Cerebellum

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                                                                 Cerebellum.

 Keywords: Paleocerebellum, archi-cerebellum, neocerebellum, Stellate cells, basket cells, Purkinje cells, Granular cells, Golgi cells, branchium conjunctivum, branchium pontis.

 The cerebellum is present in the posterior cranial fossa posterior to the brain stem. The brain stem consists of the midbrain, pons, and medulla oblongata. It appears as a separate structure at the bottom of the brain-cerebrum, from which it is separated by a fold of dura mater known as tentorium cerebelli. The cerebellum develops from the metencephalon of the rhombencephalon along with the pons. The medulla oblongata originates from the myelencephalon part of the rhombencephalon.

The neurons are present on the surface of the cerebellum, so its outer surface is gray. In the cerebellum, gray matter is present on the surface, and white matter is situated inside. Some nuclei are present deep in the white matter. The cortical surface is covered with parallel groves called folia. It is a continuous layer of grey matter in the style of a folding fan. The cerebellum consists of a folded layer of cortex in which several neurons are present. White matter is present inside the cortex in which. deep cerebellar nuclei are embedded. A fluid-filled fourth ventricle is present at the base of the cerebellum.

Structure:

Subdivision of the cerebellum:

1. Lateral view - it can be divided into anterior, posterior, and floculonodular lobe.

2. Posterior view -it can be divided into:-two parasagittal sections –central vermis, a short area on both sides of vermis is perivermis and Rt. and Lt. lateral hemisphere. Three divisions: central is vermis, due to its resemblance with a worm bent upon itself, and right and left hemisphere.

 

The primary fissure divides the cerebellum into two lobes- the anterior lobe and the posterior lobe.

The posterolateral fissure seperates the posterior lobe and foliculo nodular lobe.

The anterior lobe is known as Paleocerebellum or Spinocerebellum and receives proprioceptive input from the body. The anterior lobe is concerned with postural reflexes and control axial and limb muscles.

Foliculo- nodular lobe is also known as archi-cerebellum as during evolution; this part developed early. In lower animals, this is well developed. It is connected with the vestibular apparatus, so it is also known as the vestibulocerebellum. It is concerned with the maintenance of body posture and equilibrium.

The posterior lobe is known as the neocerebellum. This is connected with the cerebral cortex and is concerned with coordination.

In short :

Foliculo nodular lobe is the archicerebellum and is connected with the fastigial nucleus concerned with balance and equilibrium.

Paleocerebellum is the anterior lobe connected with the interpositus nucleus and also known as the spinocerebellar cerebellum.

The posterior lobe is known as the neocerebellum and is connected with the dentate nucleus.

 

 

  

Lobe of cerebellum	--cerebellum	Connected with	functions
Foliculo nodular	archicerebellum	fastigial nucleus	balance and equilibrium
Anterior lobe	Paleocerebellum	interpositus nucleus	postural reflexes and control of axial and limb muscles.
posterior lobe	neocerebellum	Dentate nucleus	movement coordination

 

Histology :

The cerebellum's cortex is divided into the outer molecular, middle Purkinje, and inner granular.

Outer

1.    molecular layer has two types of cells :

a) Stellate cells stars shaped and they are superficial and

b) Inner cells, also known as basket cells are deeply located and have tiny dendrites.

The middle layer is composed of Purkinje cells; this layer is only one cell thick. The Purkinje cell is the biggest neuron in the body. This cell provides an extensive dendrite network in the outer molecular layer. Only the Purkinje axon goes into the deep cerebellar nuclei and transmits the output of the cerebellar cortex.

Inner granular layer: In this layer, two types of cells are present a). Granular cells are small, round cells. Their axons pass into the outer molecular layer and then bifurcate to form two branches of T that run along the long axis of the foli and, therefore, parallel fibers. They are excitatory and connect with the dendrites of the basket, Golgi, Purkinje, and stellate cells.

 

Golgi cells are large cells. They are less in number. Their dendrites project outwards into the outer molecular layer and receive input from parallel fibers. The cell body receives information from Purkinje cells and climbing fibers.

 

Connections of the cerebellum:

Three peduncles connect the cerebellum to the brain stem :

Inferior cerebellar peduncle connected with the Medulla oblongata.

The Middle cerebellar peduncle is connected with the pons and is composed entirely of afferent fibers from the contralateral pontine nucleus. It is also known as branchium pontis.

 The superior cerebellar peduncle is also known as branchium conjunctivum. lt connects the cerebellum with the midbrain and consists mainly of the cerebellothalamic and cerebellorubral tracts. It is the most medial and superficial among the peduncles.

 Inferior cerebellar peduncle:

The dorsal spinocerebellar tract of Flechsig

Vestibular cerebellar tract

Reticular cerebellar tract

Cuneo cerebellar tract carries proprioceptive impulses from arm and neck muscles.

Fibers from cranial sensory nerves mainly from the trigeminal nerve.

Efferents fibers from Fastigeal nucleus pass to Diete nucleus

Middle cerebellar peduncle:

Pontocerebellar fibers from the pontine nucleus go to the opposite cerebellar hemisphere.

 Fibers from roof nuclei and Purkinje cells of the cerebellum pass to the pons and medulla of the opposite side.

 Superior cerebellar peduncle:

Ventral spinocerebellar tract,

Tacto cerebellar tract

Olivo cerebellar fibers

Main efferents: Arise from the dentate nucleus, decussate in the midbrain, end in the thalamus, and the red nucleus of the opposite side.

 

The cerebellum is connected with:

1. Spinal cord of same side and

2. Cerebral cortex of opposite side

 So lesion of cerebellar hemisphere causes ipsilateral motor signs –Cerebellar syndrome- due to a). Crossing of fibers at pontocerebellar pathway-middle cerebellar peduncle.

b). Crossing of fibers in the superior cerebellar peduncle,

c). Crossing of fibers in pyramid tract.

Lesion of the dentatothalamic tract before crossing causes symptoms and signs on the same side but, after decussation causes contralateral symptoms and signs.

However, a cerebral hemisphere lesion causes motor signs on the opposite side - pyramidal syndrome- Crossing of pyramidal fibers at medulla oblongata to reach the lower motor neuron.

Orientation of cerebellar neurons: cortical neurons and their processes have definite spatial orientation in the plane of the folia.

Tag: Paleocerebellum, archi-cerebellum, neocerebellum, Stellate cells, basket cells, Purkinje cells, Granular cells, Golgi cells, branchium conjunctivum, branchium pontis.

Internal link: https://blog.totalphysiology.com/2021/08/hypothalamus -connections and functions.

https://blog.totalphysiology.com/2021/08/hypothalamus

https://blog.totalphysiology.com/2021/08/thalamus -connections and functions

External link: en.m.wikipedia.org/wiki/cerebellum

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