Cells of the nervous sytem

Question 1

neuroglia outnumber the neurones by

Answer 1

9:1

Question 2

Parts of neurone

Answer 2

Axons
Cell body
Dendrites
Synaptic terminals
Neuronal cytoskeleton

Question 3

Axons
Conducts impulses...?
Emerge at?
How many axons per cell?
Prominent features?
3 Domains?

Answer 3

Axons (conducts impulses away from soma):
o Emerge at the axon hillock where AP is generated.
o One axon per cell but can branch extensively into
prominences known as ‘Axon Collaterals’.
o Prominent microtubules and neurofilaments.
o Myelinated or non-myelinated – axon membrane is
only exposed at the ‘Nodes of Ranvier’.
o Organised into domains:
▪ Node – Sodium channels found here.
▪ Paranode – Ends of myelin are bound to the axon
to form tight junctions.
▪ Juxta-Paranode – Area adjacent to Paranode
where potassium and calcium channels are found.

Question 4

Cell body

Features?

Answer 4

(soma)
o Large nucleus with a prominent nucleolus.
o Abundant rER.
o Well developed Golgi (due to need of transport of
proteins over long distances).
o Abundant mitochondria.
o Highly organised cytoskeleton.
o Numerous lysosomes.

Question 5

Dendrites
Function?
Features?
How many does a large neurone have?
Types
Cerebellum?

Answer 5

o Receive incoming information (electrical signals).
o Thin dendrites have protrusions called dendritic
spines that receive the majority of synapses.
o Increase surface area of neurone.
o Large neurone have ~30,000-40,000 spines.
o Primary dendrites – From vertices of pyramid.
o Secondary dendrites – From primaries.
o Tertiary dendrites – From secondary’s.
o The CEREBELLUM has a LARGE number of Purkinje
Cells – dendrites have >80,000 spines/cell.

Question 6

Synaptic terminals
Where are they?
Forms of axon terminals?

Answer 6

o Close to the target, the axon branches ‘terminal
branches’ (terminal arbor).
o Two forms of axon terminals:
▪ Boutons – A standard synapse.
▪ Varicosities – Axons may synapse with many smooth muscles cells so you have multiple swellings containing NT called varicosities.

Question 7

Neuronal cytoskeleton

What’s abundant in neurones?

Answer 7

o Axons range in length from μm to metres.
o Neurofilaments determine axon calibre and
microtubules are very abundant in neurones
oBoutons (at end of axon, forms a swelling with a synapse, normal synapse structure) or varicosities (single axon passes by structures, with multiple swellings on it, to synapse onto many structures (e.g. In smooth muscles / purkinje cell dendrites) )

Question 8

Post-synaptic neurone
features
Synaptic inputs?

Answer 8

▪ Abundant Mitochondria – 45% of total energy consumption if required for ion pumping and synaptic transmission – sensitive to hypoxia.
▪ Synaptic inputs can be excitatory or inhibitory depending on NT used.
▪ Competing inputs are integrated in the postsynaptic neurone – NEURONAL INTEGRATION

Question 9

Types of synapse

Answer 9

1. Axo-dendritic – Often excitatory (A).
2. Axo-somatic – Often inhibitory (B).
3. Axo-axonic – Often modulatory (C)

Question 10

Types of intracellular transport

Answer 10

Anterogade Transport

Retrograde Transport

Question 11

Anterogade Transport

Answer 11

Transport of materials needed for neurotransmission AWAY from soma:
1) Fast Anterograde – Synaptic vesicles, transmitters, mitochondria.
i. 400mm/day.
ii. Uses microtubular network and requires
oxidative metabolism.
iii. Uses specific molecular motors.
2) Slow Anterograde – Bulk cytoplasmic flow of
soluble constituents.

Question 12

Retrograde Transport

Answer 12

Transport of materials
TOWARDS the soma (from EC space).
1) Fast Retrograde – Return of organelles.
i. Transport of substances from EC space.
ii. Trophic growth factors, neurotropic viruses.
iii. Uses different molecular motors

Question 13

Multiple Sclerosis

Answer 13

A restriction on the axon causing swellings to occur due to accumulation of vesicles of NT at the restricted point

Question 14

Morphological subtypes of neurones

Answer 14

Pseudo-unipolar
Bi-polar
Golgi Type 1 Multipolar
Golgi Type 2 Multipolar

Question 15

Pseudo-unipolar neurones

Answer 15

o Have two fused processes that are axonal in
structure.
o Tend to be sensory neurones.
o The signal received passes directly to the axon
terminal without going through the soma.

Question 16

Bi-polar neurones

Answer 16

o Involved in the white matter of the cerebral cortex
and the retina.
o Soma is in the same line of action of the axon.

