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YEAR 2 - The Nervous System > 19. Principles of Neuronal Function > Flashcards

19. Principles of Neuronal Function Flashcards

1
Q

What are the main histological techniques used to study neurons and what is each used for?

[IMPORTANT]

A
  • Nissl staining -> For cell nuclei
  • Golgi stain (silver stain) -> For cell morphology
  • Weigert stain -> For axon tracts
  • Immunocytochemistry
  • In situ hybridisation
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2
Q

What is Nissl staining, how does it work and what is it used for?

[IMPORTANT]

A
  • Nissl staining involves a sye such as cresyl violet, which stains the RNA in cells
  • It stains blue the:
    • RER (due to the ribosomal RNA)
    • Ribosomes
    • DNA in the nucleus
  • Thus, it is used to visual the cell nucleus (and it is therefore also used in cytoarchitecture)
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3
Q

Describe Brodmann’s experiments to understand cytoarchitecture.

[EXTRA]

A
  • Brodmann used simple staining methods, such as Nissl staining to understand the cytoarchitecture of the brain (cytoarchitecture is the structural arrangement of neurons within the central nervous system, including neuronal size, shape, packing density, etc.)
  • He noticed that the cortex contained 6 layers of cells within it, but that the thickness of these cells varied between different areas, giving rise to the concept of Brodmann areas
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4
Q

What is Golgi staining, how does it work and what is it used for?

[IMPORTANT]

A
  • Involves impregnating aldehyde-fixed nervous tissue with potassium dichromate and silver nitrate.
  • Cells thus stained are filled by microcrystallization of silver chromate.
  • Used to visualise the morphology of neurons, since the axons and dendrites are clearly stained black.
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5
Q

What is Weigert staining, how does it work and what is it used for?

[IMPORTANT]

A
  • Involves the treatment of nervous tissue with potassium dichromate to preserve myelin lipids.
  • The lipids are then stained with the use of hematoxylin, causing them to appear black.
  • Used to visualise axon tracts
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6
Q

Describe the reticular theory of neuron continuity and neuron doctrine.

[EXTRA]

A
  • Reticular theory was largely supported by Camillo Golgi and it stated that all neurons in the nervous system exist as one continuous system without synapses
  • The neuron doctrine was supported by Santiago Ramon y Cajal, and it stated that there were synapses between the axons and dendrites of individual cells
  • Golgi staining combined with microscopy did not allow sufficient resolution for synapses to be seen, so it was not known which theory was correct
  • Electron microscopy allowed us to see the presence of synapses, confirming the neuron doctrine
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7
Q

What is immunohistochemistry and how can it be used in neuroscience?

[IMPORTANT]

A
  • It is the staining of a certain type of protein using labelled antibodies
  • This can be used to, for example, detecting neurons containing a certain type of neurotransmitter
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8
Q

What is in situ hybridisation?

[IMPORTANT]

A

Use of labeled complementary DNA, RNA or modified nucleic acids strand (i.e. a probe) to localise a specific DNA or RNA sequence in a portion or section of tissue (in situ).

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9
Q

What technique is this?

A

Golgi staining

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10
Q

What technique is this?

A

Nissl staining

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11
Q

What technique is this?

A

Weigert staining

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12
Q

What type of microscopy of the brain is shown here?

A

Light microscopy

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13
Q

What type of microscopy of the brain is shown here?

A

Electron microscopy

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14
Q

What type of microscopy of the brain is shown here?

A

Fluorescence microscopy

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15
Q

What is a reporter gene? Give an example.

[EXTRA]

A
  • A reporter gene is a gene that researchers attach to a regulatory sequence of another gene of interest in bacteria, cell culture, animals or plants.
  • GFP is an example.
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16
Q

Give an example of reporter genes being used to study neurons.

[EXTRA]

A

GAD65/GFP Transgenic mouse:

  • Glutamate decarboxylase (GAD) is an enzyme that catalyzes the decarboxylation of glutamate to GABA and CO2
  • Thus, using GFP as a reporter gene in these mice can be used to tell which cells are expressing GAD (and are therefore GABAergic)
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17
Q

What are some ways in which neurons can be classified?

A

Shape:

  • Multipolar
  • Bipolar
  • Unipolar

Transmitter:

  • Excitatory
  • Inhibitory

Function:

  • Projection neurons
  • Interneurons
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18
Q

Draw the different types of neuron in terms of their polarity.

A
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19
Q

Compare projection neurons and interneurons in terms of:

  • Appearance
  • Function
  • Neurotransmitters

[IMPORTANT]

A

Projection neurons:

  • Have long axons that project to distant areas of the brain and out of the brain also
  • Usually excitatory
  • Glutamatergic neurons

Interneurons:

  • Have short axons that synapse onto local cells
  • Usually inhibitory
  • GABAergic
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20
Q

Compare the excitatory and inhibitory neurons in the cerebral cortex.

