Unit 6: CNS circ systems - meninges Flashcards
name the cranial meningeal layers (including structural components) from most superficial to most deep
- dura mater
- arachnoid layer
- subarachnoid space
+arachnoid trabeculae
+subarachnoid vasculature (cerebral arteries and veins)
+CSF - pia mater
- cerebral cortex
most SDHs are caused by what types of blood vessels?
veins
majority of SDH are venous bleeds associated with the venous sinuses in the brain
most epidural hematomas are caused by which type of blood vessels?
arteries
fracture to the cranial bone could cause major arterial bleeds and most epidural hematomas are arterial bleeds
most subarachnoid hemmorhages are caused by which type of blood vessels?
arteries
CSF electrolyte composition: pH and HCO3-
pH = 7.31: lower than plasma
HCO3-: lower than plasma
bicarb will help buffer the CSF d/t the high metabolism of CO2 by the brain cells
CSF electrolyte composition: Na+
140 mOsm/L
equal to plasma
CSF electrolyte composition: Cl-
very close to sodium
~140 mOsm/L
higher than plasma
CSF electrolyte composition: K+
40%< plasma
CSF electrolyte composition: Mg2+
higher than plasma values
the combination of Cl-, K+, and Mg2+ concentration levels will contribute to “limited neurological activity”, AKA, helps us to “pump the brakes” on our nervous system. why?
CSF Cl- [ ] > plasma
CSF K+ [ ] 40% < plasma
CSF Mg2+ > plasma
a higher Cl- [ ] will make the neuronal cells more permeable to chloride (d/t GABA receptors on axon hillocks) and will make the cells less excitable (functional brake system)
lower potassium: more hyperpolarized cell
higher mag: limits overactivity
CSF electrolyte composition: glucose
normal: 60mg/dL
(plasma: 90mg/dL)
glucose [ ] is lower in CSF than plasma for the following reasons:
the NS is constantly burning glucose, and main way to get glucose into the nervous system is via GLUT-1 transporters (facilitated diffusion), which is not generally a fast transportation system
since glucose goes along its [ ] gradient, the CV needs to have a higher glucose [ ] than the CSF (90mg/dL vs 60 mg/dL) SO THAT glucose diffuse into the NS
neurons CANNOT store glucose
CNS is very sensitive to glucose fluctuations
CSF sample color
clear
CSF average volume
(if quantified in a container)
150 ml
total CSF volume production per day
~500 ml/day
(produced about 3x a day)
what do ependymal cells do?
- produce CSF
- a “transition” area for ions to flow from blood to CSF
describe how different ions are transported in/out of ependymal cells
FROM BLOOD
1. leaky Na+ channels allow Na+ INTO cell from blood
2. leaky Cl- channels allow** Cl- INTO cell from blood**
3. water can flow in/out of cell from blood
TO CSF
4. Na+ pump (via primary AT) out of cell to CSF
5. Cl- difffuses out of cell to CSF (dragged along with Na+)
6. water diffuses out of cell to CSF (follows Na+)
how can anesthetics increase/decrease the rate at which CSF is being produced in ependymal cells?
some anesthetics can increase or decrease the rate at which the primary AT Na+ pumps are pumping sodium out of the ependymal cell into the CSF
higher Na+ rate out = higher Cl- rate out = more water out
slower Na+ rate out = slower Cl- rate out = less water out
what do the astrocytes do in terms of CSF electrolyte managment?
regulates the K+ levels in the CSF
what is the name of the tissue that aggregates ependymal cells together to create CSF?
choroid plexus
where are choroid plexuses found?
the ventricles of the brain
how many ventricles are there in the brain?
- left lateral ventricle
- right lateral ventricle
- 3rd ventricle
- 4th ventricle
where are the ventricles in the brain located?
the lateral ventricles are encased in the cerebral hemispheres
the third ventricle is where the diencephalon is
the fourth ventricle is next to the cerebellum
what is another name for the Interventricular Foramen?
Foramen of Monroe
what is the Foramen of Monroe?
