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72 Cards in this Set
- Front
- Back
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How does axon diameter effect conduction spped?
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increasing the diameter increases speed because it decreases internal resistance and allows for more ion channels
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What effect does more membrane from a wider axon have on capacitance?
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more mebrane, capacitance increases, more area to separate charge
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How does axon diameter effect conduction spped?
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increasing the diameter increases speed because it decreases internal resistance and allows for more ion channels
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What effect does more membrane from a wider axon have on capacitance?
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more mebrane, capacitance increases, more area to separate charge
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How does a longer length constant effect conduction velocity
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a longer length constant means a fater conduction velocity because the membrane resistance is high and the longitudianl resistance is low
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In a current clamp experiment, you control.... and measure ....
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In a current clamp experiment, you control current and measure voltage, current is injected and changes in Vm are monitored
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In a voltage clamp experiment you control...and measure....
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In a voltage clamp experiment you control voltage and measure current
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How is voltage controled in a voltage clamp experiment
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in equal and oppositve current is injected to keep the membrane voltage constant
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How can Ohm's law V=IR be rewritten to use during a voltage clamp experimen
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Ix= gx (eclamp- Ex)
Ix is the current for a particual ion, gx is the conductance (the inverse of resistance) and (eclamp- Ex) is the net voltage of the clamp minus the equilibrium voltage for the particular ion (can be figured out with nernst equation) |
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describe an IV plot
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An IV plt gives you a profile of the voltage dependent behavior of an ion channel, you can figure out the equilibrium voltage potential for a particular ion by finding where current= 0 on the graph
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what is the purpose of patch clamping
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you control the voltage and measure the current through a single ion channel
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how can you use current clamping to figure out the theshold potential?
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Inject increasing amounts of current/ ions and watch for the membrane voltage to reach threshold and generate an action potential
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in a current clamp experiment, injecting a "negative current" will .... the membrane and a positive current will ... the membrane (think in terms of polarization)
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injecting a negative current will hyperpolarise the membrane, injecting a positive current will depolarize the membrane
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In a voltage clamp experiment, how would we expect the current to change if a hyperpolarizing voltage was maintained
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the current would not change because the hyperpolarizng voltage would not lead to an action potential
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How would we expect the current to change if a depolarizing voltage was maintained
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the current would increase. flow out of the cell because the cell would become inside positive
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why will conduction velocity be slower if the time constant is longer?
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the time it takes for the next region of membrane to charge will take longer because it takes longer to charge the capacitance even though it stays charged longer
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what type of junction can be found at electrical synapses
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gap junctions
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What is an epsp
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An post synaptic potential that brings the membrane potential closer to threshold (depolarizes)
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what is an ipsp
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a post synaptic potential that brings the membrane farther away from threshold (hyperpolerizes)
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what is temporal summation and what property of the mebrane allow for it
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temporal summation is the addition of post synaptic potentials over short time intervals, the time constant allows for temporal summation to occur
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what is spatial summation and how what property of the membrane allows it to occur
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spatail sumamtion is the sum of posp synaptic poteintails from different presynaptic cells, the length constant allows this to occur
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what is curare
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a toxin that blocks Ach neurotrasmitter receptors and causes a failure of muscle action potential by preventing / lowering the generation of an epp, by stopping the action potential in the muscle cell, researches could study the epp by itself, they determined that the epp spreads electrotronically and does not regenerate like the action potential does the AP in the motor neuron remains uneffected
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what are endplate potentials
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depolarizations that occur in response to action potentials from the motor neuron before the muscle action potential is generated, they travel electrotronically and do not regenerate like action potentials do
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how can the post synaptic current be measured?
