Download - Neural circuits
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Neural circuitsLecture 3
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Cellular neuroscience Nerve cells with ion channels and
synapses How do neurons interact? How is activity patterned? How is appropriate activity selected? How is sensory input used? How is motor output coordinated and
generated?
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Why Crayfish? Why escape
behaviour? Simple behaviour
Short duration startle response
simple nervous system
Abdominal ganglia with about 400 neurons
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2 Escape behaviours
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2 Escape behaviours Anterior tap
Goes back All segments
bend Tail tap
Goes up Segments
1-3 bend Differences in physiology match
differences in adaptive behaviour
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Abdominal tap Ventral nerve cord
Contains lateral giant LG Stimulated by tap
LG Causes motoneurons Then muscles to be active
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Neural response
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Neural circuit – anatomy
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Neural circuit - schematic
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Sense organs Tactile hairs
activated by water movement
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Sense organs Excite Sensory
interneuron Direct path () Bi-synaptic path ()
Multiplicity – lowers threshold But with safety
factor
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Abdominal gangliaMGLG
somata neuropil
neurite
Transverse section
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LG to MoG Electrical synapse
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LG Motoneuron path Indirect Chemical
Motoneuron filed with procion yellow
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LG → SG → MN Segmental giant
Prevents LG MG interaction by rectifying electrical synapse between LG and SG
SG provides chemical excitation of flexor motor neurons
SG acts as amplifier
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FF Motoneuron 9 Fast Flexor
motor neurons Individually
identifiable All excited by
LG via SG Rectifying
synapse MG and LG
separated
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LG & motoneurons
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Summary so far Excitatory pathway
sense cell to musclecontraction
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Preventing second escape
Turn off hair cell afferents CDI neurons produce delay and
postsynaptic inhibition of the SI
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Preventing second escape
Turn off hair cell afferents CDI neurons produce delay and
postsynaptic inhibition of the SI CDI neurons produce delay and also
presynaptic inhibition of the receptors
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Inhibition of Posture MRO normally excites extensor
motoneuron and flexor inhibitor MRO turned off twice
Accessory cell Fast extensor
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End of escape Inhibition of the flexion system
FFMN FI
LG spike
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Major features of net Need sensory coincidence to fire LG
Ensures safety if single cell accidentally fires
Lowers behavioural threshold below single neuron threshold (law of averages)
Fast Multiple, parallel pathways Combination of electrical feed-forward
and chemical excitation Chemical allows amplification of signal Chemical allows modulation of pathway
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Other systems Locust & Drosophila jump Cockroach running Fish C-start
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Drosophila
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Rapid activation of GF
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Photoactivation of GF Flies cannot see
http://www.sciencedirect.com/science/ MiamiMultiMediaURL/B6WSN-4FWM4P4-J/B6WSN-4FWM4P4-J-4/7051/d542b7199c07d3f274131cb29e173241/Movie_S2..mov
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Cockroach Arthropod – escapes from toads, etc Responds to air movement
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Cockroach
Air movement hairs give directionality
Escape correct way!
Giant fibres
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Teleost fish Mauthner cell
Large hindbrain, descending cell Responds acoustically
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Feed forward pathway Receptor – interneuron or Receptor – Mauthner ?
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C-start startle response
But note Mauthner cell only used in some fast starts,
other homologous cells exist in other neuromeres
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Conclusions Apparently simple behaviour has
complex neural circuit Giant fibers for fast response Feed-forward pathways Safety features so only escape when
needed Chemical systems
Amplification Modulation Inhibition