Cerebellum

Cerebellum

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Cerebellum

Hindbrain consists of:
  • Cerebellum
  • Pons
  • Medulla oblongata
Cerebellum is the largest part of the hindbrain
 
Location:
*  Situated in the posterior cranial fossa behind pons & medulla oblongata & below the tentorium cerebelli.
 
Tentorium cerebelli can as a partition between the occipital lobe of the cerebrum and cerebellum.
 

Relation of the cerebellum:

 
Anteriorly:
Fourth ventricle, pons & medulla
Posterioinferiorly:
Squamous part of occipital bone
Superiorly:
Tentorium cerebelli
 
 
External Features:
Consists of two cerebellar hemispheres which is united by vermis.
 
Two surfaces:
 *  Superior surface
 *  Inferior surface
These two surfaces are separated by horizontal fissure which lies in the middle lobe.
  • The superior surface is continuous between two cerebellar hemispheres.
  • But the inferior surface presents a median notch called vallecula.
Posteriorly between two hemispheres present a notch for the attachment of falx cerebelli.
 
 

Three lobes of the cerebellum:

1)  Anterior lobe
2)  Middle lobe / Posterior lobe
3)  Flocculonodular lobe
 
These lobes are divided by
  • Primary fissure (Fissure Prima)
  • Posterolateral fissure
* Anterior lobe & Middle lobe are separated by primary fissure.
*  Middle and Flocculonodular lobe are separated by posterolateral fissure.
 
* Anterior lobe lies on the superior surface.
* The middle lobe lies on both the inferior & superior surface.
 
A horizontal fissure cut the middle lobe into the superior half & inferior half separating the superior surface & inferior surface.
 
Parts above the horizontal fissure representing the superior surface
Parts of vermis Subdivision of the cerebellar hemisphere
Lingula   ----
Central lobule Ala
Culmen Quadrangular lobule
Declive Simple lobule
Folium Superior semilunar lobule
 

Parts below the horizontal fissure represent inferior surface
Parts of vermis Subdivision of the cerebellar hemisphere
Tuber Inferior semilunar lobule
Pyramid Biventral lobule
Uvula Tonsil
Nodule Flocculus
 
 
Note:
Two surface of vermis like cerebellum
 * Superior surface
 * Inferior surface
Each part of the vermis has a lateral extension.
However, the lingula does not have any lateral extension.

 

Morphological & Functional Divisions of Cerebellum:

 
Archicerebellum
Made up of flocculonodular lobe & lingula
It has a vestibular connection
Function:
Maintenance of equilibrium, muscle tone & posture
Neocerebellum:
Made up of the middle lobe except for the pyramid & uvula of the inferior vermis.
Function:
Regulation of Fine movements of the body
Paleocerebellum
Made up of the anterior lobe (except lingula) and pyramid & uvula of the inferior vermis.
Function:
Regulate the crude movements
 
 
Connection of Cerebellum:
The fibers entering or leaving the cerebellum are grouped to form three peduncles that connect the cerebellum to the midbrain, pons & medulla.
 
Superior cerebellar peduncle:
*  Connect the cerebellum to the midbrain

Middle cerebellar peduncle:
*  Connects cerebellum to pons

Inferior cerebellar peduncle:
* Connect cerebellar to medulla oblongata

 

Histological structures of the cerebellum:

 
Outer cortex - made of grey matter
Inner central core - made of white matter
And within the whiter matter-embedded intracerebellar nuclei.

The cerebellum is made up of outer grey matter, the cerebellar cortex, and a central core of white matter.
Embedded within the central core of white matter are the masses of grey matter called intracerebellar nuclei.
Tip:
The collection of nerve cell bodies within the CNS is called a nucleus.
* The main component of grey matter is the Nerve cell body.
 
 
Histological structure of outer cerebellar cortex:
Made up of grey matter.
 
Consists of 3 layers
  • Molecular layer
  • Purkinje cell layer
  • Granular cell layer
Molecular layer:
Outermost layer
Consists of:
  • Stellate cell & Basket cell
  • Dendrites of Purkinje cell
  • Parallel fibers
    (Axons of granule cells form parallel fibers)
  • Purkinje cell layer
The middle layer of cerebellar cortex:
* Contain only cell body of Purkinje cell
 
Granular layer
Consists of
* Granular cells
* Golgi cells
 
Note:
Climbing fiber arises from an inferior olivary nucleus and synapses with the dendrites of the Purkinje cell.
Mossy fibers synapse with the granule cell.
Basket cell synapse with the cell body of the Purkinje cell.


