#6 Cells of the CNS

Question 1

What are neurons? What is their role and how do they work?

Answer 1

Cell within the CNS that is responsible for conducting action potentials. The dendrites receive information from other neurons and the axon conducts the message down the neuron (via depolarization with Na coming in and K going out, followed by repolarization and resting to ensure the AP does not move backwards), and then the axon terminals send the info in the form of chemicals to the next neuron

Question 2

What are the four types of glia?

Answer 2

Microglia, astrocytes, and oligodendrocytes as well as their OPC precursors (oligodendrocyte progenitor cells)

Question 3

What happens to glia during disease? What are the two possible effects?

Answer 3

Glia can change function during disease and can either assume positive changes (acquire a new function) or negative function (lose their original homeostatic function)

Question 4

What are the 5 life essential processes of living organisms that glia control? How do they control this?

Answer 4

1. Reproduce: glial cells are constantly dividing
2. Remove wastes: via astrocytes, microglia, and glymphatics
3. Nutrients: BBB controls nutrient entry to the brain via astrocytes
4. Energy: glial syncytium, which are channels within the glia that allow nutrients to flow through the astrocytes to other glia via diffusion
5. Respiration: astrocytes control blood flow

Question 5

How do glia and neurons interact? How is their contribution different compared to the contribution of neurons?

Answer 5

Glia acts as the support for all neurons.
Glia are linked to all traits, and for most diseases the role of glia is larger than the role of neurons.

Question 6

What are the 8 general functions of the astrocyte?

Answer 6

Immune modulation with microglia, make/modify the ECM, promote neuronal survival, myelination, regulate glutamine (via tripartite synapses) uptake and regulation. ion regulation, glycogen energy reserves, regulate the BBB,

Question 7

How to astrocytes work at synapses?

Answer 7

They have many fine processes that interact at synapses by completely surrounding the neuronal synapses. They also interact at tripartite synapses where they regulate the concentration of glutamate in the synapse by taking it back up and recycling it back to the neuron.

Question 8

How do astrocytes interact at the ECM level and at the BBB level?

Answer 8

At ECM: astrocytes wrap around synapses by almost completely surrounding them, and they thus support and influence them
At BBB: astrocytes decide what gets into the brain, pericytes regulate the blood vessels, and both of these structures surround an endothelial cell which then surround the small blood vessels
Astrocytes facilitate movement of nutrients from the bloodstream into the brain/neurons (glucose, lactate) and contains glycogen stores

Question 9

What are the main functions of microglia? How/where are they made?

Answer 9

Immune cell of the CNS, mostly via phagocytosis of unwanted debris, NOT born in the spinal cord or brain, instead they are born in the yolk sac mainly (other places as well but not as well understood), where they then migrate to the brain.
They arrive at the brain before the oligodendrocytes and after the astrocytes.
Have many receptor systems and are very sensitive, and respond to each molecule in specific ways (not all molecules it responds to are known). They are extremely dynamic and mobile as they migrate to sites of damage and eat the damage

Question 10

What are the three roles that microglia have in the cells?

Answer 10

1. Phagocytosis
2. Synaptic remodeling
3. Secretion

Question 11

How do microglia perform phagocytosis?

Answer 11

1. Cellular debris occurs
2. “Find me” signal is released, which is usually ATP
3. Microglia are recruited to the site of interest (with debris)
4. The “eat me” signal is released, which is normally UDP
5. Phagocytosis occurs (after ATP/UDP)

Question 12

How are microglia involved in synaptic remodeling?

Answer 12

They contribute to synaptic pruning during the critical window, the retinal ganglion cells (vision cells) form to many connections with the lateral geniculate nucleus of the thalamus and microglia facilitate loss of these excess synapses via refinement

Question 13

How are microglia involved in secretion?

Answer 13

Microglia release factors in response to inflammatory signals (chemokines, and cytokines are released in response to dAMP which are damage associated molecular patterns)

Question 14

What is the main function of myelin? Do all cells need myelin?

Answer 14

Myelin becomes wrapped around axons of neurons and speeds up propagation (not always evenly) and all axons do not need myelin, however when it is added, conduction speed increases exponentially via two ways

Question 15

What are the two ways that myelin increases conduction speed?

Answer 15

LOW capacitance
HIGH resistance

Question 16

What does it mean that myelin lowers capacitance?

Answer 16

It means that myelin lowers membrane capacitance, therefore the ions move more freely in the membrane to propagate and action potential. There are less anions near the surface of the membrane to attract cations therefore the cations can move more freely, and are more available for depolarization

Question 17

How does myelin increase resistance?

Answer 17

Myelin traps cations in the membrane, therefore increasing the resistance to leakage. If less cations leak out of the membrane then there are more available for depolarization

Question 18

How are oligodendrocytes made and how do they make myelin?

Answer 18

Start with an OPC (oligodendrocyte progenitor cell) which then differentiates into an oligodendrocyte which then makes myelin. Oligodendrocytes spontaneously differentiate (no major signal required for differentiation), and once they make their myelin around the specific axon they do not make anymore. Therefore if more myelin is needed, that means that there must be more OPC to differentiate into oligodendrocyteds

Question 19

Can an oligodendrocyte make myelin on a dead axon? Or do the axons need to be alive for myelin to be made?

Answer 19

Oligodendrocytes will make myelin on both alive and dead axons

Question 20

What is the critical window for when oligodendrocytes?

Answer 20

Within 2 hours of differentiation they make myelin around their specific axons, and then they make no more sheaths

Question 21

How do oligodendrocytes respond to damage in the neuron?

Answer 21

They respond the same way that microglia do, in that they respond to the damaged area and surround/breakdown debris