AKA the interventricular foramen
the pathway for the lateral ventricles to empty into the 3rd ventricle
name the structure that drains the CSF from the 3rd ventricle to the 4th ventricle
cerebral aquaduct
or the Aquaduct of Sylvius
another name for the Cerebral Aquaduct
Aquaduct of Sylvius
what are the exit points for CSF to flow out of the 4th ventricle?
- central canal
- left lateral apertures
- right lateral aperture
- median aperture
what is the other name for the Foramen of Luschka?
Lateral Aperture (2)
what is the other name for the Median Aperture
Foramen of Magendie
name the structure that is most prone to occlusion preventing CSF flow
Cerebral Aquaduct/
Aquaduct of Sylvius
build up of CSF in the ventricles causing expansion of ventricles is called:
hydrocephalus
differentiate non-communicating vs communicating hydrocephalus
non-communicating: block in the pathway of CSF flow
will see ventricular enlargement/expansion
communicating: no occlusions, but CSF is not absorbing as it normally would
will see generalized increase in ICP
describe what the arachnoid granulations do
“pressure blow off valves”
ex) normal ICP 10; if ICP is 12, these “valves” will open to decompress and reabsorb CSF to CV circulatory system
where else does CSF get reabsorbed?
vertebral venous plexus
endoneural space
(very little CSF gets reabsorbed here)
what does the cerebellum do
coordinates complex motor functions
where is the Cisterna Magna; what does it do?
this cistern surrounds the cerebellum and circulates the CSF around it – it does this becasuse the cerebellum is important for coordinated complex motor function and keeps the CSF surrounding it “fresh”
another name for the Cisterna Magnum is “Cerebellomdullary Cistern”
what are the 7 major cranial sinuses?
superior saggital sinus
inferior saggital sinus
straight sinus
sinus confluence
transverse sinus
sigmoid sinus
cavernous sinus
SIS-SC-TSC
what is the Falx Cerebri
connective tissue that separates the L and R hemispheres and extends to the back of the brain
what is the Tenrtorium Cerebelli
it is a “shelf” for the occipital lobe to “sit on top of”
the cerebellum sits below this
Sinus Confluence
“SC”
where the superior and straight (branched off of the inferior) saggital sinuses && the transverse sinuses (L+R) “conference” together
Sigmoid Sinus
the sigmoid sinus is the “S” curved sinus that pools the blood to the IJ veins
Cavernous Sinus
a “pool” of blood collected in the front middle brain
“cavern” think: “pool”
Straight Sinus
comes off the Inferior Saggital Sinus
How many Transverse Sinuses are there?
2 (L and R)
where do all the sinuses drain into?
the internal juguluar veins
(the external jugular veins empty the more superficial structures on the side of the head)
what are the 3 major cranial arteries that feed the brain?
middle
posterior
anterior
what is the normal cerebral blood flow rate?
750 ml/min
(50 ml/min/100g of tissue)
how much cerebral blood flow goes to the grey matter? to the white matter?
80% to grey matter (where decisions are made)
20% to white matter
how much percentage of the CO is cerbral blood flow?
15%
analyze the relationship of cerebral blood flow rate to metaboic activity in the brain
the more metabolic activity there is going on in the brain, the higher the blood flow rate
the lower the metabolic activity (i.e. coma), the lower the blood flow rate
what benefit does the Circle of Willis provide for the brain in terms of perfusion?
collateral circulation
if there is a blockage somewhere in the brain, this circular structure provides many pathways to get bloow flow to different parts of the brain
which arteries are the “feed arteries” to the COW?
internal carotid artery (L+R)
verterbral artery (L+R)
what are the 3 largest arteries that branch off the COW? which of these 3 are the largest?
(2) posterior cerebral arteries
(2) anterior cerebral arteries
(2) middle cerebral arteries
+middle cerebral artery is the largeset
list the areas of the brain that the 3 largest cerebral arteries provide flow to
anterior cerebral artery: frontal lobe/mid-line
middle cerebral artery: lateral portion of the middle of the brain
posterior cerebral artery: far lateral, posterior brain/inferior side of brain
what are the “early” and “late” parts of the anterior cerebral artery?
