CONDUCTION PATHS, 899 



V. Conduction Paths Involving the Cerebellum 



A. Ascending cerebellar pathways. 

 1. Spinal ganglia. 



(a) Dorsal roots of spinal nerves. 



(6) Collaterals and descending branches of bifurcation of dorsal root fibres in spinal 

 cord, chiefly those conveying impulses of muscle-sense. 

 2x. Dorsal nucleus (Clarke's column). 



(a) Dorsal spino-cerebellar fasciculus (direct cerebellar tract). 



(b) Restiform body (inferior cerebellar peduncle) — 



(c) Joined in medulla by external arcuate fibres (crossed and uncrossed fibres arising 

 in nuclei of funiculus gracilis and cuneatus) ; 



(d) Joined in medulla by fibres arising in nuclei of termination of afferent vagus, 

 glosso-pharyngeal, vestibular, and trigeminal nerves; 



(e) Joined by fibres both to and from (ascending and descending) the inferior olivary 

 nucleus of the same and opposite sides {cerebello-olivary fibres) . 



2y. Nerve-cells in base of ventral horn of same and opposite side. 



(a) Superficial antero-lateral spino-cerebellar fasciculus (Gowers' tract), ascending 

 through spinal cord and reticular formation of medulla and pons. 



(b) Anterior medullary velum and brachium conjunctivum to cerebellar cortex 

 (vermis) . 



3. Cerebellar cortex (vermis), dentate nucleus, nucleus fastigii, nucleus emboliformis, 



and nucleus globosus. 



(a) White substance (corpus medullare) of cerebellum, associating various regions 

 of its cortex and its nuclei with each other. 



(b) Brachium conjunctivum (superior cerebellar peduncle) arising chiefly from 

 dentate nucleus. 



(c) Decussation of brachium conjunctivum. 



4. Red nucleus and ventral portion of lateral nucleus of thalamus. Most fibres of the 



brachium conjunctivum terminate in the red nucleus; many merely give off 

 collaterals to it in passing to their termination in the thalamus. Most of the 

 ascending fibres arising in the red nucleus also terminate in the ventral part 

 of the thalamus; some ascend to the cerebral cortex direct. 



(a) Internal capsule, middle third, and fronto-parietal part of corona radiata. 



(6) Somaesthetic area of cerebral cortex and cortex of frontal lobe anterior to it. 



(c) Inferior peduncle of thalamus to cortex of temporal lobe. 



B. Descending cerebrocerebellar paths. 



1. Pyramdial cells of somaesthetic area send fibres through corona radiata, internal 



capsule, and cerebral peduncle to nuclei of pons and arcuate nucleus of same and 

 opposite side. 



2. Cells of cortex of posterior part of frontal lobe give fibres to form frontal pontile 



path through frontal parts of corona radiata and internal capsule and through medial 

 part of cerebral peduncle to nuclei of pons of opposite side. 



3. Cells of cortex of temporal lobe (superior and middle gyri) give fibres to form temporal 



pontile path which passes under the lenticular nucleus into anterior segment of 

 occipital portion of internal capsule and lateral part of cerebral peduncle to nuclei of 

 pons of opposite side. This path is joined in the internal capsule by a small occipito- 

 pontile path. 



4. Cells of nuclei of pons send fibres by way of brachium pontis (middle cerebellar 

 peduncle) to cortex of cerebellar hemisphere, of side opposite to that of the origin 

 of the cerebral fibres making synapses with the cells of the pons. 



C. Descending cerebellospinal paths. 



1. From cells of nucleus fastigii of same and opposite sides and probably from other nuclei 

 of cerebellum arise fibres which terminate in the nuclei of termination of the vestib- 

 ular nerve and these send fibres into the intermediate and anterior marginal fasciculi 

 of spinal cord (fig. 619), and thence to the cells of the anterior horn. 



2. Probably connected with the cerebellum is the pathway arising in the red nucleus 

 of the opposite side and descending in the rubro-spinal tract of the lateral funiculus 

 of the spinal cord (fig. 619). The rubro-spinal tract decussates in the ventral portion 

 of the tegmentum of the mesencephalon and is said to pass through the medulla oblon- 

 gata in the medial longitudinal fasciculus. It must be noted here that some fibres 

 arising in the cortex of the frontal lobe terminate in the red nucleus. 



VI. The Vestibular Conduction Paths (Equilibration) 



1. Vestibular ganghon gives origin to the peripheral utricular and three ampullar 

 branches and to the combined and centrally directed vestibular nerve. 



2. Lateral vestibular nucleus (Deiters'), medial nucleus, superior nucleus, and nucleus 



of descending or spinal root (nuclei of termination) give origin to fibres as follows: — 

 (a) From lateral and superior nuclei to nucleus fastigii of opposite side and to 



cortex of vermis and to dentate nucleus (cerebellar connection). 

 (6) From medial and superior nuclei to nuclei of origin of eye-muscle nerves of 



same and opposite sides, by way of medial longitudinal fasciculi, 

 (c) From lateral nucleus and nucleus of descending root through reticular formation 



intojateral and ventral vestibulo-spinal tracts of spinal cord. 



