1.6 Microstructure

Question 1

A protein is produced in a neuron. How does its fate differ if it is translated at a free ribosome vs RER ribosome?

Answer 1

Free: Cytosolic protein
RER: Proteins destined for cellular/organelle membrane

Question 2

Why do neurons have so much rough endoplasmic reticulum compared to other cells?

Answer 2

Proteins translated by RER ribosomes are used for membranes. Neurons need many of these proteins, such as channels, and so they have lots of RER.

Question 3

Which organelles are present in high amounts in neurons?

Answer 3

• Mitochondria (energy)
• RER (protein production)
• Golgi body (protein transport)
• Cytoskeleton

Question 4

The thicker an axon of a neuron, the _____ the impulse travels

Answer 4

Faster

Question 5

What organelles/structures can be found in an axon terminal?

Answer 5

• “Bubbles” of synaptic vesicles (containing neurotransmitters)
• Mitochondria (active vesicle transport)

Question 6

Which protein is responsible for anterograde/retrograde vesicle transport along axons?

Answer 6

Anterograde: Kinesin
Retrograde: Dynein

Question 7

What is the most abundant cell type in the brain?

Answer 7

Astrocytes

Question 8

Describe the function of astrocytes

Answer 8

• Recycle neurotransmitters
• Structural support
• Regulate concs in environment, like ions, nutrients and dissolved gases

Question 9

How do astrocytes help in metabolism of neurons?

Answer 9

• Well positioned to access glucose from the bloodstream
• Convert glucose into lactate
• Neurons can use lactate to produce energy (perhaps even preferred during periods of activity…)

Question 10

Astrocytes regulate homeostasis of the CNS by ensuring concentrations of ions, neurotransmitters, and water. What channels do they use to regulate water conc?

Answer 10

Aquaporins (specifically, aquaporin 4, or AQP4)

Question 11

What is astrogliosis?

Answer 11

The proliferation of astrocytes to form a scar in response to CNS injury

Question 12

Describe the benefits and drawbacks of astrogliosis

Answer 12

Good: walls of area
Bad: prevents new connection, slows recovery

Question 13

What is the PNS equivalent of astrocytes?

Answer 13

Satellite cells

Question 14

What is the function of oligodendrocytes?

Answer 14

Myelinating axons

Question 15

Citing a specific kind of microglial cell, explain why neurons in the CNS cannot be regenerated in response to injury

Answer 15

In response to injury, oligo’s release inhibitory factors

Question 16

What are the two types of conduction?

Answer 16

Saltatory: myelin + nodes of ranvier
Continuous: no myelin

Question 17

What is the PNS equivalent of oligodendrocytes? What is their biggest difference to their CNS alternatives?

Answer 17

• They are called Schwann cells
• They can only myelinate one axon, whereas oligos can myelinate 15

Question 18

What is the function of microglia?

Answer 18

• Roaming phagocytes
• Synaptic pruning
• Neurodegenerative disease

Question 19

Describe the activation of microglia

Answer 19

• Injury detected
• Processes retracted
• Motility increased
• Gather around injury site, and perform phagocytosis

Question 20

True or false: microglial phagocytosis promotes inflammation

Answer 20

True

Question 21

Describe the structure of the blood brain barrier

Answer 21

• Endothelial cells (held together with tight junctions)
• Pericytes
• Basement membrane
• Astrocytes (and their “podocyte” feet processes)

Question 22

In most capillaries, transport of substances is paracellular (i.e., between cells). is this the case in the blood brain barrier?

Answer 22

• No
• Instead, transport mostly happens through cells

Question 23

Outline the different ways in which substances can be transported across the blood brain barrier

Answer 23

• Passive diffusion
• Carrier mediated transport (i.e. channel proteins)
• Receptor mediated transport (i.e. in an endosome)
• ABC transporters allow substances to go the other way (brain to blood)

Question 24

Give some examples of substances that cross the blood brain barrier via transport proteins

Answer 24

• Glucose
• Amino acids
• Peptides
• Choline

Question 25

Describe, fundamentally, how substances cross the BBB through transport proteins.

Answer 25

• Bind to first transport protein, undergoes conformational change, allowing passage into cell
• Bind to second transport protein, undergoing conformational change, and allowing passage into brain

Question 26

Receptor mediated vs adsorptive transcytosis

Answer 26

RM: Ligand must bind to receptor
Adsorptive: Binds to negative membrane charge

Question 27

Is transport via ABC transporters active or passive? What kind of substances does it remove?

Answer 27

• Active
• Removes toxins