Lecture 10/11 - CNS Circulatory Systems Meninges Flashcards
Exam 2
What is the downside of having the grey matter superficial in the brain?
Prone to concussion
Arterial vs venous bleed
Arterial bleeds get worse quicker, venous bleed slower to progress
The pia mater sits on top of _____ in the brain
Neural and glial cells, outside border of the brain
The space between the pia mater and the arachnoid mater is the ______. What is in this space?
Subarachnoid space - blood vessels and CSF
A subarachnoid hemorrhage is ______ in nature
arterial
aka arterial aneurysms
The ______ are the pillars that create space between the arachnoid and pia layers
Arachnoid trabeculaes - create space for CSF and blood vessels
A subdural hemorrhage is ______ in nature
venous - slower to develop, headache a couple days after trauma
A _______ is when the arterial blood vessels rupture with a skull fracture
Epidural hematoma
Which layer perfuses the skull?
The dura layer - cranial sinuses
What is the total volume of CSF?
150 mL
What is the rate at which the CSF is produced?
500 mL/day - replaced 3x a day on average
What cells are responsible for maintaining the electrolyte levels of the CSF?
Astrocytes
pH of CSF vs plasma
CSF pH more acidic
- blood 7.4
- brain 7.31
Why is the CSF more acidic than the blood?
- Lower bicarb level in CSF - more acidic
- Brain has its own buffer system with bicarb to remove CO2 that is produced through metabolism
Na levels of CSF vs plasma
140 - same
Cl levels of CSF vs plasma
Higher in CSF than plasma
Same as Na - 140
K levels of CSF vs plasma
40% less than normal plasma values - 2.4
The ______ doesn’t get refreshed with CSF as much as areas higher up
Lumbar cistern
Mg levels of CSF vs plasma
Higher in CSF
The changes in electrolyte concentrations in CSF helps keep the _____ on the NS
brakes
How do different electrolyte values in the CSF help keep the brakes on neurological systems?
Raising Cl - makes more (-) - hyperpolarized, GABA receptors
Lower K - hyperpolarized cell
Higher Mg - lower overactivity
Glucose levels of CSF vs plasma
Lower in CSF → 60 mg/dL
Plasma 90 mg/dL
Why is glucose lower in the CSF than in the plasma?
Glucose is transported into CSF via GLUT1 transporters
Follows concentration gradient (facilitated diffusion) so need CSF < plasma
- CSF uses glucose
- Neurons can’t store glucose as glycogen - need transport in
What are the units used for glucose concentration?
mg/dL
CSF samples should be ______ in color
clear - no RBCs or proteins
What are the units used for electrolyte concentration?
mEq/L
______ cells produce CSF and separate CSF from blood
Ependymal
Differentiate between ependymal cells, astrocytes, and microglia
All are types of glial cells
- Ependymal cells - produce CSF, line ventricles and central canal; have cilia
- Astrocytes - provide nutrients to neurons, maintain their extracellular environment, and provide structural support
- Microglia - main form of active immune defense in the CNS
Differentiate between ganglia and nuclei
Ganglia are clusters of nerve cell bodies in the PNS
Nuclei are clusters of nerve cell bodies in the CNS
Differentiate between neurons and glial cells
Neurons are the “communication” cells
Glial cells are the “support” cells of the nervous system
If you want to increase the rate of CSF production, you can give an anesthetic that
Increases the rate of sodium pumping into CSF from ependymal cells
If you want to decrease the rate of CSF production, you can give an anesthetic that
Decreases the rate of sodium pumping into CSF from ependymal cells
CSF production relies on
The active sodium pump moving sodium into the CSF from the ependymal cells
- Dictates rate of Cl and H2O movement into CSF
What regulates the potassium levels in the CSF?
Astrocytes - potassium accumulation
Where does CSF glucose come from?
Anywhere with a BBB, doesn’t need specialized cells
What tissue is CSF produced in?
Choriod Plexus - consists of ependymal cells
Where is the choroid plexus found?
4 ventricles - shown in red
The 3rd ventricle is in the location of the _______
diencephalon, right around where the hypothalamus is
Where is the 4th ventricle located?
In the middle of the brain stem, anterior to the cerebellum
What are the names of ventricles 1 and 2? Where are they located?
Lateral ventricles - in the cerebral hemispheres L/R
What is the name of the pathway that the CSF takes from the lateral ventricles to empty into 3rd ventricle
Interventricular Foramen aka Foramen of Monroe
What is the name of the pathway that the CSF takes to get from 3rd → 4th ventricle
Cerebral Aquaduct aka aquaduct of Sylvius
What is the name of the pathway that the CSF takes to get out of the 4th ventricle?