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you can voltage clamp the postsynaptic membrane
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why does a postsynaptic potential last longer than a postsynaptic current
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The time course of the potential depends on both the duration of the current and the time constant. The current will end as soon as the transmitter leaves the receptor because the channels close but because of the delay caused by the time constant, the membrane voltage remains even after the current has ended
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what controls the direction and intensity of the postsynaptic current
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the size of the conductance through the open channels and the electrochemical driving force and charge on the permeant ions
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Describe the depolarizing postsynaptic current at the neuromuscular junction
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it consists of an influx of Na+ that is partly canceled by a simultaneous flow of K+ ions, this occurs because the postsynaptic ligand gated channels are peremable to both ions
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What determines wheter or not synapse will be inhibitory or exitory
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the properties of the channels that are open by the transmitter and the identies of the ions that flow through them, it has nothing to do with the transmitter itself
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what determines the amplitude and sign of the postsynpatic potential?
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the transmembrane voltage prior to the postsynaptic potential and the species of ion(s) carrying the current
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what happens to the driving force on a particular ion as Vm approaches Ex
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the driving force decreates, when Vm=Ex there is no current flow across the membrane even though the channels are open, if the voltage is clamped on the other side of Em, the current will flow in the opposite direction and the sign of the postsynaptic potential will be reversed
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Define reversal potential
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when the postsynaptic channels open, the postsynaptic current causes Vm to shift towards Erev which is the membrane potential at which no current flows through the channels
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how can the reversal potential be calculated if a single ionic species carries the postsynaptic current
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the Nernst equation
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How can the reversal potential be calculated if multiple ionic species carry the postsynaptic current
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the goldmann equation
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what is the relationship between Ik and Ina (the current carried by postassium and the current carrier by sodium) at the reversal potential
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they are equal and opposite becase the reversal potential is defined as the point where no net curret is flowing
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Given that the Ach activated channels are approximately equally permeableto Na and K, what do the magnitudes of the currents depend on?
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the driving force of each ion which is measure as the differnce between the membrane voltage and the equilibrium potential for that ion (Vm-Ex)
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what equation represents the driving force on an ion/ how is it defined
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Vm-Ex, the difference between the membrane voltage and the equilibrium potential of the particular ion
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If the membrane potential of a postsynaptic cell is equal Ena, what happens to the curret?
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the current will flow out because the driving force for potassium to leave the cell is high
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if the membrane potential of a postsynaptic cell is less than Ena but greater than Erev, what will happen to the current?
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The current will flow out but not with the same magnitude as when Vm=Ena
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what happens to the current when Vm= Erev
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the current is 0, there is not net flow of ions
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what happens to the current in a postsynaptic cell if Vm is less than Erev but more than Ek
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the current flows in because the driving force for sodium is high, it does not flow in as fast as it would if Vm= Ek
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what happens to the current when Vm= Ek
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the current flows into the cell because the driving force on sodium is large
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what determines the maximum change in Vm after the postsynpatic channels are opend?
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Erev, once Vm approaches Erev, the net driving force on the permeant ions drops to 0 and Vm cannot change anymore
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If the Erev of a postsynaptic current is more positive than the threshold of the postsynaptic cell, what type of synapse is it?
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ecitatory, since Erev is more positive than the threshol, the current flowing in will be able to depolarize the membrane past the threshold before it reaches the point where it can't flow anymore
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if Erev is more negative than the theshold of the postsynaptic cell, what type of synapse is it?
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if Erev is more negative than the threshold, the synapse is inhibitory because the current reaches 0 before it can depolarize the membrane enough to reach threshold
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Inhibitory postsynaptic currents are usually carried through channels permeable to ... and ... because...?
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inhibitory currents are usually carried through channels permeable to K+ and Cl- because Erev for K+ or Cl- is closer to Vrest which is more negative than the threshold. By reaching Erev before the theshold, current reaches 0 before the threshold can be met
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If Erev is more positive than Vrest, is the the synapse necesarily excitatory?
