470 - Multicellular Animals, Especially Man 



sharply distinct from that of other animals. 

 Man was said to act by "reason," in contrast 

 to the instinctive behavior of other animals; 

 but no such sharp distinction can be drawn. 

 Man displays many simple reflex and instinc- 

 tive responses, while many of the higher ani- 

 mals show more or less intelligent behavior. 

 On the other hand, many writers, in attempts 

 to minimize the differences between human 

 and other animal behavior, have perpetuated 

 highly exaggerated accounts and utterly un- 

 critical interpretations of the "intelligent" 

 behavior of animals. The truth probably lies 

 in the other direction: that is, far more of 

 human behavior than is commonly supposed 

 is purely instinctive and automatic. Never- 

 theless, there is an enormous gap between the 

 achievements of man — at least of civilized 

 man — and those of other animals. The essen- 

 tial clue to this difference seems to lie in one 

 peculiar feature of human behavior: lan- 

 guage. Every known race of man has some 

 kind of language; and there is no good evi- 

 dence that any other animal has developed 



any truly equivalent system of communica- 

 tion. 



A word is both a response and a stimulus. 

 On the one hand, a word is a conditioned 

 reflex that may be elicited by a variety ol 

 substituted stimuli; and on the other hand, 

 it is a stimulus that has been substituted 

 lor many other stimuli. In short, a word is a 

 relatively simple motor act that "sums up" 

 a vast amount of experience. A word is a 

 vehicle of experience; and this distinguishes 

 words from purely instinctive or emotion;: 1 

 sounds, which are uttered by many animals. 

 Language consists not merely of words, but 

 of combinations of words. The separate 

 words are, in general, purely imitative, but 

 the word combinations are largely original. 

 Every conditioned reflex involves an element 

 of originality, in a sense; that is, it represents 

 a new combination of stimuli and responses, 

 so far as the individual animal is concerned. 

 Thus language may be described as a mode 

 of behavior that enormously extends the 

 range of original responses in all mankind. 



TEST QUESTIONS 



1. Explain how the nerve impulse (a) differs 

 from, and (b) is similar to. the state of excita- 

 tion in cells generally. 



2. Discuss the fatigue susceptibilities of nerve 

 and muscle and relate this problem to the 

 relative rates of oxidative metabolism. 



3. Differentiate between the members of each 

 pair of terms: 



a. the absolute and relative refractory 

 periods 



b. the relative refractory period and the 

 supernormal period 



c. centralized and decentralized nervous 

 systems 



d. the peripheral and central parts of the 

 nervous system 



e. afferent and efferent nerve fibers 

 1. neurons and protoneurons 



g. a nerve fiber and a neuron 

 h. axons and dendrons 



4. Nerve impulses do not grow weaker as they 

 are transmitted along an axon. Explain this 

 statement carefully. 



5. Differentiate between the members of each 

 pair of terms: 



a. a leflex arc and a reflex act 



b. unilateral and bilateral reflexes 



c. intrasegmental and intersegmental re- 

 flexes 



d. association neurons and other neurons 



6. What are the synapses and why have svnapses 

 been studied so intensively? 



7. Explain the interrelationships between 

 the synapses and the law of "forward direc- 

 tion." 



8. Discuss briefly each of the following topics 

 in relation to the behavior of an intact ani- 

 mal: (a) synaptic block; (b) synaptic resist- 

 ance; (c) synaptic summation: (d) synaptic 

 fatigue; (e) facilitation. 



9. Explain how electron microscopy has con- 

 tributed to our knowledge about svnapses. 



10. Explain the meaning and significance of the 

 following terms: (a) neurosecretions, or neu- 

 rohumors; (b) synaptic transmitters: (c) 

 acetylcholine; (d) cholinesterase: (e) cholin- 



