Neuro Flashcards
Name 4 types of glial cells:
Astrocytes
Ependymal cells
Oligodendrocytes
Microglia
What is the function of Astrocytes?
- Most abundant type of glial cell.
- Regulation of metabolic environment.
- Repair neuron after neuronal injury
What is the function of ependymal cells?
- Form the choroid plexus, which produces CSF.
- Concentrated in the roof of the 3rd and 4th ventricles and spinal canal.
What is the function of the Oligodendrocytes?
- Form the myelin sheath in the CNS.
- “Schwann cells form the myelin sheath in the PNS.
What is the function of Microglia?
-Act as macrophages and phagocytize neuronal debris.
List the name and function of the 4 lobes of the cerebral cortex:
- Fontal: contains motor cortex
- Parietal: contains somatic sensory cortex
- Occipital: contains vision cortex
- Temporal: contains auditory cortex and speech centers
- Wernicke’s area= understanding speech
- Broca’s area= motor control of speech
Name the 12 cranial nerves:
Mnemonic: oh oh oh to touch and feel virgin girls vagaina ah heaven
- Olfactory
- Optic
- Oculomotor
- Trochlear
- Trigeminal
- Abducens
- Facial
- Vestibulocochlear
- Glossopharyngeal
- Vagus
- Spinal accessory
- Hypoglossal
Cranial nerves: motor, sensory, or both?
Mnemonic: Some say marry money but my brother says big boobs matter more.
- Olfactory (SENSORY)
- Optic (SENSORY)
- Oculomotor (MOTOR)
- Trochlear (MOTOR)
- Trigeminal (BOTH)
- Abducens (MOTOR)
- Facial (BOTH)
- Vestibulocochlear (SENSORY)
- Glossopharyngeal (BOTH)
- Vagus (BOTH)
- Spinal accessory (MOTOR)
- Hypoglossal (MOTOR)
What cranial nerves provide motor control of the eyes?
How does each nerve contribute to the eye’s movement? (see photo in Neuro: CNS brain)
CN3 Oculomotor: all directions except lateral and down medial
CN4 Trochlear: eyes move down medial (cross eyed)
CN 6 Abducens: eyes move laterally
How do you test the Olfactory nerve (CN1)?
Smell
How do you test the optic nerve (CN2)?
Vision
How do you test the oculomotor nerve (CN3)?
Eye movement
pupil construction
How do you test the trochlear nerve (CN4)?
Eye movement
How do you test the trigeminal nerve (CN5)?
3 branches:
V1= ophthalmic
V2= maxillary
V3= mandibular
facial sensation
anterior 2/3 tongue sensation
chewing movement
How do you test the abducens nerve (CN6)?
eye movement
How do you test the facial nerve (CN7)?
5 branches: Temporal Zygomatic Buccal Mandibular Cervical
- Facial movement except chewing
- eyelid closing
- Anterior 2/3 taste
How do you test the vestibulocochlear nerve (CN8)?
hearing and balance
How do you test the glossopharyngeal nerve (CN9)?
Posterior 1/3 of tongue sensation
How do you test the vagus (CN10)?
swallowing
How do you test the spinal accessory nerve (CN11)?
shoulder shrug
How do you test the hypoglossal nerve (CN 12)?
tongue movement
Which cranial nerve resides in the central nervous system?
What is the implication of this?
All CN are part of the Peripheral NS except for the OPTIC nerve (CN2).
Only CN surrounded by dura and CSF.
If you inject LA into the optic nerve during regional anesthesia of the eye, you will have a big problem.
What is tic douloureux?
What CN contributes to this problem?
aka trigeminal neuralgia (CN5) causes excruciating neuropathic pain in the face.
What is Bell’s palsy?
What cranial nerve contributes to this problem?
results from injury to the facial n. (CN 7).
Causes ipsilateral facial paralysis.
What is the function of the CSF, and where is it located?
