19- Neurons and Glia

Question 1

what is the neurone doctrine?

Answer 1

neurones aren’t continuous but communicate by neurone-to-neurone contact

Question 2

describe the two stages of histological staining of neural tissue?

Answer 2

two stages - fixation and sectioning

fixation - fixing brain tissue for preservation by freezing or embedding it in paraffin

sectioning - microtome slices brain into thin sections

Question 3

describe the properties of the Nissil and Golgi stains

Answer 3

both used to visualise neural tissue

Nissil stain - a basic dye (from e.g. cresyl violet) which stains RNA in nuclei and neurone bodies, not dendrites or axons

Golgi stain - silver chromate solution which stains neurones and their projections

Question 4

how is the electron microscope used for visualising neurones?

Answer 4

has a resolution limit of 0.1nm and the spaces between neurones are 20nm

Question 5

how is the fluorescence microscope used for visualising neurones?

Answer 5

can use genetic manipulation techniques - e.g. Cre-lox - to insert a fluorescent protein into a mouse brain

see individual neurones and glial cells randomly expressing different proteins through the colours they project, and thus the morphology of the brain

Question 6

what are neurones?

Answer 6

information processing cells within the NS - highly specialised for conduction and transmission of electrical and chemical signals

Question 7

three key components of a prototypical neurone?

Answer 7

cell body/soma
axon
dendrites

Question 8

what organelles does the cell body/soma of a neurone contain?

Answer 8

nucleus, RER, SER, golgi apparatus and mitochondria

Question 9

describe the function of the neuronal cytoskeleton. what is the clinical importance of the cytoskeleton?

Answer 9

the cytoskeleton gives the neurone its characteristic shape and structure

can be used as a biomarker for neurodegenerative diseases - e.g. Alzheimer’s. an increased presence of neurofilaments in CSF as neurones degenerate is indicative of a disease.

Question 10

describe the components of the neuronal cytoskeleton

(consider what the components are made out of, diameter, where they’re found)

Answer 10

three components of the cytoskeleton - microtubules, microfilaments and neurofilaments

microtubules are tubulin polymers of diameter 20nm, located in the axon and dendrites. important in axoplasmic transport.

microfilaments are actin polymer of diameter 5nm, found throughout the axon but particularly abundant at the axon and dendrites

neurofilaments are a type of intermediate filament of diameter 10nm. found in axons, important in regulating their shape.

Question 11

what is an axon?

Answer 11

a highly specialised neuronal projection that conducts nerve impulses within the NS

Question 12

describe the three components of an axon

Answer 12

axon hillock, axon ‘proper’ and axon terminal

axon hillock - tapers away from the soma, forms the initial part of the axon

axon terminal - where the axon comes into contact with other neurones at the synapse

axon ‘proper’ - where the axon branches off to form axon and recurrent collaterals

Question 13

what is a dendrite?

Answer 13

highly specialised neuronal projection that receives synaptic input from other neurones

Question 14

what is a dendritic tree?

Answer 14

all the dendrites of a single neurone

Question 15

what is a dendritic spine? why are they ideal for their function?

Answer 15

a small sac of membrane that protrudes from the dendrites of some cells to receive synaptic input

they’re sensitive to the type and amount of synaptic activity

Question 16

what is the clinical importance of dendritic spines?

Answer 16

abnormal dendritic spine number has been associated with numerous neurological conditions - e.g. Alzheimer’s, schizophrenia

Question 17

what is the function of a prototypical neurone?

Answer 17

neurotransmission - drives transfer of information between neurones and their targets

Question 18

describe the two ways neurones can be classified

Answer 18

classified based on neuronal structure and gene expression

neuronal structure entails:
- number of projections (one being unipolar)
- dendritic features (trees and spines)
- connections (sensory, motor, interneuron)
- axon length (golgi type I and II, projecting where)

gene expression - different neurotransmitters used by different neurones due to the differential expression of proteins involved in neurotransmitter storage, synthesis and release

Question 19

in terms of neurone classification, what are pyramidal and stellate neurones? consider axon length and dendrite features

Answer 19

pyramidal neurones are type I golgi neurones = have long axons that project to other brain regions carrying signals, one apical dendrite

stellate neurones are type II golgi neurones = short axons that act locally within an area, found in the cerebellum, multiple branching dendrites

Question 20

what are glial cells? what are the four types of glial cell?

Answer 20

glial cells are the physical and chemical support cells within the NS

four types: astrocytes, microglia, ependymal cells and oligodendrocytes/schwann cells

Question 21

what is an astrocyte?

Answer 21

astrocytes are star-shaped glial cells that regulate the extracellular environment of the brain

Question 22

what are the functions of astrocytes?

Answer 22

regulate the extracellular brain environment by enclosing synaptic junctions and removing neurotransmitters from the synaptic cleft so the receptor isn’t constantly stimulated

Question 23

what are microglia?

Answer 23

a type of immune glial cells distributed across the brain and spinal cord, acts as a macrophage removing neuronal and glial debris

Question 24

what are the functions of microglia?

Answer 24

main function is the phagocytosis of neuronal and glial debris especially during traumatic brain injury

synaptic connection remodelling

directing neuronal migration during brain development

Question 25

what are ependymal cells?

Answer 25

type of glial cell that lines the CNS ventricular system, separating brain tissue from CSF

Question 26

what is the importance of the CSF?

Answer 26

provides protection for the brain against neural damage and buoyancy

Question 27

what are the functions of the ependymal cells?

Answer 27

osmotic regulation of the CSF

control flow of cerebrospinal fluid

direct cell migration during brain development

Question 28

how is hydrocephalus related to ependymal cell function?

Answer 28

hydrocephalus is a build-up of fluid in the brain causing swelling, putting pressure on the brain

deficits in ependymal cell function contribute to hydrocephalus

Question 29

compare oligodendrocytes and Schwann cells

Answer 29

oligodendrites and Schwann cells both function to provide myelin by wrapping around neurone axons

oligodendrocytes are present in the CNS, Schwann cells in the PNS

oligodendrocytes contribute myelin to several axons at a time, Schwann cells to only a single axon at a time

Question 30

compare the electron and light microscope

Answer 30

light microscopy has a resolution limit of 0.1um, whereas for electron microscopy it’s 0.1nm