Cells of the nervous sytem Flashcards
neuroglia outnumber the neurones by
9:1
Parts of neurone
Axons Cell body Dendrites Synaptic terminals Neuronal cytoskeleton
Axons Conducts impulses...? Emerge at? How many axons per cell? Prominent features? 3 Domains?
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.
Cell body
Features?
(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.
Dendrites Function? Features? How many does a large neurone have? Types Cerebellum?
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.
Synaptic terminals
Where are they?
Forms of axon terminals?
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.
Neuronal cytoskeleton
What’s abundant in neurones?
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) )
Post-synaptic neurone
features
Synaptic inputs?
▪ 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
Types of synapse
- Axo-dendritic – Often excitatory (A).
- Axo-somatic – Often inhibitory (B).
- Axo-axonic – Often modulatory (C)
Types of intracellular transport
Anterogade Transport
Retrograde Transport
Anterogade Transport
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.
Retrograde Transport
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
Multiple Sclerosis
A restriction on the axon causing swellings to occur due to accumulation of vesicles of NT at the restricted point
Morphological subtypes of neurones
Pseudo-unipolar
Bi-polar
Golgi Type 1 Multipolar
Golgi Type 2 Multipolar
Pseudo-unipolar neurones
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.
Bi-polar neurones
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.
Golgi Type 1 Multipolar
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.
Golgi Type 2 Multipolar
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.
Functional subtypes of neurones
Sensory
Motor
Interneurones
Sensory neurones
Example?
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
Motor neurones
Example?
Example – Spinal Motor Neurones:
▪ Conduct impulses from the CNS to effectors (muscles and glands).
▪ Generally multi-polar with large somas.
Interneurones
Example?
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.
Neuronal organisation
Examples for each type?
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.
Glial cells
Astrocytes/ Astroglia Oligodendrocytes Microglia Ependymal Cells Peripheral Glia
Astrocytes/ Astroglia
Structure
Function
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
Oligodendrocytes
Structure
Function
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).
Disease states of myelin
Multiple Sclerosis (loss of myelin due to autoimmune
reaction)
Adrenoleukodystrophy (leads to progressive loss of myelin).
Microglia
Structure
Function
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.
Ependymal Cells
Structure
Function
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
Peripheral Glia
2 types?
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.
