Cells of the Nervous System

Question 1

What is the neurone?

Answer 1

basic structural and functional unit of the nervous system
process information
generate/conduct electrical signals
communicate with other neurones via chemicals released at synapses

Question 2

What are neurones supported by?

Answer 2

neuroglia that consist of many cell types

Question 3

Describe neuronal structure?

Answer 3

cellular structure similar

diversity achieved by differences in number and shape of processes, where they are found and what they are connected to

Question 4

How is diversity of morphology determined? What does diversity determine?

Answer 4

by location and function
diversity in location, size, function, number and metabolic activity makes them more/less vulnerable to degeneration (environmentally, genetically, infection)

Question 5

Describe the cellular contents of the neurone?

Answer 5

large nucleus, prominent nucleolus 
abundant rER
well developed Golgi 
abundant mitochondria 
highly organised cytoskeleton
high organisation
metabolically active

Question 6

Why is rER and Golgi abundant in neurone?

Answer 6

cell is larger and has more processes
need more proteins to fill cell
neurones are secretory cells
Golgi to package proteins into vesicles and send to distant parts of cell

Question 7

What is the function of dendrites?

Answer 7

reception of incoming information
spread from cell body
branches increase SA of neuron
often covered in dendritic spines that receive the synapses

Question 8

Why neurone type has 30-40000 spines?

Answer 8

large pyramidal neurons
in cerebral/motor cortex
main output neurones of NS

Question 9

Describe the structure of a pyramidal cell?

Answer 9

Primary dendrites leave at 3 poles of pyramidal cell body that then divide to form secondary and tertiary dendrites
also have an axon

Question 10

What are dendritic spines?

Answer 10

most plastic element of NS - can be withdrawn, reduced or destroyed changing connectivity between brain areas (affected by learning, schizophrenia and alcohol damage)

contain lots of mitochondria
several inputs to one spine, may spines per cell - high computing power of brain

Question 11

What are Purkinje neurones?

Answer 11

inhibitory neurones in the cerebellum, 2D, responsible for fine movement, memory, learning
>80000 spines/cell
each cerebellum has 15 million Purkinje cells

Question 12

What are axons?

Answer 12

conduct impulses away from cell body
emerge at axon hillock (bottom of pyramid)
usually only 1 per cell
may branch into axon collaterals

Question 13

What is characteristic of axons?

Answer 13

prominent/abundant microfilaments - to maintain tensile strength along length

and microtubules to transport protein/vesicles/mitochondria from cell body which can be up to 1m away

myelinated or not at nodes of Ranvier

cable properties - need to maintain same speed of conduction from cell body to synapse

Question 14

Difference in diameter between axons and dendrites?

Answer 14

axons remain same diameter (0.5-10micrometres)

dendrites taper, much larger

Question 15

What are the domains of axons?

Answer 15

at node of Ranvier signal is amplified

• node is the site of Na channels
• end loops of myelin attached to oligodendrocyte at paranode
• at juxtaparanode K channels are localised

GAP BETWEEN Na AND K LOCALISATION

Question 16

Describe the axon terminals?

Answer 16

branch extensively near target (terminal arbor)

form synaptic terminals with the target

Question 17

What are the 2 ways in which synaptic axon terminals are formed with the target?

Answer 17

boutons - end of axons forms swelling with synapse

varicosities - single axon can pass by many structures and synapse onto many cells in different areas (particularly in smooth muscles and with axons that contact Purkinje cells dendrites)

Question 18

What is the structure of synapses?

Answer 18

• vesicles containing NT
• full of mitochondria (45% energy needed for ion pumping and synaptic transmission)
• synaptic density = high [] of proteins needed for release of vesicles, ion pumps/channels

Question 19

What are the synapses sensitive to?

Answer 19

O2 deprivation –> coma
abundant mitochondria
inefficient signal transmission

Question 20

How do synaptic vesicles make it to the plasma membrane?

Answer 20

packaged in Golgi and shipped by fast anterograde transport

specialised mechanisms for association of synaptic vesicles with the plasma membrane

Question 21

How are multiple inputs into a neurone combined?

Answer 21

• multiple synaptic inputs to a cell

- competing inputs are integrated in postsynaptic neurone via NEURONAL INTEGRATION

Question 22

Describe the organisation of synapses?

Answer 22

axo-dendritic - excitatory
axo-somatic - inhibitory (affect dendritic input)
axo-axonic - modulatory (of signal already passing down axon)

Question 23

What makes up most volume of cerebral cortex?

Answer 23

synaptic processes

Question 24

What is the neuronal cytoskeleton like?

