Comparison between tract and nerve

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  Comparison between tract and nerve Nerve Nerve contain bundle of axons (nerve fibers) in the peripheral nervous system (PNS) that transmits signals between the central nervous system (CNS) and other parts of the body. It is the most important part of peripheral nervous system Location: Peripheral nervous system. Structure: Made of axons, connective tissue layers (endoneurium: axon is surrounded by it , perineurium: bundle of axons are surrounded by it, epineurium: whole nerve trunk is surrounded by it), and blood vessels. It gets myelination by Schwann cell   Function: Carries sensory signals to the CNS (afferent) from peripheral part of body or motor signals carry from from the CNS (efferent) to target organs like skeletal muscle, cardiac muscle, smooth muscle or glands Example: Sciatic nerve, median nerve, except optic nerve (though optic nerve is technically part of CNS in develop...
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Difference between climbing fiber and mossy fiber

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Difference between climbing fiber and mossy fiber

Climbing fiber

Mossy fiber

They are the terminal fibers of the olivocerebellar tracts

They are the termical fibers of all other cerebellar afferent tract

One climbing fiber makes synaptic contact with

1-10  purkinje neuron

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

Climbing fiber arises from

·         the inferior olivary nucleus located in the medulla oblongata

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

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

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

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

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

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

 

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

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

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.

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

Keratan sulfate proteoglycan phosphacan regulates mossy fiber outgrowth and regeneration

 

Climbing fiber cannot have rosettes

Each mossy fiber can have up to 50 rosettes

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

Climbing fiber > purkinje fiber

 

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

Mossy fiber > granule cell > purkinje fiber

 

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