CNS & PNS Flashcards
The Edinger-Westphal nucleus consists of smaller preganglionic parasympathetics that travel in which cranial nerve?
CN III - oculomotor nerve
Mediates pupillary light reflex and accommodation
What sensations are transmitted by the afferent spinothalamic tract?
temperature
pain
touch
Name the main arteries from which the Circle of Willis arises.
ICAs –> MCAs
Vertebral arteries –> Basilar artery
ACA, anterior communicating, PCA, posterior communicating (connects anterior and posterior circulation)
What arteries do the ICA and VAs branch off of?
Right - brachiocephalic –> common carotid –> ICA, ECA
Left - aorta arch –> common carotid –> ICA, ECA
Subclavian –> vertebral arteries
What are the common sites of Vertebral artery dissection?
transverse foramen of C6
exiting at C2
Which artery is formed by the convergence of medial branches of the VAs just prior to the basilar junction?
Anterior spinal arteries
What is the final drainage location of the transverse sinus?
sigmoid –> internal jugular veins
What are the contents of the cavernous sinus?
CN III, IV, V1, V2, VI
ICA
Sympathetic plexus
What is a typical measure of total cerebral blood flow (CBF)?
750 mL/min
~15-20% of cardiac output
50 mL/100 g/min
List the main determinants of cerebral blood flow.
autoregulation
cerebral perfusion pressure
respiratory gas tensions
cerebral metabolic rate of oxygen consumption (CMRO2) coupling
temperature
viscosity
some autonomic influences.
When does autoregulation occur and what does it ensure?
(MAPs) of 70 and 150 mmHg
decrease in CPP or MAP –> vasodilatation
increase in CPP or MAP –> vasoconstriction
patients with chronic HTN –> autoregulatory curve is shifted to the right for the lower and upper limits
When is cerebral blood flow dependent on MAP or cerebral perfusion pressure?
At the extremes of MAP (<70 mmHg or >150 mmHg), where cerebral autoregulation is non-existent, or in situations where cerebral autoregulation has been compromised (e.g. traumatic brain injury, stroke), CBF is dependent on MAP or CPP.
How does cerebral blood flow change in response to changes in PaCO2?
CBF changes proportionately to changes in PaCO2 (1-2 mL/100g brain tissue/min/mmHg change in PaCO2)
thought to be due to CO2 diffusing across the blood brain barrier –> changes in the pH
How does cerebral blood flow change in response to changes in PaO2?
Unlike the vigorous reactivity to changes in PaCO2, CBF is only altered when there are EXTREME changes in PaO2.
minor change in CBF with hyperoxemia.
marked inc in CBF with hypoxemia (PaO2 <50mmHg)
How does cerebral blood flow change in response to changes in CMRO2?
blood flow increases or is greatest where CMRO2 is greatest
This safety mechanism provides protection against hypoxia or anoxia
By how much does cerebral blood flow change in response to a degree change in temperature?
CBF changes by 5-7% per degree Celsius change in temperature.
Both CMRO2 and CBF increase as temperature increases and vice versa
How do changes in viscosity affect cerebral blood flow?
Decreased viscosity (low Hct) –> increased CBF to preserve cerebral oxygen supply
In contrast, CBF decreases at extremes of increased viscosity, such as polycythemia
What happens to cerebral blood flow during periods of intense sympathetic drive?
parasympathetic (vasodilatory)
sympathetic (vasoconstricting)
noradrenergic fibers
intense or prolonged sympathetic drive –> vasoconstrict and restrict CBF
Under most circumstances, however, the other “drivers”(e.g., pCO2, CMRO2, PO2 at extremes) of CBF supersede sympathetic or parasympathetic effects.
What levels of cerebral blood flow are associated with an isoelectric EEG and irreversible brain damage (in ml/g/min)?
10-15 mL/100 g/min –> isoelectric EEG
<10 mL/100 g/min –> irreversible brain damage
What is the formula for cerebral perfusion pressure (CPP)?
CPP = MAP - ICP or CVP whichever is greater
Because ICP, CVP are usually <10mmHg, CPP is primarily determined by MAP
Normal CPP is ~80-100mmHg
What determines the ability of a substance to traverse the blood-brain barrier?
Size, charge, hydrophobicity and degree of protein binding determine ability to cross the BBB
Smaller, freestanding, more lipid-soluble molecules can cross the BBB >>> than larger, less lipid-soluble molecules with a higher degree of protein binding
What is the circulatory steal phenomenon or inverse steal?
In the normal brain, volatile anesthetics –> vasodilatation of cerebral vessels.
Arterioles are maximally dilated in areas of ischemia, = volatile anesthetics cannot further vasodilate these regions.
If volatile anesthetics are given in the setting of focal ischemia, blood flow may potentially be redistributed away from ischemic tissue to normal tissue and lead to further damage
Hypercarbia does the same thing
Name some factors that may alter cerebral autoregulation.