Question 17

Golgi Type 1 Multipolar

Answer 17

o Highly branched dendritic trees.
o Axons extend long distances.
o Examples include:
▪ Pyramidal cells – Cerebral cortex – all
of cortical output mediated through
these.
▪ Purkinje cells – Cerebellum.
▪ Anterior horn cells – Spinal cord.

Question 18

Golgi Type 2 Multipolar

Answer 18

o Highly branched dendritic trees.
o Short axons – axons terminate close
to soma of origin.
o Glutamate or Aspartate
transmitters.
o Examples include: Stellate cells – Cerebral cortex
and cerebellum.

Question 19

Functional subtypes of neurones

Answer 19

Sensory
Motor
Interneurones

Question 20

Sensory neurones

Example?

Answer 20

Example - Dorsal Root Ganglia.
▪ Commonly pseudo-unipolar with one major process that divides into two branches; one running to the CNS, the other to a sensory receptor

Question 21

Motor neurones

Example?

Answer 21

Example – Spinal Motor Neurones:
▪ Conduct impulses from the CNS to effectors (muscles and glands).
▪ Generally multi-polar with large somas.

Question 22

Interneurones

Example?

Answer 22

Example – Neurones inside the CNS:
▪ Neurones whose soma and processes remain inside the CNS.
▪ Can be large multipolar neurones or small bi-polar local circuit neurones.
▪ Responsible for the modification, co-ordination, integration, facilitation and inhibition that
must occur between sensory input and motor output.

Question 23

Neuronal organisation

Examples for each type?

Answer 23

1) Nucleus – Group of un-encapsulated neuronal cell bodies within the CNS:
o Usually consist of functionally similar cells.
o E.G. Brain stem nuclei, Deep cerebellar nuclei.

2) Laminae – Layers of neurones of similar type and function.
o E.G. Cerebral Cortex, Cerebellum

3) Ganglion – Groups of neuronal soma in the PNS that are encapsulated to form a ganglion.
o E.G. Dorsal Root Ganglia, Sympathetic Ganglia.

4) Fibre Tracts – Groups or bundles of axons (myelinated or non-myelinated) in the CNS.
o E.G. White matter tract – Corpus Callosum

5) Nerves – Discrete bundles of axons outside the CNS.
o E.G. Often mixed sensory/motor.

Question 24

Glial cells

Answer 24

Astrocytes/ Astroglia
Oligodendrocytes
Microglia
Ependymal Cells
Peripheral Glia

Question 25

Astrocytes/ Astroglia
Structure
Function

Answer 25

Structure:
o Multi-processed star-like shape.
o Most numerous cell in the CNS.
o There are numerous intermediate filament bundles in the cytoplasm of fibrous
astroglia.
o Presence of gap junctions suggest lots of astroglia-astroglia signaling.

Functions:
o Scaffold for other cell types and to aid axon growth development.
o Formation of blood-brain barrier.
o Transport of substances from blood to neurones.
o Removal and degradation of NT.
o Synthesis of neurotrophic factors (allows neurones to survive).
o Potassium buffering.
o Neuronal-glial, glial-neuronal signaling.
o Scar tissue formation.
o Glioma formation

Question 26

Oligodendrocytes
Structure
Function

Answer 26

Structure:
o TWO main types; Interfascicular and Perineuronal.
o Small and spherical nuclei.
o Few thin processes.
o Prominent golgi and no intermediate filaments.
o Highly metabolically active

Functions:
o Elaboration and maintenance of the myelin sheath.
o Produces numerous myelin internodes (<40).

Question 27

Disease states of myelin

Answer 27

Multiple Sclerosis (loss of myelin due to autoimmune
reaction)
Adrenoleukodystrophy (leads to progressive loss of myelin).

Question 28

Microglia
Structure
Function

Answer 28

Structure:
o Derived during early development from blood monocytes that invade the brain.
o Dense lysosomes, lipid droplets and residual bodies.

Functions:
o Macrophage population for the brain.
o Antigen-presentation.
o Tissue modelling.
o Synapse stripping.

Question 29

Ependymal Cells
Structure
Function

Answer 29

Structure:
o Apical microvilli and cilia.
o Prominent gap junctions between other ependymal cells.
o NO tight junctions.

Function
Epithelial cells that line the ventricles of the brain and central canal of the cord

Question 30

Peripheral Glia

2 types?

Answer 30

Schwann Cells:
o Axons outside the CNS are myelinated by Schwann cells.
o ONE Schwann cell myelinated ONE axon.
o Can perform function of astrocytes and also promotes repair.

Satellite Cells:
o Each soma in a spinal ganglion is surrounded by metabolically active supportive
satellite cells.
o These perform the functions of astrocytes in the grey matter of the CNS.