- cushions the brain
- provides buoyancy
- delivers optimal conditions for neurologic function
Location:
- Ventricles (left and right lateral, 3rd, and 4th)
- Cisterns around the brain
- Subarachnoid space in brain and spinal cord
What regions of the brain are NOT protected by the BBB?
The BBB separates CSF from plasma.
Contains tight junctions that restrict pass of large molecules and ions.
BBB is NOT present at:
- chemoreceptor trigger zone
- posterior pituitary glad
- Choroid plexus
- parts of hypothalamus
What is the normal volume of CSF?
150mL
What is the normal specific gravity of CSF?
1.002-1.009
CSF production:
Ependymal cells of the choroid plexus produce CSF at a rate of 30ml/hr.
CSF circulation:
see photo in Neuro: CNS brain
“Love My 3 Silly 4 Lorn Magpies
Left/Right lateral ventricles–> Foramen of Monro–> 3rd ventricle–> Aqueduct of Sylvius–> 4th ventricle–> Foramen of Luschka (paired) AND foramen of Magendie–> subarachnoid space (brain/spinal cord) and central canal of spinal cord–>superior sagittal sinus
*all ventricles are sights of production
CSF reabsorption:
Venous circulation via the arachnoid villi in the superior sagittal sinus.
What is the formula for cerebral blood flow?
CBF= cerebral perfusion pressure/ cerebral vascular resistance
What are the normal values for global, cortical, and subcortical flow?
Global: 45-55mL/100g tissue/min OR 15% of CO
Cortical: 75-80mL/100g tissue/min
Subcortical: 20mL/100g tissue/min
What are the 5 determinants of cerebral blood flow?
- Cerebral metabolic rate for O2 (CMRO2)
- Cerebral perfusion pressure
- Venous pressure
- PaCO2
- PaO2
What is CMRO2 and what are the normal value?
CMRO2 describes how much O2 the brain consumes per minute.
3.0-3.8mL/O2/100g brain tissue/min
What factors increase and decrease CMRO2?
Decreased:
- hypothermia (7% per 1degree decrease)
- halogenated anesthetics
- propofol
- etomidate
- barbiturates
Increased:
- hyperthermia
- seizures
- ketamine
- nitrous oxide
What is the formula for cerebral perfusion pressure?
What is normal?
(see chart in neuro: CNS brain)
CPP = MAP - ICP (or CVP whichever is higher)
Cerebral vasculature autoregulates its resistance (vessel diameter) to provide a constant CPP of 50-150mmHg.
This ensures relatively stable blood flow and protects against swings in BP.
*50-150 is CPP, not MAP.
To ensure CPP of 50, MAP must be 60-65 if ICP is normal 10-15. If ICP is elevated, CPP requires a higher MAP.
What influences cerebral autoregulation?
- products of local metabolism
- myogenic mechanisms
- autonomic innervation
What are the consequences of a CPP that exceeds the limits of autoregulation? (too high and too low)
Too low: < 50mmHg
- Vessels are maximally dilated
- CBF becomes pressure dependent
- Risk of cerebral hypoperfusion
Normal: 50-150mmHg
- Range of autoregulaiton
- CBF is constant over a range of pressure
Too high: >150mmHg
- Vessels are maximally constricted
- CBF becomes pressure dependent
- Risk of cerebral edema and hemorrhage
List 4 conditions that reduce CPP as a function of increased venous pressure:
High venous pressure decreases cerebral venous drainage and increases cerebral volume. This creates back pressure to brain reducing the arterial/venous pressure gradient (MAP-CVP).
Conditions that impair venous drainage:
- Jugular compression secondary to improper head positioning.
- Increased intrathoracic pressure secondary to coughing or PEEP.
- Vena cava thrombosis
- Vena cava syndrome
What is the relationship between PaCO2 and CBF? What physiologic mechanism is responsible for this?
There is a linear relationship btwn PaCO2 and CBF.
- The pH of the CSF around the arterioles controls cerebral vascular resistance.
