BODY TISSUES 



305 



J 



c 



^ 







n units of ATP 



-m 



X 



()))m)))^^-))-))))m')T)^TrnTT > 



X 



(.))))m))))-)))))))))))))-)jTym 



FIGURE 13-2. Schematic drawing of muscular contraction involving the sliding-filamcnt 

 theory of Huxley and coworkers; a in the drawing represents actin, m represents 

 myosin. ATP molecules function by bridging between the actin and myosin at suc- 

 cessive points as contraction occurs, with hydrolysis of the energy-rich phosphate 

 compound supplying the energy required for contraction. In the absence of ATP 

 the muscle components remain locked in position as in rigor mortis. 



relaxation, this ion returns to the muscle tissue. Potassium is essential 

 for normal muscular function although the mechanism of action is 

 obscure. 



NERVOUS TISSUE 



Although nerve tissues make up only about one-fortieth of the total 

 weight of human beings, this type of tissue is without doubt the 

 most important in the body, for by its functions man and lower 

 animals are clearly differentiated. Nerve tissue of the spinal cord, 

 peripheral nerves, and ganglia provide the channels through which 

 the brain exercises control over most of the functions and actions of 

 the body either directly by nerve impulses or indirectly by nervous 

 control of the blood supply. 



Composition 



Brain and other nervous tissues differ materially in certain respects 

 from most other body tissues, but as usual water is the major com- 



