Cells of the Nervous System Flashcards
What is the neurone?
basic structural and functional unit of the nervous system
process information
generate/conduct electrical signals
communicate with other neurones via chemicals released at synapses
What are neurones supported by?
neuroglia that consist of many cell types
Describe neuronal structure?
cellular structure similar
diversity achieved by differences in number and shape of processes, where they are found and what they are connected to
How is diversity of morphology determined? What does diversity determine?
by location and function
diversity in location, size, function, number and metabolic activity makes them more/less vulnerable to degeneration (environmentally, genetically, infection)
Describe the cellular contents of the neurone?
large nucleus, prominent nucleolus abundant rER well developed Golgi abundant mitochondria highly organised cytoskeleton high organisation metabolically active
Why is rER and Golgi abundant in neurone?
cell is larger and has more processes
need more proteins to fill cell
neurones are secretory cells
Golgi to package proteins into vesicles and send to distant parts of cell
What is the function of dendrites?
reception of incoming information
spread from cell body
branches increase SA of neuron
often covered in dendritic spines that receive the synapses
Why neurone type has 30-40000 spines?
large pyramidal neurons
in cerebral/motor cortex
main output neurones of NS
Describe the structure of a pyramidal cell?
Primary dendrites leave at 3 poles of pyramidal cell body that then divide to form secondary and tertiary dendrites
also have an axon
What are dendritic spines?
most plastic element of NS - can be withdrawn, reduced or destroyed changing connectivity between brain areas (affected by learning, schizophrenia and alcohol damage)
contain lots of mitochondria
several inputs to one spine, may spines per cell - high computing power of brain
What are Purkinje neurones?
inhibitory neurones in the cerebellum, 2D, responsible for fine movement, memory, learning
>80000 spines/cell
each cerebellum has 15 million Purkinje cells
What are axons?
conduct impulses away from cell body
emerge at axon hillock (bottom of pyramid)
usually only 1 per cell
may branch into axon collaterals
What is characteristic of axons?
prominent/abundant microfilaments - to maintain tensile strength along length
and microtubules to transport protein/vesicles/mitochondria from cell body which can be up to 1m away
myelinated or not at nodes of Ranvier
cable properties - need to maintain same speed of conduction from cell body to synapse
Difference in diameter between axons and dendrites?
axons remain same diameter (0.5-10micrometres)
dendrites taper, much larger
What are the domains of axons?
at node of Ranvier signal is amplified
- node is the site of Na channels
- end loops of myelin attached to oligodendrocyte at paranode
- at juxtaparanode K channels are localised
GAP BETWEEN Na AND K LOCALISATION
Describe the axon terminals?
branch extensively near target (terminal arbor)
form synaptic terminals with the target
What are the 2 ways in which synaptic axon terminals are formed with the target?
boutons - end of axons forms swelling with synapse
varicosities - single axon can pass by many structures and synapse onto many cells in different areas (particularly in smooth muscles and with axons that contact Purkinje cells dendrites)
What is the structure of synapses?
- vesicles containing NT
- full of mitochondria (45% energy needed for ion pumping and synaptic transmission)
- synaptic density = high [] of proteins needed for release of vesicles, ion pumps/channels
What are the synapses sensitive to?
O2 deprivation –> coma
abundant mitochondria
inefficient signal transmission
How do synaptic vesicles make it to the plasma membrane?
packaged in Golgi and shipped by fast anterograde transport
specialised mechanisms for association of synaptic vesicles with the plasma membrane
How are multiple inputs into a neurone combined?
- multiple synaptic inputs to a cell
- competing inputs are integrated in postsynaptic neurone via NEURONAL INTEGRATION
Describe the organisation of synapses?
axo-dendritic - excitatory
axo-somatic - inhibitory (affect dendritic input)
axo-axonic - modulatory (of signal already passing down axon)
What makes up most volume of cerebral cortex?
synaptic processes
What is the neuronal cytoskeleton like?
highly organised and maintained to ensure constant speed of signal transmission
neurofilaments determine axon calibre - fibres interlinked by cross bridges to maintain axon structure
microtubules are abundant
How are proteins targeted with from the cell body?
