. The eclectic guide to health; or, Physiology and hygiene ... an impression to be made on the centers. Theimpression made on the centers, especially on the brain,causes the mind to The impression made on thecenter may be so customary that the mind takes no noticeof it. The centers send out a nervous impulse along the fibersthat lead to the muscles. These impulses sent to the mus-cles cause motion. If your hand touches a hot object, theends of the nerves are irritated by the burn. This irritationis quickly conveyed to the brain. An impulse is sent to themuscles of your arm to move the h
. The eclectic guide to health; or, Physiology and hygiene ... an impression to be made on the centers. Theimpression made on the centers, especially on the brain,causes the mind to The impression made on thecenter may be so customary that the mind takes no noticeof it. The centers send out a nervous impulse along the fibersthat lead to the muscles. These impulses sent to the mus-cles cause motion. If your hand touches a hot object, theends of the nerves are irritated by the burn. This irritationis quickly conveyed to the brain. An impulse is sent to themuscles of your arm to move the hand away. The passageof irritation along the fibers is very rapid, so that the timeis very short between the touching of the hot object and thetaking of the hand away. If the sensory fibers connecting any part with the brainare cut or seriously injured, there is loss of feeling in thepart. If the motor fibers connecting any muscle withthe brain are cut or injured, all power of motion in themuscle is lost. If both kinds of fibers are destroyed, both Plate I\T. NERVES. 121 THE NERVOUS SYSTEM. 121 feeling and motion are lost. These different conditionsproduce the various kinds of 123. Reflex Action.—The nerve-centers may performtheir action of sending out motor impulses without the con-scious action of the mind. If the irritation is extreme, thecenters act before the mind has time to consider and directthe movement. In the case in which your hand touches thehot object, you take the hand away instantly, before themind has time to act. If any person sticks you with a pin,you flinch instantly. If you are about to fall, you instantlycatch your balance. This action of the nervous system, inwhich the mind does not seem to act, is called reflex action. If the spinal cord is cut so as to destroy all connectionwith the brain, the nerves connected with the gray matterof the cord will still perform reflex action. If the part ofthe body supplied by these nerves be burned or pinc
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