224 The Vertebrate Organ Systems 



The movements of the head and body cause the endolymph to be 

 agitated. These movements of the endolymph in the semicircular 

 canals set up vibrations in the cilia of the epithelial cells of the ampullae, 

 the sacculus, and the utriculus. These are the sensory receptors which 

 by means of one branch of the auditory nerve transmit their impulses 

 to the brain, giving rise to the sensation of balance. Although these 

 sensory endings are functional without the otoliths, they appear to 

 be more sensitive when the otoliths are present. 



These sense organs are primarily concerned with the position of 

 the head, but their function of keeping the body in proper balance is 

 coordinated with the receptors in the muscles of the body and with 

 visual impressions. 



Normally man moves in a horizontal plane and experiences no 

 discomfiture due to the movements of the endolymph in the semi- 

 circular canals. However, when the movements become vertical ones 

 —such as those occurring in the rocking boat — actual nausea and 

 vomiting may occur. This nausea can be alleviated to some degree 

 by lying down, for then the movements are of a more usual type. The 

 exact causes of the nausea are not established. 



