Module 2 - Visualizing the nervous system Flashcards

1
Q

When was the cell theory introduced?

A

1838

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2
Q

Outline the cell theory

A
  1. All living organisms are composed of cells
  2. The cell is the basic unit of structure and organization in organisms
  3. All cells come from pre-existing cells
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3
Q

Did the reticular theory of the nervous system consider the cell theory?

A

No

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4
Q

What did the reticular theory of the nervous system believe?

A

The nervous system is made up of a single continuous network, not separate cells

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5
Q

When was the reticular theory introduced?

A

1861

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6
Q

Who were two strong proponents of the reticular theory?

A

Joseph von Gerlach and Camillo Golgi

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7
Q

What did Golgi (ironically) invent?

A

“La reazione nera ‘ or “the black reaction” AKA the Golgi stain

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8
Q

Outline the process of a Golgi stain.

A

Apply potassium dichromate and silver nitrate to fixed neurons
Randomly labels a subset of neurons in their entirety, permitting single cell tracing

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9
Q

Who was Santiago Ramon y Cajal?

A

A visionary histologist who studied a broad range of nervous system tissues.

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10
Q

Why Santiago Ramon y Cajal a significant figure in the understanding of the nervous system?

A

One of the first to see the great potential of the Golgi stain
Did seminal work that disproved the reticular theory in favour of the neuron theory (along with others)

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11
Q

Who introduced the neuron theory/doctrine?

A

Heinrich Waldeyer

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12
Q

Who generated the data that was used for formulating the neuron doctrine?

A

Ramon y Cajal and colleagues

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13
Q

Outline the tenets of the neuron doctrine (4)

A
  1. Neurons are the functional units of the nervous system
  2. Law of dynamic polarization
  3. Neurons communicate via synapses
  4. Dale’s Law
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14
Q

What is the law of dynamic polarization?

A

Nerve cells have a single axon that serves as an effector (i.e., passes information)
Dendrites and cell body serve as receptor surfaces
Information travels from dendrites to axons

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15
Q

Who put forward the concept of synaptic transmission?

A

Charles Scott Sherrington

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16
Q

What is Dale’s Law?

A

Single neurons utilize a single type of neurotransmitter

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17
Q

What are the 4 issues with the neuron doctrine?

A

Extensive gap junctions (electrical synapses) in the CNS encroach upon the reticular theory
Axons can acts as dendrites and vice versa
Signals can travel against polarity (e.g., from soma/axon to dendrites)
Some neurons can secrete more than one neurotransmitter type

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18
Q

What is a common theory about gaining insight about information flow in the nervous system?

A

Understanding nervous system structure and connectivity = understanding information flow in the nervous system

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19
Q

What is the analogy used to show why connectomics might not be adequate to understand information flow?

A

If you map the entire system of roadways in a city, would that be enough to understand all the traffic patterns that flow through it at different times of day?

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20
Q

How do fluorescent dyes work?

A

Have electrons that absorb light and emit fluorescence as they drop back down to lower energy orbitals

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21
Q

How do fluorescent dyes differ from the Golgi stain?

A

Can be used to label live neurons

22
Q

Describe how labelling using fluorescent dyes works.

A

Inject into neuron
Diffuses or is transported throughout
Some dyes can travel through gap junctions, allowing us to track the flow of information

23
Q

What is MitoTracker?

A

Fluorescent dye that labels mitochondria

24
Q

What is LysoTracker?

A

Fluorescent dye that labels lysosomes

25
Q

What is Hoechst and DAPI?

A

Fluorescent dyes that label nuclei

26
Q

How can genes be used to label and identify neurons?

A

“Marker” genes are used, which are only expressed in cells of interest

27
Q

What is in situ hybridization?

A

Detecting mRNAs in cells/tissues

28
Q

How does in situ hybridization work?

A

Labelled antisense RNA that complements a target mRNA is used as a probe.

29
Q

What is a drawback of using in situ hybridization?

A

mRNAs are mostly located in the soma, preventing us from seeing where the translated proteins end up

30
Q

What is immuno-labelling?

A

Detecting proteins in situ

31
Q

How does immuno-labelling work?

A

Protein epitopes (i.e., extracted portions of protein) are used to generate antibodies
Antibodies bind target proteins and can be detected

32
Q

How do fluorescent proteins work?

A

Absorb light and emit fluorescence

33
Q

What was green fluorescent protein (GFP) cloned from?

A

The jellyfish Aequorea victoria

34
Q

What are the benefits of GFP?

A

Can genetically express GFP in specific neurons
Can create fusion proteins

35
Q

How can GFP be expressed in specific neurons?

A

Use cell-specific promoters to drive expression in neurons of interest
Labels entire neuron

36
Q

How are fusion proteins created with GFP?

A

GFP “sticks” to another protein of interest

37
Q

What is a benefit of using GFP to create fusion proteins?

A

Visualize where the protein of interest spends its time inside/outside the cell

38
Q

What is the Brainbow?

A

A technicolour Golgi stain

39
Q

Who developed the Brainbow?

A

Jeff Lichtman and his team at Harvard

40
Q

Describe the in vivo process of the Brainbow.

A

Randomly integrate XFP genes into the mouse genome, each capable of randomly recombining to express either CFP, YFP, or RFP.
Neurons will randomly express a different combination of fluorescent proteins, producing a unique fluorescence profile

41
Q

What is the key limitation of the Brainbow?

A

Neuron projections in the CNS are tightly packed. Brainbow tracing is ineffective at high magnification where synaptic connectivity takes place

42
Q

What are static tracers?

A

Static tracers are transported within the cell in either retrograde or anterograde direction, but are restricted to that cell

43
Q

What are monosynaptic tracers?

A

Tracers that can jump across a single synapse

44
Q

What are polysynaptic tracers?

A

Tracers that can jump across a series of synapses

45
Q

What are trans-synaptic tracers generally derived from?

A

Modified viruses

46
Q

Give examples of trans-synaptic tracers

A

Modified rabies and pseudorabies viruses can label neural circuits in a retrograde manner.
Modified herpes simplex viruses can label neural circuits in an anterograde manner.

47
Q

What is serial EM reconstruction?

A

Serial sections made from fixed nervous system tissue
Sections are imaged with scanning electron microscopy
Computer algorithms identify separate cells and create a 3D reconstruction

48
Q

Who reconstructed the full neural connectome for C. elegans and when?

A

Sydney Brenner and team in 1986

49
Q

How many neurons are in the C. elegans connectome?

A

302

50
Q

What was found after the neural connectome for C. elegans was reconstructed?

A

Useful to guide research, but does not explain nervous system function