CSF & Brain Barriers

Question 1

ventricular system

Answer 1

a communicating network of cavities filled with cerebrospinal fluid located within the brain parenchyma

Question 2

flow of ventricular system

Answer 2

lateral ventricles –> 3rd ventricle –> mesencephalic aqueduct –> 4th ventricle –> lateral apertures OR central canal –> subarachnoid space (from lateral ventricles)

Question 3

cerebrospinal fluid

Answer 3

selective ultrafiltration from blood plasma around the CNS

Question 4

choroid plexus

Answer 4

cluster of blood vessels; major site of CSF production

Question 5

what are the two cell layers between plasma and CSF

Answer 5

1. vascular endothelium
2. choroid plexus endothelium

Question 6

vascular endothelium

Answer 6

fenestrated capillaries
NO tight junctions

Question 7

choroid plexus endothelium

Answer 7

cuboidal epithelial cells (continuous with ependymal lining around ventricular system)
HAS tight junctions
semi-permeable
microvilli & basal infoldings increase SA

Question 8

how does CSF flow from blood –> ventricles

Answer 8

cuboidal epithelium of choroid plexus is charged –> draws in ions from capillaries –> creates osmotic gradient –> draws in water from capillaries

Question 9

composition of CSF

Answer 9

1. water (mostly)
2. low protein compared to plasma
3. low cellularity
4. less: glucose, K+, Ca2+
5. more: Na+, Cl+

Question 10

subarachnoid space

Answer 10

space between the arachnoid mater and pia mater that contains blood vessels, nerve roots (dorsal root ganglia), and CSF

Question 11

which cranial nerves are surrounded by SAS

Answer 11

CN I and II

Question 12

what does the rate of flow of CSF depend on

Answer 12

cardiac cycle
drives arterial pulsations in choroid plexus that influence intracranial pressure

Question 13

mechanisms of CSF absorption

Answer 13

1. arachnoid granulations
2. glymphatic system

Question 14

arachnoid granulations

Answer 14

bulbs of arachnoid mater that drive CSF flow into venous sinuses –> cerebral veins

Question 15

glymphatic system

Answer 15

cranial and spinal nerve sheaths drain the brain of CSF

Question 16

CSF functions

Answer 16

1. homeostasis: maintains temp, pressure, removes water, and transports NTs
2. physical support: natural buoyancy and shock absorption
3. nutrition: minor source

Question 17

clinical use of CSF analysis

Answer 17

detect CNS disease
- abnormal: indicates CNS disease
- normal: does NOT rule out CNS disease

Question 18

CSF collection

Answer 18

cisterna magna at the junction of the atlas and occipital lobe

horses: lumbar SAS

Question 19

CSF appearances

Answer 19

clear/colorless: normal
red: hemorrhage <24 hrs
yellow: hemorrhage >24 hrs
cloudiness: increased cell count or protein

Question 20

cranial compartments

Answer 20

1. plasma
2. CSF
3. extracellular fluid

Question 21

brain barriers

Answer 21

1. blood brain barrier
2. blood CSF barrier
3. arachnoid CSF barrier

Question 22

blood brain barrier

Answer 22

barrier between plasma and ECF of interstitial space at the level of the capillaries
- controls what comes in from capillaries
- critical for NVU function

Question 23

function of BBB

Answer 23

provides a controlled microenvironment by maintaining ion homeostasis, plasma molecules, NTs, and brain nutrition and protecting from neurotoxins

Question 24

characteristics of BBB

Answer 24

1. tight junctions
   - peripheral capillaries: fenestrated
   - brain capillaries: NOT fenestrated
2. abundant mitochondria
3. free diffusion of O2, CO2, and SMALL molecules
4. contains regulatory cells (pericytes/astrocytes)

Question 25

pericyte function

Answer 25

maintains BBB integrity regulates exchange of metabolites and signaling molecules with endothelial cells

Question 26

astrocyte function

Answer 26

critical for BBB integrity extend foot processes - 1 that interacts with vascular component and 1 that interacts with neural synapses - act as checkpoints for brain metabolism

Question 27

transport across BBB

Answer 27

1. passive diffusion 2. carrier mediated transport 3. receptor mediated transport 4. active efflux

Question 28

passive diffusion across BBB

Answer 28

small, lipid soluble molecules

Question 29

carried mediated transport across BBB

Answer 29

membrane bound proteins facilitate transport amino acids, carbs, fatty acids, hormones, vitamins, nucleotides

Question 30

receptor mediated transport

Answer 30

receptors on cell surface endocytose the molecule and form a vesicle to transport across membrane, then exocytose on the other side macromolecules

Question 31

active efflux

Answer 31

ATP dependent efflux pumps on endothelial cell membrane keep out toxins AND therapeutic agents

Question 32

blood CSF barrier

Answer 32

barrier between plasma and CSF at the level of the choroid plexus - coordinates with BBB to mediate ECF composition - similar transport mechanisms as BBB

Question 33

blood CSF barrier characteristics

Answer 33

1. fenestrated capillaries 2. cuboidal epithelium with tight junctions

Question 34

arachnoid CSF barrier

Answer 34

barrier between plasma and CSF at the level of the arachnoid cells

Question 35

arachnoid CSF barrier characteristics

Answer 35

1. IMPERMEABLE 2. multilayered epithelium with tight junctions 3. seals inner dural surface 4. NO transport mechanisms