FUNCTIONS OF THE SPINAL CORD 



contractions) occurring in the body itself, which changes are in turn 

 usually initiated by excitation of surface receptors by the environment. 

 Examples of superficial reflexes are the plantar reflex (the drawing-up 

 of the foot when the sole is tickled), the cremasteric reflex (retraction of 

 the testicle when the skin on the inside of the thigh just below Poupart's 

 ligament is stroked, especially in boys), the gluteal, abdominal, epigastric, 

 and inter scapular reflexes (contraction of the muscles in those regions 

 when the skin covering them is tickled). The behaviour of the toes, 

 especially of the great toe, is of considerable diagnostic importance. 

 Normally, on tickling the sole, the toes 

 are flexed towards the planta; but 

 when a lesion of the pyramidal tract 

 exists, as in hemiplegia, there is dorsal 

 instead of plantar flexion, most marked 

 in the case of the great toe, and the 

 toe moves more slowly than in the 

 healthy person (Babinski'ssign). This 

 is an instance of reversal of a reflex 

 owing to the elimination of the in- 

 fluence of the cortex. In an epileptic 

 fit there is said to be a temporary 

 reversal of the same reflex, indicating 

 probably that the cortex is temporarily 

 eliminated in consequence of fatigue 

 due to intense and prolonged discharge. 

 In children during the first few months 

 of life stimulation of the sole causes 

 normally a dorsal flexion of the big toe, 

 this reversal of the normal reaction of 

 the adult persisting until the pyra- 

 midal path has attained functional 

 completion (p. 820). During sleep 

 the reversed reaction (dorsal flexion) 

 is still obtained for a time. Examples 

 of deep reflexes are the knee-jerk (a 

 sudden extension of the leg by the 

 rectus femoris and vastus medialis- 

 components of the quadriceps muscle 

 when the ligamentum patell.ne is sharply 

 struck), the heel-jerk or foot-jerk (a 

 movement of the foot caused in most 

 healthy persons, though not in all, by 

 tapping the tendo Achillis), and the 

 periosteal radial reflex (a movement 

 of flexion and slight pronation of the Fig. 356. Diagram of Reflex Centres 

 forearm and hand elicited by tapping in Cord (after Hill), 



the lower end of the radius). The 



jaw-jerk (a movement of the lower jaw when, with the mouth open, 

 the chin is smartly tapped) and ankle-clonus (a series of spasmodic 

 movements of the foot, brought about by flexing it sharply on the leg) 

 are phenomena of the same class, which can be elicited only in 

 disease. Any condition which impairs the conducting power of the 

 afferent or efferent fibres of the reflex are necessarily diminishes or 

 abolishes the reflex movement, even if the central connections are 

 intact. E.g., in locovnotor aiaxia the disappearance of the knee-jerk 

 is one of the most important diagnostic signs. This disease involves 

 the posterior roots and the fibres that continue them in the posterior 



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