- proteins destined for similar location packaged into vesicles
- associated with motor proteins and are moved down axon via microtubules
- microtubules have positive and negative ends
Retrograde organelles and anterograde vesicles morphologically and biochemically different
What is the cause of MS?
axonal damage
swelling of vesicular proteins
= retraction bulbs
What are pseudounipolar neurones?
sensory neurones with 2 fused processes that have axonal structure
dorsal root ganglion
What are bipolar neurones?
2 processes
retinal cells
cerebral cortex white matter
What are Golgi Type 1 multipolar cells?
highly branched dendritic trees
axons extend long distances
most vulnerable to degeneration
pyramidal cells (cerebral cortex) - Alzheimers/MS
Purkinje cells of cerebellum (15mill) - ataxia
anterior horn cells of spinal cord - MND
retinal ganglion cells
What are Golgi Type 2 multipolar cells?
highly branched dendritic trees
shorter axons - axons terminate close to cell body
stellate cells of cerebral cortex/cerebellum
Functional classification of neurones?
sensory - take all input to brain
motor - main output to muscle
interneurons
modify, coordinate, integrate and inhibit/facilitate sensory input
What are neuroglia?
support cells (everything else) many functions needed for correct functioning of neurones
astroglia, oligodendroglia, microglia, immature progenitors, ependymal cells, Schwann cells, satellite glia
What are astroglia?
multiprocessed, star shape
most numerous
many intermediate filament bundles in cytoplasm of fibrous astroglia (GFAP)
signal to each other by gap junctions
2 types:
fibrous in white matter, between axon bundles
protoplasmic in grey matter (fuzzy ball)
What is the function for astroglia?
- scaffold for neuronal migration, axon growth in development
- form blood brain barrier (podocytes)
- transport substances from blood to neurones
- segregate neuronal processes (synapses)- to avoid cross firing
- remove NTs to stop action
- make neurotrophic factors
- neuronal-glial and glial neuronal signalling
- K ion buffering
- glial scar formation
Describe the barrier function of astrocytes?
glia limitans (barrier between brain and CSF fluid) formed by foot processes of astrocytes layered together
end feet wrap around blood vessel to help transport of H2O and K ions - astrocyte can contact many blood vessel and so function as interface between blood vessels and astrocytes
processed near synapses to remove NT and reduce []
Describe astrocyte-astrocyte contact?
individual astrocytes occupy own domain
communication between cells via GAP junctions (connexin 43)
forms a syncytium that allows spread of reaction and signalling (e.g. movement of Ca)
many fine processes same the microenvironment and interact with other cell types
What are oligodendroglia?
produced and maintain CNS myelin throughout life (each cell makes 1-40 sheaths)
2 types: interfasicular and perineuronal
small spherical nuclei (5 microns, 8micro cell body) vs 40 in neurone
few thin processes
prominent ER and Golgi
highly active
What can be seen on MRI if there is a depletion in oxygen supply or nutrients in first few years of life?
lack of myelin - hypomyelination
can cause physical problems
What is myelin?
lipid rich insulating membrane
50 lamellae
dark and light bands seen on EM
What remains on myelin sheath?
connection to oligodendrocyte
What is the result of loss of oligodendroglia/myelin?
MS
Adrenoleucodystrophy - congenital causes by defect in enzyme needed to make proteins in myelin
What are microglia?
derived from bone marrow and yolk sac
resident immune cells for immune surveillance of brain (become macrophages, present antigens to invading immune cells, first cells to react to infection or damage)
tissue remodelling
synaptic stripping
What is the relationship between microglia and inflammation?
microglia activated if detects change in microenvironment –> cell body enlargens and becomes rounder, processes shorten
What are peripheral glia?
Schwann cells
- myelin producing cells of PNS
- 1 cell produces 1 myelin sheath
- surrounds unmyelinated axons
promote axon regeneration
Why no Schwann cells in CNS?
too large