Inner white matter:
It consists of 3 groups of nerve fibers
 
Intrinsic fiber
Make connections within the cerebellum.
Afferent fibers (sensory) or Input
* Mossy fibers
* Climbing fibers
Efferent fibers or output
Axons of Purkinje cell
 
 
Connection...

Input from climbing fibers
     |
Directly synapse with dendrites of Purkinje cell

 

Maximum input from the brainstem & higher brain via mossy fibers to the cerebellum
     |
Synapse with granule cell
     |
The axon of granule cell form parallel fibers
     |
Parallel fibers connect with dendrites of Purkinje cell

 

Note:
All Four types of neurons of the cerebellum are inhibitory.

  1. Purkinje cells
  2. Basket cell
  3. Stellate cell
  4. Golgi cell
Only the granular cells are excitatory.
 
 
Intracerebellar nuclei of cerebellum:
  1. Dentate nucleus
  2. Emboliform nucleus
  3. Globose nucleus
  4. Fastigial nucleus
Mnemonic: DEFG
 
 
Blood supply of cerebellum:
 
Arterial supply:
Superior cerebellar artery, a branch of the basilar artery
Anterior inferior cerebellar artery, a branch of the basilar artery
Posterior inferior cerebellar artery, a branch of the vertebral artery

Venous drainage:
* Superior cerebellar veins- drain to transverse sinus & superior petrosal sinus
* Inferior cerebellar veins- drain into transverse sinus & inferior petrosal sinus
 
Tip:
The basilar artery is formed by the union of the 4th part of the vertebral artery after coursing through the foramen magnum.
Basilar artery lodges in the basilar sulcus present in the anterior of the pons.
The vertebral artery is a branch of the 1st part of the subclavian artery.



Functions of the cerebellum :

  1. Control the muscle tone, posture & equilibrium
  2. Coordinate the voluntary movements of the body (same side) so that they are smooth, balanced & accurate.
  3. All sensory information of muscles and joints regarding the movement is relayed here to correct the movement.
 
Tips:
* Cerebellum is not the initiator of voluntary movements.
* But coordinate the voluntary & decreases the error present in the voluntary movement initiated by the cerebrum.
* Thus, it is needed for fine, perfect voluntary movement.
 
* The cerebrum controls the opposite side of the body (contralateral side).
* Cerebellum control movement of the same side (ipsilateral side).
 
Development of cerebellum:
Metencephalic part of rhombencephalic vesicle of the neural tube.
 
 
Cerebellar Dysfunction:
Cerebellar lesions could give rise to
  • Disturbance of voluntary movement
  • Disturbance of posture
Clinical Features
Muscular hypotonia (low muscle tone) - less resistance
Intention tremors (tremors only during movements)
Dysdiadochokinesia:
Inability to perform rapid & regular movements like pronation & supination
Gait ataxia -
Unsteady gait/ unable to walk on a straight path like an alcoholic person.
Nystagmus-
Involuntary jerky movement of eyeball


Tips:
* Muscle tone is the partial state of contraction of muscle fibers.
* To maintain posture ie. sitting, and standing, some muscles are continuously working.
Different types of tremors:
* Parkinson’s disease (involuntary tremor- resting tremor)
* Cerebellar lesion (intention tremor - tremor during performing voluntary movement)
* Thyrotoxicosis (Fine tremor)
Three - 3 pattern:
Three parts:
Archicerebellum
Paleocerebellum
Neocerebellum
Three lobes:
Anterior lobe
The middle or posterior lobe
Flocculonodular lobe
Three fissures:
Fissura prima (primary fissure)
Horizontal fissure
Posterolateral fissure
Three histological layers of grey matter:
Molecular layer
Purkinje cell layer
Granular cell layer
Three peduncles:
Superior cerebellar peduncle to the midbrain
Middle cerebellar peduncle to Pons
Inferior cerebellar peduncle to medulla oblongata
Three arteries for each hemisphere:
Superior cerebellar
Anterior inferior cerebellar
Posterior inferior cerebellar
Three functions:
Tone, posture & equilibrium by flocculonodular lobe
Crude movements by the anterior lobe
Smooth fine movement by the middle lobe