9101598
| Question | Answer |
| Define locomotion | The ability of an organism to move in space in purposeful ways by using efficient mechanisms that are suitable for the purposes of the movement |
| What are the specific animal adaptations for locomotion? | • Muscles (locomotion requires muscles) • The nervous system (muscle contraction requires control) |
| What makes a good model system for studying the control of locomotion? | • The behaviour needs to be, reliable, reproducible and simple • The underlying control mechanisms need to be simple • The system needs to be accessible |
| Briefly describe crayfish escape behaviour in response to a tail touch. What causes the response? |
- Touching the tail with a probe triggers a downward tail flip that propels the animal up and away from the stimulus
• It's fast --> the time between the stimulus and the response is 10ms
• Contraction of the tail is caused by the rapid contraction of the flexor muscles
Image:
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| Describe the crayfish nervous system | • The brain: a collection of ganglion fused in the head region • Subesophageal ganglion complex • 5 thoracic ganglia (correspond to the 5 thoracic ganglia) • 6 abdominal ganglia (correspond to the 6 abdominal ganglia) • Each ganglion is connected by axons |
| Where is the circuitry for the tail flip response located? | In the abdominal ganglia |
| Describe the pathway for the tail flip circuitry |
• Tail afferents (bipolar sensory cells)
-> Sensory interneurons
-> Lateral Giant Interneuron (LGI)
-> Giant Motor Neurons (MoG)
-> Fast flexor muscles
Image:
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| [Diagram of tail flip circuitry] |
The zig-zag lines indicate electrical synapses
Image:
Picture1 (image/png)
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| Describe the anatomical organisation of the lateral giant interneurons |
• There is one LGI per abdominal ganglion
• They are coupled to each other via segmental electrical synapses
[The LGIs essentially operate as a single unit because of how strongly they are connected (ensures rapid spread of activity throughout the ganglia)]
Image:
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| • This experiment proves that LGI activity is necessary for the tail flip response • After electrically stimulating the sensory neuron (mimics tail touch) > depolarisation of LGI > APs in motor neuron • Injecting negative current leads to hyperpolarisation > no AP in LGI > no AP in motor neuron | |
| Describe crayfish escape behaviour in response to a head touch. What interneuron is involved in this escape response? |
• Triggers a tail flip that propels the animal backwards
• The Medial Giant Interneuron (MGI) is involved
Image:
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| What's the difference between the MGI and the LGI? | • MGI is carries sensory information from the head • LGI carries sensory information from the tail |
| What's the difference between how the MGI and the LGI cause the tail flip response? |
• LGI synapses with MoGs in abdominal segments 1 - 3 so only these muscles contract
• MGI synapses with all segments
Image:
Picture1 (image/png)
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| How are escape networks specialised for fast responses? | • Neurons have large axon diametres • Networks have many electrical synapses |
| Describe the squid jet propulsion escape response. | • It rapidly contracts body and expels water to propel itself away from the stimulus • It is triggered by the activity of the Squid Giant Axon |
| Describe the Drosophila escape jump response. | • The fly jumps upwards and backwards and flies away • Giant Fibres carry sensory information from the eyes to the tergotrochanteral muscles which contract to make them jump |
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