```                     Univ. of Illinois, Urbana-Champaign
Bio/Neuro 303

Chapter 8 - Study Questions

260.  One definition for the length (space) constant is the distance

a.  at which the membrane resistance of the neuron has changed to 37% of
its original value.
*b.  at which a voltage imposed at a point has declined to 37% of its value
at the place of origin.
c.  that a synapse can be from the spike initiation zone and still be
effective.
d.  at which an imposed increase in voltage has climbed to 63% of the value
it will eventually reach.

261.  The formula for the space (or length) constant is

a.  = SQRT(ri/rm)
*b.  = SQRT(rm/ri)
c.  = SQRT(cm/rm)
d.  = SQRT(rm/cm)

262.  The space (length) constant will be smaller in neurons with

*a.  smaller membrane resistances.
b.  larger membrane resistances.
c.  smaller internal resistances.
d.  smaller membrane capacitances.

263.  The space (length) constant will be greater in neurons with

a.  smaller membrane resistance.
*b.  larger membrane resistances.
c.  larger internal resistances.
d.  smaller membrane capacitances.

264.  The formula for the time constant is

*a.  = rm x cm
b.  = ri x ci
c.  = rm x ci
d.  = ri x cm

265.  The time constant is

a.  the time during which Na+ channels are inactivated after an AP.
b.  the time one must wait for synaptic facilitation to disappear after a
series of stimulations.
c.  the time for a G protein to act on adenylate cyclase and provoke
delayed actions.
*d.  the time it takes for an EPSP to decay by a certain percentage.

266.  The time constant will be larger in neurons with

a.  smaller membrane resistances.
*b.  larger membrane resistances.
c.  smaller internal resistances.
d.  smaller membrane capacitances.

267.  The time constant will be greater in neurons with

a.  smaller membrane resistances.
*b.  larger membrane resistances.
c.  larger internal resistances.
d.  smaller membrane capacitances.

268.  A dendritic membrane with a large time constant and a small length (space)
constant will allow a post synaptic potential to decay

a.  quickly, but spread relatively far.
b.  quickly, and spread only a short distance.
c.  slowly, and spread relatively far.
*d.  slowly, but spread only a short distance.

269.  In neurons with large dendritic arborizations, if a post synaptic potential
decays quickly and does not spread far, you would expect the cell to have

*a.  small time constant, small space constant.
b.  small time constant, large space constant.
c.  large time constant, small space constant.
d.  large time constant, large space constant.

270.  In neurons with large dendritic arborizations, in order for distant
synapses to have an appreciable effect on the spike initiation zone, you
would expect the cell to have a

a.  small time constant, small space constant.
b.  small time constant, large space constant.
c.  large time constant, small space constant.
*d.  large time constant, large space constant.

271.  A dendritic membrane with a small time constant and a large length (space)
constant will allow a post-synaptic potential to decay

*a.  quickly, but spread relatively far.
b.  quickly, and spread only a short distance.
c.  slowly, and spread relatively far.
d.  slowly, but spread only a short distance.

272.  A dendritic membrane with a small time constant and a small length (space)
constant will allow a post-synaptic potential to decay

a.  quickly, but spread relatively far.
*b.  quickly, and spread only a short distance.
c.  slowly, and spread relatively far.
d.  slowly, but spread only a short distance.

273.  A dendritic membrane with a large time constant and a large length (space)
constant will allow a postsynaptic potential to decay

a.  quickly, but spread relatively far.
b.  quickly, and spread only a short distance.
*c.  slowly, and spread relatively far.
d.  slowly, but spread only a short distance.

274.  The distance over which postsynaptic potentials from one synapse can
interact with those from another via spatial summation is strongly
influenced by

a.  the internal resistance of the axoplasm in the postsynaptic neurite.
b.  the value of the space (length) constant.
c.  the resistance across the membrane of the postsynaptic neurite.
*d.  all of the above.

275.  Spatial summation is made possible by

*a.  the fact that postsynaptic potentials spread some distance from their
point of origin.
b.  the fact that postsynaptic potentials last some time after their
instant of generation.
c.  the increase in size of postsynaptic potentials in a series.
d.  the nature of the ion channels that open at the synapse.

276.  The distance over which postsynaptic potentials from one synapse can
interact with those from another via spatial summation is strongly
influenced by the

*a.  value of the space constant.
b.  number of synaptic contacts made on the postsynaptic neuron.
c.  ratio of excitatory to inhibitory synapses.
d.  identity of the transmitter substance used.

277.  Temporal summation is made possible by

a.  the fact that postsynaptic potentials spread some distance form their
point of origin.
*b.  the fact that postsynaptic potentials last some time after their
instant of generation.
c.  the increase in size of postsynaptic potentials in a series.
d.  the nature of the ion channels that open at the synapse.

278.  A definition of facilitation is

a.  the increase in size of successive action potentials in a series.
*b.  the increase in size of successive postsynaptic responses in a series.
c.  the decrease in size of successive postsynaptic responses in a series.
d.  the summation of successive postsynaptic responses in a series.

279.  Facilitation is

*a.  the increase in the size of successive postsynaptic potentials in a
series.
b.  the increased ease of passage of action potentials in often-used
synapses.
c.  the greater liability to inhibition in often-used synapses.
d.  the increased size of successive action potentials in a series.

280.  Facilitation can often be linked to a build-up of

a.  Na+ in the presynaptic terminal.
b.  Na+ in the postsynaptic neuron.
*c.  Ca2+ in the presynaptic terminal.
d.  Ca2+ in the postsynaptic neuron.

281.  Facilitation at some neuromuscular junctions has been shown to be a
function of the amount of external ______ available at the junction.

