898 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



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Arrat front, lTmp,piriet i( 



FIG. 1 2. Neuronal chains of the central motor 

 systems, showing the relation of the lower extra- 

 pyramidal structure? with the cerebellum, the 

 cerebral cortex and the spinal servomechanisms. 



Upper part. The schematic drawing shows on 

 the ri^ht side the cerebellum with its spinal afferent 

 pathways, the spinocerebellar tracts (spi.-ce), to 

 the three longitudinal zones of the anterior cerebel- 

 lar lobe. Impulses arising in integrating corticad 

 areas (areae Jront., temp., pariet.) pass through 

 corticopontine tracts and intermediate pontine 

 nuclei iP.ini) to the semilunar lobe (5/) of the 

 cerebellar hemispheres. From there they run 

 through the parvicellular part of the dentate 

 nucleus (Dt.pc) and the dentatothalamic fibers 

 to the posterior ventral oral nucleus of the thalamus 

 (V.o.p) and to area 4 of the cerebral cortex (.^7). 

 The large fibers of the pyramidal tract originating 

 in area 4 send collaterals to the oral pontine 

 nuclei (P.O.). There a tnultineuronal reverberating 

 circuit starts to the lateral or quadrangular part 

 of the anterior cerebellar lobe iQa), leading 

 through the magnocellular dentate nucleus 

 IDl.mt:) to the red nucleus (/?«). Thus the pvrami- 

 dal impulses coordinate cerebellar and rubral 

 control systems with the reticular formation and 

 spinal cord. After one loop through the cerebellum 

 to the motor corte.x is passed, another circuit goes 

 through the red nucleus and the central tegmental 

 tract to the inferior olive ( 01) leading back to the 

 quadrangular anterior lobule, so closing the self- 

 controlling circuit of the pyramidal system start- 

 ins; in the semilunar lobe of cerebellum. From the 

 oral pontine nuclei (P.o) start two other neuronal 

 chains over the intermediate part of the anterior 

 cerebellar lobe (p.im). The first goes through the 

 emboliform nucleus (Eb) and the centrum media- 

 num (Cc) to the caudatum iCd) andputamen (Put). 

 The continuation of this first neuronal chain is 

 omitted because it spares the cerebellum. The 

 second chain passes fi'om the intermediate part 

 of the anterior lobe through the globose nucleus 

 (Gl) to the substrate for rotation in the nucleus 

 interstitialis (1st). Its main efferent pathway is the 

 interstitiospinal tract (ist-spi) to the anterior horns. 

 This postural pathway has also a self-controlling 

 circuit via the medial tegmental tract, the medial 

 accessory olive (m.ol) to the intermediate part of 

 anterior lobe near the vermis anterior (V.a). 

 From V.a., fibers arise to the vestibular nuclei 

 (Vest) and to the reticular formation (Rt) of the 

 brain stem. The efferent pathways are the vesti- 

 bulospinal and reticulospinal tracts (ve.-spi and 

 rl.-spi). .\l\ efferent fiber tracts reach the inter- 

 neuron pool of the anterior horns. In the spinal 

 cord extrapyramidal impulses do not excite the 

 motoneurons directly but probably end in inter- 

 neurons influencing the external servomechanisms 

 of muscle length and muscle tension or fire gamma 

 neurons to the intrafusal muscle fibers of muscle 

 spindles. 



Lower right. Spinal servomechanism regulating 

 muscle length. The receptors are the annulospinal 



