CH7: escape behavior in crayfish behavior features & functional anatomy neuronal architecture

1. PART 3: MOTOR STRATEGIES #15: ESCAPE BEHAVIOR IN CRAYFISH • CH7: escape behavior in crayfish • behavior features & functional anatomy • neuronal architecture • adaptive modulation • summary: chapter 7

2. BEHAVIOR & FUNCTIONAL ANATOMY • walking is normal mode of locomotion • integrated motor escape response  tail flip • tail propulsion using flexor & extensor muscles

3. BEHAVIOR & FUNCTIONAL ANATOMY • lateral giant: • tail stimulus • move up & back • rapid • 3 types of tail flip response • medial giant: • anterior stimulus • move back • rapid • nongiant • slower

4. BEHAVIOR & FUNCTIONAL ANATOMY • tail flip can be elicited by • electrical stimulus • tactile stimulus • responses are comparable • triggers initiate complex motor sequences

5. NEURONAL ARCHITECTURE • 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)

6. NEURONAL ARCHITECTURE • 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

7. NEURONAL ARCHITECTURE • giant interneurons  motor giant neurons (MoGs) • MoGs  flexor muscles • sensory input to: • head  MGI  all MoGs • tail  LGI  1-3 MoGs • focus on LGls

8. NEURONAL ARCHITECTURE • LGI tail flip circuitry • sensory input: ~1000 hairs with sensory neurons • sensory interneurons:  LGIs & brain • A: phasic • C: tonic • LGIs

9. NEURONAL ARCHITECTURE • LGI tail flip circuitry • sensory input: ~1000 hairs with sensory neurons • sensory interneurons:  LGIs & brain • A: phasic • C: tonic • LGIs • MoGs

10. NEURONAL ARCHITECTURE • 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

11. NEURONAL ARCHITECTURE • chemical synapses (slow) at input & output • electrical synapses (fast) elsewhere • sensory  LGI • directly () short latency • indirectly () long latency

12. NEURONAL ARCHITECTURE • 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 !

13. NEURONAL ARCHITECTURE • LGIs  SG (electrical) • SGs  fast flexor motor neurons (electrical)

14. NEURONAL ARCHITECTURE • LGI neurons at center of circuit • convergence of sensory input  LGI • divergence of LGI output  motor

15. NEURONAL ARCHITECTURE • 3 components of “flipping out” behavior • rapid flexion of abdomen • re-extension of abdomen • swimming • independent behavior modules

16. NEURONAL ARCHITECTURE • LGIs only involved in flexion • 2 abdominal sensory input channels •  biphasic LGI spike (EPSP) • indirect chemical • direct electrical

17. NEURONAL ARCHITECTURE • 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

18. NEURONAL ARCHITECTURE • 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

19. NEURONAL ARCHITECTURE • LGI fast speed from • large diameter axons • electrical synapses • LGI sufficient & necessary for tail flip response ?

20. NEURONAL ARCHITECTURE • LGI sufficient & necessary for tail flip response... • sufficient: • inject current •  tail flip • necessary: • sever MoG* • stimulate tail flip • hyperpolarize LGI • measure severed MoG output •  “command neurons”

21. NEURONAL ARCHITECTURE • 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

22. NEURONAL ARCHITECTURE • 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 • no single LGI satisfied criteria • they are in series, linked abdominal segments • act as functional unit

23. NEURONAL ARCHITECTURE • LGI inhibitory signals: “command-derived inhibition” • ensures that additional flexor responses do not occur

24. NEURONAL ARCHITECTURE • 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

25. NEURONAL ARCHITECTURE • further inhibition of • extension • slow flexor and slow extensor systems • widespread inhibitory influence • critical timing (details... ) • every level of tail flip circuitry

26. NEURONAL ARCHITECTURE • read and be sure you understand text sections on • re-extension • swimming • problems... journal questions

27. ADAPTIVE MODULATION • other influences on tail flip responses ? • does not always work • modulated by • restraint-induced inhibition • motivation (feeding) • learning

28. ADAPTIVE MODULATION • restraint-induced inhibition • blocked by nerve cord transection • decreased facilitation of reflex • increased inhibition at higher levels • voluntary tail flip remains

29. ADAPTIVE MODULATION • motivational modulation of escape behavior • feeding raises threshold of tail flip response • must be eating to influence response • cut nerve cord abolishes feeding- induced increase

30. ADAPTIVE MODULATION • feeding modulates LGI firing only • degree of inhibition relative to stimulus • “competition”

31. ADAPTIVE MODULATION • 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

32. SUMMARY • 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

33. SUMMARY • 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

34. NEUROBIOLOGY CALENDAR • 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