There are 2:
Lateral Apertures - aka foramen of Luschka; left and right exit of 4th ventricle
Median Aperture - aka foramen of Magendie; exit midline and out the back of 4th ventricle; allows CSF to circulate around cerebellum
What pathway allows CSF to leave the 4th ventricle and circulate the cerebellum?
Median Aperture - aka foramen of Magendie
Posterior, midline of 4th ventricle
What pathway allows CSF to leave the 4th ventricle and travel back to the circulatory system?
Lateral Apertures - aka foramen of Luschka; left and right exit of 4th ventricle
Where is the majority of the CSF reabsorbed back into the CV system? Where are they located?
Arachnoid granulations - infoldings above the longitudinal fissure
How do arachnoid granulations decide how much CSF volume to empty into the CV system?
Pressure blow-off valves - normal pressure is 10mmHg
Which pathway is the most common cause of blockage of CSF drainage?
cerebral aquaduct (tumor)
What is the term for extra fluid in the circulatory system of the brain? What does this result in?
Hydrocephalus - increased ICP, putting pressure around the surrounding tissues and neurons
What are the types of hydrocephalus?
Non-communicating - occluding of CSF pathway
Communicating - pathways are intact, but CSF not being absorbed like it normally is
Where does ICP increase based on the type of hydrocephalus?
Non-communicating - increased ICP above blockage, results in swelling of the ventricles
Communicating - generalized increase in ICP
How fast is CSF reabsorbed into the CV system?
Usually, CSF is reabsorbed into the CV system at the same rate that it is being produced
- depends on the pressure
What kind of hydrocephalus occurs as a result of a stroke caused by a clot in the arachnoid granulations?
Communicating
What kind of hydrocephalus results in ventricular enlargement?
Non-communicating
Which part of the brain is responsible for coordinating complex motor tasks?
Cerebellum
The median aperture feeds CSF to the _______
Cerebellomedullary Cistern aka Cisterna Magna
What is the role of the Cerebellomedullary Cistern aka Cisterna Magna?
It is a pool that circulates CSF around the cerebellum
- keeps CSF fresh
Where could you sample fresh CSF from? What is the catch?
Cerebellomedullary Cistern aka Cisterna Magna
- you can access CSF here through the foramen magnum, but it is highly invasive
- rarely used
What is the role of the cranial sinuses?
- venous part of CV system that allows blood to exit the brain/cord and return to CV system
What are the 7 cranial sinuses?
1: Superior Sagittal Sinus
2: Inferior Sagittal Sinus
3: Straight Sinus
4: Sinus Confluence
5: Transverse Sinus
6: Sigmoid Sinus
7: Cavernous Sinus
The cranial sinus that runs midline in the sagittal plane is the ______
Superior Sagittal Sinus (#1)
The cranial sinus that runs midline below the superior sagittal sinus is the ______
Inferior Sagittal Sinus (#2)
The _____ is the fan-like connective tissue that separates L/R hemispheres; in between inferior and superior sagittal sinuses
Falx cerebri
The cranial sinus that includes the straight portion from the inferior sagittal sinus is the ______
Straight sinus (#3)
What are the structures that separate the L/R hemispheres?
Falx cerebri and the longitudinal fissure
Where does the occipital lobe sit like a shelf?
Tentorium Cerebelli
The cerebellum is underneath the ______
Tentorium Cerebelli
Where do the superior and inferior sinuses connect?
Sinus Confluence (#4)
The cranial sinus where venous blood turns around (hairpin turn) from the transverse sinuses and empties into the internal jugular vein to exit the brain is called the ______
Sigmoid Sinus (#6)
Which cranial sinus is the veinous collecting pool in front of the brain or for runoff from the face? Where does it feed into?
Cavernous Sinus (#7-9 area) - feeds into the sigmoid sinus to exit brain
Venous blood exits the superior and inferior sagittal sinuses laterally into the ________
Transverse Sinuses (#5) - have one on each side (L/R)
What does the sigmoid sinus use to exit venous blood out of the brain?
Internal jugular veins
Describe the pathway of venous blood out of the brain
Superior/inferior sagittal sinuses
- Straight sinus - only if coming from inferior sagittal sinus
Transverse sinus
Sigmoid sinus
Internal jugular veins
Where are the cranial sinuses located in the meninges?
Dura mater
The _______ remove venous blood from the superficial areas on the side of the head
External jugular veins
Where are the cranial arteries located in the meninges?
Subarachnoid space and epidural space
What is the cardiac output per minute?
5 L/min
What is the rate of arterial blood flow to the brain? How much is it compared to the total CO?
750 mL/min
15% of total CO
50mL/min per 100 grams of brain tissue
The brain makes up ______ of total body weight
2-3%
Why does the brain get a lot of blood flow relative to its size?
High metabolic rate
How much of the blood flow to the brain supplies grey matter? How much to white matter?
80% to grey matter, 20% to white matter
Why is the blood flow to the grey matter higher than the white matter?
