neurons, glia, brain tissue

Question 1

For the following identify which is gray matter and which is white matter: nucleus, peduncle, funiculus, fasciculus, tract, lemniscus, ganglion, body, cortex, dendrites and synapses.

Answer 1

gray matter: nucleus, ganglion, cortex, body, dendrites, synapses.
white matter: lemniscus, peduncle, funiculus, fasciculus, tract.

Question 2

astrocyte location

Answer 2

CNS

Question 3

Microglia location

Answer 3

CNS

Question 4

Oligodendrocyte location

Answer 4

CNS

Question 5

Schwann cell

Answer 5

PNS

Question 6

astrocyte function

Answer 6

1) maintain ionic equilibrium (e.g. remove potassium ions from extracellular space following action potentials) 2) clear and recycle neurotransmitters from the extracellular space 3) “end-feet” envelop all CNS blood vessels and are involved in transport of nutrients from the blood vessels to nearby neurons. 4) locally regulate blood flow

Question 7

microglia function

Answer 7

major phagocytic cells of the CNS. In response to damage, they undergo rapid proliferation to clear the debris from the brain.

Question 8

oligodendrocyte function

Answer 8

form the myelin the central nervous system. Single oligodendrocyte may myelinate several nearby axons.

Question 9

schwann cell function

Answer 9

form myelin in the peripheral nervous system.

Question 10

dendrite function

Answer 10

passive conductor of electrical energy

Question 11

Nissl substance and it’s function

Answer 11

nissl substance = large granular body found in ribosomes consisting of rough ER and free ribosomes. Function is thus manufacture and release of proteins.

Question 12

describe the relationship between cerebral blood flow and fMRI/PET

Answer 12

“functional hyperemia.” increase in local blood flow due to local increase in neuronal activity. This is the basis for functional MRI (fMRI) and PET studies of brain activity. fMRI relies on hemoglobin, PET relies on an injected tracer.

Question 13

Describe the blood brain barrier

Answer 13

Capillaries of the brain are not fenestrated. Tight junctions exist between endothelial cells. Endothelial cells posses a variety of receptors and transporters that permit the cells to be selective about what to transport. Transport is done actively or passively (lipid-soluble substances can diffuse through). Astrocytes don’t form the BBB, they maintain it.

Question 14

describe how astrocytes can regulate local blood flow in proportion to the neuronal activity in the area.

Answer 14

increased neuronal activity –> increased astrocytic glutamate uptake causes release of intracellular stores of arachidonic acid –> astrocytes contain a P450 enzyme that converts arachidonic acid to epoxy-eicosatrienoic acid (EET) –> EET hyerpolarizes smooth muscle membrane –> decreased arteriole vascular tone –> larger lumen –> increased blood flow

Question 15

Describe the PNS response to damage

Answer 15

• Schwann cells → clear myelin debris + line up along endoneurium to form an attractive substrate for outgrowth of axons from the cut stump of the nerve.
• Central terminals of damaged neurons emit signals (hyperactivity and trophic substances including ATP) that activate microglia IN THE CNS, causing 1) microglia to start dividing and up-regulate expression of several cytokines and trophic factors → cytokines and trophic factors activate astrocytes which proliferate and 2) microglia strip synapses causing reorganization of synaptic systems within the affected brain areas.
• Microglial response is rapid but short lived; astroglial response is slower but much more sustained.

Question 16

Describe the CNS response to damage. What inhibits regrowth?

Answer 16

Following damage, the following 2 mechanisms inhibit regeneration of central axon tracts. Capacity for regrowth remains, however.

1) Rather than clearing myelin debris and forming a pathway permissive of axonal elongation, oligodendocyte precursors proliferate and up-regulate expression of molecules (eg chondroitin sulfate proteoglycans) that inhibit axonal outgrowth.
2) microglia activate local astrocytes which proliferate to form a glial scar which forms a chemical and physical barrier to axonal regeneration.

Question 17

what is a circumventricular organ?

Answer 17

at certain small sites along the ventricular walls in the CAUDAL MEDULLA and HYPOTHALAMUS, there is no blood-brain barrier. These areas of the CNS are involved in monitoring the composition of the blood or else produce something that is secreted into the blood. Astrocytes wall off these “circumventricular organs” to maintain the bbb.

Question 18

neuropil

Answer 18

area rich in axon terminals, dendrites, and synapses

Question 19

why is myelin white?

Answer 19

it’s mostly fat, i.e. lipid bilayers

Question 20

how do metabotropic receptors work?

Answer 20

don’t directly pass ions but rather activate second-messenger systems (e.g. G-proteins) within the neuron. Activation of the second messenger system usually causes a local biochemical cascade culminating in changes of membrane conductance, usually by altering the function of an ion channel.

Question 21

what is the major cell type implicated in chronic pain syndrome?

Answer 21

microglia

Question 22

describe the concept of autoregulation

Answer 22

as blood pressure increases in cerebral arterioles, the wall stretches. This mechanical deformation results in activation of a second-messenger cascade that culminates in inhibition of the calcium-activated potassium channels, which functions to deploarize the cell. Depolarization and subsequent Ca++ influx results in activation of the muscle in arteriole walls. The net function is to main a constant vessel diameter.

Question 23

How does increased neuronal activity result in increased blood flow?

Answer 23

1) neurons generate gaseous NO, which diffuses to reach the blood vessels. NO dilates local vessels. 2) astrocytic response