cerebellum: purkinje cells only output?

[donkeyboy]

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i never never never got the cerebellum and still after trying to read up on it, it remains one big blob in my mind.

so purkinje cells are supposed to be the only output from the cerebellum and they are always inhibitory, but then I read that they project to the deep cerebellar nuclei (dentate, emboliform, etc.) and I get confused. wouldn't that mean the axons of the deep cerebellum nuclei are the only output from the cerebellum (or do the purkinje cells not synapse on the deep cerebellum nuclei?)

and then there are granule cells with parallel fibers and mossy and climbing fibers that are excitatory to the purkinje cells or the deep cerebellar nuclei?

plus there are golgi cells, basket and stellate cells? arghh!

sorry yeah I really don't know anything.....if anyone is willing to explain any of this i'd really appreciate it, thx!

 

[turkeyjerky]

I can't give you the full deal, cause I honestly don't remember anymore. But the following should be enough, imo.

Purkenje cells are GABAergic and project to the deep cerebellar nuclei, which then project to other parts of the brain (motor thalamus, spinal cord, etc). This is the only output of the cerebellum. The purkenje cells receive input from two sources: climbing fibers from the inferior olives (these produce complex spikes and are important in learning), and parallel fibers from granule cells, which produce simple spikes. Mossy fibers are the other input fibers to the cerebellum, they form excitatory synapses on granule cells. The other types of cells aren't really important.

 

[Domenech]

Yes Purkinje cells do output onto deep cerebellar nuclei with the exception of VESTIBULAR nuclei where output is direct.

Output of deep cerebellar nuclei is EXCITATORY but purkinje inhibits that. So overall, there is an inhibitory output. Deep cerebellar nuclei output CANNOT be inhibitory because in that case, it would undergo the process of disinhibition. But don't let this confuse you.

The only inputs = direct by olivocerellar fibres (direct synapse on purkinje) and indirect by mossy fibres (every other input) through first synapse on granule cells (which are EXCITATORY and therefore have glutamate). Through parallel fibres they EXCITE purkinje which are stimulated to make GABA so INHIBIT. Just a concept you have to understand. Rest is all peanut butter 👍

Golgi, stellate and basket all have inhibitory connections with purkinje and parallel fibres. Just know that all they do is simply wipe out the signal. All are GABAergic.

 

[Raryn]

Purkinje cells are the only output of the cerebellar *cortex*. The deep cerebellar nuclei are the output through the cerebellum as a whole (and have a variety of different output pathways depending on the nucleus)

 

[NRAI2001]

Yes Purkinje cells do output onto deep cerebellar nuclei with the exception of VESTIBULAR nuclei where output is direct.

Output of deep cerebellar nuclei is EXCITATORY but purkinje inhibits that. So overall, there is an inhibitory output. Deep cerebellar nuclei output CANNOT be inhibitory because in that case, it would undergo the process of disinhibition. But don't let this confuse you.

The only inputs = direct by olivocerellar fibres (direct synapse on purkinje) and indirect by mossy fibres (every other input) through first synapse on granule cells (which are EXCITATORY and therefore have glutamate). Through parallel fibres they EXCITE purkinje which are stimulated to make GABA so INHIBIT. Just a concept you have to understand. Rest is all peanut butter 👍

Golgi, stellate and basket all have inhibitory connections with purkinje and parallel fibres. Just know that all they do is simply wipe out the signal. All are GABAergic.

So basically:

Excitatory input to purkinje fibers:
-olives (directly) (via climbing fibers)
-mossy fibers (indirectly via granule cell via parallel fibers?)

Inhibitory input to purkinje fibers (and on to parallel fibers):
-Golgi cells
-Stellate cells
-Basket Cells

** Purkinje have a net inhibitory output onto deep cerebellar nuclei (which are excitatory)**

 

[hoqhuuep]

FYI: climbing fibers from the contralateral ION use aspartate, not glutamate. I recall (not sure) that it's the only place that uses asp as an NT.

 

[JustSomePreMed]

Ok, to add to this all (because the cerebellum was taught poorly to us), let me see if I have this right (and I might be wayyyyy off).

Ascending proprioceptive input reaches the cerebellar cortex via the Cimbing Fibers (from the IO) traveling through the Inferior Cerebellar Peduncle and synapsing on the Purkinje cells. Purkinje cells (via GABA) project to the Dentate Nucleus (the most important deep cerebellar nucleus), which then projects to the contralateral Ventral Lateral nucleus of the Thalamus (which according to First Aid is responsible for "motor" functions). This is the Dentothalamic tract. Then neurons travel from the VL nucleus of the Thalamus to the Primary Motor Cortex, which then projects back down to the contralateral (so, ipsilateral to the original ascending input) pontine nuclei. Then the fibers from the pontine nuclei project to the cerebellar cortex (this time to the Granule Layer as Mossy Fibers) and synapse on Granular Cells (which is involved with the input up to the Purkinje cells again).


Whew. Is that close to being right? And are the climbing fibers coming from the contralateral IO below? We were never really taught WHAT the IO does, so I'm not really sure what kind of info it has travelling in it....

 

[hoqhuuep]

That's actually very close. The part that's off is the beginning: the inferior olives (ION) receive most of their fibers from descending rubroolivary tracts... meaning that most of their input is from the ipsilateral red nucleus (which is in the midbrain, two steps above). Now if you think of the red nucleus as the center for "posturing" of the upper limb, then that makes the ION the adjustment center for the posturing.

We just took neuro and that's what we were taught, anyways. Hope this makes sense.