1 4 1 Neural Circuits BIO 361T Fall 2014 1 If a cat steps on something sharp with its forepaw it will reflexively withdraw its foot by contracting its biceps muscle and relaxing its triceps a What other reflex do you know of that involves limbs in a tetrapod mammal Patellar reflex in human legs b 2 Use this as a model to draw a hypothetical labeled diagram of what happens in the cat Explain how excitation of the Mauthner cell on one side of a teleost fish results in inhibition of the muscles in the ipsilateral same side body wall Draw a diagram if it is helpful Mauthner cell excites an inhibitory interneuron which inhibits the contralateral Mauthner cell which controls the ipsilateral body wall 3 The reliability and speed of the escape reflex is crucial for a fish s survival For each of the following features of this neural circuit denote whether it increases reliability likelihood of responding appropriately to a stimulus speed or both Explain your answer a Convergence of multiple sensory afferents onto one Mauthner cell Reliability by spatially summing inputs the chance of reaching threshold and firing is higher b Electrical synapses between some sensory afferents and the Mauthner cell Speed electrotonic conduction is faster than diffusion of chemical signals c Large axon diameter of Mauthner cell Speed by decreasing Rm but decreasing Ri even more the length constant increases so an electrical signal can go farther in the same amount of time d Contralateral inhibition Reliability by only exciting the ipsilateral Mauthner cell only the contralateral side contracts 2 4 Scavenger hunt In this activity there is an example of each of the following principles Indicate where each one is found a Krogh s principle 2 b Excitatory chemical synapse everywhere c Inhibitory chemical synapse either cat or fish reflex d Spatial summation 3a e Increasing 3c f Pure electrotonic conduction 3b 5 Based on the three reflex arcs you have learned write out the process of a generalized reflex arc Sensory afferent detects stimulus Sensory afferent fires AP Motor efferent is excited Motor efferent fires AP Muscle contracts
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