Cerebral Flow and CNS Homeostasis

Question 1

where is CSF found?

Answer 1

• between arachnoid and pia mater
• ventricles of brain
• central canal of SC

Question 2

the lateral and 3rd ventricles are supplied by what artery?

4th ventricle?

Answer 2

lateral and 3rd: internal carotid a.

4th: inferior cerebellar a.

Question 3

how does the choroid plexus maintain blood-CSF barrier?

Answer 3

apical borders contain microvilli which are fenestrated underneath the epithelial lining with tight junctions in the apical border of epithelia

allows only small molecules and fluid through

Question 4

what is the flow of CSF?

Answer 4

lateral ventricles –> 3rd ventricle –>

4th ventricle –> central canal of SC or subarachnoid space (through medial and lateral aperatures in 4th ventricle)

Question 5

where does CSF enter the subarachnoid space and from there what does it do?

Answer 5

• cerebromedullary cistern

- goes into venous sinuses through arachnoid granulations

Question 6

how are the lateral and 3rd ventricles connected?

3rd and 4th?

Answer 6

L/3: intraventricular foramen

3/4: cerebral aquaduct

Question 7

what do the median and lateral aperatures of the 4th ventricle connect it to?

Answer 7

medial: cisterna magna
4th: arachnoid space

Question 8

which ions are found in the same concentration in both plasma and CSF?

higher in CSF?

lower in CSF?

Answer 8

= Na and HCO3

> Mg, CO2, Cl

< K, Ca, Protein, Glucose

Question 9

what substances can freely cross the BBB?

Answer 9

H20, CO2, O2, free steroid hormones

Question 10

how does glucose pass the BBB?

Answer 10

Glut 1 transporter (not insulin dependent)
- 2 forms 45K on astroglia and 55K on capillaries

Neurons use Glut3

Question 11

what moves drugs that cross the BBB back into the blood?

Answer 11

p-glycoprotein

Question 12

what 4 brain regions are not protected by the BBB?

Answer 12

• posterior pituitary (releases hormones)
• area postrema (vomiting)
• OVLT (organum vasculosum of lamina terminalis, regulates osmotic concentration of the body)
• subfornical organ

Question 13

why does disruption of one input to the circle of willis produce localized areas of ischemia?

Answer 13

because there is little mixing of blood from each different source (not really an anastomosis)

this prevents the entire brain from being damaged by lack of blood, only one area is affected

Question 14

what effect does sympathetic innervation have on cerebral circulation?

Answer 14

vasoconstriction when systemic CO/BP is increased

NE and NPY on alpha-adrenergics

helps keep blood flow constant when mean systemic arterial BP increases to prevent capillaries in brain and BBB from damage

Question 15

what effect does parasympathetic innervation have on cerebral circulation?

Answer 15

vasodilation

Ach, VIP, and PHM27 on ???

Question 16

which NTs are released in response to sensory innervation of the distal blood vessels to dilate blood vessels in cerebral circulation?

Answer 16

substance P
neurokinin A
CGRP

Question 17

what effect does decreased intracranial volume have on CSF flow?

Answer 17

low volume causes pain

pain carried by afferent neurons will cause vasodilation which increases blood flow in an effort to increase pressure

Question 18

what effect does increased intracranial pressure have on systemic blood pressure?

Answer 18

increased intracranial pressure decreases venous outflow and arterial flow

this decrease in brain perfusion activates CV control center in medulla to increase systemic BP