CerebellumCerebellum

Dr. Ameneh RezayofDr. Ameneh RezayofSchool of biology, University College of Science,

U iv sity f T hUniversity of Tehran

Maintenance of EquilibriumMaintenance of Equilibrium- balance, posture, eye movementC di iCoordinating movementTiming of movements, Timing of g , gdiscontinuous movements

lki d t i twalking and posture maintenace- posture, gaitp gAdjustment of Muscle ToneMotor Leaning Motor SkillsMotor Leaning – Motor SkillsCognitive Function

Motor Skill

Balance

Dorsal Braincerebellum = ‘little brain”

The cerebellum is located in the inferior posterior portion of the head (the hindbrain), directly dorsal to the pons, andthe head (the hindbrain), directly dorsal to the pons, and

inferior to the occipital lobe

• Because of its large number of tiny granule cells, the cerebellum contains nearly 50% of all neurons in the ybrain, although it constitutes only 10% of total brain volume.

• The cerebellum receives nearly 200 million input fibersfibers

Drawing of the cells in the chicken cerebellum byS. Ramón y Cajal.

The cerebellum is derived from the metencephalon

VermisThe cerebellum - basic divisions Lingula

Nodulus

ParavermisNodulus

LateralHemispheres

AnteriorLobeLobe

PosteriorLobe

Flocculus

longitudinal divisionlongitudinal divisionVermis, Paravermal Region, Cerebellar Hemisphere

- transverse divisionA i L bAnterior Lobe------------ primary fissurep yPosterior Lobe

t l t l fi------------ posterolateral fissureFlocculonodular Lobe

• The cerebellum is connected to the br in t m n h id bbrainstem on each side by a:

• superior peduncle (to mesencephalon) p p p

• middle peduncle (to pons)

i f i d l ( d ll )• inferior peduncle (to medulla)

• “Peduncle: Afferent and Efferent Pathways” y

The cerebellar hemispheres are divided into three lobes:three lobes:

Anterior lobe: The lobe closest to the midbrain

Posterior lobe (largest lobe): separated from thePosterior lobe (largest lobe): separated from the anterior lobe by the primary fissure

Flocculonudular lobe (Flocculus + Nodulus) or ( )Vestibulocerebellum

Classification by Phylogenetic and Ontogenic DevelopmentArchicerebellumPaleocerebllumNeocerebellum

Classification by Afferent ConnectionVestibulocerebellumVes bu oce ebe u

SpinocerebellumPontocerebellum

Classification by Efferent ConnectionVermisVermis

Paravermal RegionCerebellar Hemispherep

Cerebellar structure and function from aphylogenetic perspectivephylogenetic perspective

Archicerebellum

Paleocerebellum

N b llNeocerebellum

Archicerebellum• The archicerebellum is associated with the

flocculonodular lobe and is mainly involvedflocculonodular lobe and is mainly involved in balance (vestibular system)and eye movement functions.It i i t f• It receives input from the inferior and medial vestibular nuclei andthe inferior and medial vestibular nuclei and sends fibers back to the vestibular nuclei,

i f db k l h ll f hcreating a feedback loop that allows for the constant maintenance of balance.

Paleocerebellum• The paleocerebellum controls proprioception

related to muscle tone (constant partialrelated to muscle tone (constant, partial muscle contraction that is important for the

i t f t )maintenance of posture).

• The paleocerebellum receives its inputs from the dorsal and ventral spinocerebellar tractsthe dorsal and ventral spinocerebellar tracts, which carry information about the position and forces acting on the legs. The paleocerebellum then sends axonal pprojections to the deep cerebellar nuclei.

Neocerebellum• The neocerebellum receives input from the

b ll d j h dpontocerebellar tract and projects to the deep cerebellar nuclei.

• The pontocerebellar tract originates at the Pontine l i hi h i th i i t f th b lnuclei, which receive their input from the cerebral

motor cortex.

• Thus, the neocerebellum is associated with motor t l i ti l th di ti f fi ficontrol, in particular, the coordination of fine finger

movements such as those required by typing.

Deep Nuclei

1. Fastigial nuclei2 Globose n clei2. Globose nuclei3. Emboliform nuclei4 Dentate nuclei4. Dentate nuclei

Deep Nuclei• 4 pairs of nuclei on each side of the midline with in the white• 4 pairs of nuclei on each side of the midline with in the white

matter core of the cerebellum receive input from the cerebellarcortex and incoming afferents and cerebellar efferent. cortex and incoming afferents and cerebellar efferent.

• Fastigiald i l l l i h d– stance and gait, controls muscles only in the modes

of sitting, standing, and walking • Globose + Emboliform

– segmental reflexes, speeds the initiation ofsegmental reflexes, speeds the initiation of movements triggered by somatosensory cues that guide the response, stops unwanted and promotesguide the response, stops unwanted and promotes wanted oscillations, stabilizes holds

• Dentate• Dentate– Fine dexterity

Cerebeller CortexCerebeller Cortex

• 3 Layers: – Granular– Purkinje

Molec lar– Molecular• 5 Cell types:

– Basket, stellate, Purkinje, granule, and Golgi

Ascending Fibres:• Mossyy

– Diffuse projections through granule cells to multiple Purkinje cellsPurkinje cells

• ClimbingT i l fib f li b ll l i l– Terminal fibers of olivocerebellar tracts, multiple synaptic contacts per Purkinje cell

l il d• Multilayered– Afferents from hypothalamus, raphe n, locus ceruleus

Descending Fibres:• Purkinje FibresPurkinje Fibres

– Project from Purkinje cells in Purkinje layer to deep cerebellar nuclei inhibitorycerebellar nuclei, inhibitory

• Deep nuclei then send excitory signals to their efferent connections

• Stellate cells and basket cells cause lateral inhibition of Purkinje cellsj– Modulation in spatial resolution

• G l i ll i hibit l ll• Golgi cells inhibit granular cells– Modulation in temporal resolution

Cerebellar Ataxia

H i h i ff tHemispheric effects

AsynergiaDecomposition of movementDysarthia

k hJerky speech patternDysmetriainability to stop a movement at desired pointinability to stop a movement at desired pointDysdiadochokinesiainability to perform rapidly alternating movementsHypotoniadecreased muscle toneRemember : Lesions to the

cerebellum do not destroyIntention Tremorusually evident during powerful movements, but absent or di i i h d ith t ( t t b l li di d )

cerebellum do not destroy movement, they disrupt it.Ataxia = disordered movement

diminished with rest (contrast basal ganglia disorders)

Thank you for your attentionThank you for your attention