- At a PaCO2 of 40mmHg, CBF is 50mL/100g brain tissue/min.
At what PaCO2 does maximal cerebral vasodilation and vasoconstriction occur?
Maximal vasodilation at PaCO2 of 80-100mmHg.
Maximal vasoconstriction at PaCO2 of 25mmHg
For every 1mmHg increase (or decrease) in PaCO2, CBF will…
Increase (or decrease) by 1-2mL/100g brain tissue/min
What is the relationship between CMRO2 and CBF?
What is an exception?
Things that increase the amount of O2 the brain uses (CMRO2) tend to cause cerebral vasodilation (increased CBF). EX: hyperthermia or ketamine.
Things that decrease CMRO2 tend to cause vasoconstriction (decreased CBF). EX: hypothermia, propofol, and thiopental.
*Halogenated agents are exception. they decouple the relationship btwn CMRO2 and CBF (they reduce CMRO2 but cause vasodilation). This explains why pts with intracranial hypertension should have TIVA.
How does Acidosis affect CBF?
Respiratory acidosis increases CBF.
*metabolic acidosis/alkalosis does NOT directly affect CBF. This is b/c H+ does NOT pass through the BBB. A compensatory change in minute ventilation can affect CBF.
How does alkalosis affect CBF?
Respiratory alkalosis decreases CBF.
*metabolic acidosis/alkalosis does NOT directly affect CBF. This is b/c H+ does NOT pass through the BBB. A compensatory change in minute ventilation can affect CBF.
How does PaO2 affect CBF?
PaO2 below 50-60mmHg causes cerebral vasodilation and increases CBF.
When PaO2 is above 60mmHg, it does not affect CBF.
What is normal ICP?
What is abnormal?
ICP is the supratentorial CSF pressure.
Normal ICP is 5-15mmHg.
Cerebral HTN occurs if ICP>20mmHg.
When is ICP measurement indicated?
What is the gold standard for measurement?
when GCS score < or = 7
Intraventricular catheter is the gold standard for ICP measurement. ICP can also be measured with subdural bolt or catheter placed over convexity of the cerebral cortex.
List the s/s of intracranial HTN:
Headache N/V Papilledema (swelling of optic nerve) Focal neurologic deficit Decreased LOC Seizures Coma
Discuss the Monroe-Kellie hypothesis:
see photo in Neuro: CNS Brain
The brain lives in a rigid bony box with 3 components: Brain, Blood, CSF.
MK hypothesis describes the pressure-volume equilibrium btwn the brain, blood, and CSF w/I the confines of cranium.
Its says an increase in one component must be countered with a decrease in one of both to the others or pressure in the cranium will rise.
Causes of increased volume in the cranium:
Brain: swelling or tumor
Blood: increased CBF or bleeding
CSF:
- Increased CSF production by choroid plexus.
- Reduced CSF removal by arachnoid villi
- Obstruction to reabsorption (bleed, infection, tumor)
- Passage of fluid across the BBB
What is Cushing’s triad?
What is the clinical relevance of this reflex?
Indicates intracranial HTN.
- HTN
- Bradycardia
- Irregular respirations
Increased ICP reduces CPP. In an effort to preserve CP, blood pressure increases. HTN activates the baroreceptor reflex, leading to bradycardia. Compression of medulla causes irregular respirations.
Name 4 areas where brain herniation can occur:
- Herniation of the cingulate gyrus under the falx.
- Herniation of the contents over the tentorium cerebelli (transtentorial herniation)
- Herniation of the cerebellar tonsils through the foramen magnum.
- Herniation of contents through a site of surgery or trauma.
How does HTN affect CBF?
What is the ideal PaCO2 to achieve this effect?
