Homework attached below
Homework #9 Homework #7 (150 points) Synaptic Transmission & Central Synapses Motor neurons, like other central neurons, receive both excitatory and inhibitory inputs from a variety of sources, such as sensory neurons, spinal interneurons, and descending inputs from higher brain centers. Integration of the postsynaptic potentials (PSPs) at the trigger zone in motor neurons determines their level of activity (number and frequency of action potentials), and consequently the level of activity in the muscle they innervate. This question is meant to help you consider the relative effectiveness of excitatory and inhibitory synapses located on either the dendrites or soma/trigger zone of a neuron. Imagine a cell receives both excitatory and inhibitory input and has a threshold 15mV above Vrest. Activation of either type of synapse alone results in a PSP of 1mV (either a 1mV EPSP, or 1mV IPSP) at the synapse, and activation of 2 excitatory or 2 inhibitory synapses together results in a composite PSP of 2mV. Synapses on the dendrites are located 1 λ from the soma/trigger zone. 1) (10 pts) What would be the change in membrane potential (∆Vm) be at the soma, if you activated each of the following? • 1 excitatory synapse on the dendrite by itself? • 1 inhibitory synapse on the soma by itself? • 1 excitatory and one inhibitory synapse on the dendrite together? • 1 inhibitory synapse on the dendrite and excitatory synapse on the soma? • 2 excitatory synapses on the dendrite and 1 inhibitory synapse on the soma? Match each with the appropriate value: 0mV, 0.37 mV, 0.63 mV, 0.74 mV, 1 mV, 1.26 mV, 1.33 mV, 1.67 mV, 2 mV, -0.26 mV, -0.37 mV, -0.63 mV, -0.74 mV, -1mV, -1.26 mV 2) Synapses on the soma of neurons are most often inhibitory. Based on your answers above, why do you think that might be? This arrangement means that inhibition at the soma (close to the trigger zone) would be (least effective, most effective, not different in effectiveness). They would therefore would exert ____ (a greater, a lesser, no difference in) effect in regulating neuronal activity as inputs on dendrites. (5 points) a) least effective; a greater b) least effective; a lesser c) least effective; no difference in d) most effective; a greater e) most effective; a lesser f) most effective; no difference in g) not different in effectiveness; a greater h) not different in effectiveness; a lesser i) not different in effectiveness; no difference in 3) How much would the membrane potential change at the trigger zone, if a motor neuron receives 50 excitatory inputs on its dendrites, and 10 inhibitory inputs on the trigger zone? I.e., what is the combined effects of these inputs? (Fill-in-the-blank: answer to one decimal place; include units.) (5 pts) 4) How much would the membrane potential change at the trigger zone, if you were to block the inhibitory inputs? I.e., indicate the change with only excitatory inputs - NOT how much you’d lose by removing inhibitory inputs.) (Fill-in-the-blank: to one decimal place, and include units.) (5 pts) 5) Why would decreasing inhibition lead to increased muscle contraction? (Assume there is tonic, background excitation occurring in the muscle.) Decreasing the inhibition onto the motor neuron would allow the motor neuron to be _________ (less, more, just as) active; it would therefore activate the muscle _________ (less, more, just as). (5 points) a) less; less b) less; more c) less; just as d) more; less e) more; more f) more; just as g) just as; less h) just as; more i) just as; just as Isyn axon axon Stretch of the patellar tendon activates two separate pathways: a monosynaptic pathway and a polysynaptic pathway. The polysynaptic pathway is illustrated below. (Note: flexor motor neuron has some tonic (ongoing, background) level of activity to account for normal level of muscle activity, as shown. Please keep this in mind as you draw the responses you would expect to see in the flexor motor neuron in response to the stretches.) *6) (14 pts) Using the template above, draw the: • response (change in Vm) you would expect to observe in the axon of the interneuron for a