What are the functions of CSF?
- cushioning of neural tissue
- distribution of secretory signals
- regulates neurogenesis
- waste clearance
What is the direction of water flow in the choroid plexus cells (ependymal cells)?
Water flows from blood to ventricular lumen (opposite renal tubule cells)
What type of gradient moves water from the blood to the ventricles?
osmotic gradient
What produces the osmotic gradient required for water to move from blood to ventricles?
Na+/K+ ATPases on ventricle/apical side —> Na+ into ventricle and K+ into choroid plexus = water follows Na+
How does Na+ enter the ependymal cells from the blood?
via NHE1 & NCBE
What transports Na+ from the choroid plexus to the ventricular lumen?
Na+/K+ ATPases
How does HCO3- get into the ependymal cells?
- NCBE = (Na+/HCO3- in & Cl- out)
- CO2 is converted to HCO3- by carbonic anhydrase
How does HCO3- leave the ependymal cells and enter the ventricular lumen?
- AE2 (Cl-/HCO3- exchanger)
- HCO3- channels
Why does Cl- accumulate in the ependymal cells?
because it followed Na+ into the cells from the blood
How does Cl- leave the ependymal cells and enter the ventricular lumen?
- apical Cl- channels
- NKCCI cotransporters
What is the net movement of Na+, Cl-, HCO3- from the blood?
Net movement from blood –> ependymal cells –> ventricules
What aquaporin channel does water flow through?
AQP1
What ions are higher in the CSF than in the blood?
Na+, Cl-, & Mg2+
What is the normal ICP?
5-15 mm Hg = 112mm of CSF
As ICP increases what happens to CSF levels?
that decrease by CSF reabsorption into the subdural sinuses increases
What are the regulators of cardiac output to the brain?
- CO2
- [H+]
- [O2]
- astrocyte metabolites
An increase of CO2 levels in the CSF causes what?
increased cardiac output
How does pain sensation from cerebral blood vessels affect blood flow to the brain?
causes PNS activity –> vasodilation
If ICP increases what happens to arterial blood flow?
arterial blood flow decreases –> atrophy/necrosis of brain
What mechanism protects the brain from high blood pressure?
sympathetic induced vasoconstriction ==> increased vascular resistance = neuroprotective
decreased brain profusion causes what sort of response?
increase in systemic vascular resistance –> more blood goes to the brain
- occurs during hemorrhages/traumas
Why does acidic CSF cause an increase in cerebral blood flow?
because CO2 levels are high so increased CBF will result in removal of CO2 (replaced by O2)
What substances are nearly impermeable to the BBB?
plasma proteins, non-lipid soluble organic molecules
What is the major energy source for the brain?
glucose
How does glucose cross the BBB?
non-insulin dependent GLUT 1 receptors
What is the role of P-glycoproteins?
To remove drugs that crossed the BBB back into the blood
What brain structures express GLUT 3 receptors?
neurons
What brain structures express GLUT 5?
microglia
Where are GLUT 1 receptors expressed?
- astrocytes
- microvessels
- choroid plexus/ependymal cells
What organs/brain structures surround the brain?
- posterior pituitary
- area of podtrema
- organum vaculosum of the lamina terminalis (OVLT)
- subfornical organ
What is the role of area postrema?
initiation of vomiting in response to chemotactic triggers
What is the role of the organum vasculosum of the lamina terminalis (OVLT)?
regulation of total body water and thirst; Ang 2 target
Where is the glymphatic system found and what is its function?
macroscopic waste clearance system of the CNS; primarily engaged during sleep