CO2 dilates the cerebral vessels–> decreased cerebral vascular resistance–> increased CBF–> increased ICP
Hyperventilation (PaCO2 30-35mmHg) constricts the cerebral vessels–> increased cerebral vascular resistance–> decreased CBF–> decreased ICP
Lowering PaCO2 < 30mmHg increases the risk of cerebral ischemia d/t vasoconstriction and shifting the oxyhemoglobin dissociation curve to left (this reduces O2 offloading)
How do nitroglycerine and nitroprusside affect ICP?
Cause cerebral vasodilation–>increases CBF–>increased ICP.
How does head position affect ICP?
Head elevation >30 degrees facilitates venous drainage away from brain.
Neck flexion or extension can compress the jugular veins, reduce venous outflow, increase CBV, and increase ICP.
Head down position increases CBV and ICP.
How does mannitol reduce ICP?
What problems can arise when mannitol is used in this way?
Osmotic diuretic (mannitol 0.25-1.0g/kg) increases serum osmolarity and “pulls” H2O across the BBB towards the bloodstream.
- If BBB is disrupted, mannitol enters the brain and promotes cerebral edema.
- Mannitol transiently increases blood volume, which can increase ICP and stress the failing heart.
Describe the Anterior circulation of the brain:
Internal carotid arteries supply the anterior circulation. They enter the skull through the foramen lacer.
Aorta –> Carotid a. –> Internal carotid a.–> Circle of Willis–> cerebral hemispheres
Describe the Posterior circulation of the brain:
Vertebral arteries supply the posterior circulation. They enter the skull through the foramen magnum.
Aorta–> subclavian a. –> vertebral a. –> basilar a. –> Posterior fossa structures and cervical spinal cord
Describe the anatomy of the circle of willis:
see photo in Neuro: cos brain
the anterior and posterior circulations converge at the circle of willis.
Its primary function is to provide redundancy of blood flow in the brain. If one side occludes, the other side should theoretically be able to perfuse the affected areas of the brain.
Which population of stoke pts should receive a thrombotic agent?
Type of CVA must be determined prior to treatment. Thrombolytic should NOT be given to pt with hemorrhagic stroke. Patient should receive emergent non-contrast CT to determine type.
If treatment can begin <3 hrs after onset of s/s, pt with ischemic CVA should receive IV thrombolytic such as recombinant tissue plasminogen activator (tPA).
ASA is an acceptable alternative if tPA cannot be administered.
What is relationship btwn hyperglycemia and cerebral hypoxia?
During cerebral hypoxia, glucose is converted to lactic acid. Cerebral acidosis destroys brain tissue and is associated with worse outcomes. Monitor serum glucose and treat hyperglycemia with insulin.
Think about this when administering IV fluids that contain dextrose.
In the context of cerebral aneurysm, how is transmural pressure calculated?
TP = MAP - ICP
MAP is the pressure pushing outward against aneurysmal sac. ICP is counter pressure. In essence, ICP creates a tamponade effect. Risk of rupture is increased by hypertension and/or acute reduction in ICP (opening of dural)
What is the problem with high transmural pressures?
An increased transmural pressure predisposed the aneurysm to rupture. As vessel bursts, blood flows into the subarachnoid space.
What is the most common clinical finding in a patient with subarachnoid hemorrhage (SAH)? What are the other s/s?
“worst headache of my life”
- Consciousness is lost 50% of the time.
- focal neurologic deficits
- N/V
- photophobia
- fever
- Meningismus occurs as blood spreads throughout and irritates the subarachnoid space.
- Blood can block CSF flow, causing obstructive hydrocephalus and increased ICP.
What is the most significant source of morbidity and mortality in the pt with SAH?
Cerebral vasospasm is delayed contraction of cerebral arteries. Can lead to cerebral infarction.
Free hemoglobin that is in contact with outer surface of cerebral arteries increases the risk of vasospasm.
There is a positive correlation btwn the amount of blood observed on CT and incidence of vasospasm.
What is the incidence of cerebral vasospasm?
When is it most likely to occur?
It occurs in about 25% of pts following SAH and is most likely 4-9 days following SAH.