Term
| What does the branching of the dendritic tree of a given neuron govern? |
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Definition
| The number of inputs it receives - more complex branching = more inputs |
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Term
| When considering equilibrium potential of a cation, if concentration is greater inside, then what sign is the equilibrium potential? |
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Definition
If concentration is greater inside and you are considering a cation, then Vm will be NEGATIVE
Conversely, if the extracellular concentration is larger, Vm will be positive |
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Term
| Relative concentrations of ions inside/outside of the cell |
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Definition
Na, Cl, Ca -> ECF concentration >>> [ICF]; when permeable, move down gradient into cell (INFLUX)
K -> ICF concentration >>> [ECF]; when permeable, move down concentration gradient out of cell (EFFLUX) |
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Term
| What causes Vm of a neuron to depolarize during an AP? |
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Definition
| Increase in the permeability of Na ions due to activation of voltage-gated Na channels |
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Term
| How did Hodgkin & Katz show that Na was responsible for the upshoot of the AP (transient inward current)? |
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Definition
Removed ECF Na ions - caused a marked decrease in the amplitude of the depolarization (b/c less concentration gradient)
Generated a family of voltage clamp experiments - as they moved closer to the equilibrium potential of Na, the inward current decreased more and more until it reached 0 when Vm = Veq |
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Term
| What is conductance of an ion dependent on? |
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Definition
| The voltage across the cell membrane; also to some extent, time (see slower increase in conductance for voltage-gated K channels compared to Na channels) |
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Term
| Hodgkin & Huxley Experiment Results/Observations w/ Current |
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Definition
Used voltage clamp technique to determine whether permeability was V dependent
Depolarized the membrane to 0 mV from rest - saw transient positive inward current, then a gradual positive outward current |
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Term
| Difference between the transient inward and gradual outward positive currents seen by Hodgkin & Huxley upon membrane depolarization? |
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Definition
Transient inward - increased over a range of depolarizations, but decreases with further membrane depolarization (inactivation)
Gradual outward - continually increases with more depolarized membrane potentials (no inactivation; the more depolarized the cell is, the greater the current) |
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Term
| How did Hodgkin & Huxley determine that Na flux was responsible for the early current? |
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Definition
1) Removed all Na ions from ECF - should see that the inward current will revert to an outward current if the concentration gradient is shifted; saw a reversal in early current
2) Generated family of voltage clamp experiments, depolarizing the cell to different potentials - noted that as Vm approached Veq for Na ions, the inward current became smaller and smaller in magnitude, eventually reversing to an outward current when Vm > Veq for Na |
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Term
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Definition
TTX - specific blocker for voltage dependent Na channels
TEA - specific blocker for voltage dependent K channels
Saw that early current occurred in presence of TEA (had to be due to Na ions), and the late current occurred in the presence of TTX (had to be due to K ions) |
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Term
| Law of Dynamic Polarization |
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Definition
Proposed by Cajal after his observations of neuronal structure
Axons - TRANSMIT information
Dendrites - RECEIVE and PROCESS information
See a functional polarity in neurons |
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Term
| What cancels out the strong positive charge of K ions in the cell? What cancels out the strong positive charge of Na ions in the ECF? |
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Definition
In cell - have a large amount of negatively charged proteins (maintain neutrality)
In ECF - Cl counter-ions cancel out positive charge of Na ions (maintain neutrality) |
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Term
| Why are intracellular/extracellular concentrations of ions not significantly altered during ion fluxes across the membrane? |
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Definition
| Because relatively few ions actually move across the membrane to cause the changes in potential necessary to evoke the cellular responses seen |
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Term
| Equilibrium potential equation |
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Definition
| Veq = 58log([Ion-outside]/[ion-inside]) |
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Term
| Why is the membrane potential -65 mV at rest? |
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Definition
| It is because at rest, the membrane is primarily permeable to K ions (closer to Veq for K) |
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Term
| How can you show the K concentration gradient plays a role in determining membrane potential? |
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Definition
| Change ECF concentration of K - when ECF concentration was DECREASED, saw a depolarizing shift in the equilibrium potential for K (became more positive b/c of smaller concentration gradient) |
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Term
| How can you show that Na is responsible for the upshoot phase of the AP? |
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Definition
| Decrease ECF [Na] - when decreased notice a smaller depolarization and less current (less Na influx because of smaller concentration gradient) |
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Term
| Why do you get net loss of K into the ECF at rest? |
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Definition
Force driving K out = Eq potential for K = -90 mV
Force driving K into the cell = Vm at rest = -65 mV
