Medical Neurosciences 731 Afferent Home
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INFERIOR OLIVARY COMPLEX

This is the largest nuclear group in the brain stem. It consists of a convoluted band of cells that lie dorsal to the pyramid. This nucleus is by far the most characteristic and striking feature of the medulla. Sadly, we know little about inferior olivary function(s), but its very intimate association with the cerebellum suggests it is involved in motor coordination and most likely motor “learning”.

Cells in the inferior olivary complex project to the contralateral cerebellum via the inferior cerebellar peduncle (or restiform body). Upon reaching the cerebellum, they end as “CLIMBING FIBERS” (they “climb up” the Purkinje cells; more on this later in the course). Climbing fibers arise solely from the inferior olive. Other endings seen in the cerebellar cortex are called mossy fibers. Mossy fibers do not arise from the inferior olive, but rather from places like Clarke’s column and the accessory cuneate nucleus. Thus, axons in the dorsal spinocerebellar and cuneocerebellar tracts end as “mossy fibers.” Inputs to the inferior olive will be discussed during the “Cerebellum” part of the course.





While many questions remain regarding the function(s) of the inferior olive, selective destruction of this nuclear complex in experimental animals has acute effects similar to those following destruction of the entire one-half of the CONTRALATERAL cerebellum. Since the inferior olive sends information to the contralateral cerebellum, and the cerebellum influences the SAME side of the body, then the loss of the LEFT olive will mean that the RIGHT half of the cerebellum is no longer receiving input from the inferior olive. This will result in incoordination/ataxia of the RIGHT side of the body. Since we will cover cerebellum later in this course, don’t worry too much about it right now. We have already discussed that cerebellar deficits involve incoordination/ataxia and are IPSILATERAL to the side of the lesion. A lesion of the inferior olive will result in incoordination/ataxia of the CONTRALATERAL ARM AND LEG (contrast this with a lesion of ACC. CUNEATE NUC. = incoordination/ataxia of IPSI ARM). What about a Romberg sign? Well, this is like a DSCT lesion. Loss of input from the olive means that you are not going to be able to stand with your feet together to begin with!! So no Romberg! Besides, it’s a cerebellar afferent!!





ALSO REMEMBER:

1). the sole source of climbing fibers is the inferior olive
2). olivocerebellars CROSS and comprise most of the inferior cerebellar peduncle
3). the inferior olive lies in the ventral medulla.



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