Biology of Man 495 



in close association with the conductors. The following is a brief sum- 

 mary of the receptors of man: 



1. Chemoreceptors (receptors sensitive to chemicals) 



(a) Taste buds on the tongue are clusters of specialized epithelial 

 cells (Fig. 11) closely associated with nerves leading to the 

 brain (Figs. 246 and 247). 



(b) Ends of sensory nerves in the nasal epithelium (Fig. 11) receive 

 the stimuli of odors, thus giving us a sense of smell. 



2. Mechanoreceptors (receptors sensitive to mechanical stimuli) 

 a) Tactile (touch) receptors (Meissne/s corpuscles) over much 



of the body, but especially beneath the epidermis on the hands 

 and within the digestive tract (hunger) . 



Choroid plexua 

 Of ^ 



third 

 ventricle 



Pineal ^land—- 



Cerebral 

 aqueduct 

 Arbor vi.ta.e 



Foarth ventricle 

 Cerebellum 



Corpus 

 callosum 



.Third 

 ventricle 



Stalk op 

 hqpophqsis 



NDl^actori^ bulb 

 Pons 



Fig. 246. — Human brain in sagittal section, showing the medial aspect of the 

 left half. The convoluted cerebrum (cerebral hemisphere) is shown above the 

 corpus callosum and the spinal cord below the pons. (From Francis: Fundamen- 

 tals of Anatomy, The C. V. Mosby Co.) 



(b) Auditory (hearing) receptors which are vibrating "hair cells" 

 located in the cochlea of the inner ear (Fig. 250) . Sound waves 

 enter the external ear and vibrate the tympanic membrane 

 which transmits the vibrations along the bones of the middle 

 ear (hammer, anvil, and stirrup bones). From the latter a 

 fluid in th^ cochlea (resembHng a snail shell) carries the vibra- 

 tions to the "hair cells" which in turn set up action currents to 

 be conducted over th^ auditory (acoustic) nerve to the tem- 

 poral lobe of the brain (Fig. 247) . 



