CHAPTER VI 

 PERIPHERAL NERVE TERMINATIONS: END ORGANS 



All peripheral nerve fibers end either as terminal fibrils or in rela- 

 tion to a highly specialized end organ. The function of these latter 

 bodies is apparently included in the changing of ordinary stimuli- 

 mechanical, thermal, chemical, etc. into a nerve impulse, or, vice versa, 

 the changing of a nerve impulse to a cell stimulus which results in 

 motion, secretion, etc., according to the nature of the tissue cells which 

 are thus stimulated. Some of the nerve end organs are connected with 

 efferent (motor) fibers, others with afferent (sensory) fibers. Nerve 

 endings are found in nearly all the tissues of the body with the exception 

 of cartilage and the calcareous tissue of the bones. 



NERVE ENDINGS IN EPITHELIUM 



Intra-epithelial nerve fibrils are derived from the nerve fiber plexuses 

 in the subjacent connective tissue ; the epithelium usually receives a very 

 abundant nerve supply. The following types of intra-epithelial nerve 

 endings have to be considered. 



1. End Fibrils. This form of nerve termination has been demon- 

 strated in all the varieties of epithelium. Terminal nerve fibers enter 

 the epithelial tissue as naked fibrils, often somewhat varicose, which form 

 a delicate plexus between the epithelial cells. The terminal fibrils of this 

 plexus frequently end in minute knoblike enlargements which are in 

 contact with the surface, but rarely, if ever, penetrafe the interior of the 

 epithelial cells. The 'trefoil plates' of Bethe represent unusually large 

 end knobs. 



2. Tactile Cells (Mcrkel). These are modified epithelial cells, 

 with clear cytoplasm and a slightly vesicular nucleus, which are found 

 in the deeper layers of the stratified epithelium of the epidermis and 

 in the root sheaths of hairs. These cells are recognized by their vesicu.- 



159 



