. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. THE NERVOUS SYSTEM 407 and these, together with observations made on persons who had lost the power of movement of certain parts of the hodv, and who, after death, were found to have had diseases localized in certain' parts of the cerebrum, have given to us our knowledge on this sub- ject. Reflex Actions, their Meaning. — If through disease or for other reasons the cerebrum does not function, no will power is exerted, no intelligent acts per- formed, and no in- ^al^^B^^^ coming impulses are
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. THE NERVOUS SYSTEM 407 and these, together with observations made on persons who had lost the power of movement of certain parts of the hodv, and who, after death, were found to have had diseases localized in certain' parts of the cerebrum, have given to us our knowledge on this sub- ject. Reflex Actions, their Meaning. — If through disease or for other reasons the cerebrum does not function, no will power is exerted, no intelligent acts per- formed, and no in- ^al^^B^^^ coming impulses are received as sensations. All acts performed in such a state are known as rejiex actions. An example of a reflex may be obtained by crossing the legs and hitting the knee a sharp blow. The leg, below the knee, will fly up as a result of reflex stimu- lation. The involun- tary brushing of a fly from the face or the attempt to move away from the source of an- noyance w^hen tickled with a feather, are other examples. In a reflex act, a person does not think before acting. The nervous impulse comes from the outside to cells that are not in the cerebrum. The message is short-circuited back to the surface by motor nerves, without ever having reached the thinking centers. The nerve cells which take charge of such acts are located in the cere]-)ellum or spinal conl. But some reflex acts may be controlled in part by the will. Wo need not, for instance, brush away a fly, although we cannot stop the churning of the stomach or the process of breathing, yet sud- den fright may cause us to take a certain sharp or long breath or. Regions of the head and action of the different partx of the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hunter, George William, 1873-1948. New York, American book company
Size: 1533px × 1630px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., boo, bookpublishernewyorkamericanbookcompany, booksubjectbiology
