Transcript central pattern generator

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 gregaria CNS
 brain
 S1-3
 T1-3
 A1-11
FLIGHT SYSTEM
 Schistocerca gregaria CNS
 brain
 S1-3
 T1-3
 A1-11
FLIGHT SYSTEM
 Schistocerca gregaria CNS... flight-relevant bits...
 brain
 S1-3
 T1-3
 pro
 meso
 meta
 A1-11
FLIGHT SYSTEM
 Schistocerca gregaria CNS... 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
BREAK