General Neurophysiology

Question 1

What are the two barriers in the brain?

Answer 1

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

Question 2

CSF is located in what three places?

Fx?

Answer 2

Ventricles, cisterns, subarachnoid space

Cushioning, distribution of secretory signals, regulates neurogenesis, waste clearance

Question 3

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?

Answer 3

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

Question 4

What three pumps help filter the CSF from the blood to the ventricular lumen?

Where are they located?

Answer 4

Aquaporin channels: ventricular (apical) and basolateral (blood) membranes

NCBE (Na/HCO3 exchanger): basolateral membrane (blood)

Na/K ATPase: ventricular membrane (apical)

Question 5

What flows from the blood to the CSF?

What flows from the CSF to the blood?

Answer 5

H2O, Na, Cl, HCO3

K

Question 6

____ 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?

Answer 6

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

Question 7

What is equal in CSF and serum?

What is greater in CSF than serum?

What is greater in serum than CSF?

Answer 7

Na, osmolarity

Cl, CO2, H2O, Mg

K, HCO3, Ca, protein, glucose, pH

Question 8

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 ____.

Answer 8

Constant

Arachnoid villi

Intracranial pressure

Will not absorb

Question 9

The brain receives ____ of cardiac output.

What regulates blood flow to the brain?

Increasing ____ in the blood greatly increases cerebral blood flow.

Answer 9

15%

CO2 regulation

Hydrogen ion concentration

O2 concentration

Astrocyte metabolites

Carbon dioxide (disassociates with water, form carbonic acid, gives off H+ which causes vasodilation)

Question 10

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?

Answer 10

Sympathetics and parasympathetics

Vasoconstriction; NE, NPY, receptors alpha-adrenergics

Vasodilation: ACh, VIP, CGRP, SP

Question 11

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?

Answer 11

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

Question 12

ICP influences cerebral blood flow by ____.

What five things can increase ICP?

Answer 12

Leading to obstruction of venous outflow -> reduced arterial pressure

Hydrocephalus, edema, infection, intracranial bleeding, tumor blockage

Question 13

Describe the affects of pressure on cerebral blood flow.

Answer 13

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

Question 14

____ maintains blood flow in the presence of changing mean arterial blood pressure. It is mediated by ____.

How?

Answer 14

Autoregulation; sympathetics

Drop in BP-> vasodilation -> increase cerebral blood flow

Question 15

_____ induce vasoconstriction in the face of high BP.

What are the effects?

Answer 15

Sympathetics

Vasoconstriction increases systemic vascular resistance but protects the BBB and capillaries

Question 16

When there is reduced brain perfusion, ____ are activated.

What is the effect?

Answer 16

Vasomotor centers

Increases systemic BP and drives blood to the brain

Question 17

What extrinsic factors can affect cerebral blood flow?

Answer 17

Systemic blood pressure: baroreceptor

Blood viscosity: erythrocytes concentration, anemia=increase CBF, polycythemia=decrease CBF

Occlusions in the carotid or vertebral A lumens

Question 18

What intrinsic factors regulate cerebral blood flow?

Answer 18

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

Question 19

What neural factors influence cerebral blood flow?

Answer 19

Sympathetics -> vasoconstriction

Parasympathetics -> vasodilation

Question 20

What are the barrier interfaces associated with the brain?

Answer 20

BBB, blood CSF, CSF arachnoid, fetal CSF, adult CSF

Question 21

The BBB and blood CSF barrier are not present in ____.

What is their fx and what are they permeable to?

Answer 21

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

Question 22

What are the fx of the BBB?

What are the cells in the BBB?

Answer 22

Protection, maintains electrolyte composition of CSF and neural parenchyma, excludes toxins, contains neurotransmitters

Astrocyte endfeet, pericyte (contractile) endothelial cell (with tight junctions)

Question 23

What can cross the BBB through passive diffusion?

What is the major energy source for the brain?

Answer 23

H2O, CO2, O2, unbound steroid hormones, lipid soluble stuff

Glucose

Question 24

What pathways allow molecules to cross the BBB?

Answer 24

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

Question 25

What are three transporters in the BBB and what do they transport?

Answer 25

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

Question 26

What are the three glucose transporters in the brain and what cells use them?

Answer 26

Glut 1: astrocytes, microvessels, choroid plexus, ependymal cells

Glut 3: neurons

Glut 5: microglia

Question 27

What are the circumventricular organs?

Answer 27

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

Question 28

What is the theory of the glymphatic system?

Answer 28

Macroscopic waste clearance system

Primary engaged during sleep