General Neurophysiology Flashcards
What are the two barriers in the brain?
BBB: between blood and capillaries and neuronal cells
CSF barrier: blood meets the cells of the choroid plexus that are secreting the fluid of the ventricular system
CSF is located in what three places?
Fx?
Ventricles, cisterns, subarachnoid space
Cushioning, distribution of secretory signals, regulates neurogenesis, waste clearance
The choroid plexus epithelial cells are ___.
What are its two membranes?
What is the pathway blood takes to be filtered into the ventricles?
What drives this process and where?
Polar
Ventricular lumen (apical) and blood side (basolateral)
Fluid goes across the basolateral membrane -> filtering it in a choroid plexus cell -> cross apical membrane -> and fill up ventricles with CSF
NA/K ATPase pump on the ventricular membrane
What three pumps help filter the CSF from the blood to the ventricular lumen?
Where are they located?
Aquaporin channels: ventricular (apical) and basolateral (blood) membranes
NCBE (Na/HCO3 exchanger): basolateral membrane (blood)
Na/K ATPase: ventricular membrane (apical)
What flows from the blood to the CSF?
What flows from the CSF to the blood?
H2O, Na, Cl, HCO3
K
____ moves water from the blood to the ventricles, across the choroid plexus.
What is the first step in this process?
What is the result of this step?
Osmotic gradient
Na/K ATPase on the apical membrane creates an electrochemical gradient for Na
Net influx of Na, HCO3, and Cl from the blood crossed the epithelium into the ventricles -> this creates the osmotic gradient that drives H2O through aquaporin 1 and into the ventricles
What is equal in CSF and serum?
What is greater in CSF than serum?
What is greater in serum than CSF?
Na, osmolarity
Cl, CO2, H2O, Mg
K, HCO3, Ca, protein, glucose, pH
The production of CSF is ___ over a wide range of intracranial pressures. What changes is how it is reabsorbed.
CSF is reabsorbed by an ____. Occurs by bulk flow with some evidence of pinocytosis.
Absorption of CSF is proportional to ____. If ICP drops below 68 mm, CSF ____.
Constant
Arachnoid villi
Intracranial pressure
Will not absorb
The brain receives ____ of cardiac output.
What regulates blood flow to the brain?
Increasing ____ in the blood greatly increases cerebral blood flow.
15%
CO2 regulation
Hydrogen ion concentration
O2 concentration
Astrocyte metabolites
Carbon dioxide (disassociates with water, form carbonic acid, gives off H+ which causes vasodilation)
The cerebral circulation is innervated by ____ and _____.
Sympathetics lead to ____ when systemic CO of BP increases. What neurotransmitters influence this?
Parasympathetics lead to ____ when systemic CO or BP decreases. What neurotransmitters influence this?
Sympathetics and parasympathetics
Vasoconstriction; NE, NPY, receptors alpha-adrenergics
Vasodilation: ACh, VIP, CGRP, SP
Cerebral blood vessels are innervated by ____. This innervation monitors the ____ and renders the blood vessels sensitive to torsion/manipulation, leading to pain.
What neurotransmitters are involved?
What can affect the sensory afferents and cause pain?
Reciprocal activation of sensory afferents activate what?
Sensory afferents; sensation of distal blood vessels
SP, NKA, CGRP
Decreased CSF volume renders brain heavier, simple motion torques blood vessels
Vasodilation, increase blood flow, increase CSF volume
ICP influences cerebral blood flow by ____.
What five things can increase ICP?
Leading to obstruction of venous outflow -> reduced arterial pressure
Hydrocephalus, edema, infection, intracranial bleeding, tumor blockage
Describe the affects of pressure on cerebral blood flow.
High ICP=Low cerebral blood flow
High PaCO2=High cerebral blood flow (because of vasodilation)
Low PaO2=High cerebral blood flow -> plateaus -> High PaO2=Low cerebral blood flow
____ maintains blood flow in the presence of changing mean arterial blood pressure. It is mediated by ____.
How?
Autoregulation; sympathetics
Drop in BP-> vasodilation -> increase cerebral blood flow
_____ induce vasoconstriction in the face of high BP.
What are the effects?
Sympathetics
Vasoconstriction increases systemic vascular resistance but protects the BBB and capillaries
When there is reduced brain perfusion, ____ are activated.
What is the effect?
Vasomotor centers
Increases systemic BP and drives blood to the brain
What extrinsic factors can affect cerebral blood flow?
Systemic blood pressure: baroreceptor
Blood viscosity: erythrocytes concentration, anemia=increase CBF, polycythemia=decrease CBF
Occlusions in the carotid or vertebral A lumens
What intrinsic factors regulate cerebral blood flow?
Autoregulation: alters the tension in the wall of small vessels; sympathetic
Arterial CO2 and O2: high PaCO2-> increases CBF, very low PaO2-> increases CBF
pH: acidosis -> ++H -> vasodilation -> increase CBF
alkalosis -> low decrease CBF
What neural factors influence cerebral blood flow?
Sympathetics -> vasoconstriction
Parasympathetics -> vasodilation
What are the barrier interfaces associated with the brain?
BBB, blood CSF, CSF arachnoid, fetal CSF, adult CSF
The BBB and blood CSF barrier are not present in ____.
What is their fx and what are they permeable to?
Circumventricular organs (CVOs)
Facilitated transport that carries necessary molecules across the barrier
Highly permeable: water, CO2, O2, lipid soluble substances
Slightly permeable: Na, Cl, K
Nearly impermeable: plasma proteins, non-lipid soluble organic molecules
What are the fx of the BBB?
What are the cells in the BBB?
Protection, maintains electrolyte composition of CSF and neural parenchyma, excludes toxins, contains neurotransmitters
Astrocyte endfeet, pericyte (contractile) endothelial cell (with tight junctions)
What can cross the BBB through passive diffusion?
What is the major energy source for the brain?
H2O, CO2, O2, unbound steroid hormones, lipid soluble stuff
Glucose
What pathways allow molecules to cross the BBB?
Paracellular aqueous: water-soluble agents
Transcellular lipophilic: lipid-soluble agents
Transport proteins: glucose, AA, nucleosides, cyclosporin A, AZT
Receptor-mediated transcytosis: insulin, transferrin
Adsorptive transcytosis: albumin, plasma proteins
What are three transporters in the BBB and what do they transport?
Glut 1: transports glucose from blood, not insulin dependent
Na-K-Cl: transports ions from CSF to blood, expression tied to endothelin 1 & 3, endothelin production tied to astrocyte signals
P-glycoprotein: moves drugs that don’t belong across the BBB, back into the blood
What are the three glucose transporters in the brain and what cells use them?
Glut 1: astrocytes, microvessels, choroid plexus, ependymal cells
Glut 3: neurons
Glut 5: microglia
What are the circumventricular organs?
Posterior pituitary: secretory
Area postrema: sensory, initiation of vomiting response to chemotactic triggers
Organum vasculosum of the lamina terminalis (OVLT): sensory, regulation of total body water and thirst-> target of angiotensin II
Subfornical organ: sensory
What is the theory of the glymphatic system?
Macroscopic waste clearance system
Primary engaged during sleep
