PHYSIOLOGY 183 



Functions of the Spinal Cord 



This organ serves as a system of reflex centers which control the 

 actions of glands of the trunk, visceral organs, and skeletal muscles. 

 The spinal cord is also a nervous pathway between the brain and 

 numerous organs of the body. It is said that more than half a million 

 neurones join the cord through the dorsal roots of the spinal nerves. 



Functions of the Divisions of the Brain 



Conscious sensations and intelligence are centered in the gray 

 matter or cortex of the cerebrum. This section controls voluntary 

 actions and provides memory associations. The diencephalon serves 

 as a center for spontaneous actions. The midbrain is one of the cen- 

 ters of coordinated movement which has to do with posture and eye 

 muscles. The cerebellum is another center of coordinated movement, 

 particularly with reference to equilibrium. The impulses from the 

 muscles, tendons, joints, and semicircular canals of the ear are co- 

 ordinaiod so that in a movement or posture the proper muscles may 

 be contracted to the proper extent at the proper time. Below and 

 behind the cerebellum is the medulla oblongata which controls breath- 

 ing and may be an inhibitor on heart action. It also regulates 

 digestive secretions, movements of digestive organs, and vasomotor 

 activity of the blood vessels. As a whole, the brain serves as the 

 organ of communication between the sense organs and the body 

 and is the coordinator of the bodily activities. 



Sense Organs and Their Function 



There are five special senses which have rather particularly 

 defined function, and, in at least four of them, quite specialized or- 

 gans for perception. These five are sight, hearing, smell, taste, and 

 touch. They are all in contact with, and referred to, the external 

 world. The organs in which these senses are stimulated are, respec- 

 tively, the retina of the eye, the org^n of Corti of the ear, the olfac- 

 tory membrane of the nose, taste buds in the epithelium of the 

 tongue and related parts, and the tactile corpuscles, as well as free 

 nerve endings in the epithelium. 



In addition to the senses centered in these specialized sense or- 

 gans, there are several general senses, such as hunger, nausea, re- 

 spiratory sensations, and sexual sensations. 



Cutaneous Sense Organs (Touch, Pressure, Temperature). — There 

 are endings of sensory nerves in all parts of the skin and the mucous 



