2 理论应当联系实践,请看如何解下面的样题。
Our multimillion nerve-cell central nervous system has its roots in the scat- tered nerve cells of tiny,lowly organisms that lived in water half a billion years ago. Nerve cells evidently first appeared in coelenterateshollow-guttedorganisms like the hydra(水螅)and the sea anemone(海葵).A coelenterates nerve network lacks any kind of centralized control.This probably began with flatwormsthe first creature to posses a head.
Specialized sense cells help flatworms respond more flexibly than sea anemones to outside stimuli.But like most animals without a backbone,flatworms act almost by instinct and reflex.
Intelligent behavior remained impossible until the appearance of relatively big,complex types of brainthe types we find among the backboned animals,or verlebrates.The tiniest fish has a large brain than the largest insect.But the de- velopment of a fishs three-part brain reflect that beasts unintellectual priorities. Much of the forebrain deals only with smell.The midbrain handles vision,the hind brain,balance.
With early mammals the brain grew larger and more complex.Sense coordination shifted from the midbrain to the forebrain,a developing structure capped by folded cerebrum(大脑)to handle memory and learning.Meanwhile the hindbrain gained a large cerebellum(小脑)to coordinate complicated movements.
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