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17 Cards in this Set
- Front
- Back
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In what ways do neurons and brains resemble each other?
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Brain has many synapses.
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What is the neuron’s trigger zone?
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The lowest threshold part of the cell with the most Na+ channels); Trigger zone also called spike initiation site, initial segment; is near axon hillock)
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What is the integration area?
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This is the soma, for both dendritic and somatic input
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List 4 input regions on the neuron and indicate what kinds of synapses are generally found at each?
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1. Direct on dendrites (excitatory)
2. Direct on spines (excitatory) 3. Direct near axon initial segment (inhibitory) 4. Axo-axonic (excitatory and inhibitory) |
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Define spatial summation.
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If you have many dendrites and they all have synapses, if you sum their activity you can get a bigger synaptic response; synaptic voltage is non-linear
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Do synaptic potentials sum linearly?
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No (it is not the arithmetic sum of each of the synaptic potential amplitudes), because of reversal potential
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Define temporal summation. How is it related to the shape of synaptic potentials?
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Fast rise occurs when ligand-gated ion channels are opened-up and Na+ enters and K+ exits. Once the channels close, the cells are not at their resting membrane potential. It doesn’t say high, however, because of GHK equation, so much return from positive value to resting potential; cannot return quickly, however, because can only used channels that are open at the particular time (it doesn’t have the ligand-gated channels that were opened during rising phase); slow fall is necessary, because if fast fall the only way to get temporal summation was if inputs were exactly at the same time; slow allows EPSP to sit on the falling phase of the previous synaptic potential (it ‘piggy-backs’)
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How and why does inhibition affect temporal summation?
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During inhibitory synapse, rm is low so τ is short
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What might be the functional advantages of a lot of axonal convergence? What are the advantages of not having convergence (ex. The neuromuscular junction)?
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Multiple transmitter can converge to affect the same effector systems; can occur at the level of the G-protein, the second messenger cascade, or the type of ion channel; not having convergence can make the neuromuscular junction dependent upon the firing of a singe unit rather than many integrating together
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What is axonal divergence? What is it good for?
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Axonal divergence is the ability of one transmitter to activate more than one subtype of receptor and cause more than one type of postsynaptic response. Divergece is useful, for example, when a single pain neuron is excited to activate the entire body.
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Roughly how many synapses are there in the human cortex?
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164*1012
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List 4 approaches that may provide a way of understanding the vast synaptic circuitry of the brain.
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1. Do large scale reconstructions (connectomics)
2. Iterated circuits 3. Label each cell uniquely using transgenic mice or other techniques that provide for a Technicolor Golgi stain 4. Monitor the timing of neuronal activity |
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What is the value of electron microscopy in studying synaptic circuits?
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Construct thin 3D structure by shaving off a very tiny portion, taking a picture of it, and then repeat; Useful to look at “iterated” circuits, such as cerebellum and the retina
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What 3 properties of the cerebellum make it advantageous for studying synaptic circuits?
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1. Homogeneous
2. Modular 3. Few cell types |
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What is fluorescence?
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The molecular absorption of a photon triggers the emission of another photon with a longer wavelength
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What is GFP and how might it be useful in the study of synaptic circuits?
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Absorbs blue light emitted from aequorin and emits green light (shifts light to longer wavelength); Consists of 238 amino acids in a single chain that forms an 11-stranded beta-barrel with an alpha-helix running up the center. The chromophore of GFP is formed by post-translational modification of the amino acids in the alpha-helix almost perfectly in the center of the cylinder
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What is the value of fluorescent indicators of Ca++?
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-Two step process, calcium levels raised → blue light released → GFP absorbs blue and emits green (like paints that glow under a blacklight)
- Mutations in protein structure of GFP (amino acids inside alpha helix) can change colors that are emitted - Basis of Brainbow |