a.  sodium
b.  chloride
c.  potassium
*d.  calcium

282.  Reducing the concentration of external calcium at a facilitating synapse
will

a.  increase the magnitude of facilitation.
b.  reduce the size of the presynaptic action potential and therefore of
the postsynaptic response.
c.  reduce the size of the postsynaptic spike.
*d.  reduce or eliminate the postsynaptic facilitation.

283.  Slightly reducing the concentration of external calcium at some
non-facilitating synapses will

a.  prevent all synaptic transmission.
b.  reduce the size of the postsynaptic spike.
c.  reduce the size of the presynaptic spike.
*d.  turn them into facilitating synapses.

284.  Posttetanic potentiation is a type of facilitation in which

a.  several synapses are involved.
*b.  the facilitated effect may last for many minutes.
c.  muscle is involved.
d.  many hours of training are required for its effects to become visible.

285.  One factor common to all types of facilitation is

a.  the morphology of the synapse at which it occurs.
b.  the long time necessary in order to evoke it.
c.  the pairing of two different stimuli.
*d.  an increase in size of a postsynaptic potential.

286.  All types of facilitation seem to be dependent on the availability of
sufficient amounts of

*a.  Ca2+.
b.  Na+.
c.  K+.
d.  Cl-.

287.  Heterosynaptic facilitation in Aplysia is thought to be due to

*a.  an excitatory presynaptic mechanism.
b.  an inhibitory presynaptic mechanism.
c.  a dual excitatory-inhibitory postsynaptic mechanism.
d.  a dual inhibitory postsynaptic mechanism.

288.  Heterosynaptic facilitation is

*a.  the facilitation of spikes involving two different synapses.
b.  facilitation of slow muscle activity as a consequence of firing a fast
axon in polyneuronally innervated muscle.
c.  known to be the basis of habituation in Aplysia, the sea hare.
d.  a type of facilitation found only at sensory motor synapses.

289.  In heterosynaptic facilitation

a.  the test stimulus must be paired with two separate priming stimuli in
order for facilitation to appear.
b.  the test and priming stimuli must be separated by many minutes (priming
first) in order for facilitation to appear.
*c.  the test and priming stimuli must be closely paired (priming first) in
order for facilitation to appear.
d.  the priming stimulus can always elicit facilitation even when not
paired with the test stimulus.

290.  In heterosynaptic facilitation, the train of "priming" stimuli

a.  increases the number of functional ion channels in the postsynaptic
neuron, so that a "test" stimulus creates a larger epsp in it.
*b.  causes an increase in the  amount of transmitter released when the
"test" stimulus is applied.
c.  activates protein kinases so that more second messenger is available
for the response in the postsynaptic cell.
d.  none of the above.

291.  Heterosynaptic facilitation in Aplysia is thought to be due to

*a.  an excitatory presynaptic mechanism.
b.  an inhibitory presynaptic mechanism.
c.  a dual excitatory-inhibitory mechanism.
d.  the interaction of neurons from within a single ganglion only.

292.  N-methyl-D-aspartate (NMDA) receptors involved in long term potentiation
(LTP)

a.  are activated by the neuromodulator serotonin.
*b.  can be blocked by Mg2+ ions.
c.  allow the entry of glutamate into the postsynaptic neuron.
d.  all of the above.

293.  Which of the following synaptic effects has NOT been described for the L10
cell in Aplysia?

a.  Excitation, mediated by Na+ influx.
b.  Dual excitation-inhibition, mediated by Na+ and Cl- influx.
*c.  Inhibition, mediated by a reduction of Na+ influx.
d.  Inhibition, mediated by Cl- influx.

294.  One of the synapses from Aplysia cell L10 is dual excitatory-inhibitory.
The ionic bases of these effects are the movement of ______ for the
excitatory, ______ for the inhibitory function.

a.  potassium; potassium
b.  potassium; chloride
*c.  sodium; chloride
d.  sodium; potassium

295.  The dual excitatory/inhibitory synapse of L10 in Aplysia is said to be
frequency sensitive because

a.  homosynaptic facilitation works at high frequencies but not low ones.
*b.  high frequency stimulation has a predominantly inhibitory effect while
low frequency stimulation has a predominantly stimulatory one.
c.  low frequency stimulation has a predominantly inhibitory effect while
high frequency stimulation has a predominantly stimulatory one.
d.  the synapse is active only at low frequencies of stimulation, due to
depletion of the transmitter substance at high frequencies.

296.  A dual function excitatory/inhibitory synapse of the L10 cell in
Aplysia is stimulated at high frequency.  The response of
the postsynaptic cell

a.  is an inhibition followed by an excitation.
*b.  is an excitation followed by an inhibition.
c.  does not depend on the frequency but on the amount of transmitter
released by each presynaptic action potential.
d.  is a prolonged excitation because large amounts of Na+ have entered the
cell.

297.  The importance for integration in Aplysia of the dual inhibitory synapse
formed by cell L10 is that it shows

a.  the versatility of ionic mechanisms for a single synaptic effect.
b.  the conservation of transmitter substance, since only a single
transmitter is used.
*c.  how at a single synapse, different postsynaptic effects can be brought
about by different frequencies of input.
d.  how biologically meaningful decisions can be made without reference to
any external stimulus.

298.  The functional role of the dual excitation/inhibition synapse between
Aplysia cell L10 and one of its follower cells seems to be to

a.  save the metabolic expense of having to make more than one transmitter
substance.
*b.  allow the animal to generate different responses to inputs that differ
in frequency.
c.  ensure that the animal notices inputs of different intensities.
d.  take advantage of the ability of a single transmitter substance to
activate different channels.

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