[IMPORTANT]

A

Excitatory

  • 80% of neurons
  • Usually glutamatergic
  • Projection neurons tend to be excitatory

Inhibitory

  • 20% of neurons
  • Usually GABAergic
  • Interneurons tend to be inhibitory
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21
Q

Describe a technique that can be used to separate different neuron types for study.

[EXTRA]

A
  • Fluorescence-activated cell sorting (FACS)
  • This can be used in combination with GFP to sort certain subtypes of neurons out for study
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22
Q

What is the transcriptome?

A

Complete set of RNAs found in a cell or group of cells under specified conditions.

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23
Q

What is the function of microtubules in neurons?

A

Transport within the cell.

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24
Q

What are the two proteins involved in the transport along microtubules in neurons?

A
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25
Q

What is another name for glia?

A

Neuroglia

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26
Q

What are glia?

[IMPORTANT]

A

Non-neuronal cells in the CNS and PNS.

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27
Q

What is the ratio of neurons to glia in the body?

A
  • 1:1 (it is sometimes erroneously quoted as 1:10)
  • The ratio varies throughout the body, with it being as low as 1:0.22 in the cerebellum and as high as 1:11.3 in the basal ganglia.
28
Q

What are the two main categories of glial cells?

A
  • Macroglia
  • Microglia
29
Q

What are the different types of glial cells in the CNS and PNS?

A
  • Macroglia:
    • Astrocytes (in CNS), Satellite cells and enteric glial cells (in PNS)
    • Oligodendocytes (in CNS), Schwann cells (in PNS)
    • (Ependymal cells are sometimes considered macroglia too)
  • Microglia (only in CNS)
30
Q

What are radial glial cells?

A

The term can be used to mean two things:

  • Progenitor cells that give rise to all neurons of the cerebral cortex, as well as astrocytes and oligodendrocytes
  • Specialised astrocytes (Muller cells and Bergmann glial cells)
31
Q

Define glial cells.

A
  • Glial cells used to be defined by the fact that they (1) separate neuronal elements from mesodermal layers and (2) should originate from embryonic ectoderm.
  • However, this excluded microglia, which are of mesodermal origin.
  • Therefore, glia are not defined by the types of proteins they express.
32
Q

Describe the shape of astrocytes.

A

They are star-shaped.

33
Q

What are the different types of astrocytes and where is each found?

A
  • Protoplasmic (grey matter, velate in cerebellum)
  • Fibrous (white matter)
  • Radial (ovoid cell body and elongated processes)

(Ependymal and retinal pigment epithelial cells are also sometimes considered as astrocytes)

34
Q

What are radial astrocytes and what happens to them?

A

They are progenitor cells involved in early development, which then turn into stellate (star-shaped) astrocytes, but some remain radial (Bergmann glia, Müller cells).

35
Q

What are tanycytes?

A

Specialised ependymal cells that make up barrier between interstitial fluid and CSF in brain circumventricular organs.

i.e. Astrocytes (are sometimes argued to) include ependymal cells, which include tanycytes

36
Q

How are astrocytes connected to each other?

A

Astrocytes form a functional syncytium using gap junctions. This allows astrocytes to communicate, even between distant parts of the brain.

37
Q

What are the functions of astrocytes?

[IMPORTANT]

A

In spec:

  • CNS development
  • Ion homeostasis
  • Neurotransmitter uptake
  • Local control of blood flow
  • Blood brain barrier
  • Inhibitory role in CNS repair

Other:

  • Metabolic support
  • Structural support
  • Synpatic transmission
  • Brain defence + Post-injury remodelling
38
Q

How are astrocytes involved in CNS development?

A
  • Needed for neurogenesis
  • Guide neuronal migration -> Cells can migrate along their radial fibres
  • Aid formation of grey matter
  • Involved in synaptogenesis
39
Q

How are astrocytes involved in homeostasis?

A

They control levels of extracellular potassium, extracellular pH, water and are involved in neurotransmitter removal.

40
Q

How are astrocytes involved in support?

A
  • Metabolic support -> Provide lactate to neurons
  • Structural support -> Formation of neuro-vascular unit (since they link the cells of the vessel with the neurons)
41
Q

How are astrocytes involved in the blood brain barrier?

A

Astrocytes induce the blood brain barrier.

42
Q

How are astrocytes involved in blood flow regulation?

