Neuro: Brain Metabolism

Question 1

mitochondria in the brain are preferentially located where? why is this?

Answer 1

at the synapses - most of the energy of brain metabolsim is spent here

Question 2

True or false: most of the ATP required for brain metabolism comes from glycolysis.

Answer 2

False (93% comes from Krebs Cycle followed by Ox Phos in the mitochondria)

Question 3

True or false: the brain can draw energy from anaerobic metabolism when needed.

Answer 3

False (and because oxygen and glycogen stores in the brain are very slight, this constrains information processesing capability)

Question 4

Lesions of the nervous system due to interruption of blood supply are the most common type of CNS disorders, and they are known as what?

Answer 4

strokes

Question 5

Irreversible brain damage occurs at what amount of blood flow in the brain if it persists for several minutes?

Answer 5

<20 ml/min/100g of tissue (normal is 40-55 ml/min)

Question 6

What are the 4 primary mechanisms of regulation of cerebral blood flow?

Answer 6

1. cerebral pressure autoregulation
2. Metabolic factors (CO2)
3. Neurogenic factors
4. Blood viscosity

Question 7

This is the intrinsic ability of brain vascular beds to maintain a constant perfusion despite changes in blood pressure

Answer 7

cerebral pressure autoregulation

Question 8

autoregulation of cerebral pressure is controlled by what mechanism?

Answer 8

changes in diameter of cerebral arterioles (they constrict when systemic blood pressure goes up and dilate when systemic blood pressure falls)

Question 9

at what blood pressure range does autoregulation begin to fail and start to linearly match systemic pressures? what are 3 reasons this may happen?

Answer 9

at BP below 50mm Hg and above 200mm Hg; decreased cerebral blood flow may be caused by:

1. old age
2. epilepsy
3. arteriosclerosis of cerebral vessels

Question 10

Under what circumstances does hypertension result in decreased cerebral blood flow?

Answer 10

1. when there’s damage to the vessels
2. when there’s edema
3. raised intracranial pressure

Question 11

what is the response of the brain when arterial CO2 increases?

Answer 11

vessels dilate to get more blood flow to the area

Question 12

what is the effect of alkalosis and acidosis on cerebreal blood flow?

Answer 12

alkalosis –> decreased blood flow

acidosis –> increased blood flow

Question 13

what is steal syndrome (aka, reverse robin hood syndrome)?

Answer 13

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 14

even though everyone does this, so it’s kind of stupid, why should you not give oxygen to someone in a coma?

Answer 14

O2 causes vasoconstriction of arterioles so you fisk a further drop in cerebral blood flow, exacerbating the problem
NOTE: at blood pressure <50 mm Hg, the opposite (an adaptive) response is seen

Question 15

why would blood flow be greater to gray matter than to white, and to neurons than to glia?

Answer 15

these are the areas of the brain with greatest functional activity

Question 16

In contrast to CT and MRI scans, which provide anatomical images, these 3 measurement tools utilize the metabolic activity and blood flow of neurons to provide information about the activity of specific regions of the brain or about specific groups of neurons

Answer 16

PET (glucose utilization)
SPECT (blood flow)
fMRI (blood oxygen level)

Question 17

sympathetic regulation of the cerebral arteries comes from where?

Answer 17

postganglionic sympathetics from the superior cervical ganglion
NOTE: this is only important outside of the range of autoregulation, e.g., during heavy exercise blood pressure increases and sympathetic innervation will constrict large and intermediate size vessels of brain to reduce pressure on smaller arteries of the brain

Question 18

True or false: anemia decreases cerebral blood flow.

Answer 18

False
CBF is inversely proportional to blood viscosity. In anemia, blood is less viscous (lower hematocrit and erythrocytes) so it will increase CBF

Question 19

what is the path of flow for cerebral spinal fluid?

Answer 19

produced in choroid plexus in the walls of the lateral ventricle –> foramen of Monro –> IIIrd ventricle –> cerebral aqueduct (of Sylvius) –> IVth ventricle –> exit thru formina of Luschke and Magendie –> cisterns of the subarachnoid space

Question 20

the type of cells in the choroid plexus that create and secrete CSF, and help circulate CSF through the system by beating their cilia

Answer 20

ependymal cells

Question 21

enlarged reservoirs within the subarachnoid space where CSF collects

Answer 21

cisterns

Question 22

small protrusions of the arachnoid mater through the dura mater which form lacunae that empty CSF into the venous sinuses

Answer 22

arachnoid granulations

Question 23

how many times a day does CSF turn over?

Answer 23

3.7

Question 24

an interventricular obstruction (e.g., stenosis of the cerebral aqueduct) would cause what?

Answer 24

noncommunicating hydrocephalus (the CSF does not “communicate” with the subarachnoid space)

Question 25

In the CNS, these channels facilitate the removal of interstitial fluid and clearance of metabolic waste from the brain, as well as allow immune cells to enter

Answer 25

para-vascular

Question 26

this feature of the brain is formed by cerebral capillaries with non-fenestrated endothelial cells joined by
complex interendothelial tight junctions, and serves to protect the brain from harmful substances that may be in the blood

Answer 26

blood brain barrier

Question 27

capillaries in the ____ _____ differ from those of the brain in that they are fenestrated and contain intercellular gaps permitting the free movement of molecules across the endothelial cell

Answer 27

choroid plexus

Question 28

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

Answer 28

1. diffusion of lipid-soluble substances
2. receptor-mediated transport of specific water-soluble substances
3. ion channels