NB1-0 - Neurons, Glia, and Action Potentials DLAs

Question 1

Which two cells make up the nervous system and what are their primary functions? During development which cells appear first?

Answer 1

Neurons - receive and transmit information (APs)

Glia - support, protect, regulate, and electrically insulate the neurons

Neurons appear first during development

Question 2

What are the following structures:

Soma

Nissl Bodies

Axon Hillock

Axolemma

Axoplasm

Answer 2

Soma - neuron cell body

Nissl Bodies - granules of rER in the soma

Axon Hillock - the initial part of the axon

Axolemma - axon plasma membrane

Axoplasm - cytoplasm of axon

Question 3

List the cytoskeletal elements of the neuron and their primary functions.

Answer 3

Microfilaments - form network near membrane that controls movement of the growth cone (development and repair) and endocytosis

Microtubules - provide track for transportation of supstances up and down the axon

Neurofilaments (neuronal intermediate filaments) - regulate axon diameter

Question 4

Which proteins transport substances up and down the axon? How do they do this and in which direction do they do this?

Answer 4

Dynein and Kinesin do this by dragging vesicles up and down microtubule tracts.

Kinesins carry cargo in the anterograde or positive direction (toward the axon terminal)

Dyneins carry cargo in the retrograde or negative direction (toward the soma)

Dying is a negative thing. Dyneins travel in the “-“ direction

Question 5

What is the importance of the tau protein to neurons?

Answer 5

It cross links the MTs together in the axon. If these proteins dont function properly then the anterograde/retrograde transport of the neuron ceases to function

Question 6

List the differences between fast and slow neuronal transport.

Answer 6

For a substance to undergo fast transport it has to be in a vesicle and trasnported via the MT network

Slow transport only occurs in the anterograde direction and is usually just for cytoskeletal molecules and soluble proteins

Question 7

List the neuronal morphotypes and provide nerve examples for each.

Answer 7

• Psedounipolar - primary examples are the primary sensory afferents with the soma in the DRG
• Biploar - special sesory nerves (olfactory bulb)
• Multipolar
  
  • ​Golgi Type I (long axons) - motor neurons
  • Golgi Type II (short axons) - local interneurons

Question 8

Answer 8

Question 9

What are the two primary ways to increase AP velocity?

Answer 9

Increase the diameter of the axon (which decreases resistance)

Myelinate the axons

Question 10

What is an IPSP and EPSP and what determines which one occurs?

Answer 10

An Inhibitory Post Synaptic Potential occurs when the neurotransmitter released by a presynaptic neuron reploarizes the post synaptic cell

An Excitatory Post Synaptic Potential occurs when the neurotransmitter released by a presynaptic neuron depolarizes the post synapti cell

What determines which occurs are the receptors on the postsynaptic membrane

Question 11

List the central glial cells.

Answer 11

• Astrocytes
• Oligodendrocytes
• Microglia
• Ependymal Cells
  
  • ​Ependymocytes
  • Tanycytes
  • Choroidal Epithelial Cells

Question 12

What are radial glia and what are their primary functions? What do these cells become after development is complete?

Answer 12

They are progenitors of the central glial cells and they provide a scaffold for neuronal migration during development. Radial glia will become Bergman glia in the cerebellum and Muller cells in the retina

Question 13

What are the primary functions of astrocytes?

Answer 13

• They regulate neurons by regulating ion flow, NT release, and regional cerebral blood flow
• They protect neurons by forming the blood brain barrier (BBB), limiting oxidative damage, and supplying lactate
• They also release gliotransmitters

Question 14

What are gliotic scars?

Answer 14

When certain pathologies affect the brain, the astrocytes will hypertrophy forming gliotic scars which can affect normal brain function

Question 15

How do astrocytes regulate ion flow and why is this important?

Answer 15

During an AP, an axon will release K+ and Ca++ into the stroma. A build up of these ions could trigger APs in neighboring cells. Astrocytes from a syncitium with one another and can absorb and spread these ions out.

