CENTRAL CONTROL OF EYE MOVEMENTS 



1093 



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FIG. 2. Action potentials of an 

 afferent fiber from a muscle spin- 

 dle in the superior oblique of the 

 goat. A. Effect of pulling on its 

 tendon : upper record, time in J -j 

 and Vioo sec. ; middle record, signals 

 of active stretch; lower record, 

 action potentials in one large 

 and several small fibers. B. Effect 

 of stimulating the nerve supply to 

 the intrafusal muscle fiber: upper 

 record, tension (calibration, 5 gm) ; 

 middle record, 50 cycle time 

 marker, tower record, action poten- 

 tials from a single muscle spindle; 

 arrow marks the stimulus arte- 

 facts. [From Whitteridge, unpub- 

 lished observations.] 



of the gamma efferent at aljout 100 impulses per sec. 

 may increase the sensitivity of a spindle receptor to 

 stretcli by a factor of 7 to 8 (147). 



Single unit discharges hav'e also been recorded in 

 fibers from cat and monkey eye muscles (42). The 

 discharges during passive stretch resemble those 

 from muscle spindles and give proof of low threshold 

 stretch receptors in these muscles. Technical diffi- 

 culties prevented observation of the effect of a motor 

 twitch on these discharges. 



Responses from tendon endings in goat eye muscles 

 have also been recorded (35). Their discharge is 

 similar to that of the B endings described by 

 Matthews (102). They discharge, often with an in- 

 creased burst of impulses, during the rising phase of 

 a muscle twitch. Their threshold to stretch may not 

 be higher than that of muscle spindle endings, but 

 their response to rate of change of stretch is com- 

 paratively slight. During steady stretch the dis- 

 charge is regular both when the motor nerve is intact 

 and when it is cut. 



Afferent Paths From Eye Muscles 



It is now well established that the eye muscles can 

 send afferent discharges to the brain (40) and it is of 

 interest to know the pathway taken by such dis- 

 charges. Reference has already i:)een made to the 

 special afferent nerve trunks froin the eye muscles in 

 sheep and goats (fig. 3). These were first seen by 

 Winckler (149-151) who found that they ran from 

 the muscles to the ophthalmic or rarely to the maxil- 

 lary division of the fifth nerve in various ungulates. 



go. 



FIG. 3. The orbit of the goat seen from above to show the 

 afferent branches. //, optic nerve; IV, trochlear nerve; V, part 

 of ophthalmic division of trigeminal nerve; r, levator palpebrae; 

 d.s., rectus superior; g.o., superior oblique; n, branches of the 

 nasociliary ner\'e. [From W'inckler (151).] 



The work was confinned and extended to other 

 ungulates, birds and reptiles by Kiss (91). These 

 trunks are usually completely separate from the 

 motor nerves but in a few instances join the motor 



