#05

Question 1

Lack of significant anaerobic
metabolism by the brain means that

Answer 1

• Neuronal glycogen storage is very slight
• Brain oxygen stores are very slight

Question 2

Cerebral blood
flow rate is approximately a ml/100g of brain tissues per min
Cerebral blood flow less than b/100 results in irreversible brain damage

Answer 2

a: 50
b:15

Question 3

4 mechanisms to regulate cerebral blood flow (CBF)

Answer 3

Cerebral pressure autoregulation (homeostatic)
Metabolic factors (CO2)
Neurogenic factors
Blood viscosioty

Question 4

Under what conditions may autoregulation become impaired?

Answer 4

• Old age – mean CBF decreased
• Epilepsy – mean CBF increased 2-3×
• Arteriosclerosis – if severe, mean CBF decreased

Question 5

Under what circumstances does hypertension result in decreased blood flow?

Answer 5

Damage to vessels
Edema (odem)
Raised intracranial pressure

Question 6

When arterial CO2 ↑ brain arterioles

Answer 6

dilate (CBF ↑).

Question 7

Steal Syndrome (Reverse Robin Hood
Syndrome):

Answer 7

After prolonged ischemia, normal
CO2 response fails, and blood flows away from the region where CO2 is elevated, i.e. from the region where it is most needed.

Question 8

PET measures

Answer 8

glucose utilization

Question 9

SPECT measures

Answer 9

blood flow

Question 10

Cerebral vessels are innervated by a
(from superior cervical ganglion), but, due to b, this innervation doesn’t
usually affect blood flow

Answer 10

a: noradrenergic postganglionic sympathetic fibers
b: autoregulation

Question 11

CBF is a to blood viscosity

Answer 11

a: inversely proportional

Question 12

How are the ventricles interconnected?

Answer 12

lateral ventricles -> interventricular foramina (of Monro) -> IIIrd ventricle -> cerebral aqueduct (of Sylvius) -> IVth ventricle

Question 13

Core functions of CSF

Answer 13

• Maintains a constant external environment for neurons and glia (communicates with brain interstitial fluid)
• Primarily one-way flow of CSF serves as a functional waste clearance pathway (glymphatic system) for removal of potentially harmful brain metabolites
• Provides a mechanical cushion to protect the brain from impact with the bony calvaria when the head moves
• By its buoyant action, CSF allows the brain to float, thereby reducing its effective weight in situ to less than 50g
• May serve as a conduit for polypeptide hormones (secreted by hypothalamic neurons) acting at remote sites in the brain
• Homeostatic role (pH of CSF affects both pulmonary ventilation and CBF)

Question 14

Ependymocytes

Answer 14

These cells create and secrete CSF and beat their cilia to help circulate CSF
through the system

Question 15

CSF is mostly produced in modified ependymal cells called

Answer 15

choroid plexus.

Question 16

all four ventricles (L and R lateral ventricles, IIIrd ventricle, and IVth
ventricle) have choroid plexus, but the vast majority (~70%) is located in

Answer 16

lateral ventricles

Question 17

Foramina of Luschka (location?) empty ventrally into a

Answer 17

loc: lateral apertures of ventricle IV
a: pontine cistern

Question 18

Foramen of Magendie (location?) empties dorsally into the a

Answer 18

loc: median aperture of ventricle IV
a: cisterna magna

Question 19

CSF production

Answer 19

Choroid plexus (%50-70)
other ependymal cells
around blood vessels in subarachnoid space
produced at a rate of 500 ml/day

Question 20

CSF absorption

Answer 20

Arachnoid granulations (majority)
along crnial and spinal nerves into lymph system
Brain can contain only 135-150 ml, so CSF must turn over 3.7 times daily

Question 21

Monro-Kellie doctrine

Answer 21

An increase in the volume of any one of the contents of the calvaria—brain tissue, blood, CSF, or other brain fluids—will produce increased intracranial pressure because the bony calvaria rigidly fixes the total cranial volume.

Question 22

noncommunicating hydrocephalus vs communicating hydrocephalus

Answer 22

• Interventricular obstructions (e.g., stenosis of the cerebral aqueduct) cause noncommunicating hydrocephalus (the CSF does not “communicate” with the
  subarachnoid space).
• Extraventricular obstructions (e.g., obstruction at the tentorial notch, blockage of the arachnoid granulations) cause communicating hydrocephalus. Tracer die injected
  into the lateral ventricle will ccumulate in the lumbar cistern in the case of
  communicating hydrocephalus, as CSF is able to evacuate the ventricular system and enter the subarachnoid space.

Question 23

Entry into the blood/CSF is achieved primarily in three ways

Answer 23

1. by diffusion of lipid-soluble substances – substances with high lipid solubility (e.g., ethanol, nicotine) enter the brain rapidly, those with low/no lipid solubility (e.g., sodium, dopamine) enter the brain slowly or not at all
2. by facilitative (e.g., Glutl) and energy-dependent (e.g., Na+-K+-ATPase)
   receptor-mediated transport of specific water-soluble substances
3. by ion channels (e.g., Na+ channels)

Question 24

advantages of BBB

Answer 24

Maintains a precisely regulated microenvironment for reliable neuronal signaling
Keeps out bacteria

Question 25

disadvantages of BBB

Answer 25

Keeps out white blood cells
Keeps out drugs