THE SPINAL CORD 



681 



it be of a similar nature. Stimuli of a harmful or sexual nature are 

 the most potent in obtaining command of the final common path. 



The spinal cord has already been referred to as the reflex centre 

 concerned in micturition and movements of the large intestine. Ii* 



FIG. 407. DIAGRAM INDICATING CONNECTIONS AND ACTIONS OF Two AFFERENT 

 SPINAL ROOT CELLS (a AND e) IN REGARD TO THEIR REFLEX INFLUENCE ON THE 

 EXTENSOR AND FLEXOR MUSCLES OF THE Two KNEES. 



a, Afferent fibre from skin below knee; a', afferent from flexor muscle of knee i.e. r 

 in hamstring nerve; e and e', efferent neurous to extensor muscles of the knee, 

 left and right; 5 and 5', efferent neurons to flexor muscles; E and E', extensor 

 muscles; F and F', flexor muscles. The sign + indicates that at the synapse 

 which it marks the afferent fibre a (and a') excites the motor neuron to dis- 

 charging activity, the sign - indicates that at that synapse the afferent fibre a 

 (and a') inhibits the discharging activity of the motor neurons. The effect of 

 strychnine and tetanus toxin is to convert into + . (From Sherrington's 

 " Integrative Action of the Nervous System,'' by permission of Yale University 

 Press and Messrs. Constable and Co., Ltd.) 



diseases of the spinal cord affecting these centres, these processes 

 will be impaired. It also contains the centres controlling the erection 

 of the penis and the ejaculation of the seminal fluid. The. spinal 

 cord is also normally concerned in the process of parturition. It i* 



