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

walking is normal mode of locomotion integrated motor escape response tail flip tail propulsion using flexor & extensor muscles

BEHAVIOR & FUNCTIONAL ANATOMY

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

tail flip can be elicited by electrical stimulus tactile stimulus

responses are comparable triggers initiate complex motor sequences

BEHAVIOR & FUNCTIONAL ANATOMY

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

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

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

LGI tail flip circuitry sensory input: ~1000 hairs with sensory neurons sensory interneurons: LGIs & brain

A: phasic C: tonic

LGIs

NEURONAL ARCHITECTURE

LGI tail flip circuitry sensory input: ~1000 hairs with sensory neurons sensory interneurons: LGIs & brain

A: phasic C: tonic

LGIs MoGs

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

NEURONAL ARCHITECTURE

chemical synapses (slow) at input & output electrical synapses (fast) elsewhere sensory LGI

directly () short latency indirectly () long latency

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 !

NEURONAL ARCHITECTURE

LGIs SG (electrical)

SGs fast flexor motor neurons (electrical)

NEURONAL ARCHITECTURE

LGI neurons at center of circuit

convergence of sensory input LGI

divergence of LGI output motor

NEURONAL ARCHITECTURE

3 components of “flipping out” behavior

rapid flexion of abdomen

re-extension of abdomen

swimming

independent behavior modules

NEURONAL ARCHITECTURE

LGIs only involved in flexion

2 abdominal sensory input channels

biphasic LGI spike (EPSP)

indirect chemical

direct electrical

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

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

NEURONAL ARCHITECTURE

LGI fast speed from large diameter axons electrical synapses

LGI sufficient & necessary for tail flip response ?

NEURONAL ARCHITECTURE

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

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

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

LGI inhibitory signals: “command-derived inhibition” ensures that additional flexor responses do not occur

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

NEURONAL ARCHITECTURE

further inhibition of

extension

slow flexor and slow extensor systems

widespread inhibitory influence

critical timing (details... )

every level of tail flip circuitry

NEURONAL ARCHITECTURE

read and be sure you understand text sections on

re-extension

swimming

problems... journal questions

NEURONAL ARCHITECTURE

other influences on tail flip responses ?

does not always work

modulated by

restraint-induced inhibition

motivation (feeding)

learning

ADAPTIVE MODULATION

blocked by nerve cord transection

decreased facilitation of reflex

increased inhibition at higher

levels

voluntary tail flip remains

restraint-induced inhibition

ADAPTIVE MODULATION

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

feeding modulates LGI

firing only

degree of inhibition

relative to stimulus

“competition”

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

ADAPTIVE MODULATION

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

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

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

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