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HANDBOOK OF I'H"lSIOLOG V 



NEUROHH^SIOLOGV II 



Thi'ough ihc nineteenth century the unravelling 

 of the pattern of reflex response advanced rapidly. 

 In 1823 Mayo showed that the pupillary reflex to 

 light depended on the integrity of one small segment 

 of l)rain stem. Legallois in 1826 discovered that 

 injury to one small portion of the medulla paralyzed 

 respiration. Prochaska and Marshall Hall refined the 

 idea of 'reflex function' and greatly stimulated in- 

 terest in the subject (35, 47). The considerable con- 

 tributions of biologists and general physiologists, 

 such as Bethe and I^oeb, in the following 80 years, 

 should also be mentioned. It was the painstaking 

 observations of Goltz (39) and his associate Freusberg 

 on the chronic spinal dog that established the general 

 pattern of mammalian spinal behavior that was 

 later to be subjected to detailed analysis by Sherring- 

 ton. 



If segments of lumbosacral spinal cord survive, 

 the skeletal musculature, after an initial period of 

 inert flaccidity ol variable duration, begins to show 

 reflex responses. In the dog this period of severe 

 'spinal shock' may last several hours. In monkey and 

 man it lasts from one day to three weeks. The first 

 reflex to recover is usually some contraction of the 

 adductors of the thigh, or dorsiflexors of the ankle 

 in response to a pinch of the foot. In some animals 

 the knee jerk is the first response to be obtained. In 

 man a small flexion movement of the toes in response 

 to stimulation of any part of the sacral segments 

 may be the first to appear (28). Day by day the flex- 

 ion of hip, knee and ankle becomes more regularly 

 elicitable and requires less intense stimulation. At 

 the same time the area from which this, the flexion 

 reflex, can be elicited spreads from its 'focus' in the 

 outer border of the foot to include the whole plantar 

 surface, then the dorsum of the foot, the anterior 

 aspect and then the whole leg. Finally it may be 

 obtainable from any part below the level of transec- 

 tion, including the abdominal wall if the segmental 

 level is high enough. As the nociceptive flexion 

 reflex thus recovers, the automatic response of the 

 bladder and rectum, at first exhibiting only the weak 

 rhythmical contractions in response to distention re- 

 sembling those of the animal with exsected spinal 

 cord, abruptly begins to discharge the contents of 

 these organs more forcefully and completely. At this 

 point more effective bladder and rectal contractions 

 can be initiated by stimulation of the perineum and 

 later of the limbs. This more coordinated reaction is 

 reflex urination and defecation. 



In the acute decapitate-cat preparation commonly 

 used in classroom experiments, natural stimulation 



produces little if any response; the tendon reflex is 

 present and stimulation of nerve trunks and roots 

 can elicit flexion reflexes. In the chronic spinal state, 

 as the flexion reflex gains in recovery, its elicitation 

 in one limb is associated with extension of the op- 

 posite limb (crossed extension). In the first weeks the 

 hind limbs of the dog are found in a posture of tremu- 

 lous flexion, apparently the result of multiple minor 

 reflex flexions, though at times a feeble stretch 

 reflex ("the pluck reflex') is observable. The knee 

 jerk is brisk and of large amplitude. Under favorable 

 circumstances, particularly when ulceration of the 

 skin and infection of the bladder have been avoided, 

 and with greater frequency in the spinal dog than in 

 other animals, the limbs may then begin to extend 

 at intervals, the knee jerk becomes clonic, and pas- 

 sive flexion of the limb meets a resistance that 

 increases, then melts as the limb is passively flexed. 

 This is due to recovery of the stretch reflexes of the 

 extensor muscles. Passive flexion of one limb then 

 commonly initiates extension of the other (Phillip- 

 son's reflex), followed by an alternating stepping 

 movement. The flexion phase of the step is the 

 proprioceptive flexion reflex. A moving coarse con- 

 tact from the ball of the foot onto the toes while the 

 limb is flexed may then initiate a sudden powerful 

 extension of both limbs (the exten.sor thrust) which 

 in full recovery becomes the first phase of a gallop 

 rhythm. 



When such a state of reflex recovery in the iso- 

 lated segments of spinal cord is reached, a number of 

 other reflexes make their appearance, for example 

 the coitus reflex from appropriate stimulation of the 

 perineum, the shake reflex from stimulating broad 

 areas of the skin of the back and thorax, and the 

 scratch reflex from nociceptive, particularly moving, 

 stimuli in any part of a saddle area that covers the 

 shoulders and neck. The focus of the scratch reflex 

 lies behind the ear. The whole field covers the back 

 of the head and neck and a saddle-shaped area over 

 the shoulders. Only the caudal part of this area is 

 demonstrable by spinal transection. The focus behind 

 the pinna can be shown in the decerebrate animal 

 (90). Goltz and Freusberg observed shivering in the 

 muscles supplied by isolated thoracic seginents of 

 spinal cord in response to cold applied to the corre- 

 sponding skin segment, although shivering of the 

 limbs is not obtainable in the chronic spinal prepara- 

 tion (91). For further details of these responses the 

 reader is referred to the original works of Goltz (39) 

 and the writings of Sherrington (87, 92). 



