General Neurophysiology Flashcards
What transporters are present on the apical and basolateral membranes of the choroid plexus cell and function in the production of CSF?
Basolateral: NCBE (Na/HCO3 exchanger), aquaporin 1
Apical: Na/K-ATPase, aquaporin 1
T/F: the blood and CSF isosmotic
True
H2O, Na, Cl, and HCO3 are found in higher concentrations in CSF, while ____ ion is found in higher concentrations in the blood
K+
An osmotic gradient moves water from the blood to the ventricles across the choroid plexus. What creates the gradient?
Na/K-ATPase creates an electrochemical gradient for Na (increasing its intracellular concentration)
Final result is net flux of Na, HCO3, and Cl from blood across the epithelium and into the ventricles
Where are protein, glucose, and pH greater — in serum or CSF?
Serum
Production of CSF is constant over a wide range of intracranial pressures. CSF is typically absorbed by ____ ____ which occurs mostly by bulk flow. This absorption is proportional to intracranial pressure, so when intracranial pressure decreases, what happens to absorption?
Arachnoid villi
When ICP decreases, no absorption occurs
The brain is 2% of body weight but receives ____% of cardiac output
15
Regulators of blood flow to the brain
CO2 regulation
H+ concentratoin
Oxygen concentration
Astrocyte metabolites
What effect does increasing CO2 in the blood have on cerebral blood flow?
Increases it
Effect of sympathetics on cerebral circulation (and the neurotransmitters involved)
Leads to vasoconstriction when systemic CO or BP increases (protective of brain vasculature)
NTs = NE, NPY
[receptors are alpha-adrenergic]
Effect of parasympathetics on cerebral circulation (and the neurotransmitters involved)
Leads to vasodilation when systemic CO or BP decreases (to maximize blood flow to brain)
NTs = ACh, VIP, CGRP, SP
How do changes in cerebral circulation cause pain?
Cerebral circulation is innervated — sensory innervation monitors sensation of distal blood vessels using NTs SP, NKA, and CGRP
This renders blood vessels sensitive to torsion/manipulation, leading to pain! Likely to occur in cases of decreased CSF volume which renders the brain heavier
Effect of reciprocal activation of sensory afferents on cerebral circulation and CSF volume
Reciprocal activation of sensory afferents activates vasodilation and increases blood flow, perhaps to increase CSF volume
Causes of ICP include hydrocephalus, edema, infection, intracranial bleeding, and tumor blockage. What effect does increased intracranial pressure have on cerebral blood flow?
Increased ICP —> obstruction of venous outflow —> reduced arterial flow
Sympathetics vasoconstrict vasculature in the face of high BP.
Vasoconstriction by sympathetics ______ systemic vascular resistance but protects the BBB and capillaries
Increases
Autoregulation of cerebral blood flow is mediated by _____ stimulation
Sympathetic
In the event of reduced brain perfusion, _____ centers are activated which _______ systemic blood pressure and drives blood to the brain
Vasomotor; increases
Extrinsic regulators of cerebral blood flow include systemic BP, blood viscosity, and carotid/vertebral vessel lumen occlusions.
Things that affect blood viscosity, like anemia vs. polycythemia would hve what effect on cerebral blood flow?
Anemia (low erythrocyte count, low viscosity) —> increased CBF
Polycythemia (high viscosity) —> decreased CBF
Intrinsic factors that affect cerebral blood flow include autoregulation, arterial CO2 and O2, and pH. What effect does CO2 concentration and pH have on cerebral blood flow?
High Pa CO2 (acidosis) —> increased CBF
Low PaCO2 (alkalosis) —> decreased CBF
In what parts of the brain would you NOT find the BBB or blood-CSF barrier?
Circumventricular organs (CVOs)
Characteristics of BBB in terms of permeability
Highly permeable to water, CO2, O2, and lipid-soluble substances
Slightly permeable to Na, Cl, and K
Nearly impermeable to plasma proteins and non-lipid-soluble organic molecules
Majority of capillaries lack typical slit pores
Functions of BBB
Protection
Maintains electrolyte composition of CSF and neural parenchyma
Excludes toxins
Contains NTs
Cellular consituents of BBB
Astrocyte endfeet
Pericytes
Endothelial cells
What is the major energy source for the brain and how does it cross the BBB?
Glucose; crosses via GLUT1 transport protein (NOT insulin dependent)
What transporter transports ions from CSF to the blood across the BBB?
Na-K-2Cl
[expression tied to endothelin 1 and 3; endothelin production tied to astrocyte signal; may be related to [K] in CSF]
What role does P-glycoprotein play in transportation across BBB?
Moves drugs that don’t belong that crossed BBB back into the blood
[member of ABC transporter family]
The most important glucose transporters in the brain are GLUT1, 3, and 5. Where are these found?
GLUT1 = astrocytes, microvessels, choroid plexus, ependymal cells
GLUT3 = neurons
GLUT5 = microglia
What are the 4 circumventricular organs?
Posterior pituitary (secretory; endocrine)
Area postrema (sensory; initiation of vomiting from chemotactic trigger)
Organum vasculosum of lamina terminalis (sensory; regulation of TBW and thirst - target angiotensin II)
Subfornical organ (sensory)
What theorized system may assist in macroscopic waste clearance system and is thought to be primarily engaged during sleep?
Glymphatic system
