PROBLEM 2. Why Co?nplex Behavior Is Possible 28:; 



1 1. What is the relation of nerves to nerve cells? Of axons to nerves? 



12. How fast does a nerve impulse travel? What changes take place in 

 a fiber as an impulse travels along it? How are impulses relayed from 

 neuron to neuron? What is a synapse? Why does the number of 

 synapses affect the speed of an impulse? 



13. What is the result of having neurons closely packed in the gray 

 matter? 



14. Trace the path of the impulse in a simple reflex using the terms re- 

 ceptor, dendrite, cell body, axon, afferent neuron, gray matter of 

 cord, efferent neuron, muscle. 



15. Explain how you become conscious of heat when you accidentally 

 touch a hot stove. 



16. What kind of muscles are controlled by the autonomic nervous sys- 

 tem? In which parts of the body are such muscles found? Describe 

 the structure of the autonomic nervous system. 



17. Name three kinds of receptors found in the skin. What sensations do 

 we get through internal receptors? 



18. What lines the back of the eyeball? With what does it connect? 

 What name is given to the opening into the eyeball? What lies di- 

 rectly behind this opening? Which part regulates its size? What is 

 the result of having an eyeball which is shorter than normal? Longer 

 than normal? 



19. Explain how sound waves travel to the receptors from the time they 

 hit the drum at the entrance to the middle ear. Of what importance is 

 the inner ear besides receiving sound stimuli? 



Exercises 



1. How does the skull protect the brain? Examine the skull of a human 

 being, of a dog, of a cat. What is the advantage in having the skull 

 rounded on top? How many different bones do you see? How are they 

 joined together? Note where the brain stem leaves the skull. 



2. How does the spinal column protect the spinal cord? Examine two 

 or three vertebrae from the backbone of some mammal, or if possible a 

 human backbone. Fit the vertebrae on top of each other. In the living 

 organism, what keeps the separate bones together? Why is the backbone 

 flexible? Using a pencil, show the position of the spinal cord. Where do 

 the nerves pass through the spinal column? Examine the surface of a 

 vertebra at the point where it touches the next. In the living organism 

 there is a pad of cartilage between every two vertebrae. Of what use is it? 



3. What is the structure of the brain of a mammal? If possible, obtain 

 a fresh sheep's brain. Notice the thin coverings over the brain. They are 

 called meninges (men-in'jees). Compare with the picture of the human 

 brain (or, better, with a model) and distinguish cerebrum, cerebellum, 

 and medulla. Compare the number of ridges in the sheep's brain with 

 those in our brain. Feel the brain; which tissues seem to be lacking? Cut 