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No. Even though Erev is more positive than Vrest, it still may be more negative than the threshold. The current will still be depolarizng but not depolarizing enough to reach threshold
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describe presynpatic inhibition
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an inhibitory transmitter is released from a terminal that ends on the presynaptic termianl of an excitatory axon, it reduces the amount of transmitter released from the ecitatory axon which in turn reduces excitation in the postsynaptic cell
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Some transmitters modify calcium channels in the presynaptic membrane and make them less resonsive to depolarization. How would this effect the release of transmitter molecules
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this is an example of presynaptic inhibition, transmitter release is dependent on calcium entry into the terminal so reducing calcium entry reduces transmitter release
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Compare the effects of pre and post synaptic inhibiton
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postsynaptic inhibition globally reduces the exitability of the postsynaptic cell making it less able to respond to any exitatory input, presynaptic inhibitoin acts only on 1 specific input so the cell can still respon normally to all other inputs
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describe presynaptic release of neurotransmitters
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released in packets called quanta in a manner similar to exocytosis
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how do we know that neutransmitters are release in quanta
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there is minimal end plate potential that is caused by the release of a discrete number of NT molecules, the magnitude of the potential increases in discrete units as the number of quanta increases
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The release of a NT vesicle from the readily releasable pool depends heavily on...
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the intracellular concentration of calcium
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which toxin blocks sodium channels
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tetrodotoxin TTX
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which toxin blocks potassium channels
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TEA tetraethylammonium
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what is the relationship between transmitter release and depolarization
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more depolarization leads to more transmitter release
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Does transmitter release depend on the prescence of an action potential
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no, reference Katz's experiment when TTX and TEA were used to block channels and prevent an AP,and the Vm of the presynaptic cell was controlled experimentally. They showed that the amount of transmitter release varied directly with the amount of depolarization that occured
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does NT release depend on the chemical identity of the ions causing the depolarization
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no, release will occur in proportion to depolarization reguarless of how it occurs
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Describe how the concentration of calcium must change over an action potential and release of an NT
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In order for the NT to be released,, the concentration of calcium in the presynaptic terminal must rise after the action potention, in order for the synapse to transmitt signals at high frequency the terminal must return to resting state quickly after NT release so the [Ca] must be brough back down
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List the 4 steps invovled in NT vesicle exocytosis
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1. vesicle moves to the active zone
2. proteins attach the vesicle to the active zone 3. SNARE proteins dock vesicle to membrane 4. fustion between vesicle and membrane when [Ca2+] increases |
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what is nonspiking release?
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Some neurons never carry APs but rather release NTs in response to electrotronic voltage signals, the amount of NT released depends on Vm which controls the activity of the voltage gated Ca2+ channels
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what are some benefits of electrical synaptic transmission
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fast, faithful, bidrectional, used when many cells need to fire synchronously such as in cardiac muscle
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How is calcium able to move into the presynaptic cell and assist with NT release
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the action potential generated in the presynaptic cell moves to the nerve terminal and opens the voltage gated calcium channels
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how do NTs travel across the synaptic clef?
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diffusion
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What does binding of an NT to a post synaptic membrane generate
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an ipsp or an epsp, may or may not cause an action potential
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How can a neurotransmitter be removed from the synaptic clef
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enzymes, transport proteins that take it back into the presynaptic cell, degradation by glial cells
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what proteins are responsible for trafficking NTs to the active zone
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actin and myosin
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Compare and contrast how fast and slow chemical synapses open the ion channels
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fast synapses open the channes directly because they are ligand gated, slow synpases open the channels via 2nd messenger action (phosphorylation of the channel, transcription factor changes synthesis of ion channel protein, etc)
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How do the signaling molecules differ between fast and slow chemical synaptic transmission
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fast- small molecules
slow- large molecules |
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Describe an excitatory synapose
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influx of positive charge depolarizes the membrane, increase of sodium and potassium permeabiltiy or increase of calcium permeabilty in the postsynaptic membrane
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what ions are invovled in inhibitory synapses
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potassium or Cl-
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what propery eventually allows ipsps or epsps to generate action potentials
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summation, the small changes in potential caused by each ipsp or epsp to add up and eventually cross the threshold for generation of an AP
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which Ach receptor causes epp at the neuromuscular junction
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nicotinic
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