A1/PRE-COMMUNICATING: “early portion” of the anterior cerebral artery (this is part of the COW)
A2/POST-COMMUNICATING: “late portion” of the anterior cerebral artery (this is the more distal portion of the artery; this part delivers blood to the tissue
what is the anterior communicating artery?
this small artery connects the L and R anterior cerebral arteries so that they can “communicate”; allows cross-talk
at what point do the internal carotid arteries become the middle cerebral artery?
once they reach the COW
what are the “early” and “late” parts of the posterior cerebral artery?
P1/PRE-COMMUNICATING: “early portion” of the posterior cerebral artery (this is part of the COW)
P2/POST-COMMUNICATING: “late portion” of the posterior cerebral artery (this is the more distal portion of the artery; this part delivers blood to the tissue
what is the posterior communicating artery?
the small arteries that connect the posterior cerebral arteries and the middle cerebral arteries
how many anterior communicating arteries are there? how many posterior communicating arteries?
1 anterior
2 posterior
what 3 main structures supply blood flow to the
cerebellum?
name their respective areas they provide blood flow to.
delineate where they branch from.
-
superior cerebellar artery (2)
+feeds front and top of cerebellum
+delineates from the basilar artery -
anterior inferior cerebellar artery (AICA) (2)
+feeds middle cerebellum
+delineates from basilar artery -
posterior inferior cerebellar artery (PICA) (2)
+feeds back/bottom of cerebellum
+delineates from vertebral arteries
why is a subarachnoid hemorrhage considered “messier” than a subdural/epidural hematoma?
this bleed can be caused by a ruptured aneurysm (poor genetics/poor chronic health issues) in the subarachnoid space where there are many other supportive structures/blood vessels; it would be hard to “tease out” all the blood without damaging the underlying structures (neurons/glial cells) while doing so
what is the main byproduct of cerebral metabolism?
CO2
if you have high cerebral metabolism, you would have a(n) _____ in CO2 levels in the brain
increase
explain the concept of autoregulation in relation to cerebral blood flow
blood pressure drives cerebral blood flow
with small fluctuations in blood pressure, cerebral blood flow autoregulates itself to remain fairly constant (a horizontal line on the graph)
autoregulation is kept constant between MAPs of 50 to 150
if MAP drops <50 or rises above >150, then cerebral vasculature cannot vasodilate further and cannot vasoconstrict any further, which drives blood flow up or down as blood pressure increases or decreases linearly
if your MAP is <50, what are the associated risks if cerebral autoregulation is absent?
risk of cellular death
if your MAP is >150, what are the associated risks if cerebral autoregulation is absent?
risk of ruptured aneurysms; bleeding
what would autoregulation look like in a person with chronic HTN normally walking around with a MAP of 150?
their LLA and ULA would be higher than the average person (as in a LLA of 100 and an ULA of 200)
MAP numbers not accurate, but you get the idea
how do p-type calcium channels work?
much like fast VG Na+ channels, p-type Ca2+ channels will influx Ca2+ into a neuron once threshold potential is met and depolarization has occured
list out the steps of NT release in a motor neuron
a multi-polar neuron (decision making neuron) will receive input from the brain and will propogate an AP accross the axon to the synaptic terminal
- AP propogates through axon, depolarizing fast VG Na+ channels on membrane to allow Na+ influx into neuron
- p-type Ca2+ channels depolarize to influx Ca2+ into neuron
- Ca2+ signals VP2 (storage vesicle) to exocytose the ACh into the NMJ
- once enough ACh has been released into the NMJ, primary AT Ca2+ channels will regulate the Ca2+ in the neuron and pump it back out of the neuron
- to help the cell repolarize:
a.) Na+/K+/ATPase pumps will pump Na+ out of the cell
b.) VG K+ channels will diffuse K+ into the cell
c.) Ca2+ sensitive K+ channels will allow K+ to efflux out of the neuron
what is the “end plate potential”
the initial stimulus that precedes an AP in the motor end plate
this is mediated first by the n-ACh-Rs
the end plate potential converts to an AP once VG Na+ channels are depolarized to aide in the propogation of the AP
