NS: 07 Cytology I
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- the brain has very little extracellular space. why is this important?
- minute amounts of ions and NT's can create large concentration chnages in these substances
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are there more neurons or glial cells in brain?
which takes up more volume? -
neurons 10%-30%, glia 50%-90%
they occupy roughly the same volume - neurons are the most pleomorphic cell type. what does this mean?
- they can assume the greatest number of different forms
- why is it that dendrites grow smaller but axons stay same diameter.
- dendrites passively propagate a graded signal. as the dendrites get closer to the perikaryon, their diameter increases, increasing the velocity of the signal. (amplitude too?) the dendrite gets wider and wider to avoid losing the signal over the distance from the outskirts of the dendritic arbor to the perikaryon. the sum of many depolarizations along many dendrites may be great enough cause an action potential to be generated at the axon hillock (sorting site). an action potential is all or nothing. information is frequency encoded. if the axon diameter changed, the velocity and therefore the frequency would change.
- what kind of relationship do neurons and glia have?
- symbiotic
- where does most of the energy used by the CNS go?
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maintaining the Na/K gradient. and restoring it after an AP.
it all goes into the Na/K ATPase - basal dendrites vs. apical dendrites
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basal dendrites come directly all off the soma
apical dendrites branch off of the dendritic arbor - what kind of cells have dendrites only?
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retinal amacrine cells.
use dendrites to transfer AP's b/t photoreceptor cells
shaped like a turnip or something - how many genes are active in CNS cells?
- 5000 CNS genes
- where are mitochondria located in a neuron
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mitochondria are generally located where there is the most metabolic activity and the greatest demand for ATP
they are located in the dendrites
in the nodes of ranvier (concentrated!)
along the perikaryon just outside the nucleus - why is mtDNA useful in neurons
- mitochondria out in the axon can make some of their own oxphos proteins when they are so far away from the nucleus.
- how does an axon grow
- it has a growth cone which sends out filopodia to sample the ECF to find places to invade (attracted/repelled by diff factors)
- why would vincristine cause paresthesia?
- vincristine is a chemotherapeutic drug that targets the MT's of the mitotic spindle. it also can damage the MT's in axons and prohibit axonal transport. NT's and other products dont reach the synaptic terminal, and thus the nervous system doesnt function correctly
- rate of axonal growth?
- 1mm/day
- rate of axonal transport via kinesins down an MT?
- 40mm/day
- what is NGF (nerve growth factor)?
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NGF is a neurotrophic factor that is transported retrograde from axon to perikaryon. neurotrophic factors tell the nucleus that the synapse is being used / doing its job. "reward factors". neurotrophic factors promote growth.
ex. BDNF - which classes of NT's must be transported and which are made in axon?
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Amino acid NT's - made in axon
Neuropeptides - made in soma and transported via kinesins. can take days to replenish if depleted in a synaptic terminal. - what is tau?
- tau is a MAP that is involved in neurofibrillary tangles in AD.
- how wide is the synapse?
- 20-30 nm wide
- which neurotransmitter vessels are clear / dense?
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amino acid NT - clear vesicle
neuropeptide - dense - where are most excitatory and inhibitory synapses located?
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excitatory - on dendritic spines
inhibitory - on base of dendrite or on soma near axon hillock
thus, inhibitory synapses are downstream from excitatory synapses and can inhibit them - why is there actin and myosin in dendritic spines?
- spines contract dynamically in learning and memory