^4. Erection — normal 



Sensory 

 (stimulation of glans) 



i 

 via pudendal nerve 



i 

 Lumbar center 



Psychic 

 (higher centers of cerebral cortex) 



i 

 diencephalon 



i 

 cord 



Inhibition of vasoconstrictor fibers (sym- 

 pathetic) dorsal and lumbar 



Parasympathetic sacral (S2 — S4) 



i 

 Vesical plexus 



i 

 Vascular supply of penis 



i 

 Dilatation of vessels 



i 

 Engorgement of sinuses 



i 

 Passive compression of veins and retarda- 

 tion of venous outflow 



B. Ejaculation — normal 



Sensory stimuli from glans 



I 

 via pudendal nerve 



Psychic stimuli from higher centers 



i 

 diencephalon 



i 

 cord 



i 

 Summation of sensory and psychic stimuli producing so-called orgasm 



i 

 Lumbar center 



Sympathetic motor 



i 

 Smooth-muscle contraction of prostate, 

 seminal vesicles and vas deferens. Closure 

 of internal sphincter 



i 

 Emission 



Parasj-mpathetic motor 



i 

 Contraction of striated muscle, ischiocaver- 

 nosus, bulbocavernosus and contractor- 

 urethrae muscles 



i 

 Ejaculation 



Fig. 13.4. The probable neural pathways involved in (A) erection and (B) ejaculation in 

 man, based on observations after partial sympathectomy. (From G. P. Whitelaw and R. H. 

 Smithwick, New England J. Med., 245, 121-130, 1951.) 



724 



