mod 2 Flashcards
3 main elements of the cytoskeleton
microtubules, neurofilaments, microfilaments
microtubule structure
hollow tube of protein tubulin, large, 20nm, polarised made of beta and alpha tubulin dimers, oriented lengthwise
microtubule function
trafficking of proteins, vesicles, mitochondria
microtubule fast axonal transport
bidirectional
microtubule slow axonal transport
anterograde
kinesine
anterograde - transports things down end of axon
dyenin
retrograde - transports back to the soma
what drives polymerization/depoly within microtubules
GTP bound to beta tubulin
what does a tau protein do
stabilises microtubule and links one microtubule to the next
where are taus found
dendrite and axon inclu distal axon
where is MAP-2 found
soma and dendrite
what does anterograde transport
mitochondria, vesicles, membrane lipids
what does retrograde transport
used materials
motor domain
contains ATP, conserved across specied
tail domain
binds to specific cargoes, diverse across/within species
neurofilament structure
intermediate: neurofilament light, medium and heavy (NFL, NFM, NFH) 10 nm diameter
neurofilament function
structural framework, is most stable of cytoskeleton having huge mechanical strength
microfilaments structure
small, actin molecule, 5nm diameter.
dynamic positive barbed and negative pointed ends
actin tredmilling
a dynamic turnover of actin filament while filament length is maintained. get a new net flow of G-actin through filament
actin in presynaptic terminal
is enriched and regulates the vesicle pool
actin in postsynaptic terminal
regulate surface receptor diffusion and the exo-endocytic trafficking of receptors to surface
microfilaments function
endo/exocytosis as well as spine growth, strength
failure of axonal transport
leads to a number of different diseases, alzheimers, parkinsons, auto-immune, motor neuron
what does nisssl stain detect
RNA, dark staining represents large stacks of RER
technique to identify and locate proteins
immunohistochemistry
immunohistochemistry
primary antibodies bind to target antigen, secondary antibodies bind to primary antibody and also contains a fluorescent tag enabling protein to be identified
inside of cell membrane
hydrophobic
inside/outside of cell membrane
hydrophilic
cleft protein
trans-synaptic proteins, secreted presynaptically, cell adhesion molecules, interact with molecules on surface of adjacent cell
myosin
found in muscles, travel along actin
Fluorescence in situ hybridization (FISH)
use DNA probes to target different chromosomal locations
oligodendrocytes function
myelinates multiple axons
small diameter myelinated axons with short internodes fire at what frequencies
low
how much do action potentials and ion currents take of the axons surface
restricted to less than 0.5%
what do monocarboxylate transporters MCT in extracellular membrane channels transport?
lactate pyruvate and ketone bodies 14 or more MCTs
how do oligodendrocytes provide neurons with energy
carry molecules with one carboxylate group e.g. lactate and pyruvate across biological membranes
what is the metabolic supportive function of oligodendrocytes regulated by
glutamate binding to NMDA receptor
what is an NMDA receptor
glutamate - major excitatory neurotransmitter
deleterious effect of excessive NMDA receptor signalling
excitotoxicity
multiple sclerosis
destruction of myelination, oligodendrocyte/schwann cell dysfunction. scars refer to particularly in white matter of brain and spinal cord
microglia structure
small, high branched cells. 5-20% of all glia cells
how to identify microglia
immuno-cytochemical identification and Iba1-actin binding proteins
microglia function
defence function, synapse elimination, phagocytosis, homeostasis
distribution of microglia
large phenotypic diversity, more in grey matter, near synapses, concomitant with astrocytes
response to injury
when they detect and intruder, they call for help by releasing cytokines which makes the BBB permeable. they become motile, apoptosis, phagocytic
microglia neuronal functions
neurogenesis, induction + phagocytosis of apoptotic neurons, synaptic pruning
microglia immune functions
phagocytosis, antigen presentation, pro/anti inflammatory response, immuno-surveilance through extra/intracellular receptors
during what stage of development do microglial invade the CNS
late embryonic development, developing from haemopoietic cells of bone marrow
microglia lifespan
lasts 20+ years, renewing slowly ~30% / year
microglia resting
not moving, but ramified branched process survey the microenvironment
microglia activated
amoeboid, move freely throughout neural tissue, phagocytose debris, pruning of cells/dendrites
cytokines/inflammation synaptic and neural development
pruning and apoptosis
growth factors synaptic and neural development
plasticity and neurogenesis
what do microglia actively survey the environment with
pattern recognition receptors - e.g. toll-like receptors
extracellular side of toll-like receptor
recognition of the microbial product
cytoplasmic side of toll like receptor
TIR domain, recruit signalling molecules, alter kinase activation/transcription
good microglia
ligand recognised, internalized, eliminated
bad microglia
overactivated, produce cytotoxic factors
overactivation of microglia
causes unknown, environmental toxins - pesticide can lead to neurodegenerative diseases like alzheimers.
