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4-7. Beaded Fibers

The cerebellar cortex receives not only mossy fibers and climbing fibers, but also beaded fibers, which contain various amines, such as serotonin, norepinephrine, or histamine, or neuropeptides, such as angiotensin II or orexin (Haines and Dietrichs, 1984; Haines et al., 1984; Airaksinen and Panula, 1988; King et al., 1992; Onat and Cavdar, 2003; Zhu et al., 2006; Ito, 2009). The beaded fibers extend fine varicose axonal fibers sparsely throughout the granular and molecular layers to form direct contacts with Purkinje cells and other cerebellar neurons. These axonal fibers are often called the third type of cerebellar afferent. On the basis of their diffuse extensions, it is considered that this third type of afferent does not convey specific information to the cerebellar cortex. Rather, its role could be modulatory. Akin to stomatogastric ganglia (Marder et al., 1986), such neuromodulation would set the activity level or switch the operational mode of a cerebellar microcomplex (Chapter 9, “Network Models”) to match a behavioral demand (Schweighofer et al., 2004) (for further description, see Chapter 6).


  

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