Dr. P. Ravisankar, Ph.D Professor of Anatomy SRM Dental College & Hospital SRMIST, Ramapuram Chennai-600089 CEREBELLUM – Little brain  Largest part of the hind brain.  Wt 150gms  Situated in the posterior cranial fossa beneath tentorium cerebelli.  Antrly separated from pons & medulla by the cavity of fourth ventricle.  Responsible for equilibrium, muscle tone & skillfully co-ordinated performance of voluntary activities. Cerebellum Connections with brain stem  It is connected to the three parts of brain stem, by three pairs of cerebellar peduncles.  Medulla – Inferior cerebellar peduncle.  Pons – Middle cerebellar peduncle.  Midbrain - Superior cerebellar peduncle. EXTERNAL FEATURES

 3 parts  2 surfaces  2 notches  3 fissures EXTERNAL FEATURES - parts  Right & Left hemispheres  Midline vermis – made up of superior & inferior vermis  Supr vermis continuous with divisions of cerebellar hemispheres laterally  Infr vermis lies deep in a sulcus - vallecula EXTERNAL FEATURES - surfaces

 Supr surf – convex, 2 cerebellar hemispheres continuous with each other

 Infr surf – presents a deep notch – Vallecula that separates 2 cerebellar hemispheres EXTERNAL FEATURES - notches  Anterior cerebellar notch – accomodates pons & medulla

 Posterior cerebellar notch – accomodates falx cerebelli EXTERNAL FEATURES - fissures  Three major fissures which divide the cerebellum into three lobes.  FISSURA PRIMA – situated on the superior surface at the junction of anterior 2/3rd & posterior 1/3rd.  HORIZONTAL FISSURE – situated between superior & inferior surface. EXTERNAL FEATURES - fissures  POSTEROLATERAL FISSURE – situated on the inferior surface & anterior end. Subdivisions of cerebellum  Anatomical subdivisions  Anterior lobe – on supr surf, antr to fissura prima  Postr / Middle lobe – between fissura prima & postrlat fissure  Flocculonodular lobe – smallest lies on infr surface in front of postrlat fissure subdivisions of vermis & hemispheres Subdivisions of cerebellum  Morphological subdivisions

 Archicerebellum

(Vestibular cerebellum)

 Paleocerebellum

(Spinal cerebellum)

 Neocerebellum

(Cerebral cerebellum) Archicerebellum (Vestibular cerebellum)

 Phylogenetically oldest part  Fishes & amphibians  Flocculonodular lobe & lingula  Chiefly vestibular connections  Maintains equilibrium, tone & posture of trunk muscles Paleocerebellum ( Spinal cerebellum)  Next part to appear in terrestrial vertebrates with the development of limbs ( reptiles & birds)  Antr lobe(except lingula), pyramid & uvula of Infr vermis  Spinocerebellar connections  Tone, posture & crude movements of limbs Neocerebellum (Cerebral cerebellum)  Most recent part to develop  Develops in primates along with enlargement of telencephalon & cerebral cortex  Well dev in higher mammals  Middle lobe ( except pyramid & uvula of infr vermis)  Cortico-ponto-cerebellar connections  Smooth performance of skilled voluntary movements INTERNAL FEATURES  Surface is divided into numerous small lobules called folia by multiple fissures.  Like cerebral cortex- grey matter outside (cerebellar cortex) & white matter inside.  Submerged inside the core of white matter are intra- cerebellar nuclei.  Due to the fissures, C.S.of cerebellum has a classical branching pattern of tree – ARBOR VITAE CEREBELLI INTRA-CEREBELLAR NUCLEI Dentate nucleus, crumpled bag-like appearance, hilum antrmedial. Largest & Neocerebellar nucleus. Most laterally placed. Responsible for skillful co-ordination of muscular activity. Connections of dentate nucleus

Neo-cerebellum

Dentate nucleus

Red nucleus Thalamus

Spinal cord Cerebral cortex NUCLEUS INTERPOSITUS

 Two nuclei.  Globose & Emboliform nuclei.  Emboliform is lateral & Globose medial.  Mainly related to paleocerebellar cortex.  Responsible for maintenance flexor muscle tone. Paleo cerebellum

Connections of Nucleus Interpositus Emboliform & Globose

Red nucleus

Spinal cord FASTIGIAL NUCLEUS  Most medially placed nucleus.  Connected to archi-cerebellum.  Responsible for equilibirium.  Influences extensor muscle tone. Connections of fastigial nucleus