what happens to microglia in alzhiemers
their activation increases
what happens to microglia in alzhiemers
their activation increases (bad)?. however the tau tangles produce cytokines which attract microglia
neuotoxicity from overproduction of microglia do what to NADPH oxidase
cause neurotoxicity through activation of NADPH oxidase –> increased reactive oxygen species. this is activated in alzheimers and parkinsons
ependymal cell structure
cuboidal, columnar shape, apical microvilli, cilia, contain intermediate filaments
ependymal cell distrubtuion
line the ventricular system of CNS
ependymal cell function
inflammatory response, trophic and metabolic support, secrete cerebrospinal fluid, regulator of osmotic pressure, control concentrations fo regulatory peptides, function as neural stem cells
what did einstein have in abundance
astrocytes
astrocytes structure
star shaped, long branched, dominated by intermediate filaments, microtubules, actin/mitochondria, gap junctions
astrocytes function
communication, nutrient transport from blood to neuron, support myelin coverage of neurons
how do astrocytes communicate
pick up and pass on information via calcium waves through Ca2+ binding protein
astrocytes role in glutamate/glutamine
astrocytes uptake glutamate and GABA from neurons and then release glutamine for neurons to uptake
activation of ionotropic glutamate receptors and metabotropic receptors
released from astrocytes to postsynaptic neurons to activate extrasynaptic NR2B - containing NMDA receptors to trigger slow inward currents
how do astrocytes get energy
through blood flow
vasodilation
glutamate receptors -> Ca transient travels to end-feet -> release of vasodilators
distribution of astrocytes
numerous in grey matter, adjacent to blood vessels, in contact with synapses
gap junctions of astrocytes
ensure minimal overlap, are between astrocytes and between end-feet at blood vessel
hemichannel
gap junction to release into extra-cellular space
reflexive gap junction
gap junction onto itself
astrocytes three type of gap junctions
reflexive gap junction
intracellular gap junction
hemichannel gap junction
astrocytic dysfunction in alzheimers disease
reactive astrocytes produce amyloid beta.
AB inhibits glutamate uptake, increasing Ca2+ signalling leading to abnormal vascular responses and inhibition of LTP and memory loss
astrocytes and BBB
astrocytic end foot makes up part of BBB, interface between epithelial cells and rest of brain. if cells active, require more nutrition, they pump more lactate
role of astrocytes during non-inflammatory conditions
one end at vasculature other end-foot on BBB, carries out neurotransmitter clearance and buffering of K+ and metabolic support
astrocytes during inflammatory conditions
reactive astrocytes become branched and fuzzy, end-feet can detach from BBB and gap junctions break down. astrocytes respond by forming a scar
astrocytes reponse in inflammatory conditions
moderate astrogliosis - more production of GFAP, which makes astrocytes get more branched and densely rigid
role of reactive astrocytes for neuroprotection
- debris clearance
- BBB repair of leakiness
- glial scar as barrier
- secretion of anti-inflammatory factors
- sequestering of excess glutamate (glutamate excitatoxicity)
3 ways to make reactive astrocytes
- resting astrocyte undergoes hypertrophy
- ependymal cell undergoes gliogenesis
- stem cell undergoes gliogenesis
BBB structure
endothelial cells on inside, pericytes around, basal lamina matrix - fibrous around whole thing and astrocytic end-feet form third layer round the outside
what makes the BBB really impermeable
tight junctions that form between endothelial cells
glutamate from endothelial cells to astrocytes
glucose broken down into pyruvate –> to lactate –> further broken to acetylcholine to use internally within the astrocyte
what mechanism allows for astrocytes and neurons to get lactase
MCT4 (astrocytes) MCT2 (neurons)
what do astrocytes give oligodendrocytes to support synapse
monocarboxylate
diffusion of BBB
lipid soluble agents like alcohol, nicotine, antidepressants
protein transporters of BBB
glucose, amino acids, and more
receptor-mediated transcytosis of BBB
insulin, transferrin, interleukins
absorptive transcytosis of BBB
albumin, other plasma proteins
efflux transporters of BBB
cetirizine
paracellular transport of BBB
water soluble agents
pericyes of BBB
regulates permeability and immune function
tight junction of BBB composition
claudin and occludin
if BBB gets leaky:
reative oxygen species, hypoxia and/or thrombin + fibrin
hypoxia in BBB
when leaky, albumin leaks in –> edema –> capillary blood flow -> hypoxia
reactive oxygen species in BBB
red blood cells leak into brain -> hemoglobin -> iron -> reactive oxygen species
what causes leaky BBB
aging, radiation, stress, hypertenion, trauma, toxicants
thing that strengthen BBB
diet, circadian rhythm, physical activity
what can bacterial factors do to BBB
infiltrate the blood lumen
changes to the bacterial factors in BBB
can upregulate inflammatory cytokine levels affecting integrity and promote neuroinflammation
BBB role in multiple sclerosis
BBB gets dyregulatated
BBB role in HIV and AIDS
damage to tight junctions of BBB allows macrophages to cross into brain leading to HIV encephalitis
BBB role in alcoholism
exposure to ethanol injures the endothelial cells that form tight junctions in the BBB
BBB role in alzheimers
AB accumulation -> BBB dysregulation -> decreased AB clearance across the BBB
