Afferent fibers of cerebellum : climbing and mossy fiber

 Afferent fibers of cerebellum : climbing and mossy fiber 

climbing fiber 

Climbing fibers  are the terminal fibers of the olivocerebellar tracts

One climbing fiber makes synaptic contact with

1-10  purkinje neuron

Climbing fiber arises from

·         the inferior olivary nucleus located in the medulla oblongata

They passes through the granular layer and purkinje layer and terminate into  the molecular layer

These axons pass through the pons and enter the cerebellum via the inferior cerebellar peduncle

These fibers provide very powerful, excitatory input to the cerebellum which results in the generation of complex spike excitatory postsynaptic potential (EPSP) in Purkinje cells

 In this way climbing fibers (CFs) perform a central role in motor behaviors.

They influence 

·         Motor timing.

·         the control & coordination of movements

·         They contribute to sensory processing and cognitive tasks likely by encoding the timing of sensory input independently of attention or awareness

Climbing fibers cross the midline in the brain stem, enter the cerebellum through the inferior cerebellar peduncle, and terminate contralaterally within the cerebellum.

In the central nervous system, these fibers are able to undergo remarkable regenerative modifications in response to injuries, being able to generate new branches by sprouting to innervate surrounding Purkinje cells if these lose their CF innervation.

This kind of injury-induced sprouting has been shown to need the growth associated protein GAP-43

Climbing fiber cannot have rosettes

A single purkinje neuron makes synaptic contact with only one climbing fiber

Climbing fiber > purkinje fiber

Mossy fiber 

 

Mossy fibers are the termical fibers of all other cerebellar afferent tract

One mossy fiber makes synaptic contact with 1000 purkinje neuron through granule cells of cerebellum

Mossy fiber arises from many sources

·         cerebral cortex ( largest),

·         the vestibular nerve and nuclei,

·         the spinal cord,

·         the reticular formation, and

·         feedback from deep cerebellar nuclei

They terminate in the granular layer of the cortex within the glomeruli

Axons of mossy fiber enter the cerebellum via the superior , middle and inferior cerebellar peduncles

They serve as inhibitory interneuron , they influence the degree of purkinje cell excitation

They  modify muscle activity through the motor control areas of the brain stem and cerebral cortex

Depending on the source of the mossy fibers, their termination within the cerebellum can be predominantly ipsilateral or contralateral and is restricted to particular lobules.

Keratan sulfate proteoglycan phosphacan regulates mossy fiber outgrowth and regeneration

Each mossy fiber can have up to 50 rosettes

unlike climbing fibers, mossy fibers DO NOT go directly to the Purkinje cell.

Mossy fiber > granule cell > purkinje fiber