- chronic hypertension - shifted to the right
- hypercapnia –> vasodilaion
- hypocapnia –> vasoconstriction
- Anemia and hemodilution –> decrease the vascular tone –> increase CBF
- mild hypothermia impairs cerebral autoregulation
- mild hyperthermia enhances cerebral autoregulation
- Volatile anesthetics
How do volatile anesthetics influence cerebral blood flow auto-regulation?
significantly impair autoregulation
CBF is preserved to lower MAP
autoregulation in response to rising MAP is impaired
1 MAC or less, sevoflurane causes less impairment than other volatile anesthetics
Name disease states that may abolish autoregulation.
acute ischemia
mass lesions
trauma
inflammation
diabetes mellitus
The most medial portions of the motor homunculus are responsible for movement of what body parts?
Gentials
Toes
Feet
Legs
What circuit links the hippocampus with the cingulate cortex?
The Papez circuit links the hippocampus with the cingulate cortex via the mammillary bodies and the anterior thalamus
What structure assists with vestibular balance?
Cerebellum
What part of the brainstem plays a large role in consciousness and awareness?
reticular activating system
Which area of the frontal lobe is MOST responsible for coordinating patterns of movement?
Premotor cortex
Match the following areas of the brain with its associated neurotransmitter:
raphe nuclei, cerebral cortex, substantia nigra
locus ceruleus
raphe nuclei - serotonin
cortex - glutamate or GABA
substantia nigra - dopamine
locus ceruleus - norepinephrine
What is a penumbra?
area of ischemic brain in which cellular dysfunction is temporarily reversible
neuronal cell death can be avoided if cerebral blood flow is restored
What are two potential ways that focal cerebral ischemia can occur?
surgical clip/clamp placed on a vessel
hypotension
What is the value for normal cerebral blood flow?
50 mL/100g/minute
How does hyperglycemia contribute to injury during ischemia?
During an ischemic event, glucose –> increased lactate production via anaerobic glycolysis
hyperglycemia –> poor neurologic outcome
How do brain tumors affect cerebral blood flow?
Not much data
lower CBF than normal brain tissue
may increase ICP –> reduce CPP, CBF –> ischemia
How much CSF is present in the cranium at any given point in time?
150 mL of CSF in the CNS (half in the cranium, and half in the spinal space)
Produces - 20 mL/hour, or approximately 500 mL/day –> replenished 3-4 times daily
60ml in neonates
Where does most CSF flow begin?
Ependymal cells of the choroid plexus (lateral ventricles) +
Brain interstitium (via transependymal diffusion)
produce CSF
Where does CSF absoprtion occur?
arachnoid villi and granulations in the superior sagittal sinus
What are the areas of the brain that lack a traditional blood-brain barrier?
choroid plexi
hypothalamus
pituitary
area postrema (implicated as the chemoreceptor trigger zone for emesis)
Compared to blood, describe relative concentrations of major electrolytes and macromolecules in CSF
isotonic
lower protein, glucose, calcium and potassium
higher sodium, chloride and magnesium
What are the different types of cognitive changes that manifest after anesthesia?
delirium
post-operative cognitive dysfunction (POCD) or dementia
What is the definition of delirium?
acute cognitive disorder, characterized by change in attention, cognition, consciousness, and perception
What are the different types of delirium in the perioperative setting?
- Emergence Delirium (ED) - during or immediately after emergence from general anesthesia (GA) and resolves within minutes or hours
- Post-operative Delirium (PD) - peaks between POD 1 and 3 and usually resolves within hours to days
What are the risk factors for emergence delirium?
predominance in children, and a peak incidence between ages 2 and 4
rapid emergence (most often with sevoflurane and desflurane)
Risk factors include pre-operative medication with midazolam, breast surgery, abdominal surgery, and prolonged duration of surgery
What are the risk factors for post-operative delirium?
older patients
higher incidence after hip fracture surgery
greater intraoperative blood loss
pain
more post-operative blood transfusions
post-operative hematocrit < 30%
What drugs have been used to treat or prevent emergence and post-op delerium?
midazolam
clonidine
dexmedetomidine
fentanyl
ketorolac
What is post-operative cognitive dysfunction (POCD)?
mild cognitive disorder after surgery or anesthesia
impairment of memory
learning difficulties
reduced ability to concentrate
What are the risk factors for POCD?
advanced age
type of surgery (major surgery such as cardiac or neurosurgery)
increased duration of anesthesia
pre-operative cognitive impairment
depression
fewer years of education
second operations during the same hospitalization
post-operative infections and respiratory complications
history of previous cerebrovascular accident (CVA) with no residual impairment
POCD at hospital discharge
What are the risk factors for POCD in cardiac surgery?
E4 allele of the ApoE gene
poor left ventricular function
longer duration of CPB
presence of atrial fibrillation or peripheral vascular disease
prior stroke
diabetes.
