2- Cells Of The Nervous System

Question 1

What are some structural features of neurones

Answer 1

Large nucleus
• Prominent nucleolus
• Abundant rER
• Well developed Golgi (because of need to transport proteins over long
distances)
• Abundant mitochondria
• Highly organised cytoskeleton
• HIGHLY ORGANISED METABOLICALLY ACTIVE CELL

Question 2

Describe dendrites

Answer 2

Spread from the cell body and branch frequently
• Increase the surface area of the neuron that can receive signals
• Thin dendrites have protrusions called Dendritic Spines - these receive the
majority of synapses
• Dendritic spines can have multiple synapses
• Large pyramidal neurones may have 30,000/40,000
spines
• You get primary dendrites coming off the vertices
of the pyramid
• There are secondary dendrites branching off the
primary
• Tertiary dendrites branch off the secondary
• There are a large number of Purkinje Cells in the
CEREBELLUM
• Dendrites have over 80,000 spines per cell

Question 3

Describe axons

Answer 3

Emerge at the AXON HILLOCK
• Usually only ONE per cell
• May branch after leaving the cell body and at the
target - these form axon collaterals
• Prominent microtubules and neurofilaments
• After leaving the axon hillock it maintains the
same diameter the whole way down (thereby
maintaining the same speed)
• Contains abundant intermediate filaments and
microtubules
• The intermediate filaments are needed for tensile strength as the cells can be very long
• Axons can be myelinated or unmyelinated
• The axonal membrane of a myelinated fibre is only exposed at the Nodes of Ranvier

Question 4

What is the paranode and juxtaparanode

Answer 4

PARANODE - the area where the ends of the myelin is bound to the axon to form tight junctions - this prevents leakage of current under the myelin sheath
• JUXTAPARANODE - an area adjacent to the paranode where you find potassium channels and calcium channels

Question 5

What are the 2 types of axon terminal

Answer 5

Boutons and vericosites

Question 6

What are the three types of synaptic organisation

Answer 6

Axo-dendritic = often excitatory
• Axo-somatic = often inhibitory
• Axo-axonic = often modulatory

Question 7

What components make up the neuronal cytoskeleton

Answer 7

Neurofilaments play a critical role in determining axon caliber
• Microtubules are very abundant in the nervous system

Question 8

Describe fast axon transport

Answer 8

Transport of membrane associated materials
• Vesicles with associated motors are moved
down the axon at 100-400mm per day
• Proteins are packaged into a vesicle and then
the vesicle is targeted down towards the
presynaptic membrane
• The microtubules are polarised (positive and
negative) so the vesicles can only move in one
direction

Question 9

What is retrograde transport

Answer 9

Retrograde Transport - moving vesicles
containing various molecules back to the cell
body

Question 10

Describe neuronal damage in multiple sclerosis

Answer 10

If there is a restriction to the axon (e.g. traumatic injury or inflammatory disease) you begin to see SWELLINGS
SWELLINGS - vesicles of neurotransmitter keep being transported down the axon and they accumulate because they have no where to go

Question 11

Describe neuronal subtypes

Answer 11

• Pseudounipolar
Tend to be sensory neurons
They have two fused processes which are axonal in structure
The signal received passes directly to the axon terminal without going
through the soma
• Bipolar
Involved in the white matter of the cerebral cortex
• Golgi Type I Multipolar
Highly branched dendritic trees Axons extend long distances Pyramidal Cells of the cerebral cortex Purkinje Cells of the cerebellum Anterior Horn Cells of the spinal cord Retinal Ganglion Cells
• Golgi Type II Multipolar
Highly branched dendritic trees
Short axons
Axons terminate quite close to the cell body of origin Stellate Cells of the cerebral cortex and cerebellum

Question 12

What are the types of neuroglia

Answer 12

Astroglia Oligodendroglia Microglia

Immature progenitors Ependymal cells Schwann cells Satellite glia

Question 13

Describe astroglia

Answer 13

Astroglia
• Multi-processed - star shape
• MOST NUMEROUS CELL TYPE
• There are numerous intermediate filament bundles in the cytoplasm of fibrous
astroglia
• GAP JUNCTIONS - suggest astroglia-astroglia signalling
•

Question 14

Name astroglia functions

Answer 14

Functions of Astroglia:
Scaffold for neuronal migration and axon growth during development Formation of blood-brain barrier
Transport of substances from blood to neurons
Segregation of neuronal processes (synapses)
Removal of neurotransmitters - astrocytes soaks up neurotransmitter to terminate its function
Synthesis of neurotrophic factors (allows neurons to survive) Neuronal-glial and Glial-neuronal signalling
Potassium ion buffering
Glial scar formation

Question 15

Describe oligodendricytes

Answer 15

TWO main types of oligodendroglia:
Interfascicular
Perineuronal
• Small spherical nuclei
• Few thin processes
• Prominent ER and Golgi
• Metabolically highly active
• Functions of oligodendroglia:
Production and maintenance of myelin sheath Each cell produces 1-40 myelin sheaths

Question 16

Describe microglia

Answer 16

Developed from bone marrow during early development - the only cells that are NOT derived from the brain
• Resident macrophage population of the CNS
• Involved in immune surveillance
• Present antigens to invading immune cells
• First cells to react to infection or damage
• Role in tissue remodelling
• Synaptic stripping
• Microglial Morphology
When they respond to a change, the cell shape changes and if the stimulus is strong enough it becomes phagocytic
MS - microglial cells could be the ones destroying the myelin sheath

Question 17

Describe Schwann cells

Answer 17

Myelin producing cells of the PNS
• Each schwann cell produces one myelin sheath
• Promote axon regeneration
• Wrap themselves around the nerve axon rather than just wrapping a process
around the axon