RESPIRATION 143 



Annotation. The superior laryngeal nerve is chiefly a sensory nerve, but also 

 embraces a certain number of motor fibers which innervate the cricothyroid muscle. 

 Consequently, the stimulation of the intact nerve must give rise to an inhibition of 

 respiration and forced expiratory efforts, and secondly, to an approximation of the 

 cricoid and thyroid cartilages and a greater tension of the vocal cords. 



6. The Inferior Laryngeal Nerve. Place the intact inferior laryn- 

 geal nerve in shielded electrodes. Stimulate briefly and note the effects 

 of the stimulation upon (a) the general character of the respiratory 

 movements, and (6) the action of the laryngeal muscles. 



Divide the inferior laryngeal nerve between two ligatures. Stimu- 

 late its distal as well as its central end, and study the effects (if any) 

 produced in each case. 



w 



A 



FIG. 91. DIAGRAM ILLUSTRATING THE ABDUCTION AND ADDUCTION OF THE VOCAL CORDS. 

 A, Abduction: 1, point of insertion of the post, crico-arytenoid muscle; Or, glottis. B, 

 adduction: 2, points of insertion of the lat. crico-arytenoid and thyro-arytenoid muscles; 

 3, point of insertion of the arytenoid muscles. The dot indicates the position of the 

 center of rotation of the arytenoid cartilages. 



Annotation. The inferior laryngeal nerve is a motor nerve, innervating the 

 muscles of the larynx, except the cricothyroid. Consequently, its stimulation must 

 give rise to peripheral effects only. These consist chiefly in contractions of the 

 arytenoid muscles which have to do with the approximation of the vocal cords and 

 the size of the glottis. In the dog the innervation of this nerve, as well as that of 

 the superior laryngeal nerve, is unilateral. 



7. The Main Trunk of the Vagus Nerve. Expose both vagi nerves 

 below their superior laryngeal branches. Divide each nerve between 

 two ligatures. Observe that the rate of the respiratory movements is 

 now greatly reduced, whereas their depth is increased. The total gas 

 interchange is not seriously impaired. Stimulate the central end of 

 either nerve with weak, medium, and strong currents. Discuss the 

 part which the vagi nerves play in regulating the frequency and am- 

 plitude of the respiratory movements, formulating a concise picture of 

 the self-regulation of respiration by means of these nerves. Administer 

 an overdose of ether to the animal. 