higher amplitude of stretch (B); your drawing should be relative to the activity shown for stretch ‘A’. • calcium current (ICa) you would expect to observe in the presynaptic terminal of the interneuron to lower (A) and higher (B) amplitudes of stretch. (For the current, I am interested in the direction, and relative amplitude and duration for A versus B.) • synaptic current (Isyn) you would expect to observe in the input region of the flexor motor neuron to the lower (A) and higher (B) amplitudes of stretch. (For the current, I am interested in the direction, and relative amplitude and duration for A versus B.) • response (change in Vm) you would expect to observe in axon of the motor neuron to the lower (A) and higher (B) amplitudes of stretch. A B<- tonic activity in motor neuron before stretch ia afferent in extensor muscle interneuron flexor motor neuron flexor muscle ica 0 na -65mv vm 1msec +10mv ica vpsp a vrest 7) would you expect the level of activity in the muscle to change (from the background level of activity) with the 2 intensities of stretch? (5 points) a) yes. there would be less inhibitory neurotransmitter released with the larger stretch, since the inhibitory interneuron would be activated less. b) yes. there would be less inhibitory neurotransmitter released with the larger stretch, since the inhibitory interneuron would be activated more. c) yes. there would be more inhibitory neurotransmitter released with the larger stretch, since the inhibitory interneuron would be activated less. d) yes. there would be more inhibitory neurotransmitter released with the larger stretch, since the inhibitory interneuron would be activated more. e) no. there would be no change in inhibitory neurotransmitter released with the larger stretch. 8) if you stretched the flexor muscle, would you excite or inhibit the flexor motor neuron, and the flexor muscle? the flexor motor neuron would be _______ (excited, inhibited) and the flexor muscle would be_______ (excited, inhibited). (5 points) a) excited, excited b) excited, inhibited c) inhibited, excited d) inhibited, inhibited *9) an action potential in a ia sensory neuron produces an excitatory postsynaptic potential (epsp) in the agonist motor neuron, as shown below. a) imagine the presynaptic terminal of the ia afferent is treated with ttx and tea, and then voltage-clamped to +10mv. draw the calcium current (ica) you would expect to record in the presynaptic terminal of the ia afferent and any change in membrane potential that would result (vpsp) in the input region of the motor neuron. (consider: under what condition do these channels close?) (10pts) 1 msec 0 na -65mv vm 1msec -30mv ica vpsp a vrest b) imagine the presynaptic terminal of the ia afferent is treated with ttx and tea, and then voltage-clamped to -30mv. draw the calcium current (ica) you would expect to record in the presynaptic terminal of the ia afferent and any change in membrane potential that would result (vpsp) in the motor neuron. (10pts) the following questions also refer to the stretch reflex circuit. 10) imagine you were to use curare to block nicotinic acetylcholine-gated receptors. would there be any effect on the activity in either the monosynaptic or polysynaptic components of the stretch reflex when the muscle is stretched, as compared to when the muscle is stretched without curare present? (in answering this question, just consider the components in the stretch reflex, including the muscle) (6 points) a) no, curare would not have any effect on the components in either the monosynaptic or polysynaptic stretch reflex circuit. b) yes, curare would cause a decrease in the activity of one or more components in the monosynaptic stretch reflex circuit(s). c) yes, curare would cause a decrease in the activity of one or more components in the polysynaptic stretch reflex circuit(s). d) yes, curare would cause a decrease in the activity of one or more components in the both stretch reflex circuit(s). e) yes, curare would cause a an increase in the activity of one or more components in the monosynaptic stretch reflex circuit(s). f) yes, curare would cause an increase in the activity of one or more components in the polysynaptic stretch reflex circuit(s). g) yes, curare would cause an increase in the activity of one or more components in the both stretch reflex circuit(s). 