Since the outward driving force is stronger, will have net loss of K ions |
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Term
| Relation of current, potential, and conductance in equation form |
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Definition
| I = VG (derived from Ohm's law, V = IR) |
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Term
| How can you measure the current entering a cell? |
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Definition
| Need to use to voltage clamp technique to keep the Vm constant; know Vm because you set the command voltage - current is measured by being equal and opposite to the current you are injecting to keep the membrane potential constant |
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Term
| Conventions in drawing current on graphs in voltage clamp experiments |
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Definition
Down = POSITIVE INWARD current
UP = POSITIVE OUTWARD current |
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Term
| When the ECF concentration of Na is reduced to 0, what happens to the transient inward current? |
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Definition
| It is REVERSED to a positive outward current; this is because the concentration gradient of Na is reversed so that Na efflux occurs from the cell (because it is higher in the cell, so it causes positive outward current) |
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Term
| Equation for driving potential |
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Definition
Driving V = Vm - Veq
As Vm approaches Veq, see a decrease in current until it reaches 0 when the two are equal to each other |
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Term
| Sharp vs. Patch Electrodes |
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Definition
Sharp - used in Hodgkin & Huxley voltage clamps; penetrates CM to enter cell so it measures current across ENTIRE CM
Patch - attach to lipids on CM, doesn't penetrate; measure current across small region of membrane (ideally one ion channel) |
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Term
| Patch clamp experiments w/ K channels |
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Definition
Used TTX to isolate all K channels; start Vm = -100 depolarize - intitially see nothing, then increase in K ion current (delayed onset of increased conductance)
If the sum of ALL trials is taken together, see a similar current as was seen on the sharp electrode measurement of Vm across the entire membrane |
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Term
| How can you tell that voltage-gated Na channels inactivate? |
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Definition
| Due to the cessation of the Na current, despite the continued depolarization of the CM |
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Term
| What does the ion flux of Na depend on? What does this tell us about inactivation? |
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Definition
Depends on the membrane potential from which the cell was depolarized
At more hyperpolarized potentials, less Na channels are inactivated, leading to a higher likelihood of activation of the channels
Note from these observations that INACTIVATION of Na channels is also VOLTAGE DEPENDENT |
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Term
| How can you cause more Na channels to be available for activation? |
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Definition
| Hyperpolarize the membrane - when the Vm is more hyperpolarized, more Na channels are not inactivated, leading to a higher likelihood of activation |
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Term
| What are some example dependencies of K channels? |
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Definition
| Voltage dependent, chemical dependent (dependent on intracellular Ca), pH dependent, etc. |
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Term
| Features of structure of voltage gated Na channels |
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Definition
6 transmembrane segments in each subunit
Typically made of 4-5 subunits
All channels belong to 1 family (Nav1) |
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Term
| Features of structure of voltage-dependent K channels |
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Definition
6 transmembrane zones
Made of 4 to 5 subunits
Most diverse of all channels
9 different families of subunits |
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Term
| What two features are common to all voltage dependent channels? |
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Definition
Voltage Sensor - positive region in 4th transmembrane zone
Pore - in between 5th and 6th transmembrane zones |
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Term
| Path of synaptic transmission @ axon terminal |
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Definition
AP arrives at terminal - depolarization opens voltage gated Ca channels to cause Ca influx
Influx causes localized increase in [Ca] in microdomains of the cell; stimulates process of synaptic vesicle fusion to the membrane
NT's released into synaptic cleft to exert effects on receptors on post-synaptic cell |
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Term
| What is the synaptic vesicle release proportional to? |
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Definition
| Proportional to the strength of the depolarization arriving at the axon terminal, stronger depolarization = more Ca influx = more influx = more fusion = more NT release |
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Term
| Where do you see a plateau of synaptic depolarization at? |
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Definition
| +65 mV; makes sense that AP's typically cause depolarizations of 75-85 mV (max NT release) |
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Term
| Evidence that increased Ca is responsible for synaptic transmission |
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Definition
Record Ca currents in presynaptic terminal using voltage clamp in presence of TEA and TTX - see positive inward current which must be due to Ca influx
Use Ca chelators within the terminal to mop up free Ca; essentially causes a blockage in synaptic transmission
Physically inject Ca ions into the synaptic terminal - this causes NT release
Use fluorescence imaging to detect changes in Ca concentration in presynaptic terminal during transmission |
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Term
| What NT mediates axo-axonic synapses? What type of PSP is generated? |
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Definition
| GABA mediates these synapses and it causes a slow EPSP at the axon terminal |
