CNS Cell Types

Question 1

Defects in the following neural systems results in which disorder?

1. sensory defects
2. motor defects
3. associative defects

Answer 1

1. sensory defects - neuropathies
2. motor defects - movement disorders
3. associative defects - cognitive decline

Question 2

what are the two main CNS cell types?

Answer 2

neurons and glia

Question 3

how many and what are the types of differentiated glia?

Answer 3

there are 3 types:

• oligodendrocytes
• microglia
• astrocytes

Question 4

name some other CNS cell types apart from neutrons and differentiated glia?

Answer 4

• glial stem cells
• oligodendrocytes precursors
• ependymal cells

Question 5

Neurons are exclusively formed during brain development

1. True
2. False

Answer 5

False, neurons are mainly formed during brain development but not exclusively

Question 6

what is the prime role of neurons?

Answer 6

it is specialised for intercellular communication and electrical signalling via synapses

Question 7

how do the neurons communicate via synapses?

Answer 7

1. dendrites receive inputs (dendritic spines)
2. transmit the signal to cell body (soma)
3. action potentials propagate along axons from axons hillock

Question 8

A real neuron is a tissue section

1. True
2. False

Answer 8

True

Question 9

what are the two ways via which neurons communicate?

Answer 9

1. chemical - majority

2. electrical - allow synchronized electrical activity- brainstem neurons, breathing- hypothalamus, hormone secretion

Question 10

synapses are concentrated on dendritic spines

1. True
2. False

Answer 10

True

Question 11

why is neural plasticity significant and its role in neural diseases?

Answer 11

• it forms the basis of learning and memory
• spine remodelling is linked to neural activity
• it is highly relevant to diseases like AD, SZ

Question 12

give an example to illustrate neuronal heterogeneity

Answer 12

1. Upper motor neurons – large, excitatory, glutamatergic, long projections, pyramidal
2. Striatal interneurons – small, spiny, inhibitory, GABAergic

Question 13

what is arborisation of axons and dendrites?

Answer 13

a fine branching structure at the end of a nerve fibre

Question 14

what are the features of oligodendrocytes and the significance of myelin sheath to OG?

Answer 14

1. unique to vertebrates
2. myelinating cells of CNS
3. provides metabolic support for axons
4. myelin insulated axon segments, bales rapid nerve conduction
5. myelin sheath segments interrupted by nodes of Ranvier - saltatory conduction
6. demyelinating diseases e.g. multiple sclerosis

Question 15

what does oligodendrocytes look like in histology?

Answer 15

appear like fried egg

Question 16

1. how is myelin sheath formed?
2. what is its composition?
3. name few myelin specific proteins and its function?

Answer 16

1. formed by wrapping of axons by oligodendrocytes processes (membranes)
2. they are highly compact - 70% lipid and 30% protein
3. myelin specific proteins - MAG,MOG, MBP, PLP, PMP22 - mainly involved in compaction, excellent markers

Question 17

what are the features of microglia?

Answer 17

• resident of immune cells in CNS
• derived from erythromyeloid progenitors that migrate into CNS up to ~P10 in rodents
• resting state - highly ramified, motile processes, survey environment (2-3µm/min)
• Upon activation (e.g. by ATP), retract processes, become “amoeboid” & motile
• Proliferate at sites of injury - phagocytic

Question 18

what is the function of microglia?

Answer 18

1. Immune surveillance
2. Phagocytosis – debris/microbes
3. Synaptic plasticity –pruning
4. Process dynamics

Question 19

do normal microglia differ in appearance in cortex and white matter? if so, how?

Answer 19

yes, they are ramified in cortex and more bilaterally branded in the white matter

Question 20

what is the difference between good and bad microglia?

Answer 20

good microglia - ↓inflammation and ↑phagocytosis

bad microglia - ↑inflammation and ↓phagocytosis

Question 21

what are the features of astrocytes?

Answer 21

1. “Star-like cells”
2. Highly heterogeneous – not all star-shaped
3. Most numerous glial cells in the CNS
4. Common “marker” glial fibrillary acidic protein (GFAP)

Question 22

what are the two types of astrocytes?

Answer 22

1. Fibrous – white matter, less elaborate, processes contacts as below & with nodes of Ranvier
2. Protoplasmic – grey matter, extremely elaborate, processes contact blood vessels & pial surface

Question 23

what are the physical differences of fibrous astrocyte and protoplasmic astrocyte?

Answer 23

fibrous - long branches and less bifurcation (less elaborate)
protoplasmic - shorter branches but more ramified (extremely elaborate)

Question 24

what are the functions of astrocytes?

Answer 24

1. Developmental – radial glia
2. Structural - define brain micro-architecture
3. Envelope synapses – “tripartite synapse”
4. Homeostatic – buffer K+, glutamate, etc.
5. Support neurons - Glutamate-Glutamine shuttle, lactate shuttle, etc.
6. Neurovascular coupling (basis of fMRI)
7. Disease relevance – gliosis/astrocytosis

Question 25

name three specialised astrocyte and where are they found?

Answer 25

1. radial glia - cortex - neural stem/progenitor cells (like enoki mushrooms) 2. bergmann glia - cerebellum (like ER or mitochondria with lots of processes in the sides) 3. muller cells - retina (phospholipids of cell membrane)

Question 26

name three diseases which are disease of both neurone and glia?

Answer 26

1. epilepsy 2. multiple sclerosis 3. motor neuron disease (ALS)

Question 27

what does the grey and white matter contain?

Answer 27

- Grey matter contains neural cell bodies & processes – neuropil contains few cell bodies - White matter contains abundance of myelinated tracts & commissures

Question 28

complete the sentences for PNS 1. Cell bodies & supporting cells located in _______ 2. Axons bundled into _______ 3. Many PNS axons are enveloped by _______

Answer 28

1. ganglia 2. nerves 3. Schwann cells(myelinating cells of the PNS,different developmental origin)

Question 29

which are the myelinating cells in CNS and PNS?

Answer 29

CNS - oligodendrocytes | PNS = Schwann cells

Question 30

what is the BBB formed of?

Answer 30

1. endothelial cells 2. pericytes 3. astrocytes

Question 31

what is the BBB sensitive to?

Answer 31

- Sensitive to inflammation, hypertension, trauma, ischaemia | - Problem for drug delivery!

Question 32

what are the features of BBB?

Answer 32

1. Endothelial tight junctions 2. Astrocyte end feet 3. Pericytes 4. Continuous basement membrane, lacks fenestrations 5. Need specific transporters for glucose, essential ions etc.

Question 33

which organs lacks normal BBB?

Answer 33

circumventricular organs

Question 34

what are the features of ependymal cells?

Answer 34

1. Epithelial-like, line ventricles & central canal of spinal cord 2. CSF production, flow & absorption 3. Ciliated – facilitates flow 4. Allow solute exchange between nervous tissue & CSF

Question 35

what are the features of choroid plexus?

Answer 35

1. Frond-like projections in brain ventricles 2. Formed from modified ependymal cells, villi form around network of capillaries, large surface area 3. Main site CSF production by plasma filtration (secretes solutes to drive) 4. Gap junctions between cells form effective blood-CSF barrier