11) would there be any change in muscle activity in the agonist muscle with curare? (4 pts) a) no. b) yes, decrease. c) yes, increase. 12) would there be any change in muscle activity in the antagonist muscle with curare? (4 pts) a) no. b) yes, decrease. c) yes, increase. 13) imagine you were to block glycine receptors, for example with strychnine. would there be any effect on the activity in either the monosynaptic or polysynaptic components of the stretch reflex when the muscle is stretched, as compared to when the muscle is stretched without the glycine receptors being blocked? (in answering this question, just consider the components in the stretch reflex, including the muscle.) (6 points) a) no, strychine would not have any effect on the components in either the monosynaptic or polysynaptic stretch reflex circuit(s). b) yes, strychine would cause a decrease in the activity of one or more components in the monosynaptic stretch reflex circuit(s). c) yes, strychine would cause a decrease in the activity of one or more components in the polysynaptic stretch reflex circuit(s). d) yes, strychine tonic="" activity="" in="" motor="" neuron="" before="" stretch="" ia="" afferent="" in="" extensor="" muscle="" interneuron="" flexor="" motor="" neuron="" flexor="" muscle="" ica="" 0="" na="" -65mv="" vm="" 1msec="" +10mv="" ica="" vpsp="" a="" vrest="" 7)="" would="" you="" expect="" the="" level="" of="" activity="" in="" the="" muscle="" to="" change="" (from="" the="" background="" level="" of="" activity)="" with="" the="" 2="" intensities="" of="" stretch?="" (5="" points)="" a)="" yes.="" there="" would="" be="" less="" inhibitory="" neurotransmitter="" released="" with="" the="" larger="" stretch,="" since="" the="" inhibitory="" interneuron="" would="" be="" activated="" less.="" b)="" yes.="" there="" would="" be="" less="" inhibitory="" neurotransmitter="" released="" with="" the="" larger="" stretch,="" since="" the="" inhibitory="" interneuron="" would="" be="" activated="" more.="" c)="" yes.="" there="" would="" be="" more="" inhibitory="" neurotransmitter="" released="" with="" the="" larger="" stretch,="" since="" the="" inhibitory="" interneuron="" would="" be="" activated="" less.="" d)="" yes.="" there="" would="" be="" more="" inhibitory="" neurotransmitter="" released="" with="" the="" larger="" stretch,="" since="" the="" inhibitory="" interneuron="" would="" be="" activated="" more.="" e)="" no.="" there="" would="" be="" no="" change="" in="" inhibitory="" neurotransmitter="" released="" with="" the="" larger="" stretch.="" 8)="" if="" you="" stretched="" the="" flexor="" muscle,="" would="" you="" excite="" or="" inhibit="" the="" flexor="" motor="" neuron,="" and="" the="" flexor="" muscle?="" the="" flexor="" motor="" neuron="" would="" be="" _______="" (excited,="" inhibited)="" and="" the="" flexor="" muscle="" would="" be_______="" (excited,="" inhibited).="" (5="" points)="" a)="" excited,="" excited="" b)="" excited,="" inhibited="" c)="" inhibited,="" excited="" d)="" inhibited,="" inhibited="" *9)="" an="" action="" potential="" in="" a="" ia="" sensory="" neuron="" produces="" an="" excitatory="" postsynaptic="" potential="" (epsp)="" in="" the="" agonist="" motor="" neuron,="" as="" shown="" below.="" a)="" imagine="" the="" presynaptic="" terminal="" of="" the="" ia="" afferent="" is="" treated="" with="" ttx="" and="" tea,="" and="" then="" voltage-clamped="" to="" +10mv.="" draw="" the="" calcium="" current="" (ica)="" you="" would="" expect="" to="" record="" in="" the="" presynaptic="" terminal="" of="" the="" ia="" afferent="" and="" any="" change="" in="" membrane="" potential="" that="" would="" result="" (vpsp)="" in="" the="" input="" region="" of="" the="" motor="" neuron.="" (consider:="" under="" what="" condition="" do="" these="" channels="" close?)