Lecture 12

Question 1

What are three characteristics of glia cells?

Answer 1

• contribute to half the volume of the brain
• can proliferate (increase rapidly) throughout life
• neuronal stem cells can transform into neurons or glia

Question 2

What are oligodendrocytes?

Answer 2

CNS myelin sheath

Question 3

What are Schwann cells?

Answer 3

PNS myelin sheath

Question 4

What is white matter?

Answer 4

Regions of the brain that are dominated by myelinated tracts

Question 5

How does a myelin sheath work

Answer 5

The leading edge of one sheath wraps around the axon many times

Question 6

What is compaction

Answer 6

The cytoplasm is then squeezed out of many cell layers surrounding the axon

Question 7

What is myelin

Answer 7

Layer on layer of tightly compressed membranes

Question 8

How many axons does one oligodendrocyte myelinate?

Answer 8

Multiple axons

Question 9

How many axons does one Schwann cell myelinate?

Answer 9

One axon

Question 10

Can PNS damaged axons regenerate

Answer 10

Yes with restoration of loss of function

Question 11

True or false?

Axon damage in the CNS do not show functional regrowth

Answer 11

True

Question 12

Why is myelination important?

Answer 12

Responsible for Saltatory conduction in the propagation of action potentials
Saltatory conduction is faster and efficient

Question 13

What are the steps of nerve degeneration?

Answer 13

1) synaptic terminals distal to the lesion in the axon degenerate
2) wallerian degenration
- loss of axonal structure distal to lesion
3) myelin degenerates leaving debris behind
4)

Question 14

What are the two strategies to improve conduction?

Answer 14

Increase diameter (increase a, decrease Ri) 
Myelin (increase Rm)

Question 15

How does local current work

Answer 15

• A signal causes a transient Vm change
• the cytosol is slightly positive compared to adjacent inactive regions of the cytosol which is negative
• the charge imbalance causes currents to flow from the excited region to adjacent regions
• current flows in a complete circuit along pathway of least resistance and spreads
• because of flow of current the region of the membrane immediately adjacent to the active region becomes more depolarized

Question 16

How does current spread?

Answer 16

Longitudinally from positive to negative
Across membrane conductance pathways
Along extracellular médium back to the site of origin thereby closing current loop

Question 17

What constant measures temporal spread?

Answer 17

Time constant:

Tm=Rm•Cm

Question 18

What is the time constant?

Answer 18

Influences the spread of voltage changes in time and thus the velocity of signal propagation

Question 19

What happens if you shorten the tm?

Answer 19

The quicker neighboring region of membrane will be brought to threshold
The faster the speed of impulse propagation

Question 20

For unmyelinated axons how does velocity conduction increase?

Answer 20

Increases with the square root of the axons diameter just as the length constant increases with the square root of axons diameter

Question 21

For myelinated axons how does velocity conduction work?

Answer 21

Conduction velocity is a linear function off diameter and increases 6m/s per 1-um increases in outer diameter

Question 22

What is a disease of demyelination in the cns??

Answer 22

MS causing impaired conduction of action potentials

Question 23

What are astrocytes?

Answer 23

Strength support, promote bbb, in embryo regulate growth migration interconnection

Question 24

What are microglia?

Answer 24

Phagocytes, immune cells, big role in pathological conditions

Question 25

What are the characteristics for astrocytes?

Answer 25

Control the environment of neurons
Brain glycogen contain all enzymes required for glucose metabolism
Provide fuel to neurons in the form of lactate
Astrocytes buffet excess extracellular k+
Synthesis of glutamate and GABA provides glutamine to neurons
Removal of glutamate from synaptic cleft

Question 26

What are the 3 mechanisms that astrocytes take up k+?

Answer 26

Na-K pump
Na/k/cl cotransporters
The uptake of k+ and cl- through channel

Question 27

What is astrocyte gap junction coupling important for?

Answer 27

Spatial buffering

Question 28

What are microglia?

Answer 28

Macrophages of the CNS

Question 29

What are the characteristics of microglia?

Answer 29

Represent ~20% of total glia cells within mature CNS
Rapidly activated by injury to the brain
Proliferate, change shape, and become phagocytic
Activated microglia releasing substances that are toxic to neurons (free and radical NO)