548 



COLLEGE ZOOLOGY 



Free sensory nerve endings in 

 cornea of eye 



Receptor of heavy pressure, Pacinian 

 corpuscle in mammary gland 



Taste bud 

 Taste papilla 



Taste pore 

 Taste fiair 

 Tongue epithelium 



Supporting cell 

 Taste cell 



Sensory nerve 

 fiber 



Taste bud in longitudinal section showing 

 taste cells and afferent nerve fibers asso 



ciated with them 



Motor nerve endings on gland cells of 



pancreas 



Figure 395. Receptors and effectors, the nerve endings of sensory and motor nerves. (After 

 Kimber, Gray, and Stackpole.) 



ing from stimulation of nerves in the phar- 

 ynx or in other tissues affected by prolonged 

 deprivation of water. 



Proprioceptors are receptors that occur 

 in connection with muscles, tendons, and 

 joints; they are stimulated by the activities 

 of these tissues and are responsible for the 

 coordination necessary for proper posture 

 and for the movements of the body. To the 

 nerves in the skin of man are due the sensa- 

 tions of pressure, heat, cold, and pain. The 

 skin surface is a mosaic of sensory spots; 

 more than 2,000,000 are pain points, 500,000 

 are pressure points, 150,000 are cold points, 

 and 16,000 are warm points. 



The sensation of taste is due to the con- 

 tact of substances in solution with taste 

 buds, chemical receptors ( chemoreceptors ) , 

 that are distributed over the surfaces of the 

 tongue, soft palate, fauces, tonsils, and 

 pharynx. The 4 primary taste sensations are 

 (1) salty, (2) bitter, (3) acid, and (4) 

 sweet. 



The sensation of smell results from the 

 contact of minute particles dissolved in 

 water with olfactory nerve endings (chemo- 

 receptors) in the nose. The nose is a testing 

 place of the chemical nature of the air taken 

 into it. Man is a poor smeller compared with 

 dogs and many other mammals. 



The essential part of the auditory appa- 

 ratus (Fig. 396) of land vertebrates is the 

 cochlea. In man and other mammals there 

 is an external ear or pinna which collects 

 sound waves. In aquatic animals this is not 

 necessary since water carries the sound 

 waves to the tissues, which transmit them 

 directly to the internal ear. The middle ear 

 or tympanic cavity is separated from the 

 external ear by the tympanic membrane 

 ( eardrum ) ; the Eustachian tube leads from 

 the middle ear to the pharynx. The internal 

 ear includes an osseous labyrinth compris- 

 ing the saccule, utricle, the three semi- 

 circular canals, and the cochlea. Within the 

 osseous labyrinth is the membranous 



