COORDINATION 



395 



same temperature as the skin to various 

 regions. Other sensory nerve endings are 

 located in the tendons and muscles which 

 respond to tension placed on these tendons 

 and muscles. These are important in bal- 

 ance and will be discussed under that topic 

 later. 



Chemo-receptors 



All of the receptors of the skin have to 

 do with identifying energy changes that oc- 

 cur at or very near the body. In addition, 

 there are chemo-receptors that identify sub- 



composite sensation which is called taste. 

 The difference in the "taste" of hot and 

 cold foods is due to stimuli other than those 

 which are caused by dissolved chemicals. 

 The sense of smell is also important to taste, 

 as anyone with a bad cold is well aware. 

 The end organs of taste are called taste 

 buds and are distributed over the surface 

 of the tongue, laryngeal region, and parts of 

 the roof of the mouth ( Fig. 16-2 ) . They are 

 oval-shaped bodies made up of several cells 

 which terminate in a slender sensory proc- 

 ess on tlie end toward the mouth cavity. 



olfactory tract. 



olfactory bulb. 

 olPdc^ory nerv* 



taste troct 



tbngue with, 

 haste areos 



Fig. 16-2. The end organs for chemo-reception 

 and on the tongue (taste). They are shown 

 ways that conduct the impulses to the brain. 



stances dissolved in the saliva of the mouth, 

 giving one the sense of taste, and chemicals 

 dissolved in the mucus of the nasal cham- 

 bers, imparting the sense of smell. In the 

 latter case, the organism is made aware of 

 changes in its environment some distance 

 away. The sense of smell is, in this respect, 

 like the senses of hearing and seeing which 

 extend perception to great distances. 



Taste. The so-called sense of taste is actu- 

 ally a combination of stimuli coming from 

 the mouth cavity. Stimuli from the end or- 

 gans of touch, heat, and cold located in 

 various parts of the mouth cavity give a 



taste bud 



are located in the nasal chambers (smell) 

 here in detail together with the nerve path- 

 There are four kinds of taste sensations 

 and consequently there are four different 

 kinds of taste buds, each with a rather spe- 

 cific distribution on the tongue and other 

 mouth parts (Fig. 16-2). The taste buds 

 registering bitter are located at the base of 

 the tongue, salt and sweet on the tip and 

 sour along the edges. These can all be 

 identified both microscopically and experi- 

 mentally. No matter how these buds are 

 stimulated the resultant sensation is always 

 sweet, sour, salt, or bitter. Some chemicals 

 stimulate two kinds of taste buds, but in 

 each case the taste bud responds as it 



