Neuro 2a – Cells of the Nervous System
Anil Chopra
1. Draw and label and diagram of a neurone.
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Neurone is basic structural unit of the nervous system
Processes information
Generates and conducts electrical signals
Synapses with other neurones
Supported by neuroglia which are 9 times more abundant than neurones.
Diversity is achieved by the shape and number of processes as all neuronal
structure is similar.
 Brain has 100 000 000 000 (100 billion) cells in 1.5litres.
2. Define the Role of Each cellular component in the specialised function of the
neuron.
 Cell Body/Soma:
 Has large and prominent nucleus
 Abundant rough endoplasmic reticulum
 Many mitochondria (drive Na+/K+ pump)
 Highly developed Golgi apparatus
 Well-organised cytoskeleton
 Generally organised and very metabolically active
 Dendrites:
 Receive incoming information
 Can spread far from cell body and have many branches
 Increases neuronal surface area.
 Covered in protrusions called spines (as many as 40 000) which
receive most of the information.
 Purkinjie cells of the brain have over 80 000 spines.
 Axons:
 Emerges at axon hillock where action potential is generated and carried
away from cell body.
 Only one per cell but branches near target.
 Have prominent microtubules and neurofilaments
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 Can be unmyelinated or myelinated and the exposed parts of
myelinated ones are Nodes of Ranvier.
Axon Terminals
 Branches near target cells
 Synaptic terminals formed
 Boutons or varicosities
Neuronal Cytoskeleton
 Cytoskeleton required
 Consists of microfilaments,
intermediate filaments and
microtubules.
 Neurofilaments determine axon calibre.
 Adult axons can be micrometres or up to 1 metre
 Microtubules are abundant in the nervous system.
3. Outline the organisation and functions of intracellular transport in the neurons.
Fast Axonal Transport
Anterograde Transport:
- Substances transported away from cell body
- Fast transport of synaptic vesicles, transmitters and mitochondria
- 400mm/day, microtubular network used, molecular motors used.
- Slow transport of bulk cytoplasm
Retrograde Transport:
- Fast transport consists of the return of organelles
- Growth factors, viruses extracellular substances
- Uses different molecular motors.
4. Define the functional subtypes of
neurones and list the ways in which they
are organised collectively in the nervous
system.
Morphological Subtypes of Neurones
There is a wide range of structural diversity
with cell bodies varying in size from 5μm to
135μm.
Pseudounipolar Neurones
o Two fused processes (axons) arising from
dorsal root ganglia.
o The ganglionic neurones have dendrites or
synapses; they simply travel straight from
the peripheral receptor to the central spinal
cord.
Bipolar Neurones
o Found in the retina and the cerebral cortex.
o Have one axon and one dendrite.
Golgi Type I Multipolar Neurones
o Highly branched dendritic trees.
o Axons extend long distances
o Pyramidal and Purkinjie cells of cerebral cortex & cerebellum.
o Anterior horn cells of spinal cord.
o All cortical output mediated through pyramidal neurones.
Golgi Type II Multipolar Neurones
o Also highly branched dendritic trees
o Shorter axons remain close to soma
o Stellate cells of the cerebral cortex
o Represent other input cortical pyramidal cells
o Small multipolar cells
o Use glutamate and aspartate as transmitter.
Functional Subtypes of Neurones
Sensory Neurones
o Usually pseudounipolar from receptor to CNS.
o Dorsal root ganglia neurones. (central nervous system)
Motor Neurones
o Usually Multipolar from CNS to effectors
o Spinal motor neurones
Interneurones
o Bodies and processes of cells in CNS.
o Large Multipolar or small bipolar local circuit neurones.
o Responsible for modification, coordination, integration, facilitation, amplification,
inhibition e.t.c. that occurs between sensory input and motor output.
Organisation of Neurones
Groups of neurones tend to collect together when of similar function.
Nucleus:
 Unencapsulated cell bodies/somae in the CNS.
 Functionally similar cells
 E.g. brainstem nuclei, cerebellar nuclei
Laminae
 Layers of neurones of similar type and function
 E.g. cerebral cortex & cerebellum, grey matter.
Ganglion
 Small groups of cell bodies in the peripheral nervous system. They are
encapsulated e.g. dorsal root ganglia.
Fibre Tracts
 Groups/bundles of unmyelinated/myelinated axons in the CNS.
Nerves
 Groups/bundles of unmyelinated/myelinated axons outside CNS.
5. Describe the organisation of synapses.
Synaptic Organisation
 Neurones receive multiple synaptic inputs from
a variety of different chemical transmitters.
 Terminal parts of axons synapse with other
neurones.
 Different inputs compete for response in
postsynaptic neuron.
 Different types of synapse
o Axo-dendritic: neurones synapse onto dendrites. Often excitatory.
o Axo-somatic: neurones synapse onto soma. Often inhibitory.
o Axo-axonic: neurones synapse with axon. Often modulatory.
 Synaptic vesicles packaged and sent down axon by fast Anterograde transport
 Many mitochondria – 40% of energy needed for ion pumping and synaptic
transmission therefore very sensitive to O2 deprivation.
 Rounded clear vesicles (Gray’s type I) are excitatory
 Oval or flattened vesicles (Gray’s type II) are inhibitory.
6. Name the main causes of neuroglia and explain their functions.
Neuroglia
Support cells of the CNS which perform varied support functions. They are in close
contact with neurones and are essential to their functioning.
Astroglia
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Star shaped
Most numerous of all CNS cells
Have intimate associations with other cells
Divided into different types
o Fibrous astrocytes (in white mater)
o Protoplasmic astrocytes (close to cell bodies)
o Radial glia (long axon from surface to brain)
Many filament bundles in cytoplasm
Gap junctions between them  suggests signalling between the glia.
Used to scaffold during neuronal migration and growth of axons in development
Forms blood-brain barrier.
Transport substances from blood to neurones
Segregates neuronal processes (synapses)
Removes neurotransmitters
Synthesise neurotrophic (growth of neurones) factors.
Signalling between neurones and glial cells
Buffer potassium ion levels
Form glial scars.
Oligodendroglia
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Small circular nuclei
2 types of interfasicular and perineuronal
Prominent ER and Golgi apparatus
Highly metabolically active
No intermediate filaments
Few thin processes
Form the lipid-rich myelin sheath in CNS.
Can be up to 50 layers (lamellae) and produce up to 40 internodes.
Dark and light bands seen at EM level
Very susceptible to nutritional state, toxins and infections
Various disease states including adrenoleucodystrophy, multiple sclerosis.
Microglia
 Derived from bone marrow in early development from blood monocytes invading
the brain.
 They are characteristic of phagocytes in that they have dense lysosomes, lipid
droplets, residual bodies e.t.c.
 They are the resident macrophages of the CNS
 Present antigens to invading immune cells
 Involved in immune surveillance.
 Synapse stripping
 Tissue remodelling
 They are the first cells to react to infection or damage
 Form a widespread network throughout the brain.
Ependymal Cells
 Epithelium that line the ventricles and central canal of the spinal cord
 Have microvilli and cilia
 Have gap junctions but not tight junctions.
Peripheral Glia
Consist of
 Schwann cells
o Make myelin sheath in PNS
o Only one wraps around axon
o Promote repair and function as Astroglia
 Satellite cells
o Surround cell bodies in spinal ganglia
o Function as astrocytes in grey matter.