="" (10pts)="" 1="" msec="" 0="" na="" -65mv="" vm="" 1msec="" -30mv="" ica="" vpsp="" a="" vrest="" b)="" imagine="" the="" presynaptic="" terminal="" of="" the="" ia="" afferent="" is="" treated="" with="" ttx="" and="" tea,="" and="" then="" voltage-clamped="" to="" -30mv.="" draw="" the="" calcium="" current="" (ica)="" you="" would="" expect="" to="" record="" in="" the="" presynaptic="" terminal="" of="" the="" ia="" afferent="" and="" any="" change="" in="" membrane="" potential="" that="" would="" result="" (vpsp)="" in="" the="" motor="" neuron.="" (10pts)="" the="" following="" questions="" also="" refer="" to="" the="" stretch="" reflex="" circuit.="" 10)="" imagine="" you="" were="" to="" use="" curare="" to="" block="" nicotinic="" acetylcholine-gated="" receptors.="" would="" there="" be="" any="" effect="" on="" the="" activity="" in="" either="" the="" monosynaptic="" or="" polysynaptic="" components="" of="" the="" stretch="" reflex="" when="" the="" muscle="" is="" stretched,="" as="" compared="" to="" when="" the="" muscle="" is="" stretched="" without="" curare="" present?="" (in="" answering="" this="" question,="" just="" consider="" the="" components="" in="" the="" stretch="" reflex,="" including="" the="" muscle)="" (6="" points)="" a)="" no,="" curare="" would="" not="" have="" any="" effect="" on="" the="" components="" in="" either="" the="" monosynaptic="" or="" polysynaptic="" stretch="" reflex="" circuit.="" b)="" yes,="" curare="" would="" cause="" a="" decrease="" in="" the="" activity="" of="" one="" or="" more="" components="" in="" the="" monosynaptic="" stretch="" reflex="" circuit(s).="" c)="" yes,="" curare="" would="" cause="" a="" decrease="" in="" the="" activity="" of="" one="" or="" more="" components="" in="" the="" polysynaptic="" stretch="" reflex="" circuit(s).="" d)="" yes,="" curare="" would="" cause="" a="" decrease="" in="" the="" activity="" of="" one="" or="" more="" components="" in="" the="" both="" stretch="" reflex="" circuit(s).="" e)="" yes,="" curare="" would="" cause="" a="" an="" increase="" in="" the="" activity="" of="" one="" or="" more="" components="" in="" the="" monosynaptic="" stretch="" reflex="" circuit(s).="" f)="" yes,="" curare="" would="" cause="" an="" increase="" in="" the="" activity="" of="" one="" or="" more="" components="" in="" the="" polysynaptic="" stretch="" reflex="" circuit(s).="" g)="" yes,="" curare="" would="" cause="" an="" increase="" in="" the="" activity="" of="" one="" or="" more="" components="" in="" the="" both="" stretch="" reflex="" circuit(s).="" 11)="" would="" there="" be="" any="" change="" in="" muscle="" activity="" in="" the="" agonist="" muscle="" with="" curare?="" (4="" pts)="" a)="" no.="" b)="" yes,="" decrease.="" c)="" yes,="" increase.="" 12)="" would="" there="" be="" any="" change="" in="" muscle="" activity="" in="" the="" antagonist="" muscle="" with="" curare?="" (4="" pts)="" a)="" no.="" b)="" yes,="" decrease.="" c)="" yes,="" increase.="" 13)="" imagine="" you="" were="" to="" block="" glycine="" receptors,="" for="" example="" with="" strychnine.="" would="" there="" be="" any="" effect="" on="" the="" activity="" in="" either="" the="" monosynaptic="" or="" polysynaptic="" components="" of="" the="" stretch="" reflex="" when="" the="" muscle="" is="" stretched,="" as="" compared="" to="" when="" the="" muscle="" is="" stretched="" without="" the="" glycine="" receptors="" being="" blocked?="" (in="" answering="" this="" question,="" just="" consider="" the="" components="" in="" the="" stretch="" reflex,="" including="" the="" muscle.)="" (6="" points)="" a)="" no,="" strychine="" would="" not="" have="" any="" effect="" on="" the="" components="" in="" either="" the="" monosynaptic="" or="" polysynaptic="" stretch="" reflex="" circuit(s).="" b)="" yes,="" strychine="" would="" cause="" a="" decrease="" in="" the="" activity="" of="" one="" or="" more="" components="" in="" the="" monosynaptic="" stretch="" reflex="" circuit(s).="" c)="" yes,="" strychine="" would="" cause="" a="" decrease="" in="" the="" activity="" of="" one="" or="" more="" components="" in="" the="" polysynaptic="" stretch="" reflex="" circuit(s).="" d)="" yes,="">