CH7: escape behavior in crayfish behavior features & functional anatomy neuronal architecture
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Transcript of CH7: escape behavior in crayfish behavior features & functional anatomy neuronal architecture
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CH7: escape behavior in crayfish
behavior features & functional anatomy
neuronal architecture
adaptive modulation
summary: chapter 7
PART 3: MOTOR STRATEGIES#15: ESCAPE BEHAVIOR IN CRAYFISH
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walking is normal mode of locomotion integrated motor escape response tail flip tail propulsion using flexor & extensor muscles
BEHAVIOR & FUNCTIONAL ANATOMY
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nongiant slower
medial giant: anterior stimulus move back rapid
lateral giant: tail stimulus move up & back rapid
3 types of tail flip response
BEHAVIOR & FUNCTIONAL ANATOMY
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tail flip can be elicited by electrical stimulus tactile stimulus
responses are comparable triggers initiate complex motor sequences
BEHAVIOR & FUNCTIONAL ANATOMY
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typical invertebrate CNS plan (ganglia + connectives) brain SOG complex 5 thoracic ganglia 6 abdominal ganglia... contain tail flip circuitry
ganglia communicate & are coordinated via connectives peripheral comm. via roots
1: swimmerets 2: extensors 3: flexors (motor only)
NEURONAL ARCHITECTURE
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2 pairs of prominent giant axons lateral giant interneurons (LGI)
cell bodies & dendrites in each abd. segment electrical synapses (septate / segmental) axons project next segment lateral giant escape
medial giant intern. (MGI) cell bodies & dendrites in brain ~ single fast neuron medial giant escape
NEURONAL ARCHITECTURE
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giant interneurons motor giant neurons (MoGs) MoGs flexor muscles sensory input to:
head MGI
all MoGs tail LGI
1-3 MoGs focus on LGls
NEURONAL ARCHITECTURE
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LGI tail flip circuitry sensory input: ~1000 hairs with sensory neurons sensory interneurons: LGIs & brain
A: phasic C: tonic
LGIs
NEURONAL ARCHITECTURE
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LGI tail flip circuitry sensory input: ~1000 hairs with sensory neurons sensory interneurons: LGIs & brain
A: phasic C: tonic
LGIs MoGs
NEURONAL ARCHITECTURE
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LGI tail flip circuitry sensory input: ~1000 hairs with sensory neurons sensory interneurons: LGIs & brain
A: phasic C: tonic
LGIs MoGs flexor muscles:
5 / segment + other input
NEURONAL ARCHITECTURE
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chemical synapses (slow) at input & output electrical synapses (fast) elsewhere sensory LGI
directly () short latency indirectly () long latency
NEURONAL ARCHITECTURE
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chemical synapses (slow) at input & output electrical synapses (fast) elsewhere sensory LGI
directly () short latency indirectly () long latency
sensory influence fast flexor motor neurons LGI MoGs & segmental giant (SG)... very fast !
NEURONAL ARCHITECTURE
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LGIs SG (electrical)
SGs fast flexor motor neurons (electrical)
NEURONAL ARCHITECTURE
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LGI neurons at center of circuit
convergence of sensory input LGI
divergence of LGI output motor
NEURONAL ARCHITECTURE
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3 components of “flipping out” behavior
rapid flexion of abdomen
re-extension of abdomen
swimming
independent behavior modules
NEURONAL ARCHITECTURE
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LGIs only involved in flexion
2 abdominal sensory input channels
biphasic LGI spike (EPSP)
indirect chemical
direct electrical
NEURONAL ARCHITECTURE
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rapid flexion response to abrupt tail stimulus because sensory - interneuron chemical synapses depress
with prolonged stimuli electrical synapses LGI
have high threshold & short
time constants sensory input presynaptic
LGI inhibition
NEURONAL ARCHITECTURE
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2 pathways from LGI (elect) MoG (chem) flexor muscles SG (elect) FFs (chem) flexor muscles
FFs threshold below that of signal from SG... no delay in signal
NEURONAL ARCHITECTURE
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LGI fast speed from large diameter axons electrical synapses
LGI sufficient & necessary for tail flip response ?
NEURONAL ARCHITECTURE
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necessary: sever MoG* stimulate tail flip hyperpolarize LGI measure severed MoG output
LGI sufficient & necessary for tail flip response...
“command neurons”
sufficient: inject current tail flip
NEURONAL ARCHITECTURE
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LGI makes all-or-nothing decision to escape ? what about upstream sensory decision ? ... graded, not all-or-none synaptic input together... explains why there is no partial tail flip
NEURONAL ARCHITECTURE
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no single LGI satisfied criteria they are in series, linked abdominal segments act as functional unit
command neuron firing or stimulation elicits complex behavior... eg, coordinated / rhythmic appendage movement
criteria: neuron should demonstrate activity necessary & sufficient to elicit behavior normal response to sensory stimulus normal pattern of activitation
NEURONAL ARCHITECTURE
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LGI inhibitory signals: “command-derived inhibition” ensures that additional flexor responses do not occur
NEURONAL ARCHITECTURE
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LGI inhibitory signals: “command-derived inhibition” ensures that additional flexor responses do not occur
LGI spikes inhibit further LGI & MGI spikes sensory, LGIs, MoGs & muscles inhibited
NEURONAL ARCHITECTURE
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further inhibition of
extension
slow flexor and slow extensor systems
widespread inhibitory influence
critical timing (details... )
every level of tail flip circuitry
NEURONAL ARCHITECTURE
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read and be sure you understand text sections on
re-extension
swimming
problems... journal questions
NEURONAL ARCHITECTURE
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other influences on tail flip responses ?
does not always work
modulated by
restraint-induced inhibition
motivation (feeding)
learning
ADAPTIVE MODULATION
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blocked by nerve cord transection
decreased facilitation of reflex
increased inhibition at higher
levels
voluntary tail flip remains
restraint-induced inhibition
ADAPTIVE MODULATION
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cut nerve cord
abolishes feeding-
induced increase
must be eating to
influence response
motivational modulation of escape behavior
feeding raises threshold of tail flip response
ADAPTIVE MODULATION
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feeding modulates LGI
firing only
degree of inhibition
relative to stimulus
“competition”
ADAPTIVE MODULATION
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modulation of escape behavior by learning repetition... what is important & what is not habituation: reduced response with repeated stimuli self-induced habituation by water movement ? prevented by command-derived inhibition
ADAPTIVE MODULATION
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anterior tactile stimulus tail flip response mediated by lateral giant interneurons (LGI) sensory hair inputs LGIs sufficient & necessary for response
widespread activation of flexor system command neurons, trigger escape response command-derived inhibition, cancels competing
response, enables subsequent elements
SUMMARY
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command-derived inhibition, cancels competing response, enables subsequent elements
reextension from sensory feedback (reafference), via stretch receptors (muscle receptors, MROs) & sensory hairs on tailfan
swimming from central pattern generator activated by sensory input with prolonged delay
modulated by various influences... restraint, feeding, learning
SUMMARY
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NO CLASS on T.3.20
SECTION 3 REVIEW on R.3.22
2nd MIDTERM EXAM:
written, 15% of final grade
ASSIGNED (web page) @ 6 pm T.3.27
DUE (eMail) @ 3 pm R.3.29
NEUROBIOLOGY CALENDAR