Maintenance of the CNS Environment

Question 0

does CSF recirculate?

Answer 0

NO, so we make about 550ml/day

Question 1

How much CSF is there at any given moment

Answer 1

150 ml

Question 2

Where is most of the CSF made?

Answer 2

The specialized tissue of the choroid plexus (50-70%)

Question 3

Where is the remainder of the CSF made

Answer 3

the tissue that lines the ventricles and blood vessels

Question 4

What is the two step process of CSF formation

Answer 4

1. passive filtration of serum
2. modification of CSF (HCO3-, Cl- and K+ concentrations controlled by channels on epithelial cells, aquaporins also exist)

Question 5

Important note regarding CSF production and ICP

Answer 5

production of CSF is constant over a wide range of ICPs

Question 6

things that ed up in equal concentrations in plasma and CSF (3)

Answer 6

Na
Cl
HCO3

Question 7

things that are present in higher concentration in the CSF than plasma (2)

Answer 7

Mg2+

CO2

Question 8

Things that are present in lower concentrations in CSF than plasma
(4)

Answer 8

K
Ca
protein
glucose

Question 9

CSF flows through the _______. Flow is _______ and CSF must be ________.

Answer 9

ventricular system
one way
reabsorbed at the end

Question 10

Absorption of CSF is through

Answer 10

arachnoid villi

Question 11

arachnoid villi - how is CSF reabsorbed

Answer 11

endothelium of sinus and the membrane on the villi have fused.
bulk flow of CSF into venous sinus is primary
pinocytosis is also documented

Question 12

Absorption of CSF related to ICP

Answer 12

absorption of CSF is proportional to ICP
at pressures below 68mm CSF, no absoption
normal pressure =112 mm CSF
increased pressure causes damage to neurons

Question 13

Role of CSF

Answer 13

to protect the brain
weight in air= 1400g
weight in CSF= 50g

Question 14

BBB - two components that limit exchange in cpillaries in brain

Answer 14

tight junctions between endothelial cells

glial endfeet come in close contact with blood vessel

Question 15

things that can passively diffuse across the BBB

Answer 15

H2O
CO2
O2
FREE steroid hormones (most are bound to protein)

Question 16

major energy source for neurons? Does it cross BBB

Answer 16

glucose, does NOT cross BBB readily

Question 17

How does glucose cross the blood brain barrier

Answer 17

GLUT1 transporter

Question 18

Is the GLUT 1 transporter insulin dependent?

Answer 18

no

Question 19

Two forms of GLUT1 transporters

Answer 19

45K= astroglia
55K= capillaries

Question 20

Importance of NaK2Cl transporter at BBB

Answer 20

moves all those ions from CSF to blood
expression tied to endothelin 1 and 3
ET production tied to a signal from the astrocytes, may be related to [K] in CSF

Question 21

Many drugs do cross the BBB, but are moved back to the blood via?

Answer 21

P-glycoprotein

Question 22

Function of BBB

Answer 22

to protect the chemical composition of the CSF from blood-borne agents, maintain electrolyte composition, protect from toxins, prevent escape of NTs

Question 23

BBB in particular maintains electrolyte composition related to _____. Why?

Answer 23

K+ to keep Vm maintained

Question 24

Circumventricular organs

Answer 24

places in teh brain where we want the brain exposed to the blood.

Question 25

Circumventricular organs are different in that they dont have a BBB. What is different

Answer 25

the capillaries do not have tight junctions between endothelial cells.

Question 26

4 circumventricular organs

Answer 26

area postrema - vomitting
posterior pituitary - releases hormones into the blood
OVLT - control of body water/thirst/ blood volume, angiotensin control
subfornical organ - control of body water/thirst/blood volume, angiotensin control

Question 27

Cerebral circulation receives _______ml (___% of CO)

Answer 27

750

14

Question 28

Circle of Willis is formed by

Answer 28

2 internal carodtids and the basilar artery

Question 29

Does blood from different sources mix in the Circle of willis? What is the impact?

Answer 29

NO

disruption of one of the inputs prduces localized (discrete) areas of ischemia.

Question 30

Sympathetic Innervation of the vasculature
NT
R
effect

Answer 30

NE, NPY
alpha adrenergics
leads to constriction when systemic cardiac output/BP increases

Question 31

Parasympathetic innervation of cerebral circulation
where
NT
effect

Answer 31

larger blood vessels
Ach, VIP, PHM-27 (derived from pre pro VIP)
cause vasodilation

Question 32

Sensory innervation
NT
effect
impact

Answer 32

substance P, neurokinin A, CGRP
DILATION
these sensory fibers render the blood vessls of the brain extremely sensitive to torsion/manipulation - lead to pain

Question 33

Role of Sensory innervation

Answer 33

in reduced CSF volume, the brain is effectively heavier and simple motion can cause bain bc of torsion of the blood vessels
the activation of those afferents will also cause vasodilation and increase blood flow (returns total intracranial volume closer to normal?)

Question 34

Cerebral blood flow is under what kind of control

Answer 34

local control

oxygen consumption dictates where in the brain blood will go

Question 35

What happens to cerebral blood flow as ICP increases

Answer 35

venous outflow is obstructed, leading to reduced arterial flow

Question 36

cerebral bloodflow is strongly autoregulated, meaning

Answer 36

it is held constant over a wide range of systemic (mean arterial) blood pressures

Question 37

In the face of high BP (which could damage the BBB), sympathetics in the brain will _______ the vasculature

Answer 37

vasoconstrict

although this will increase the systemic vascular resistance, it protects the capillaries in the brain from damage - sacrifice the heart for the brain

Question 38

a decrease in brain perfusion will activate the vasomotor centers and _______systemic BP

Answer 38

increase, sometimes drastically. –> the brain will drive the body’s bp up in hopes of sending enough blood to the brain to get adequate perfusion

Question 39

what might incrrease the ICP

Answer 39

hydrocephalus of any variety
edema
bleeding within the skull