290 



BIOPHYSICAL STUDIES ON NERVE AND MUSCLE 



110 A 



A- band 

 "(~I000A) 



Figure 10-14. Stretched and Contracting Muscle — Molecular Model. Myosin mole- 

 cules in the thick filaments contract and expand depending upon the ionic character 

 of the medium. Ends stick out and join to actin molecules contained in thin filament. 



It is a bit ironic that, after carrying about 60 lb of these little machines, 

 and using them himself, day and night, for many thousands of years, homo 

 sapiens still does not know exactly how they work. 



EFFECTS OF ENVIRONMENT ON CONTROL 



Both nerve and muscle are pretty complicated molecular machines. The 

 statement is also very true for the neuromuscular junction or synapse. The 

 neuron-neuron synapse was depicted schematically in Figure 10-7. Fig- 

 ure 10-15 is a beautiful display of the substructure of a neuromuscular junc- 

 tion in which the nerve ending, the synaptic gap, the continuous, infolded 

 sarcolemma, and substantial portions of two myofibrils with their thick and 

 thin filaments and the black Z-line perpendicular to them, are all clearly 

 visible. Repeated study of this and of Figures 10-5 and 10-13 discloses the 

 fine, detailed design. 



Although the neuromuscular system is inherently subject to disturbances 

 of even molecular dimensions, it is remarkably well protected, and can adapt 

 to many environmental conditions. Both the nerve fiber and the contractile 

 molecule are buried deep within tough tissue, well fed by capillaries of the 

 blood and lymphatic systems. Response to environmental changes is 

 directive, and remedial action usually is swift and accurate. 



However, response to the environment of radiations — both matter waves 

 and electromagnetic — is a matter of increasing concern as our environ- 



