Crayfish Escape Behavior

Question 1

Medial giant escape

Answer 1

Rapid escape response to head touch in crayfish: moves directly back away from the source of the touch

Question 2

Lateral giant escape

Answer 2

Rapid escape response to tail touch in crayfish: recoils tail, curls up slightly, and moves in direction of tail

Question 3

What is the tail flip escape behavior?

Answer 3

A rapid (<0.2 s) and powerful flexion of the abdomen away from the stimulus, cancels all other current behaviors (other behaviors are released from inhibition after tail flip)

Question 4

Tail flip escape muscles

Answer 4

Mediated by flexions and extensions of abdominal muscles, each of the five anterior abdominal segments contain these muscles (medial giant escape - requires flexion of all segments, lateral giant escape - requires flexion of anterior three segments)

Question 5

Giant interneurons

Answer 5

Two pairs of giant axons traverse the entire length of the nervous system, arise from two pairs of giant interneurons (Lateral Giant Interneuron (LGI) - lateral giant escape, Medial Giant Interneuron (MGI) - medial giant escape)

Question 6

Differences between LGI and MGI axons

Answer 6

All MGI cell bodies and dendrites are found in the brain, axons extend all the way to the last abdominal segments
LGI cell bodies and dendrites are found in the individual abdominal ganglia (one in each), connected with each other electrically

Question 7

Connectivity patterns of giant axons with motor giants

Answer 7

Axons from both LGI and MGI are connected to the flexor motor neurons called motor giants (MoGs) - MGIs connected to MoGs in every abdominal segment, LGIs connected to only the three anterior segments

Question 8

The command neuron concept

Answer 8

A neuron whose activity (sufficient and necessary) causes a Fixed Action Pattern (FAP)

Question 9

Is the LGI a command neuron?

Answer 9

Yes - lesion experiment demonstrated that tail flip does not occur when LGI is inactivated (necessity), action potentials in LGIs are necessary to elicit response

Question 10

Basic tail flip circuit (what neurons are required?)

Answer 10

Mechanosensory neurons → interneurons (A - phasic responders, and C - tonic responders) → command and decision neurons (LGI) → premotor neurons and motor neurons (SG, FFs, MoGs) → muscles

Question 11

Classification of synaptic transmission

Answer 11

Chemical - synaptic cleft (neurotransmitters are involved)
Electrical - electrical synapse

Question 12

Basic escape circuitry for crayfish

Answer 12

1,000 neurons → 25-50 sensory interneurons → lateral giant interneuron (all connections to LGI are electrical) → motor giants (MoGs) → fast flexor muscles

Question 13

Components/steps of escape

Answer 13

1. Tail flip (abdominal flexion) - only step that requires LGI activity (prevents competing behaviors and allows expression of subsequent steps in escape behavior)
2. Abdominal re-extension
3. Swimming away

Question 14

Sources to inhibition to make sure that flexion is followed by re-extension and swimming

Answer 14

1. LGI are rapidly inhibited after initiating a spike, this inhibition keeps the # of spikes in check (3-4)
2. Sensory input is inhibited by pre- and post-synaptic inhibition
3. MoGs are inhibited after some time has elapsed, allowing them to discharge only once (prevents flexor discharge from occurring before re-extension can be accomplished)
4. Flexor muscles are inhibited at just about the time when peak flexion is accomplished, in anticipation of re-extension phase

Question 15

Modulation of escape behavior

Answer 15

Restraint - causes an adaptive shift from reflexive to more volitional control of tail flips
Feeding - during feeding the stimulus strength that evokes a tail flip response is increased (higher threshold for LGI-mediated response)