A
  • They secrete vasoconstrictors or vasodilators
  • These act on the pericytes that surround capillaries (the mechanism is not known)
  • This means that blood flow can be regulated depending on the requirements of the neurons
43
Q

How are astrocytes involved in synaptic transmission?

[EXTRA]

A
  • Synapse maintenance and assistance of synaptic pruning
  • Provide glutamate (directly and through glutamate-glutamine shuttle)
  • Synaptic plasticity
  • Integration of synaptic fields
  • Take up ions and neurotransmitter, but also release neurotransmitters and modulators out
44
Q

How are astrocytes involved in brain defence and post-injury remodelling?

[IMPORTANT]

A

Assist in:

  • Scar formation
  • Immune responses and secretion of pro-inflammatory factors (cytokines, chemokines and immune modulators)
45
Q

How many synapses is each astrocyte associated with?

A

Up to 100,000.

46
Q

Are astrocytes found in the CNS or PNS?

A

CNS -> Their PNS equivalents are satellite cells and enteric glial cells.

47
Q

What are the myelin-expressing cells in the CNS and PNS?

A
  • CNS -> Oligodendrocytes
  • PNS -> Schwann cells
48
Q

Is the myelin the same in the PNS and CNS?

A

No, it has slightly different lipid composition.

49
Q

When does myelination in development start and finish?

A
  • Starts in 3rd trimester and continues throughout infancy
  • This leads to improvement in motor and cognitive skills, as well as faster pain perception
50
Q

What is multiple slerosis?

[IMPORTANT]

A
  • It is an autoimmune demyelinating disease that affects the CNS
  • The first symptoms tend to include motor problems since the cerebellum is frequently affected first
51
Q

What is a demyelinating disease of the PNS?

[EXTRA]

A

Guillain-Barre syndrome

52
Q

What is the function of oligodendrocytes and Schwann cells?

[IMPORTANT]

A

They are involved in myelination, which increases the speed with which action potential are propagated along the axon.

53
Q

Compare how oligodendrocytes and Schwann cells work.

A
  • In the PNS, each Schwann cell myelinates only one axon, while in the CNS, each oligodendrocyte myelinates multiple axons.
  • This may in part explain why repair is easier in the PNS thatn in the CNS.
54
Q

Are microglia found in the CNS or PNS?

A

CNS

55
Q

What are microglia?

[IMPORTANT]

A

They are the endogenous macrophages of the CNS.

56
Q

What germ layer are microglia derived from?

A

Mesoderm

57
Q

Describe the formation and replacement of microglia.

A
  • Derived from the monocyte lineage of the yolk sac
  • Proliferate postnatally and migrate throughout brain to target areas where they fully differentiate
  • Not replaced by exogenous sources, but self-renew
58
Q

Draw the appearance of microglia.

A

However, their appearance can vary depending on their state, so they sometimes look more likes the archetypal round monocyte.

59
Q

What are the different states that microglia can be in?

A
  • Ramified (surveilling; resting) -> This is where the cell looks stellate and is not active, but is instead surveilling
  • Activated (reactive)
  • Phagocytic -> This is similar to the activated state, but not all activated microglia are phagocytic
  • Dystrophic -> This is when the microglia is aged and the morphology may be abnormal
60
Q

What are the main functions of microglia?

A

They are the macrophages of the CNS, involved in:

  • Brain development
  • Maintenance of physiological homeostasis
  • Pain
61
Q

How are microglia involved in brain development?

A

Microglia phagocytose and also release diffusible chemicals that act on other brain cells. This is involved in:

  • Myelination
  • Oligodendrogenesis and neurogenesis
  • Synaptogenesis
  • Induction of cell death or survival
  • Synaptic pruning: phagocytose weak synapses
62
Q

Give some experimental evidence for the importance of microglia in synaptic pruning.

[EXTRA]

A
  • In cats, when one eye is sewn closed, the lateral geniculate nucleus receives diffuse branches from the retina
  • This means there is blindness in that eye, since the LGN cannot process the information
  • Therefore, synaptic pruning of weak synapses is an important process, driven by microglia
63
Q

How are microglia involved in maintaining physiological homeostasis?

A
  • They respond to various types of CNS disruption, including trauma, infection and toxins
  • They do this by proliferating, changing their morphology, presenting antigens (if appropriate) and releasing pro/anti-inflammatory molecules
64
Q

How are microglia involved in pain?

A
  • Dysregulation of microglia has been implicated in neuropathic pain
  • For example, in peripheral nerve injury there is proliferation of microglia, as well as upregulation and activation of microglial P2X4 receptors necessary for PNI-induced pain-hypersensitivity (hyperalgesia)
65
Q

What are some other glial cells you may come across?

[EXTRA?]

A

YEAR 2 - The Nervous System (18 decks)

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