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Term
| Why is an EPSP seen at the axo-axonic synapse in the presence of GABA? |
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Definition
| Consider Vm at rest for the axon (V = -65 mV); the eq potential for Cl ions is -40 mV in axons - when the membrane becomes permeable to Cl ions, the Vm will want to move towards the eq potential - therefore get a Cl efflux from the cell (because it is too negative) so the cell becomes relatively more positive (depolarization = EPSP) |
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Term
| How are axo-axonic synapses considered inhibitory? |
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Definition
| When the original axon is stimulated, its Vm approximately becomes +20 mV; when the axo axonic synapse is activated, and the membrane becomes permeable to Cl ions, they will flow down their concentration gradient (influx) into the cell to hyperpolarize it (more negative) - this reduces the size of the AP, decreasing syn transmission |
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Term
| Another name for inhibition by axo-axonic synapses? |
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Definition
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Term
| Equilibrium potential comparison for Cl in dendrites vs. axons and its effects on the generation of EPSPs vs. IPSPs |
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Definition
In axons = -40 mV; in dendrites = -80 mV (due to smaller intracellular concentration of Cl ions)
So in axons - from rest (-65), the Cl will move towards the eq potential (Cl efflux) - causes depolarization = EPSP
In dendrites - from rest (-65) the Cl will also move towards its eq potential (Cl influx to hyperpolarize cell because it wants to become more negative) = IPSP |
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Term
| 1st evidence that synaptic transmission occurred in quanta |
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Definition
| Saw that with low ECF Ca concentrations, subtreshold EPP's generated were approximately the size of mEPP's - conclusion that mEPP = 1 quanta = 1 vesicle |
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Term
| How was it proved that 1 quanta = 1 vesicle? |
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Definition
Used freeze fracture to count the # of release sites on the CM (corresponded to the number of vesicles released)
Used a K channel blocker so that the membrane could not fully repolarize after each AP to maximize vesicle release
Saw that vesicle release and quanta released (measured by EPP amplitudes) were related in a linear fashion (1 quanta = 1 vesicle) |
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Term
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Definition
Postulated by Katz
Referred to specific set of release sites on presynaptic membrane where vesicles can fuse to (n = 1,2,3...); once a vesicle had found a site the chance of it binding and releasing its contents was governed by the Probability of Release (Pr) |
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Term
| What causes the physiological noise seen in the original experiments used to try to prove the quantal hypothesis? |
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Definition
The continuous activity on a given neuron by the multiple synapses there; continual input by EPSP's and IPSP's causes constant fluctuation in the Vm
Solved by DECONVOLUTION |
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Term
| What was the simplification of the quantal hypothesis that caused the experimental results w/ noise to not match those predicted by the binomial distribution? |
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Definition
It assumed that Pr of each individual release site was the same for a given synapse; NOT TRUE, each release site has its own unique Pr value
Needed the compound binomial equation developed by Walmsley to create a model to mimic these effects |
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Term
| Types of small molecule NT's |
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Definition
Amino Acids - Gly and GABA (inhibitory); Glu (excitatory)
Biogenic Amines - dopamine, serotonin, NE
Purines - ATP
Cholinergics - ACh |
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Term
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Definition
| Substance P, enkephalins, endorphins, CGRP (all involved in pain perception; 4 listed) |
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Term
| Differences between voltage gated and ligand gated channels: |
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Definition
Voltage gated have 6 transmembrane zones; ionotropic have 4
Voltage gated channels change conformation based on the membrane potential; ionotropic change conformation based on ligand binding |
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Term
| Where are the binding sites located on the ionotropic receptors? |
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Definition
| The ALPHA subunits; typically have two a subunits per ionotropic channel because need NT binding in both sites for conformational change to occur |
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Term
| What is a consequence of the variety of subunit combinations that can occur to form ionotropic channels? |
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Definition
| Have binding sites for other moc as well (e.g. drugs, steroids, etc.) |
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Term
| Characteristics common to all ionotropic channels/receptors |
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Definition
Binding - need NT bound in 2 spots for change in shape
Subunit Composition - see a variety of combinations
Ion Selectivity - most ligand channels which bind excitatory NT's are permeable to Na and K (moreso to Na)
Timing - most ligand dependent channels bind to NT and lose binding very quickly |
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Term
| DIfferences between ionotropic and metabotropic receptors |
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Definition
Metabotropic receptors have an intracellular G-protein binding site
Metabotropic receptors have only 1 subunit which forms the receptor; ionotropic have 4-5 subunits
Metabotropic receptors have 7 transmembrane zones; ionotropic receptors only have 4
Metabotropic receptors don't function as ion channels also; ionotropic receptors are also channels
Metabotropic receptors can regulate gene expression |
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Term
| Types of effector proteins in GPCR signal cascades |
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Definition
Adenylyl cyclase (increase intracellular cAMP)