Flocculonodular lobe

Fastigial nucleus

Vestibular & Reticular nuclei Connections of Cerebellum

Cerebral cortex, spinal cord, vestibular apparatus, red nuc, tectum

Cerebellum

Red nuc, thalamus, vestibular comp, reticular formation Cerebellar peduncles

 Superior, Middle & Inferior cerebellar peduncles

Connections of Superior cerebellar peduncle

 main eff pathway from cerebellum

 fib arise mainly from dentate nucleus Afferents:  Antr spinocerebellar tract  Tecto-cerebellar tract  Trigemino-cerebellar tract  Ceruleo-cerebellar tract  Hypothalamo-cerebellar tract Efferents :  Cerebello-rubral fibres(frm glob & emb nuc to opp red nuc)  Dentato-rubral & dentato-thalamic fibres(to opp red nuc & thalamus)  Cerebello-olivary fibres(to opp infr oliv nuc)  Cerebello-reticular fibres(frm fastigial nuc to retic nuc) Connections of Middle cerebellar peduncle Afferents:  Pontocerebellar fibres (cortico-ponto-cerebellar pathway)  Reticulocerebellar fibres  Seratogenic fibres

Efferents:  No efferents fibres pass thru middle cerebellar peduncle Connections of Inferior cerebellar peduncle Afferents :  Posterior spinocerebellar fibres  Olivo-cerebellar fibres  Parolivocerebellar fibres  Cuneo-cerebellar fibres  Anterior external arcuate fibres  Vestibulo-cerebellar fibres – juxtarestiform body  Reticulo-cerebellar fibres Connections of Inferior cerebellar peduncle Efferents :  Cerebello-vestibular fibres(frm ipsilat flocculonodular lobe & fastigial nuc of both sides)  Cerebello-reticular fibres(frm fastigial nuc of both sides to brain stem reticular formation)  Cerebello-olivary fibres Main Connections of Cerebellum Comparator function

 Plays a key role in accomplishing smooth & co-ordinated movements by its comparator function.

CEREBRAL CORTEX

Cerebellum

Spinal cord Antr horn cells  Movements produced with the influence of cerebellum – accurate in time, rate, force & direction.  With training, a person can develop highly skilled & rapid movements.  Thus plays a vital role in the LEARNING OF MOTOR SKILLS. Arterial supply

 Superior cerebellar art – br of basilar art

 Anterior inferior cerebellar artery(AICA) – br of basilar art

 Posterior inferior cerebellar artery(PICA) – br of vertebral artery

Clinical Anatomy  Cerebellar lesions due to trauma, vascular occlusion, tumors – various signs & symptoms -- CEREBELLAR SYNDROME I Involvement of Archicerebellum:  Trunkal ataxia & Staggering gait  Nystagmus – involuntary to & fro oscillatory movts of eyeball  Rhomberg’s sign II Involvement of Paleocerebellum:  Hypotonia asthenia - muscle tone of limb muscles  Flail joints – lack of stability of joints  Disturbances of tendon reflexes – Pendular knee jerk (patellar reflex results in oscillating movts of leg)  Ataxia – inability to maintain balance while walking III Involvement of Neocerebellum:

 Asynergia -Muscular incoordination

 Dysmetria – Past-pointing (Finger-nose test)

 Intention tremors – occur during purposeful movts & disappear at rest

 Dysdiadochokinesia -- inability to execute alternate movts in quick succession (pronation & supination of forearm)

 Dysarthria / Scanning or Staccato speech – slurred, prolonged, explosive with pauses in wrong places

 Rebound phenomenon Past-pointing  Cerebellar lesions – signs & symptoms on same side as lesion, b’cos cerebellar hemispheres are connected by tracts with same side of body.  Cerebellum & basal ganglia both control motor functions but have opposite effects

Cerebellar lesion Basal ganglia Hypotonia & lesion intention tremors Hypertonia & resting tremors REFERENCES

1. TEXT BOOK OF ANATOMY 3rd VOLUME 3rd ED. VISHRAM SINGH 2. GRAY’S ANATOMY 40th ED. – SUSAN & SANDRING 3. BD CHAURASIA’S HUMAN ANATOMY 3RD VOLUME, 8th ED- KRISHNA GARG 4. CLINICALLY ORIENTED ANATOMY 3rd ED. KEITH L.MORE 5. TEXT BOOK OF CLINICAL NEUROANATOMY 3rd ED. BY VISHRAM SINGH