2- Cells Of The Nervous System Flashcards
(17 cards)
What are some structural features of neurones
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
Describe dendrites
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
Describe axons
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
What is the paranode and juxtaparanode
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
What are the 2 types of axon terminal
Boutons and vericosites
What are the three types of synaptic organisation
Axo-dendritic = often excitatory
• Axo-somatic = often inhibitory
• Axo-axonic = often modulatory
What components make up the neuronal cytoskeleton
Neurofilaments play a critical role in determining axon caliber
• Microtubules are very abundant in the nervous system
Describe fast axon transport
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
What is retrograde transport
Retrograde Transport - moving vesicles
containing various molecules back to the cell
body
Describe neuronal damage in multiple sclerosis
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
Describe neuronal subtypes
• 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
What are the types of neuroglia
Astroglia Oligodendroglia Microglia
Immature progenitors Ependymal cells Schwann cells Satellite glia
Describe astroglia
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
•
Name astroglia functions
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
Describe oligodendricytes
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
Describe microglia
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
Describe Schwann cells
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
