144 Muscles /8 : 3 



B. Interaction with the Nervous System 



In the intact animal, the muscle contracts following stimulation by the 

 nervous system. The incoming impulses in the nerve fibers are called 

 electrical spike potentials; similar spike potentials travel along the 



Humerus 



Triceps Group 



Figure 5. The muscles and the bones of the arm. The lower 

 arm acts as a lever pivoted at the elbow. The biceps, which 

 applies force to the lever, is attached to the radius near the 

 elbow. The load is applied to this lever at the wrist. There- 

 fore, the theoretical mechanical advantage (TMA) is about 

 0.1. Muscles moving most limbs have TMA's of 0.05 to 0.4. 

 Adapted from THE WORLD BOOK ENCYCLOPEDIA 

 with permission © 1961 by Field Enterprises Educational 

 Corporation. All rights reserved. 



muscle fibers. The interactions of the nerve and muscle fibers and the 

 magnitude and form of the electrical potentials across the sarcolemma are 

 important physical characteristics of muscle. 



Each muscle fiber is separately innervated. Each has at its end a 

 special structure called the muscle end plate, near which one or more nerve 

 fibers also end. The nerve and muscle endings, together with the space 

 between them, is called the myoneural junction. When a spike potential 

 reaches the nerve endings, the latter secrete a special chemical substance, 



