Cerebellum | Anatomy2Medicine
Anatomical-Position-Cerebellum

Cerebellum

    • The Cerebellum
      • develops from the alar plates (rhombic lips) of the metencephalon.
      • is located infratentorially within the posterior fossa
      • it lies between the temporal and occipital lobes and the brainstem.
      • three primary functions
        • maintenance of posture and balance
        • maintenance of muscle tone
        • coordination of voluntary motor activity.
    • Major Divisions of the Cerebellum
      • consists of a midline vermis and two lateral hemispheres.
      • is covered by a three-layered cortex, which contains folia and fissures.
      • contains a central medullary core
        • white matter that contains myelinated axons
        • four cerebellar nuclei (dentate, emboliform, globose, and fastigial nuclei).
          • The emboliform and globose nuclei are called the interposed nucleus.

 

  • Cerebellar lobes

 

      • Anterior lobe

 

  • receives input from stretch receptors (muscle spindles) and Golgi tendon organs

 

        • (GTOs) via the spinocerebellar tracts.
        • plays a role in the regulation of muscle tone.
      • Posterior lobe
        • receives massive input from the neocortex via the corticopontocerebellar fibers
        • plays a role in the coordination of voluntary motor activity.
      • Flocculonodular lobe (vestibulocerebellum)
        • consists of the nodulus (of the vermis) and the flocculus
        • receives input from the vestibular system.

 

  • plays a role in the maintenance of posture and balance.

 

    • Longitudinal organization of the cerebellum

 

  • includes three functional longitudinal zones that are associated with specific cerebellar nuclei and pathways.

 

      • Median (vermal) zone of the hemisphere
        • contains the vermal cortex, which projects to the fastigial nucleus.
      • Paramedian (paravermal) zone of the hemisphere

 

  • contains the paravermal cortex, which projects to the interposed nuclei (emboliformand globose nuclei).

 

      • Lateral zone of the hemisphere
        • contains the hemispheric cortex, which projects to the dentate nucleus.
    • Cerebellar peduncles

 

  • Inferior cerebellar peduncle

 

        • connects the cerebellum to the medulla.
        • consists of two divisions:

 

  • Restiform body

 

            • is an afferent fiber system containing:

 

  • Dorsal spinocerebellar tract
  • Cuneocerebellar tract
  • Olivocerebellar tract
  • Juxtarestiform body

 

            • contains afferent and efferent fibers:

 

  • Vestibulocerebellar fibers (afferent)
  • Cerebellovestibular fibers (efferent)
  • Middle cerebellar peduncle
  • connects the cerebellum to the pons.

 

        • is an afferent fiber system containing pontocerebellar fibers to the neocerebellum.

 

  • Superior cerebellar peduncle

 

        • connects the cerebellum to the pons and midbrain.
        • represents the major output from the cerebellum.

 

  • Efferent pathways
  • Dentatorubrothalamic tract
  • Interpositorubrothalamic tract
  • Fastigiothalamic tract
  • Fastigiovestibular tract
  • Afferent pathways
  • Ventral spinocerebellar tract
  • Trigeminocerebellar fibers
  • Ceruleocerebellar fibers

 

    • Cerebellar Cortex
      • Three-layered cerebellar cortex

 

  • Molecular layer

 

          • is the outer cell-sparse layer that underlies the pia mater.
          • contains
            • dendritic arborizations of Purkinje cells
            • parallel fibers of the granule cells.
            • stellate (outer) cells and basket (inner stellate) cells.

 

  • Purkinje cell layer
  • is found between the molecular layer and the granule cell layer.
  • Granule cell layer

 

          • is found between the Purkinje cell layer and the cerebellar white matter
          • contains granule cells, Golgi cells, and cerebellar glomeruli.
    • Neurons and fibers of the cerebellum

 

  • Purkinje cell

 

        • conveys the only output from the cerebellar cortex.(MCQ)

 

  • projects inhibitory output (gamma-aminobutyric acid [GABA]) to the cerebellar and vestibular nuclei.

 

        • is excited by parallel and climbing fibers.

 

  • is inhibited (by GABA) by basket and stellate cells.
  • Granule cell

 

        • excites (by glutamate) Purkinje, basket, stellate, and Golgi cells via parallel fibers. is inhibited by Golgi cells.
        • is excited by mossy fibers.

 

  • Mossy fibers

 

        • are the afferent excitatory fibers of the spinocerebellar and pontocerebellar tracts
        • terminate as mossy fiber rosettes on granule cells.
        • excite granule cells to discharge via their parallel fibers.
      • Climbing fibers
        • are the afferent excitatory fibers of the olivocerebellar tract.

 

  • terminate on neurons of the cerebellar nuclei and on dendrites of Purkinje cells.
  • Major Cerebellar Pathways
  • Vestibulocerebellar pathway
  • plays a role in the maintenance of posture, balance, and the coordination of eye movements.
  • receives its major input from the vestibular receptors of the kinetic and static labyrinths.
  • Semicircular ducts and otolith organs

 

          • project to the flocculonodular lobe and the vestibular nuclei.

 

  • Flocculonodular lobe

 

          • receives visual input from the superior colliculus and the striate cortex.
          • projects to the vestibular nuclei.

 

  • Vestibular nuclei

 

          • project via the medial longitudinal fasciculi (MLFs) to the ocular motor nuclei of CN III, CN IV, and CN VI
            • it coordinate eye movements.
          • project via the medial and lateral vestibulospinal tracts to the spinal cord
            • it regulates neck and antigravity muscles, respectively.

