • (rarely)-extreme fluctuations in blood pressure • Types, based on where blood accumulates • Subarachnoid: b/w arachnoid and pia (most common, from • aneurysm • arteriovenous malformation (AVM) • Subdural: under dura (esp. from TBI) • Epidural: b/w dura and skull (esp. from TBI) • After bleeding stops, left with hematoma

  21. Clinical application: Extracerebralhemorrhages (cont.) • Types, based on where blood accumulates • Subarachnoid: b/w arachnoid and pia (most common, from • aneurysm • arteriovenous malformation (AVM) • Subdural: under dura (esp. from TBI) • Epidural: b/w dura and skull (esp. from TBI) • After bleeding stops, left with hematoma

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