REFLEX ACTION 



109 



Fig. 61. — A. Diagram of a cross-section of the spinal cord showing a pair 

 of spinal nerves and the essential parts of a reflex arc. The neurones neces- 

 sary for the simplest tv-pe of reflex action are present on the left, while those 

 of a typical reflex arc are represented on the right. B. Diagram of spinal 

 cord to show some relations of neurones in reflex arcs. The brain would lie 

 to the right as the diagram is constructed. Arrows in both diagrams indicate 

 the direction of transmission of the nervous impulses. 



a.n., afferent or sensory neurone; ad.n.\, adjuster neurone, transmitting impulses ven- 

 trally; ad.n.:, adjuster neurone, transmitting impulses longitudinally; ad.nx, adjuster 

 neurone, transmitting impulses from one side of the cord to the other; d.r., dorsal or sensory 

 root; d.r.g., dorsal root ganglion; E, effector; e.n., efferent or motor neurone; g.m., gray 

 matter; R, receptor; s.n., spinal nerve; v.r., ventral or motor root; w.m., white matter. 