Answer 24

highly organised and maintained to ensure constant speed of signal transmission

neurofilaments determine axon calibre - fibres interlinked by cross bridges to maintain axon structure

microtubules are abundant

Question 25

How are proteins targeted with from the cell body?

Answer 25

• proteins destined for similar location packaged into vesicles
• associated with motor proteins and are moved down axon via microtubules
• microtubules have positive and negative ends

Retrograde organelles and anterograde vesicles morphologically and biochemically different

Question 26

What is the cause of MS?

Answer 26

axonal damage
swelling of vesicular proteins
= retraction bulbs

Question 27

What are pseudounipolar neurones?

Answer 27

sensory neurones with 2 fused processes that have axonal structure

dorsal root ganglion

Question 28

What are bipolar neurones?

Answer 28

2 processes

retinal cells
cerebral cortex white matter

Question 29

What are Golgi Type 1 multipolar cells?

Answer 29

highly branched dendritic trees
axons extend long distances
most vulnerable to degeneration

pyramidal cells (cerebral cortex) - Alzheimers/MS
Purkinje cells of cerebellum (15mill) - ataxia
anterior horn cells of spinal cord - MND
retinal ganglion cells

Question 30

What are Golgi Type 2 multipolar cells?

Answer 30

highly branched dendritic trees
shorter axons - axons terminate close to cell body

stellate cells of cerebral cortex/cerebellum

Question 31

Functional classification of neurones?

Answer 31

sensory - take all input to brain
motor - main output to muscle
interneurons
modify, coordinate, integrate and inhibit/facilitate sensory input

Question 32

What are neuroglia?

Answer 32

support cells (everything else)
many functions
needed for correct functioning of neurones 

astroglia, oligodendroglia, microglia, immature progenitors, ependymal cells, Schwann cells, satellite glia

Question 33

What are astroglia?

Answer 33

multiprocessed, star shape
most numerous
many intermediate filament bundles in cytoplasm of fibrous astroglia (GFAP)
signal to each other by gap junctions

2 types:
fibrous in white matter, between axon bundles
protoplasmic in grey matter (fuzzy ball)

Question 34

What is the function for astroglia?

Answer 34

1. scaffold for neuronal migration, axon growth in development
2. form blood brain barrier (podocytes)
3. transport substances from blood to neurones
4. segregate neuronal processes (synapses)- to avoid cross firing
5. remove NTs to stop action
6. make neurotrophic factors
7. neuronal-glial and glial neuronal signalling
8. K ion buffering
9. glial scar formation

Question 35

Describe the barrier function of astrocytes?

Answer 35

glia limitans (barrier between brain and CSF fluid) formed by foot processes of astrocytes layered together

end feet wrap around blood vessel to help transport of H2O and K ions - astrocyte can contact many blood vessel and so function as interface between blood vessels and astrocytes

processed near synapses to remove NT and reduce []

Question 36

Describe astrocyte-astrocyte contact?

Answer 36

individual astrocytes occupy own domain
communication between cells via GAP junctions (connexin 43)

forms a syncytium that allows spread of reaction and signalling (e.g. movement of Ca)

many fine processes same the microenvironment and interact with other cell types

Question 37

What are oligodendroglia?

Answer 37

produced and maintain CNS myelin throughout life (each cell makes 1-40 sheaths)
2 types: interfasicular and perineuronal

small spherical nuclei (5 microns, 8micro cell body) vs 40 in neurone
few thin processes
prominent ER and Golgi
highly active

Question 38

What can be seen on MRI if there is a depletion in oxygen supply or nutrients in first few years of life?

Answer 38

lack of myelin - hypomyelination

can cause physical problems

Question 39

What is myelin?

Answer 39

lipid rich insulating membrane
50 lamellae
dark and light bands seen on EM

Question 40

What remains on myelin sheath?

Answer 40

connection to oligodendrocyte

Question 41

What is the result of loss of oligodendroglia/myelin?

Answer 41

MS

Adrenoleucodystrophy - congenital causes by defect in enzyme needed to make proteins in myelin

Question 42

What are microglia?

Answer 42

derived from bone marrow and yolk sac

resident immune cells for immune surveillance of brain (become macrophages, present antigens to invading immune cells, first cells to react to infection or damage)

tissue remodelling

synaptic stripping

Question 43

What is the relationship between microglia and inflammation?

Answer 43

microglia activated if detects change in microenvironment –> cell body enlargens and becomes rounder, processes shorten

Question 44

What are peripheral glia?

Answer 44

Schwann cells

• myelin producing cells of PNS
• 1 cell produces 1 myelin sheath
• surrounds unmyelinated axons

promote axon regeneration

Question 45

Why no Schwann cells in CNS?

Answer 45

too large