RESPONSIVENESS IN VERTEBRATES 



Dorsal root White matter Gray matter 



Afferent 

 neuron ^^ / / 



Dorsal root 

 ganglion 



Afferent 

 neuron 



Effector 



Receptor 



Fig. 4.10. A, the spinal cord, in cross section, showing a pair of spinal nerves and the essen- 

 tial parts of a reflex arc; diagrammatic. The neurons necessary for the simplest type of reflex 

 action are shown on the left, and those of a typical reflex arc are represented on the right. B, 

 the spinal cord, from the side, showing some relations of neurons in reflex arcs; diagrammatic. 

 The brain would lie to the right as the diagram is constructed. Arrows in both diagrams indicate 

 the direction of conduction of the nerve impulses. 



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