Intro to NS, Glia, tissues - Finger

Question 1

What is a metabotropic synapse?

Answer 1

A metabotropic synapse activates second-messenger systems within the cell (eg G-protein).

Question 2

What is an ionotropic synapse?

Answer 2

Activates ion channels which either depolarize or hyperpolarize the axon.

Question 3

What are the three principal types of glial cells in the CNS? In the periphery, what is the cell type?

Answer 3

CNS: microglia, oligodendrocytes (oligodendroglia), astrocytes.
PNS: Schwann cells

Question 4

What is the origin and function of the microglia? What is a major focus of research with regard to these cells?

Answer 4

Are the major phagocytic cell of the CNS. Originate from outside the neural tube. Are implicated with chronic pain syndrome. Clear “debris” from the brain after damage (rapid proliferation of cells).

Question 5

What are the myelin-forming cells?

Answer 5

Schwann cells and oligodendrocytes (oligodendroglia)

**Oligodendroglia can assx with more than one axon. Schwann cells assx with only one.

Question 6

What is the function of astrocytes?

Answer 6

Astrocytes help maintain the ionic balance in the ECF. By regulating K levels, it keeps the efflux of K during a depolarization from depolarizing neighboring axons. They associate with the synapses to prevent leakage of neurotransmitters.

They also play a large role in the clearance and recycling of neurotransmitters like glutamate.

Astrocytes also help regulate blood flow by sensing glutamate levels and signalling smooth muscle relaxation.

The pia (outermost layer of the brain) is formed by astrocytic processes.

They also tell the endothelial cells to tightly seal (bb barrier). Eg without astrocytes there would be fenestrations as in muscle.

The astrocytes also pull nutrients from the blood vessels for supply/transport.

Question 7

What happens peripherally vs centrally during nerve damage?

Answer 7

Peripheral nerves can repair themselves (Schwann cells). Lasting damage occurs due to changes in the CNS, specifically, reorganization of synaptic systems which can lead to neuropathic pain states.

Pharmacologic blockade can prevent the microglial signalling cascade that leads to these changes.

Question 8

What happens in response to CNS damage?

Answer 8

Oligodendrocytes prevent CNS regrowth through a number of mechanisms (upregulation of proteoglycans, astrocyte proliferation leading to a glial scar), though CNS axons are capable of such repair.

Question 9

The blood-brain barrier is created because capillaries in the brain lack ______.

Answer 9

fenestrations

Astrocytes are also important as they signal to the endothelial cells to maintain tight junctions.

Question 10

What are the circumventricular organs?

Answer 10

Areas of the brain (along the ventricular walls by the caudal medulla and hypothalamus) that are not isolated behind the bb barrier. These areas are walled off by astrocytes and are involved in monitoring the composition of the blood.

Question 11

For each of the following, know which is gray matter and which is white matter: nucleus, lemniscus, ganglion, peduncle, cortex, funiculus, body, fasciculus, tract.

Answer 11

Grey: nucleus, ganglion, cortex, body

White: leminiscus, peduncle, funiculus, fasiculus, tract

Question 12

What is the Nissl substance (nissl bodies)?

Answer 12

Rough ER, site of ATP synthesis and protein production.

Question 13

Describe autoregulation of blood flow in the brain. Specifically, what is the sequence of events that will occur due to an increase in blood pressure?

Answer 13

The brain wants to maintain a constant diameter within the blood vessels. Increases in pressure tend to expand the diameter, and must be countered. The mechanism is: increased pressure stretches the arteriolar walls, which triggers a second-messenger system that results in inhibition of Calcium Activated Potassium Channels (Kca). This results in DEpolarization (think about it, you’ll get there), and DEpolarization results in smooth muscle contraction.

Question 14

What is the name of the phenomenon responsible for PET and fMRI scans?

Answer 14

Functional hyperemia –> substantial increase in local blood flow in areas of neuronal activity.

(fMRI uses properties of Hb, PET requires a tracer).

Question 15

What two mechanisms allow/create functional hyperemia (ie how is blood flow increased, mechanistically)?

Answer 15

1) NO
2) astrocyte involvement (complex reaction starting with glutamate uptake into the astrocyte, but the end result is formation of EET [epoxy-eicosatrienoic acid] which acts on arterioles to hyperpolarize the membrane and decrease vascular tone, increasing blood flow)

Question 16

What is a neuropil?

Answer 16

area rich in axon terminals, dendrites and synapses (sounds like this area will be associated with an astrocyte).

Question 17

Nissl stain

Answer 17

Common for looking at neural cells. Named for the dark bodies around the nucleus of the cell. Stains RNA.

Nucleolus is dark because that is where ribosomes are made. The area around the nucleus stains dark because there are a ton of ribosomes (tons of RER).

Neurons are making tons of proteins, so the DNA is unpacked and stains dark. Neurons are big cells, and all proteins must all come from the cell body (axoplasmic transport - bidirectional)

Question 18

What accounts for the histological difference between the glial cells and neurons under Nissl stain?

Answer 18

Nuclei are compacted in the glial cells b/c they do not have high levels of protein synthesis (as compared to the neurons which have massive purple cytoplasm under Nissl stain.

Question 19

What is the origin of the microglia?

Answer 19

Hematopoietic. They are macrophage-like cells of the nervous system. They are active, moving around, sampling the environment. They are attracted to ATP (video of microglial cells coalescing around a pipette-injected dose of ATP).

Question 20

Cutting through the skull, name the layers you hit from superficial to deep.

Answer 20

Skull–> dura–> arachnoid –> subarachnoid space (veins) –> pia (astrocytic end feet layer) –> brain

Question 21

In the CNS the grey matter is (superficial/deep) to the white matter? In the PNS?

Answer 21

CNS –> grey matter is superficial, white matter is deep

PNS –> grey matter is deep, white matter is superficial

Question 22

What is chromatolysis? It occurs in response to what?

Answer 22

Damage to the axon causes chromatolysis, which is disassociation of the RER/ribosomes, often as a response to injury.

Question 23

What is the limitation of fMRI studies that focus on increased blood flow?

Answer 23

The statistical significance becomes very low when studying increasingly small areas of the brain, so studies have largely reached the limit of resolution for this type of mapping. Proceed with caution.