Phospholipase C (generates 2nd messengers) |
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Term
| What type of enzyme do all GPCR signal cascades involve? |
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Definition
| Kinases - affect protein phosphorylation |
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Term
| Example of 5-HT action on its GPCR |
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Definition
Binds extracellularly - intracellularly, alpha-subunit of G-protein dissociates and activates phospholipase C
PLC makes DAG & IP3 - IP3 increases intracellular Ca to activate PKC
PKC phosphorylates channels to alter behavior |
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Term
| How to eliminate pain in non-anesthetized animals? |
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Definition
| Cut section of brainstem to cerebral cortex or make area hypoxic so that they cannot perceive pain |
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Term
| Effect of serotonin on plateau potentials? |
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Definition
Plateau potentials were only seen in the presence of 5-HT at serotinergic synapses (w/o serotonin, saw no plateau potential after nerve stimulation had stopped)
Therefore, 5-HT is crucial to maintaining sustained activity |
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Term
| What does serotonin do to alter activity in spinal motor neurons? |
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Definition
| 5-HT primes Ca channels on the membrane so they are more likely to open to a depolarization (EPSP) |
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Term
| What occurs to Ca influx after chronic SCI? |
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Definition
| It doubles - see hyperactivity of Ca channels (allow greater influx); however this occurs in the absence of 5-HT |
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Term
| What causes priming of the Ca channels in chronic SCI? |
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Definition
| Constituitively active 5-HT receptors (just because there is no more 5-HT at synapses, doesn't mean receptors have disappeared); these receptors are inherently active so they continually prime the Ca channels to increase Ca influx seen in chronic SCI patients |
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Term
| Main findings of SCN9A channelopathy and its effects on Nav1.7 |
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Definition
Nonsense mutations in the SCN9A gene caused loss of function to Nav1.7 voltage gated Na channels in nociceptive neurons
Patch clamping experiments showed them unable to conduct any current - significant compromise in nociceptive neurons ability to fire AP's
Leads to a congenital insenitivity to pain |
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Term
| What are changes in the Nav1.7 channel that make it HYPEREXCITABLE (due to A863P mutation) and lead to erythromelalgia? |
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Definition
1) Depolarizing shift in inactivation (less Na channels inactivated at rest) and hyperpolarizing shift in activation (channels open at weaker depolarizations) - combination of the two creates a window current occurring between -55 and -35 mV which may contribute to a more depolarized resting Vm
2) Slower inactivation of Na currents (prolonged response)
3) Faster recovery from fast-inactivation potentials
4) Increase in current caused by slow ramp depolarizations - may boost subthreshold stimuli to generate more AP's
5) Lower AP threshold |
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Term
| What are changes in the Nav1.7 channel (due to mutation A863P) which cause it to become LESS EXCITABLE? |
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Definition
1) Channels are inactivated more rapidly from a closed state at more hyperpolarized pre-pulse potentials
2) Hyperpolarizing shift in voltage dependence of slow inactivation - more channels inactivated at resting membrane potential |
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Term
| Overall consequences of A863P mutation for Nav1.7 channels |
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Definition
See that the DRG and sympathetic neurons are HYPEREXCITABLE compared to WT
1) Lower threshold for AP initiation = increased firing frequency; could be caused by window current (depolarizing shift in inactivation, hyperpolarizing shift in activation)
2) Resting membrane potential is more depolarized (window current) |
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Term
| Evidence that ankG deficient mice develop dendritic spines on their axons? |
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Definition
- Morphologically appear the same as dendritic spines in ankG knockout mice
- See presence of F-actin and spinophilin in axonal spines, typical of normal dendritic spines (not seen in ankG positive mice)
- Saw ProSAP/Shank proteins which identified as part of PSD's seen in normal dendrites
- Saw that glutamatergic presynaptic terminals of axons came in close contact with spines
- Loss of myelination of AIS in ankG deficient mice |
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Term
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Definition
| Membrane protein found in AIS of neurons; scaffolding protein believed to maintain axo-dendritic polarity |
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Term
| Evidence that ankG deficient mice grow dendritic spines: |
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Definition
Morphologically have similar appearance to dendrites
Express F-actin & Spinophillin - both are found w/in normal dendritic spines
Express ProSAP/Shank proteins - normal proteins of PSDs
Express mGluR1 - post-synaptic glutamate receptor (only shown in spines)
Saw contact between spines & presynaptic glutamatergic synapses
Lack of myelination in the AIS (where the spines formed) |
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Term
| Evidence for dendrite derived supernumerary axons present on axotomized neurons: |
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Definition
Morphologically, ALPs were distinct from the cell's normal axon
Expressed Nav channels at the AIS of the ALP w/ the assumption that these could INITIATE AP's
Presence of Nav1.2 channels along the ALP - ability for axon to CONDUCT AP's
SV2 and Synaptophysin - axons were capable of synaptic vesicle release |
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Term
| What channel was affected in both papers looking at pain in relation to certain channelopathies? |
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Definition
| Nav1.7 (voltage gated Na channel) |
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