White matter is very efficient without needing a lot of energy - myelination
Grey matter is where decisions are made - a lot of synapses with neurotransmitter activity
- Change in membrane permeability requires a lot of energy
Why are the cranial sinuses called sinuses?
Sinus = big vein with a structure to it - more robust than other veins
Walls made up of dura mater
What are the major feed arteries for the cranial blood supply?
2 carotid arteries - anterior
2 vertebral arteries - posterior
What kind of bleed is a hemorrhagic stroke?
Subarachnoid Hemorrhage aka ruptured aneurysm
What would make a subarachnoid hemorrhage more messy than other hematomas?
Way more messy than other types of injuries
- Because the blood has infiltrated the neurons and glial cells
- Harder to get blood out without damaging the surrounding structures - deep
What usually causes a subarachnoid hemorrhage?
Result of genetics and lifestyle (alcoholism, HTN)
Rate of blood flow to the brain is dependent on
what the cerebral metabolic rate is (more metabolic activity = more brain blood flow) - CO2
Where is the circle of willis?
At the base of the brain, in the subarachnoid space
What is the role of the circle of willis?
A pathway in the brain that increases the likelihood that we’ll have “collateral circulation” if there is a problem in one of the arteries
If one of the feed arteries is blocked, the blood should still have a way to get to the tissue that needs to be perfused
Which structure sits above the basilar artery?
The pons
What are the 3 major arteries on each side of the circle of willis?
Anterior, middle, and posterior cerebral arteries
What is the largest of the 3 major arteries of the circle of willis?
Middle cerebral artery
Which of the 3 major arteries of the circle of willis provides circulation to the frontal lobe?
Anterior cerebral artery
Which areas of the brain do the middle cerebral arteries perfuse?
Middle and lateral cerebral cortex
Which of the 3 major arteries of the circle of willis would be the worst area to have a stroke in?
Middle cerebral artery - takes up the majority of the brain circulation
Which areas of the brain do the posterior cerebral arteries perfuse?
rear and far lateral parts of the brain
Differentiate between the 2 portions of the anterior cerebral arteries
Early or A1 portion (pre-communicating): part of the circle of willis
Late or A2 portion (post-communicating): extends from the circle of willis to deliver perfusion to the tissues
What is the name of the artery that allows cross-talk between the L and R anterior cerebral arteries of the circle of willis?
Anterior Communicating Art
Once the internal carotid arteries become a part of the circle of willis they’re called the
Middle cerebral arteries
Differentiate between the 2 portions of the posterior cerebral arteries
Early or P1 (pre-communicating) - part of circle of willis
Late or P2 (post-communicating): Extends from the circle of willis to provide perfusion to the back of the brain
What structures connect the posterior cerebral arteries to the middle cerebral arteries?
Posterior Communicating Arteries
What are the 3 cerebellar arteries?
Each side of the brain (L/R) gets a set:
1. Superior Cerebellar Artery
2. Anterior Inferior Cerebellar Artery
3. Posterior Inferior Cerebellar Artery
Which portion of the cerebellum do the Superior Cerebellar Arteries perfuse?
Provides blood for the front/top of the cerebellum
Projects from the top of the basilar artery
Which portion of the cerebellum do the Anterior Inferior Cerebellar Arteries perfuse?
- Provides blood for the middle portion of the cerebellum
- Arises from the basilar artery
Which portion of the cerebellum do the Posterior Inferior Cerebellar Arteries perfuse?
- Provides blood for the back of the cerebellum
- Right below the pons
- Arises from each of the vertebral arteries (right before they come together to form the basilar artery)
What is the top byproduct of metabolism that is involved in the regulation of brain blood flow?
CO2
- More CO2 in brain → more brain blood flow
- CO2 moves into blood vessels surrounding tissues and dilates them
Describe the autoregulation response in the brain to a systemic decrease in BP
Decrease in systemic BP → decreased BP in feed vessels → brain decreases vascular resistance to prevent under-perfusion - dilation
Describe the autoregulation response in the brain to a systemic increase in BP
Increase in systemic BP → increased BP in feed vessels → brain increases vascular resistance to prevent over-perfusion - constriction
What is the pressure that drives blood flow through the vessels?
MAP or CPP (cerebral perfusion pressure)
Without autoregulation, the graph of blood flow and pressure would be ______
linear - BBF would change with blood pressure
- Over-perfusion would blow up an aneurysm
- Under-perfusion → cell death
What is the normal autoregulation range for BP?
50-150 mmHg for MAP or CPP
- Lower limit of autoregulation (LLA) - below 50 brain blood vessels can’t dilate more - drop in BBF
- Upper limit of autoregulation (ULA) - above 150: brain blood vessels can’t constrict more - increase in BBF
Constriction or dilation of blood vessels at the capillary level in response to change in systemic BP is called _________
Autoregulation
How is autoregulation different for patients with hypertension? What is the consequence?
