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craywebnotes - VI.B.1.a. Sequential coordinated contraction...

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VI.B.1.a. Sequential coordinated contraction of different segments VI.B.2. Simplified view of escape : the contraction pathways Slow pathway Fast pathway There is a timing relationship between the fast and slow pathways. The fast pathway guarantees a short latency for the reflex to occur. The slow pathway kicks in right after the reflex begins and maximizes the strength of the escape response VI.B.1.a. Coordinated contraction of muscles moves the crayfish away from danger Once the escape response begins, it cannot be altered or stopped. The crayfish escape response habituates or is reduced when repetitive unimportant stimulation is applied. i) The crayfish uses large diameter, "giant" neurons to convey electrical signals rapidly. As a general rule, larger diameter neurons conduct action potentials more rapidly. The crayfish escape response is specialized for speed. ii) The crayfish uses electrical synapses to ensure quick initiation of the escape response (see below on the advantages and disadvantages of electrical synapses). Chemical transmission would add unwanted delay to initiation of the escape response VI.b.3. The lateral giant (LG) neuron plays a critical role in many aspects of escape Can you find the two pathways in the more complex circuit? Disadvantages of electrical synapses Cannot amplify – If you have a small presynaptic terminal, very little of the electrical signal will get to a large post-synaptic cell (physics again). In a sense, an action potential will propagate to the terminal of the neuron and then will passively spread through the gap junction to the next neuron. The advantages and disadvantages of electrical synapses are as follows: Advantages of electrical synapse Speed, speed, speed - electrical synapses allow for electrical signals to travel from neuron to neuron with almost no delay (chemical synapses take almost 1 msec). Therefore, electrical synapses are often found in escape pathways which require speed or death. Synchronization
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craywebnotes - VI.B.1.a. Sequential coordinated contraction...

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