Neurons, glia and myelination Flashcards
cells of the nervous system
neuron: conductive cells capable of sending signals across long distances electrically excitable
Glial cell: provide structural and metabolic support to neurons
visualizing neurons
nissl stain: basic purple/pink stains rough ER and free ribosomes, will only really stain cell body
Golgi stain: silver stain that shows up as yellow: shows cell body and processes more detailed morphology
Immunostain: uses antibodies to label specific parts of the cell
cell body
aka soma, perikaryon- contains nucleus, RER, golgi, and mitochondria
dendrite
extension, can have RER dendritic field is the overall shape can be variable
dedritic spine, small protrusions from a dendrite usually post synaptic site, they are dynamic and can move change size or shape throughout life
axon
consistent diameter along its length can be long, myelinated or unmyelinated
DOES NOT CONTAIN RER OR GOLGI
can have free ribosomes and local axonal proteins
Microtubules
largest of the cytoskeletons- 20-25 nm diameter, polar, GTPase activity, hollow tubes of tubulin (a+B)
Formed by heterodimers of a and B tubulin constantly undergoing polymerization and depolymerization aka treadmilling
GTP bound tubulin is polymerized and grows and GDP bound tubulin is depolymerized (via GTPase)
Heterodimer already has one non hydrolyzed GTP which can bind to a second hydrostable GTP
In axon the - end is facing the soma and the + end is facing the terminal, in dendrite it can be oriented either way
antimitotic chemotherapy target the microtubule
Colchicine depolymerizes, Taxol sabilizes
Microtubule associated Proteins (MAPs)
Stabilize microtubules against abnormal depolymerization
MAP-2 only present in dendrites
Kinesin: transports cargo in + end
dyenin/ MAp1c: transports retrograde in - end
Low molecular:
Tau: facilitates assembly and stabilization of microtubles
hyperphosphorylated tau is found in alzheimers
neurofilaments
medium thickness cytoskeleton 10 nm in diameter intermediate filaments
monomers form coilded coils in antiparallel tetramers of protofilaments–> fibril–>10 nm neurofilament
Present in cytoplasm of the whole neuron
Neurofibrils are aggregates of neurofilaments visible by light microscopy
microfilaments
the smallest cytoskeleton only 5-8 nm in diameter polar ATPase activity strands of actin
most abundant protein in neurons
Single strand of globular actin (G-actin) hydrolyzes ATP filamentous actin (F-actin)
Fast growing + end and slow growing - end
neuron growth and shape
glia
supportive cells of the NS, they are mostlikely to cause cancer in the CNS out number neurons ridiculously and are smaller than neurons
Astrocytes
star shaped cells in the CNS, most abundant cell type in the brain
Protoplasmic astrocytes- shorter, thicker and in gray matter, while fibrous astrocytes are long thin and present in white matter
End feet may attach to capillaries or neurons
Functions: regulate extracellular ion concentration especially K+, remove and recycle NTs, secrete growth factors, help form and maintain synapses
Contribute to BBB
Communicate with one another via waves of calcium which propogates from one cell to another through gap junctions
they respond to injury and multiply
microglia
immune cells of the CNS, small and phagocytic cells
Smallest glial cell, and phagocytose cell debris and pathogens
Function during development to prune unwanted synapses
Ependymal cells
line ventricles in the brain and central canal of the spinal cord
Resemble a simple cuboidal epithelium, cilia on their apical surface help circulate cerebrospinal fluid
Modified ependymal cells and capillaries form the choroid plexus which produces CSF
Forms brain/CSF barrier
Oligodendrocytes
myelinate axons in the CNS
Each oligodendrocyte can myelinate multiple axons at a time, mostly in white matter
Cytoplasm is electron dense
Express proteins that inhibit regeneration of CNS Axons
Schwann cells
myelinate axons in PNS
can only myelinate one axon at a time, but there are hundreds of them
Schwann cells will surround axons in the PNS even if they are not myelinating
Satellite cells- specialized schwann cells that wrap around the cell body
may secrete growth factors-> facilitate axon regrowth after peripheral nerve injury
Myelination
Fatty substance insulating axons for faster conduction
Myelin sheath
Formed by extended plasma membrane of schwann cells or oligodendrocyte
Larger diameter=thicker myelin sheath
Small diameter= so small or even unmyelinated
Function: insulation, decrease ion flux across cell membrane, allows for altatory conductin where the membrane is only depolarized at the node of R
AP pass along axons slower in unmyelinated
Node of R
internode- segment of sheathed axon
Node: unmyelinated segment of axon between myelin sheath, allows for saltatory conduction of APs, high concentration of voltage gated Na channels on the node
Dense lines
visible in electron micrographs of myelin sheaths
Major dense line: compacted cytoplasm side of glial cell memebrane
Minor dense line: opposed extracellular side of glial cell membrane
Clefts/incisures
pockets of cytoplasm left behind during myelination
Split in the major dense filled with myelin forming cell cytoplasm, function to allow cytoplasmic nutrients to enter leaflets
Schmidt-lanterman incisures- PNS
longitudinal incisures-CNS
demyelinating diseases
MS: oligodendrocytes are attached: sensory and motor deficits
G-Barre syndrome: Schwann cells defect: acute inflammatory in PNS, Sensory perception and motor coordination
Gray matter
Composed of neuron cell bodies
Ganglia: PNS
Nucleus: CNS
White matter
Composed of neuron axons
Nerve: bundle of axons bound together by CT sheaths in the PNS
Epineurium: outermost covering of nerve
Perineurium: divides nerve into bundles called fasicles which can split off the nerve to innervate groups of structures
Endo neurium: membran surrounding individual neurons
in the CNS the axons travel in bundles that arent bound
