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What Are Mossy Fibers?

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  • Written By: Mary McMahon
  • Edited By: Shereen Skola
  • Last Modified Date: 04 December 2016
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Mossy fibers carry signals along nerve pathways into the cerebellum. Messages from these neurons play an important role in motor coordination, mediated by specialized structures called Purkinje cells. This term is also used to refer to a different kind of structure inside the hippocampus. Despite the similarity of the names, they perform different functions and are not related. The type of fiber under discussion may be made clear from the context, since they are in different regions of the brain.

Each mossy fiber has a number of projections with bulbous tips which give it the appearance of a fruiting moss when it’s stained and viewed under a microscope. These tips communicate with granule cells in the cerebellum, which can in turn fire the Purkinje cells. The result can be a triggered movement to respond to a stimulus, such as an adjustment to the position of the hands in order to grasp something, or a jerk back to avoid an unpleasant stimulus like extreme cold or heat. Constant communication between different parts of the brain allows for seamless coordination in complex tasks.

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Several pathways to the cerebellum contain mossy fibers. They follow the route taken by the spinal cord, signals from the cerebral cortex, and vestibular nerve, for example. Each pathway allows mossy fibers to carry signals of importance for cerebellar function. These can include things like feedback from the vestibular system to help the brain understand the body’s position in space as well as signals carried up the spinal cord as nerves respond to stimuli like physical sensations.

In the hippocampus, the mossy fibers contain dentate granule cells, which play an excitatory role in certain neurological processes. They appear to be closely connected with spatial learning. Research has also demonstrated that these hippocampal cells can be involved in epilepsy. Patients with epilepsy may have mossy fibers with unusually long axons that arrange themselves to form abnormal pathways that can trigger and sustain seizures.

Neuroanatomy, as the study of the anatomy of the brain is known, can be a complex subject. Researchers work with tools like stains and microscopy to identify different kinds of cells and trace the pathways they follow in the brain. They also take advantage of functional imaging studies to see which cells fire in response to specific stimuli, to learn more about how the brain functions. Understanding cell types and their role in the brain can provide insight into neurological conditions, explaining how people get sick and which kinds of treatments might help them.

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