Cells of the Nervous System 1 & 2 Flashcards
neurons
are excitable cells
conduct impulses
integrate and relay info in a neural circuit
glia
supporting cells, found around neurons
maintain homeostasis
protection
assist neural function
Nissl (franz) staining
allows to distinguish between neurons and glia
nucleolus of all cells stained
neurons have Nissl bodies
- allows visulaisation of variation in size, density and distribution of neurons
if only nucleolus stained = glia
if area around nucleolus is stained too = neuron
highlight rRNA
dye binds to negatively charged things e.g. nucleotides
The soma
nucleus
organelles for protein synthesis and processing: ribosomes, RER, Golgi
mitochondria = dense in neurons, movement of ions requires energy
4 major components of neuron
1 - cell body, soma, perikaryon 2 - dendrites 3 - axon 4 - presynaptic terminal dendrites and axons = neurites = any process coming off a neuron
Golgi (camillo) staining
silver chromate
small % stained - only highlights some neurons - randomly
cytoskeleton (internal scaffolding)
microtubules - longitudinally down neurites, hollow tube made of polymers of tubulin
microfilaments - polymers of actin, longitudinally and membrane associated
both dynamically regulated - polymerisation and depolymerisation
neurofilaments = long protein molecules, wound together - very strong
axon segments
axon hillock - wide part that attaches to soma
axon inital segment - specific ion channels, where action potentials are generated
axon collaterals - branches
axon terminal/terminal bouton
features of axon
no RER or free ribosomes
different membrane composition
<1mm to >1m in length
1 micrometer to 25 micrometer in diameter - affects speed of conduction
immunohistochemistry
specific primary antibodies bind to protein of choice, secondary one binds to primary and it fluoresces.
presynaptic terminals
specialisation of terminal cytoplasm: no microtubules, synaptic vesicles, specialsed proteins or mitochondria
synaptic cleft
terminal arbour - lots of presynaptic terminals at end of axon
boutens en passent
axoplasmic transport
moving things down axon, can be slow or fast
fast - radioactive amino acids, 1m a day, uses microtubules, kinesis and ATP
anterograde transport = moving down cell
retrograde transport = moving up cell, by dyenin
manipulating axoplasmic transport
allows visualisation of cells
using antero/retrograde labelling, inject dye ino spinal cord - taken up by terminals and transported around body
dendrites
branches form dendritic trees (arbours)
structure to function relationship - convergence = how many different synaptic inputs is one neuron dealing with
can have thousands of synapses
dendritic spines = increase surface area
plasticity - structure vs activity - can take in spines if not used
abnormalities = cognitive impairment
staining methods
nissl stains
golgi stains
immunohistochemistry
live imaging of fluorescent dye - genetic or injected
electron microscope - synapses and organelles
retrograde tracers - HRP, find cell body location
types neuron classification
1 - number of neurites
2 - dendritic geometry
3 - connections
number of neurites classification
(axon or dendrites)
unipolar/pseudopolar
bipolar
multipolar
unipolar / pseudopolar
splits in 2 e.g. dorsal root ganglion
peripheral process is part of axon too
small area for receiving synaptic input - highly specialised function
relay info reliably
bipolar
e.g. retina - little integration, small area for recieving synaptic input
highly specialised for function
reliable relay of info
multipolar
bigger tree = more integration
majority of neurons in brain
large area for reciving input
high levels of convergence
dendritic geometry
pyramidal
stellate
pyramidal geometry
distinct apical and basal dendritic trees, pyramidal shaped soma
common in cerebral cortex and hippocampus
stellate geometry
star shaped dendritic arbour e.g. layers in neocortex
connections in:
sensory
periphery —-> CNS
afferent
connections in:
motor
ventral horn —-> peripheral
efferent
interneuron connections
largest class, only in CNS relay or projection neurons - connect brain regions local interneurons - neighbouring cells - short axons - process info in local circuits
nerve glue
glia fills space around neurons
extracellular space of 20nm between glia and neurons
can proliferate throughout life, neurons cant be replaced
homeostatic
myelinating
phagocytic cells in:
CNS
homeostatic = astrocytes myelinating = oligodendrites phagocytic = microglia
homeostatic
myelinating
phagocytic cells in:
PNS
homeostatic = satellite cells myelinating = Schwann cells phagocytic = schwann cells and macrophages
homeostatic cells in:
ENS
enteric glia
astrocytes
control environment surrounding neurons, have spacial domains
contains unique marker - GFAP - glia fibrillary acidic protein, only expressed by astrocytes
also - buffer extracell potassium and form part of blood brain barrier
subtypes of astrocytes
fibrous protoplasmic radial glial cells - developmental muller cells - retina bergmann glia - cerebellum ependymal cells - line ventricles and central cord
astrocytes as fuel suppliers
they supply fuel and add protection to brain
glycogen stores of brain contain 5-10 mins supply
metabolise glycogen and supply lactate
endfeet take up glucose - help keep controlled environment
tripartite synapse
terminates neuronal activity
recycles neurot to presynaptic terminals, prevents over excitation
asrocytes have receptors too
microglia
macrophages of CNS, approx 15% of CNS glial cells
neural development - growth factors, help neurons grow
phagocytosis - apoptosis, clear debris
oligodendrocyte myelination
synaptic pruning
however not always beneficial e.g. in neurodegenerative diseases
oligodendrocytes
myelinating oligo form myelin sheaths of CNS axons
insulate and change electrical activity
can have 15-30 processes from cell body to myelin sheath
schwann cells
form myelin sheaths of PNS
one schwann cell provides one myelin segment to a single axon
myelin sheath
formation - process of oligodendrocyte cytoplasm wraps many times around axon
cytoplasm squeezed out of layers by compaction
maintain contact with glial cells for nourishment
function - insulate and create nodes of ranvier enabling saltatory conduction
