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64 Cards in this Set
- Front
- Back
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Golgi technique
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only stains nerve cells
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What did Cajal(and Ramon) show?
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that neurons are distinct entities
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how are signals carried from neuron to neuron?
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electrical- APs
electrical to electrical |
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how does current move?
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down path of least resistance
EC space has least amount of resistance |
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Eccles/Katz
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concluded that communication was biochemical
-katz said it first |
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End Plate
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myelinated motor neuron axon that LOSES ITS MYELINATION as it contacts the mucle cell
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how many nerves innervate a single muscle cell?
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ONE
however, one nerve can branch and innervate many mucles. but each muscle cell gets 1 nerve |
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what are the terminal ends of axons called?
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Buttons
make up pre-synaptic membrane |
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Post synaptic membrane called
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Junctional Folds
help w/ NTs diffusing quickly away from site of action |
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Active Zone
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on presynaptic side
has lots of vessicles and lots of Ca channels |
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Receptors
density of Ach Rec? |
on post-syn side
10,000/micrometer sq |
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How is the synapse optimized?
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Anatomically
pre and post-syn membrane are very close together -tons of rec in jxnl fold |
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Synapse has a high Safety Factor
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not probablistic
signal will activate muscle |
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Curare
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from poison dart frogs
only affects muscle fibers blocks post-syn jxn |
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how long do post-syn responses last?
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a few milliseconds
in both PNS and CNS |
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decay in synaptic transmission is due to?
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membrane time constant
fxn of res and capacitance |
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alpha-bungarotoxin
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snake venom
blocks nicotinic ach receptors in the NMJ |
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how are Ach rec gated?
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Ligand-Gated
ligand binds and opens activation gate, ions move in based on conc gradients |
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how do Ligand gated channels inactivate
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Desensitization- NOT same as voltage gated inactivation mech
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with channels, what is most impt in movement?
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relative permeability
mostly Na, K, and some Ca |
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driving force at RMP
driving force at 0mv driving force at +voltage |
Na will have greated driving force
driving forces for Na/K are balanced K will have greater driving force |
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when is there reversal in driving forces?
what does this mean? |
reversal at 0mv
proves that the channel is permeable to more than one ion |
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at RMP what is the current like
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largely an inward Na current
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ideal fxn of NMJ
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respond rapidly, precisely, and with high fidelity
rapidly on order of milliseconds *Ach Rec does this* |
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Process of synaptic trans
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1. vesicle fuses w/ membrane
-diffusion into cleft (ms) -NOT RATE LIMITING 2. 2 molec of Ach bind to rec -10us to open 3. get rid of Ach by diffusion or degradation (AchE) |
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Law of Mass Action
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a reaction will proceed as proportional to reactants
ie- high conc of Ach and Rec=fast reacion |
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Ach is close to a full agonist
receptor affinity? |
99% of rec will be simultaneously opened
Ach has low affinity for rec |
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do Ach normally desensitize?
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NO. Ach is removed too quickly.
Ach would have to be bound for 10s of ms for desensitization AchE inhib can do this(ie myesthenia) Time Dependent |
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Active/Regenerative Propogation
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via Na channels
evokes an End Plate Potential(EPP) and can carry on |
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Far away from synapse
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lose synaptic response
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Synaptic Responses
what do regenerative processes require? |
will decay
voltage gated channels |
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Smallest Evoked EPP
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=spontaneous mEPP
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Unitary Response
Synaptic Event is made up of what? |
the smallest response possible of neuron vessicle release
multiple unitary responses |
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Quantal Content
Quantal Size |
The number of vessicles released per stimulation
the amplitude of the individual response |
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How do yo affect quantal size?
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dec the density of rec on post-syn membrane
or dec Na conduction |
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Docking and Priming
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when vessicles are moved to the active zone
lots of protein interactions |
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what allows the presynaptic membrane to remain the same size?
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recycling of vessicles
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calcium channels are where?
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on plasma membrane
necessary for docking, fusion, and transmitter release |
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what senses intracellular calcium
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protein on vessicle, will lead to fusion
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Necessary but not sufficient for vessicle release
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Calcium
Timing is impt. Ca has to be there when you stimulate axon depolarization of membrane opens ca channels |
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which is faster: Ca or Na channels
what is the rate limiting step? |
Na chan are much faster. Ca chann do not open synchronously
Calcium chan openings have to have high ca conc to trigger rel of NT |
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Low affinity is important for what?
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high efficiency
ca-synaptotagmin and Ach-Rec are very low affinity |
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What is vessicle fustion tightly timed to?
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the period when Ca conc is HIGH
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spatial relationship of Ca channels to vessicles
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they are very close to one another.
micro domains of ca channels near Vessicles |
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Ribbon Synapses
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post synaptic channels and Ca channels
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Myasthenia Gravis
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autoimmune to NMJ ach rec
use AchE inhibitors |
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why doesnt diffusion work at NMJ
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its too big. would take too long
have to use AchE-ensures rapid termination |
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inhibiting AchE
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makes the synaptic response 4-5xs longer
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NMJ
vs CNS |
big, fast synaptic jxn. Always gets an AP and contraction
(only fast trans in auditory corex) CNS neurons have multiple synapses. Localized |
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Localization of Synapses in CNS
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axosomatic- inhibitory
somadendritic- proximally, GABA axodendridic- mostly excitatory* Axoaxonic- allow regulation, cross talk -presynaptic inhibition |
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Main excitatory NT
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glutamate
synapses at dendritic spines |
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Olfactory Bulb has what type of synapses/excitation?
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reciprocal excitation of dendrities via Dendrodendritic
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what determines the AP in the CNS
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Dendritic Integration
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excitatory synapses occur where?
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dendritic spines (mostly Glu)
each dendritic spine is a fraction of an endplate. fraction of NMJ |
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do same principles apply to dendritic zone as NMJ?
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yes. the only difference is that there are a fraction of the active zones
takes multiple synapses from then to fire an AP |
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CNS cells must be able to do what?
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listen to dfft sources (dendritic synapses) to fire 1 AP
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Inhibitory ligand CNS synapses
Exciatory ligand CNS synapses |
inhibitory ligand chan use CL-
-GABA or Gly use Na and K -Ach, Glu, Serotogenic |
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Inhibitory response does what
Excitatory (Ach/Glu) do what? |
reverses MP to Equilib potential for Cl- (-60mV) near RMP
reverse to around 0mV |
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Shunting Inhibition
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when cl- channels open and cl pours in, it counteracts the mvmt of cations and holds the membrane at RMP
via GABA chan, Cl- will shunt out any activation |
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EPSP
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excitation input near dendrites
EPP is for NMJ, but same for EPSP |
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GABA and Gly use what
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CL- channels to keep membrane near RMP. prevent excitation
are inhibitory |
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Temporal Summation
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closely occuring synaptic repsonses dont decay-->they sum up
dependent on Time Constant spatial summation kind of does the same thing |
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Terminating a Signal in the CNS
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diffusion is usually enough
Too much Glu is bad. Astrycytes suck it up out of synapses -Glu to Gln, then shuttle back |
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Reuptake mechanisms in the CNS
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are mainly used to prevent neurotoxicity
NOT the primary removal mech Diffusion is MAIN one |
