Biology 360: Motor Behaviors and Review

1) What is a central pattern generator and describe one example that was discussed in class?

The central pattern generator is a group of neurons that act as a network to produce rhythmic patterned outputs with little or no sensory feedback. Two examples discussed in class came from Tritonia (the sea slug) and the leech. See your notes for detailed circuits.

2) You have a dog named Sparky. When you scratch him in the right spot on his back, Sparky immediately lifts his leg up and starts scratching. When you stop, he puts his leg down. Which example of motor behaviors is he exhibiting and why? Describe a simple experiment to test this. This motor action could either be described as a simple reflex or a fixed action pattern. Several tests could be done to determine the difference such as changing how hard you scratch Sparky to see how the response changes (checks the rule that the response should be graded - reflex) or switch the stimulus to see if there is an assigned stimulus to activate the response (fixed action pattern). Other experiments may be performed. With many behaviors, there is a continuum between reflexive and more complex behaviors which is not always simple to ascertain the line between the two.

3) You are at an aquarium admiring the red belly of the red-bellied stickleback fish when an employee tells you it is their mating season. You notice the males are swimming around normally in the tank, but as soon as they see another red-bellied stickleback fish, they immediately attack the other male until it retreats. These behaviors are not directed at any other male fish in the aquarium. After a few minutes you see the male red-bellied stickleback fish attacking a red plant. Which example of motor behaviors are these fish exhibiting and why? Describe a simple experiment to test this. This is a fixed action pattern because this is a more complex instinctive behavior. A simple experiment to test this would be to isolate a single male and add varying stimuli to see what causes the aggressive behavior (checks the rule that there is an assigned stimulus). It turns out that the stimulus which activates the aggressive behavior in red-bellied stickleback fish is the red on the fish. If you change the stimulus to anything red, it will induce aggressive behavior in the stickleback fish. Once you determine this, you could vary the shade of red or the amount of red present to determine whether or not there is a threshold. Other experiments may be performed. November 19, 2014

Use the following Diagram to answer the following questions.

1

2b 2a

3a 3b 3c

4) Describe what would happen in cell 1 if an object touched the outer surface of the skin.

This would activate the receptors on the dendrites to cause a generator potential within the cell. A generator potential is a passive potential and therefore will decrement over time.

5) The connection between cell 1 and cell 2a is called? ______synapse______

6) What happens in this region?

Electrical information passing through the axon of cell 1 will be transduced into a chemical signal. This occurs when the action potential has reached the synapse (presynaptic terminal) allowing voltage-gated calcium channels to open. Calcium allows fusion of synaptic vesicles to the membrane and subsequent exocytosis of neurotransmitter into the extracelluar space. These will interact with receptors on cell 2 (the postsynaptic cell) allowing the chemical signal to be transduced back into an electrical signal. The mechanism of how this occurs depends on the type of receptor (metabotropic vs ionotropic).

7) What type of cells are 3a, 3b, and 3c? ____motor neurons______

8) What occurs when an action potential reaches the terminal of all three cells described in 7? What will occur in the postsynaptic cell?

These cells will release acetylcholine which will bind to acetylcholine receptors on the muscle. This will cause the muscle cells to contract.

9) Assume the above circuit is involved in a reflexive behavior. What criteria must be met in order for this to be a reflexive behavior? November 19, 2014 a) The response to the stimulus is graded (the strength of the response is dictated by the strength of the stimulus). b) The latency is inversely proportional to the stimulus (The bigger the stimulus, the faster they will respond). c) A threshold must be met for the reflex to occur. d) Nothing can stop the organism from performing the reflex (output). e) You will perform this behavior even if there are other sources of input (inhibition of other behaviors – summation).