cells of the nervous system Flashcards
what is the neuron
basic and main structural and functional unit of the nervous system
information processing unit
release chemicals at a synapse - communicate with other neurons
supported by microglia
describe the structure of neurons
more complex than other cells
cellular structure similar between neurons
diversity achieved by where it si found and what it is connected to, arrangement, morphology - some are complex and well ordered, function and how hard they work
vulnerability of neurones
it is the diversity in size, anatomical location, function and how hard they work make vulnerable to degeneration caused by genetics, environment and infection in MS, Alzheimers, parkinsons, ALS
cellular components of neurons and their functions
many mitochondria - high metabolic activity
highly organised cytoskeleton - they’re large and have many processes abundant RER - larger than most cells, processes extend large distances, cells need more proteins
well developed Golgi - protein partly glycosylated, packaged in vesicles and trafficked to distant sites
what type of cells are secretory cells and how does this affect their function
secretory cells
machinery reflects this
describe dendrites
input signals from sensory receptors
spread from soma - branch frequently
large SA - receive more inputs from different places
tree reflects where the inputs are coming from
spines - receive all synapses and connectivity
structure of a pyramidal cell
in cerebral cortex
3 primary dendrites - thick, they branch to secondary and primary dendrites
one axon after axon hillock
what are dendritic spines
one of most plastic areas off nervous system
they withdraw and are made - can see this with a genetic label
they can be destroyed by alcohol and Alzheimer’s
full of mitochondria - supply energy
each large pyramidal neuron has 30-40000spines
spines can have 10 sites of input each
Purkinje neurons
cerebellum
inhibitory neurons
trees are 2D
>80 000 spines - lots of inputs
involved in fine movements eg piano and memory
human cerebellum 15million Purkinje cells
dendritic trees make forest of processes that aaxons link onto
describe axons
conduct impulses away from cell body only 1 per cell emerge at axon hillock - swelling may branch just after leaving the cell body they can link to near cells small compared to dendrites
features of axons
stay the same diameter
intermediate filaments - maintain tensile strength, 5-10um diameter, travel down spinal chord so must be tough
microtubules - transport mitochondria/vesicles to synapse from cell body
myelinated/unmyelinated
myelinated only exposed at node of Ranvier - electrical signal boosted, where Na channels are then have end loop of myelin firmly attached to the axon then K channels
have cable properties - mean there is the same speed of conduction from soma to synapse
describe axon terminals
bouton - endo of axon form swelling
varicosities - axon has multiple points of swelling - pass onto different cells and purkinje dendrites
axons branch extensively close to target - terminal arbor
describe the synaptic structure
vesicles - some translucent, packaged in Golgi - shipped by fast anterograde transport
mitochondria - 45% total energy consumption required for ion pumping and synaptic transmission - sensitive to oxygen deprivation
synaptic density - increased number of proteins responsible for the machinery releasing vesicles and neurotransmitter, and ion channels and pumps in this region
mechanisms to target membrane and dock vesicles with membrane and release contents
describe synaptic organisation
neuron receive many input signals at different strengths - analogue
electrical potential is interpreted
output signal is digital
use inhibitory and excitatory neurotransmitters
competing inputs are integrated in post-synaptic neuron - neuronal integration
most volume of cerebellum is synapse
type of synapse
axo-dendritic - main ones, excitatory
axo-somatic - inhibitory
axo-axonic - modulate signal already travelling down axon
describe the neuronal cytoskeleton
maintained because of length of axons
neurofilaments - tight bundle fibre linked by cross borders
maintain axon calibre and the thickness of the axon which determines the speed
axons range in length - cytoskeleton required
neurotransmitters important in determining axon calibre
microtubules very abundant in nervous system
how do proteins and mitochondria move in neurons
all proteins that need to go to 1 area are packaged into 1 vesicle
vesicle attach to microtubule
using motor proteins the vesicles move down microtubules 100-400mm per day
microtubules have +ve and -ve end depending on direction (anterograde/retrograde - morphologically/biochemically distinct
describe axon damage in MS
swelling - axon compressed/transected all proteins accumulate at end happens in hours sign of trauma in CNS called retraction bowls
pseudounipolar neurons
sensory
2 fused processes that are axonal in structure
process bypasses cell body
transmit into spinal chord
bipolar neurons
retinal bipolar cells
2 processes
small number in white matter - cerebral vascular tone maintained
Golgi type 1 multipolar neurons
highly branched dendritic trees
very metabolically active - a lot of vulnerabilities
axons extend long distance
pyramidal cells of cerebral cortex - Alzheimer’s and MS
purkinje of cerebellum - ataxia
anterior horn cells of spinal cord - motor neuron disease
retinal ganglion cells - many conditions
Golgi type 2 multipolar
highly branched dendritic trees
short axons
axons terminate close to cell body of origin
stellate cells of cerebral cortex and cerebellum
sensory neurons
input to brain
motor neurons
main output
skeletal and smooth muscle
interneurons
connect other neurons - some very large
modification, coordination, integration, facilitation and inhibition of sensory input
what are neuroglia
glia = glue
neuron can’t function without them
in neurodegenerative conditions
support cells
describe astroglia
star
intermediate filament bundles in cytoplasm of fibrous astroglia - different protein to axons
most numerous cell type
gap junction - astroglia-astroglia communication, pore for Ca2+ pass between cells
astroglial functions
scaffold for neuronal migration and axon growth during development
formation of blood brain barrier - feet into BV
some end feet contact neurons
transport of substances from blood to neurons - nutrition of neurons
segregation of synapses - otherwise cross firing of synapse
remove neurotransmitter
synthesis of neurotrophic factors - support neurons
neuronal-glial and glial neuronal signalling
K ion buffering
Glial scar formation
individual astrocytes fill their own domain - function as a syncytium - allows calcium movement. Acts as a calming level in brain - controls ion levels in microenvironment
might contain 1000s of synapses
glia limitans - barrier between brain and CSF fluid
describe oligodendroglia
small - nucleus 5um, cell 8um small, dense, spherical nuclei dense cytoplasm - compress into small space few thin processes prominent ER and Golgi - make myelin many mt - metabolically highly active
oligodendrocyte functions
production and maintenance of myelin sheath - make and degrade proteins
each cell makes many sheaths
make vast membrane early in life
hypomyelination - undernutrition in first 2 years - physical damage in brain
describe myelin
lipid rich insulating membrane up to 50 lamellae
dark and light bands
still attached to oligodendrocyte by 1 process
very metabolically active - damaged by MS and adrenoleukodystrophy
what is adrenoleukodystrophy
defect of enzymes that make protein in myelin
can survive 15years
what are microglia
derived from bone marrow during early development
resident microphage population of CNS - immune surveillance
make sure everything in homeostatic state
present antigens to immune cells
first cell to react to infection/damage
role in tissue modelling
synaptic stripping - remove synapse and spines if not required
processes moving in and out all the time
describe microglial morphology
own domain
techniques to label them
processes move all the time - surveillance
activated - when change in organisms/ionic make up in brain, move to some extent
phagocytic - remove debris, rounded cells - divide
microglia and inflammation
set around neuron cell body
don’t know if protecting/damaging
what are peripheral glia
schwann cells more primitive only produce 1 myelin sheath astrocyte functions promote axon regeneration cell surrounds axon
why can’t you have schwann cell in CNS
need cell body near every neuron
increase the size of the brain