Adaption - autoregulation curve will shift
Eventually arteries will harden up to withstand higher pressures - arterial sclerosis
- Consequence is that the vessels won’t be able to relax
- Ischemia would be worse in these situations because reduced collateral circulation
If you’re trying to get an idea of overall vascular health, you can look at
the ability of blood vessels to dilate to normal stuff - need to be able to relax easily to changing pressures (HTN and diabetes)
All of the important tissues in the body have _______
collateral circulation
Autoregulation can be reduced via _______
drugs - volatile anesthetics
The more that autoregulation is impacted, the steeper the slope will be
Explain error bars in autoregulation studies
Error bars on graph show variability - limitations of experiment
- Larger error bars = more variability
- If error bars are within normal horizontal error bars → autoregulation isn’t statistically significantly affected with the drug
- Just because not “statistically significant”, doesn’t mean the drug isn’t impacting autoregulation at all
What are the 2 examples from class of things that can change membrane potential in target tissues?
- Heart: activity mediated via ACh receptors that alter potassium permeability of the cell wall
- NMJ: change in response to neurotransmitter release at the NMJ
Describe how the CNS sends a signal to muscle to contract
CNS wants to turn on a muscle group → sends message to muscle via motor neuron (depolarization) → V-G Ca++ channels open, causing vesicles to fuse to the presynaptic neuron, releasing ACh into the NMJ → ACh binds to receptors on skeletal muscle opening ion channels that allow Na+ and Ca++ into the cell (a little K+ out) → local depolarization causes fast Na+ channels to open → action potential → excites the muscle → contraction
What is the cell type of motor neurons? What is their role? Where are they located?
Multipolar neurons - decision-making neurons
Cell bodies found in the anterior horn of the spinal cord
What determines if the motor neuron is turned on?
How many things are stimulating it within the spinal cord
If neuron gets enough stimulus it will fire an AP
How does AP travel down the length of the motor neuron? When does it end?
AP moves down the length of the motor neuron utilizing fast (V-G) Na+ channels - allows Na+ to come into the cell, opening more V-G Na+ channels until it reaches the axon
What is the sending portion of the motor neuron called?
The axon
What helps the cell reset after the AP passes through the motor neuron
K+ channels and Na+/K+ ATPase pump in cell wall
- Na+/K+ ATPase pump also helps skeletal muscle reset
What is the second set of V-G ion channels called that opens when the AP reaches the end of the motor neuron? What do they do?
P-Type Ca++ channels to let Ca++ into the end of the motor neuron
Ca++ is the stimulus for the neuron to release its neurotransmitter - acts on storage vesicles to fuse with the cell wall and empty their contents into the synapse/NMJ (VP-2)
What is the motor neuron neurotransmitter called?
ACh
What are the 2 types of vesicles in the motor neuron?
VP-2 ACh storage vesicles: ready to go, next to cell wall
VP-1 ACh storage vesicles: not ready to go, maybe not full, not sitting next to cell wall - higher up
VP = vesicular pool
VP-1»_space; VP-2
How is the AP at the end of the motor neuron turned off?
Ca++ pumps remove Ca++ from the cell using ATP
- ATP-dependent Ca++ transport pump; fast process
- Removing the Ca++ gets the VP-2 vesicles to stop emptying ACh into the synapse
How does the motor neuron reset after an AP?
- ATP-dependent Ca++ transport pump: Ca++ removed from cell - no more VP-2 emptying
- Na+/K+ ATPase pump
- V-G K+ channels - out of cell
- Ca++ sensitive K+ channel: intracellular Ca++ opens the channels to allow K+ back into the cell
What would be the pre and post-synaptic cells in the NMJ example?
Pre - motor neuron
Post - skeletal muscle
Describe the neurotransmitter action at the synapse after release from the motor neuron
Neurotransmitter hits ACh receptors (cylinders) that have 2 binding sites (occupied by ACh at the same time) → channel opens up
Receptors (millions at the NMJ) located at skeletal muscle of synapse fairly close to the motor neuron
Which ions move in what directions when the nACh-R opens up after ACh binds?
Na+ enters skeletal muscle cell, with small amount of Ca++ in and K+ out
How does end plate potential become an AP?
End plate potential: localized depolarization from Na+ entry into skeletal muscle cell (from nACh-R opening up)
Becomes an AP when the V-G Na+ next to nACh-R get involved
AP mediated through V-G Na+ channels - allows AP to travel down skeletal muscle cell → contraction of skeletal muscle
Why does end plate potential ALWAYS trigger an action potential?
In healthy muscle, end plate potential will always result in an AP because we have tons of extra receptors and neurotransmitters (excess)
The bare minimum required to reach end plate potential is small compared to what we have available