Question 16

What are the primary functions of the microglia? How can microglia be harmful?

Answer 16

They are immunocompetent phagocytes that protect neurons from microorganisms and cellular debris. They will do this by phagocytosing them or releasing cytotoxins around them. They will also release neuron survival factors upon activation.

Sometimes microglia can release too many cytotoxins or not enough survival factos which could initiate pathological neuronal degeneration

Question 17

What are the primary functions of oligodendrocytes?

Answer 17

Form myelin sheath

Question 18

Where are ependymocytes found and what are their functions?

Answer 18

They line the spinal cord and brain ventricles. They’re held together by tight junctions so they assist in forming the BBB. They also possess cilia and microvili that will manage the composition of the CSF. They do secrete some CSF but they mostle adjust its contents.

Question 19

What are the primary functions of the choroid plexus epithelial cells?

Answer 19

Secrete CSF and transfer molecules from blood to CSF. Obviously, this occurs within the choroid plexus.

Question 20

Where are tanycytes found and what are their primary functions?

Answer 20

They are found near circumventricular organs and they function as the interface between blood and CSF for these organs

Question 21

List the peripheral glial cells

Answer 21

• Schwann Cells
• Enteric Glia
• Satellite Glia

Question 22

What are the primary functions of schwann cells? From what do these cells develop?

Answer 22

These cells develop from neural crest cells and mainly serve to form the myelin sheath for peripheral neurons. They also will release trophic factors to guide axonal growth.

Question 23

What are the primary functions of enteric glia?

Answer 23

They perform similar functions to astrocytes but within the enteric nervous system.

Question 24

What are the primary functions of satellite glia?

Answer 24

These are essentially specialized schwann cells that cover the soma and dendrites found within the peripheral ganglia.

Question 25

What is Wallerian degeneration and how does it occur?

Answer 25

When an axon is damaged, the axonal segments distal to that injury will degrade away, releasing lipid droplets (shwann debris). Invading macrophages and local microglia will then phagocytose these lipid droplet. Over time that degenerated segment will regenerate.

If the cell body is damaged then the entire neuron regenerates in a similar fashion. However, the new soma will be more swollen, have more nissl bodies, and a peripheral nucleus.

Question 26

What is chromatolysis?

Answer 26

That is the name given to the process of soma regeneration that takes place after Wallerian Degeneration. After this takes place, the neuron is said to be chromatolytic.

Question 27

Why can peripheral neurons regenerate but not central ones?

Answer 27

The lipid droplets released during Wallerian degeneration are inhibitory of regeneration. If they’re not cleared away within two weeks then regeneration will not occur. Lipid droplet clearing usually occurs too slowly within the CNS.

Question 28

What is retrograde and anterograde transneural degeneration? What causes these things?

Answer 28

If a neuron becomes chromatolytic, it’s presynaptic neuron’s axon terminal will withdraw and be replaced with glial cells. This will then trigger the presynaptic neuron to degrade. This is called retrograde transneural degeneration

When a neuron undergoes Wallerian degeneration, the lack of input to the postsynaptic neuron causes it to degrade as well. This is called anterograde transneural degeneration.

Question 29

Review the important stages of the neuronal action potential with focus on the different ion channels. Indicate when the different refactory periods start and stop.

Answer 29

1. A deoplarizing stimulus depolarizes the membrane past threshold, triggering the v-gated Na+ and Ka+ channels to open. The K+ channels open and close very slowly.
2. At the peak of the AP, the Na+ channels inactivate (meaning they cannot be activated again, this is when the absolute refactory period starts) but the Ka+ channels reamin open, this starts to repolarize and eventually hyperpolarize the cell before the K+ channels close. The Na+ channels close (but are reactivated) right when the cell is repolarized but not yet hyperpolarized (this is when the relative refactory period starts)
3. K+ reentering the cell through leak channels brings the cell back to its resting membrane potential. This is when the relative refactory period has ended.