 

  • Vermal spinocerebellar pathway

 

        • maintains muscle tone and postural control over truncal (axial) and proximal (limb girdle) muscles.

 

  • Vermis

 

          • receives spinocerebellar and labyrinthine input
          • projects to the fastigial nucleus.

 

  • Fastigial nucleus

 

          • has excitatory output.

 

  • projects via the vestibular nuclei to the spinal cord.

 

          • projects to the ventral lateral nucleus of the thalamus.

 

  • Ventral lateral nucleus of the thalamus

 

          • receives input from the fastigial nucleus.
          • projects to the trunk area of the precentral gyrus.

 

  • Precentral gyrus
  • gives rise to the ventral corticospinal tract, which regulates muscle tone of the truncal and proximal muscles
  • Paravermal spinocerebellar pathway

 

        • maintains muscle tone and postural control over distal muscle groups.

 

  • Paravermis

 

          • receives spinocerebellar input from distal muscles.
          • projects to the interposed nuclei.

 

  • Interposed nuclei (emboliform and globose)

 

        • have excitatory output.

 

  • project to: Ventral lateral nucleus and Red nucleus
  • Ventral lateral nucleus

 

            • projects to the extremities area of the precentral gyrus
            • The precentral gyrus gives rise to the lateral corticospinal tract, which regulates the distal muscle groups.

 

  • Red nucleus
  • gives rise to the crossed rubrospinal tract, which mediates control over distal muscles.
  • receives input from the contralateral nucleus interpositus and bilateral input from the motor and premotor cortices.
  • Lateral hemispheric cerebellar pathway
  • is also called the neocerebellar or pontocerebellar pathway.

 

        • regulates the initiation, planning, and timing of volitional motor activity.

 

  • Cerebellar hemisphere

 

          • receives input from the contralateral motor and sensory cortex via the corticopontocerebellar tract.

 

  • projects via Purkinje cell axons to the dentate nucleus.
  • Dentate nucleus

 

          • has excitatory output.

 

  • projects via the superior cerebellar peduncle to the
  • contralateral red nucleus
  • ventral lateral nucleus of the thalamus
  • inferior olivary nucleus.
  • Red nucleus pathway
  • The red nucleus projects to the inferior olivary nucleus.
  • The inferior olivary nucleus projects via the contralateral inferior cerebellar peduncle to the cerebellum.
  • Ventral lateral nucleus pathway
  • The ventral lateral nucleus of the thalamus projects to the motor (4) and premotor (6) cortices.

 

            • The motor and premotor cortices give rise to the following tracts:

 

  • Corticobulbar tract
  • innervates cranial nerve nuclei.
  • Lateral corticospinal tract

 

                • regulates volitional synergistic motor activity.

 

  • Corticopontocerebellar tracts

 

                • regulate the output of the neocerebellum.
        • Inferior olivary nucleus pathway
          • The inferior olivary nucleus receives direct input from the dentate nucleus via the crossed descending fibers of the superior cerebellar peduncle.

 

  • The inferior olivary nucleus projects directly to the dentate nucleus via the contralateral inferior cerebellar peduncle.

 

 

 

  • Cerebellar Lesions and their clinical presentation

 

      • Cerebellar Dysfunction  is characterized by the triad

 

  • Hypotonia
  • Disequilibrium

 

        • dyssynergia.

 

  • Hypotonia

 

        • is a loss of the resistance normally offered by muscles to palpation or to passive manipulation.

 

  • results from the loss of cerebellar facilitation of the motor cortex via tonic firing of the cerebellar nuclei.

 

        • results in a floppy, loose-jointed, rag-doll appearance with pendular reflexes; the patient appears inebriated.

 

  • Disequilibrium
  • refers to loss of balance, characterized by gait and trunk dystaxia.
  • Dyssynergia

 

        • is a loss of coordinated muscle activity and includes:
        • Dysarthria – is slurred or scanning speech.

 

  • Dystaxia

 

        • is a lack of coordination in the execution of voluntary movement (e.g., gait, trunk, leg, and arm dystaxia).

 

  • Dysmetria

 

      • is the inability to arrest muscular movement at the desired point (past-pointing). Intention tremor

is a type of dysmetria that occurs during a voluntary movement.

  • Dysdiadochokinesia
        • is the inability to perform rapid alternating movements (e.g., rapid supination and pronation of the hands).

 

  • Nystagmus

 

        • is a form of dystaxia consisting of to-and-fro eye movements (ocular dysmetria).
      • Decomposition of movement (by-the-numbers phenomenon)

 

  • consists of breaking down a smooth muscle act into a number of jerky awkward component parts.
  • Rebound or lack of check

 

        • results from the inability to adjust to changes in muscle tension.

 

  • is caused by loss of the cerebellar component of the stretch reflex.
  • How is it tested : Ask patient flex the forearm at the elbow against resistance; sudden release results in the forearm striking the patient’s chest.
  • Cerebellar Lesions

 

      • Anterior vermis syndrome

 

  • involves the leg region of the anterior lobe.
  • results from atrophy of the rostral vermis

 

        • most commonly caused by alcohol abuse.
        • results in gait, trunk, and leg dystaxia.
      • Posterior vermis syndrome
        • involves the flocculonodular lobe.

 

  • is usually the result of brain tumors in children.

 

      • is most frequently caused by medulloblastomas or ependymomas
      • results in truncal dystaxia.
    • Hemispheric syndrome
      • usually involves one cerebellar hemisphere.
      • is frequently the result of a brain tumor or an abscess.
      • results in arm, leg, trunk, and gait dystaxia.
      • results in cerebellar signs that are ipsilateral to the lesion.