exam 1 CH6: flight in locusts locust flight flight system sensory integration during flight

PART 3: MOTOR STRATEGIES #13: FLIGHT IN LOCUSTS I • exam 1 • CH6: flight in locusts • locust flight • flight system • sensory integration during flight • summary

LOCUST FLIGHT • locusts can sustain flight for hours  100s of miles • phytophageous – eat living plants • travel in swarms & strip vegetation • order: Orthoptera • family: Acrididae • > 1200 spp. • research: large tropical / subtr. spp. • Schistocerca gregaria* • Locusta migratoria

LOCUST FLIGHT • 2 main problems associated with locust flight • coordinated rhythmic wing beat • course control

BEHAVIOR • tethered locust flight • triggered by wind (receptors on head)... later • measure everything... to study flight motor behavior • lift • body position • wing position • muscle recording

BEHAVIOR • tethered fly flight

ANATOMY • 2 prs of wings... • 2 sets of flight muscles... • 2nd & 3rd thoracic segments

BEHAVIOR • wing beat stable • ~ 20 Hz, cycle 50 ms • ~ 7 ms out of phase • hindwing > forewing

BEHAVIOR • complex pattern • up (elevation) & down (depression) • back & forth  pronate • can vary angle of attack rather than wing beat

ANATOMY • 10 muscle prs / wing • 4 depressors... activated at top of stroke • 6 elevators... activated at bottom of stroke • hind 1st ... fore 2nd • subtle timing differences • cuticle flexibility important

FLIGHT SYSTEM • Schistocerca gregariaCNS • brain • S1-3 • T1-3 • A1-11

FLIGHT SYSTEM • Schistocerca gregariaCNS... flight-relevant bits... • brain • S1-3 • T1-3 • pro • meso • meta • A1-11

FLIGHT SYSTEM • 1 – 5 motor neurons drive each muscle •  10 muscles / wing • ~ few neurons

CENTRAL PATTERN GENERATOR • old idea... sensory input leads to motor output (eg, reflexes such as knee-jerk) • if so... how does rhythmic behavior occur (eg ,flight)? • proprioceptive feedback to CNS: • information about internal state • monitored by receptors (eg, posture in humans)

CENTRAL PATTERN GENERATOR • proprioception in rhythmic movement • triggered by preceding component of movement • eg, backward swing of leg (R2)  proprioceptive sensory signal (S1)  forward swing (R1)... etc • chain reflex or peripheral-control hypotheses: • sensory feedback critical for rhythmic behavior

CENTRAL PATTERN GENERATOR • proprioception in locust flight ? • 3 classes of proprioceptors • wing hinge stretch receptors:  wing  • tegula:  wing  • campaniform sensilla: on wing veins,  by force of lift as wing 

CENTRAL PATTERN GENERATOR • proprioception in locust flight ? • sufficient receptors to explain chain reflex mechanism for flight • once triggered, keeps going because of proprioception • does this happen?

CENTRAL PATTERN GENERATOR • proprioception in locust flight ? • cut sensory nerves between wings & thorax (deafferentation).. • tethered flight • air to head • normal flight pattern • ½ frequency (10 Hz) • some form of central pattern generator in CNS

CENTRAL PATTERN GENERATOR • proprioception in locust flight ? • cut sensory nerves between wings & thorax (deafferentation) • later showed normal • muscle action potentials • CNS motor neuron output • stimulation of sensory nerves  wing beat freq  normal • not ~ phase !

CENTRAL PATTERN GENERATOR • conclusions: proprioceptive feedback... • modulates average activity level of central pattern generator • not needed for basic pattern

CELLULAR ORGANIZATION • small # of motor neurons for each muscle... •  measure EMG of muscles to estimate action potentials of innervating neurons • recordings with 14 electrodes in flight muscles during flight • revealed fundamental features of normal flight

CELLULAR ORGANIZATION • features of normal flight: • elevators & depressors of wing activated by alternating 20 Hz bursts • elevators & depressors of opposing wings synchronous • hindwing depressors active ~ 5 ms before forewing • ~ motor neurons

CELLULAR ORGANIZATION • is a neuron part of the pattern generator?... test with reset experiment... • if YES... depolarizing neuron (injecting current) should rest rhythm of behavior / muscle contraction • if NO... may only receive signals from pattern generator

CELLULAR ORGANIZATION • conducted reset experiment with ~ 80 motor neurons • none showed reset...  not pattern generator • fig. 6.10a shows normal • firing of motor neurons (top) • recordings from muscles (bottom)

CELLULAR ORGANIZATION • what about interneurons? • 3 goals achieved: • reset experiments • inject current & record from other neurons • fill with dye to follow patterns of innervation

CELLULAR ORGANIZATION • what about interneurons? • bilateral pairs in thoracic ganglia • extensive branching... as might be expected ~ motor control

CELLULAR ORGANIZATION • reset experiment with interneurons... • several showed reset...  pattern generator ! • fig. 6.10b shows normal • phasic firing of interneurons (IN301 & IN511) • recordings from muscles (M112)

CELLULAR ORGANIZATION • reset experiment with interneurons... • several showed reset...  pattern generator ! • fig. 6.10b shows normal • phasic firing of interneurons (top) • recordings from muscles (bottom) • further studies showed flight rhythm from excitatory & inhibitory activity within the network  motor neurons

CELLULAR ORGANIZATION • rhythm from excitatory & inhibitory activity within the network  motor neurons • IN504 EPSP  IN301 • IN301 IPSP  IN511 • IN301 EPSP*  IN501 • IN501 IPSP  IN301 • delay suggests additional intercalating interneuron

CELLULAR ORGANIZATION • connectivity among flight interneurons complex • how do circuits  rhythmic output ? • focus on simple part of circuit • IN301 fires... excites IN501 • IN501 fires... inhibits IN301 • delay • something excites IN301 • oscillatory properties

CELLULAR ORGANIZATION • reset of IN501... part of the pattern generator ? • depolarization • shifts IN501 spiking • shifts muscle activity

CELLULAR ORGANIZATION • IN301 & IN501... 2 of the known parts of the pattern generator

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exam 1 CH6: flight in locusts locust flight flight system sensory integration during flight