cerebellum 2010
TRANSCRIPT
CEREBELLAR CONTROL OF MOVEMENTS
ORGANIZATION OF CEREBELLUM
FUNCTIONAL ORGANIZATION OF CEREBELLUM
INPUT OF CEREBELLUM
CEREBELLAR OUTPUT
VESTIBULOCEREBELLUM
NEOCEREBELLUM
THE SPINOCEREBELLUM CONTAINS TWO SOMATOTOPIC NEURAL MAPS OF THE BODY
CEREBELLAR PATHWAY
CEREBELLUM:ANATOMY,CONNECTIONS,&FUNCTIONS
Dr.Rupjyoti Das
The cerebellum (Latin: "little brain") is a region of the brain that plays an important role in the integration of sensory perception and motor control.
The cerebellum is located in the inferior posterior portion of the head (the hindrain), directly dorsal to the pons, and inferior to the occipital lobe &
separated from cerebrum by tentorium cerebelli.
Weight=150 gm
On axial & coronal planes,a midline portion,the vermis, and two lateral portions, the cerebellar hemispheres,can be recognized.
The vermis is developmetally older & receives mainly spinocerebellar afferents, whereas the hemispheres have more complex fibre connections.
SCHEMATIC REPRESENTATION OF THE MAJOR ANATOMICAL SUBDIVISIONS OF THE CEREBELLUM.
The cortex is convoluted into many folia. Three major transverse divisions (lobes) are
recognized— The anterior lobe is most rostral, posterior lobe and flocculo-nodular lobe more
caudally. These lobes are divided by the primary fissure
and the posterolateral fissure, respectively. Larsell described 10 lobules (subdivisions of the
lobes) that can be recognized in all animals. Lobules I-V are within anterior lobe, lobules VI-IX are in posterior lobe and lobule X comprises the floccular-nodular lobe.
Spinocerebellum
Pontocerebellum
Vestibulocerebellum
Because of its large number of tiny granule cells, the cerebellum contains more than 50% of all neurons in the brain, but it only takes up 10% of total brain volume.
The cerebellum receives nearly 200 million input fibres.
Anatomical division- : the anterior lobe (rostral to the "primary
fissure"), the posterior lobe (dorsal to the "primary
fissure") and the flocculonodular lobe, The first two can be further divided in a
midline cerebellar vermis and lateral cerebellar hemispheres.
THE CEREBELLUM CAN BE DIVIDED ACCORDING TO THREE DIFFERENT CRITERIA: GROSS ANATOMICAL, PHYOLOGENETICAL, AND FUNCTIONAL:
Classification by Phylogenetic and Ontogenic Development :
Archicerebellum Paleocerebllum Neocerebellum
Classification by Afferent Connection
Vestibulocerebellum Spinocerebellum Pontocerebellum
Classification by Efferent Connection
Vermis Paravermal Region Cerebellar Hemisphere
Functional denomination (phylogenetic denomination)
Anatomical parts Role
Vestibulocerebellum (Archicerebellum)
Flocculonodular lobe (and immediately adjacent vermis)
The vestibulo cerebellum regulates balance and eye movements. Lesions of the vestibulo cerebellum cause disturbances of balance and gait.
FROM THE PHYLOGENETICALLY OLDEST TO THE NEWEST, THE THREE PARTS ARE:
Spinocerebellum (Paleocerebellum)
Vermis and intermediate parts of the hemispheres ("paravermis")
The spino cerebellum regulates body & limb movements.The spino cerebellum is able to elaborate proprioceptive input in order to anticipate the future position of a body part during the course of a movement.
Cerebrocerebellum (Neocerebellum)
Middle portion of the vermis & Lateral parts of the hemispheres
The neo cerebellum is involved in planning & initiation of movement.It has purely cognitive functions as well.
During the early stages of embryonic development, the brain starts to form in three distinct segments:
the prosencephalon, mesencephalon, and rhombencephalon. The rhombencephalon is the most caudal
(toward the tail) segment of the embryonic brain.
DEVELOPMENT OF CEREBELLUM
Archicerebellum (nodulus)
Archicerebellum (flocculus) Paleocerebellum
Neocerebellum
Along the embryonic rhombencephalic segment develop eight swellings, called rhombomeres. The cerebellum arises from two rhombomeres located in the alar plate of the neural tube, a structure that eventually forms the brain and spinal cord.
The specific rhombomeres from which the cerebellum forms are rhombomere 1 (Rh.1) caudally (near the tail) and the "isthmus" rostrally (near the front).
The cerebellum is of archipalliar phylogenetic origin. The pallium is a term for gray matter that forms the cortex. The archipallium is the one of the most primitive brain regions. The circuits in the cerebellar cortex look similar across all classes of vertibrates, including fish, reptiles, birds, and mammals.
Subdivision of Flocculonodular Lobe
Nodulus Flocculus
Subdivision of Anterior Lobe
Vermis Hemisphere
Lingula Central Lobule Ala Central Lobule
postcentral fissure
Culmen Quadriangular Lobule
CEREBELLUM-EXTERNAL CONFIGURATION
Subdivision of Posterior Lobe
Vermis Hemisphere
Declive Simple Lobule
postcentral fissure
Folium Superior Semilunar Lobule horizontal fissure
Inferior Semilunar Lobule Tuber Gracile Lobule prepyramidal fissure
Pyramid Biventral Lobule
secondary fissure
Uvula Tonsil
Grey matter of cerebellum:
1.Cerebellar cortex.
2.Cerebellar nuclei
CYTOARCHITECTURE
1.Molecular layer Consists mainly of neuropil and is the site of synapses. Contains scanty neurons consisting of stellate and basket
cells.
2.Purkinje cell (Piriform) layer Single layer of neurons. Consists of large (25 micrometer) pear-shaped neurons .
3.Granular cell layer Very small(7 micrometer) granular neurons. Very numerous – 3 to 7 million neurons per cubic mm.
4.White matter – forms the core of the foliae.
THE CEREBELLAR CORTEX CONSISTS OF THREE LAYERS ON A CORE OF WHITE MATTER.
1.Outer stellate layer(In molecular layer)
2.Basket cells ( -do- )
3.Purkinje cells.
4.Granule cells. (In granule cell layer)
5.Golgi cells ( -do- )
NEURONS OF CEREBELLAR CORTEX
The white matter of the cerebellum is made up of intrinsic,afferent & efferent fibres.
Incoming impulses to the cerebellum reach the dendrites and cell bodies of Purkinje cells.
The afferent fibres form the greater part of the cerebellar white matter and on entering the cerebellum,segregate into one of three fibre systems: the climbing,mossy or multilayered.
The climbing fibres are the terminal fibres of the olivocerebellar tracts & make multiple synaptic contacts with one Purkinje cell.
The mossy fibre system includes all other cerebellar afferent tracts.In contrast to the climbing fibre system the mossy fibre system is diffuse,having multiple branches;so a single mossy fibre may stimulate thousands of Purkinje cells through the granule cell.
The multilayered fibre system includes afferents to the cerebellum from the hypothalamus,raphe nuclei & locus ceruleus & projects into the cerebellar cortex & deep cerebellar nuclei.
In striking contrast to the 100,000-plus inputs from parallel fibers, each Purkinje cell receives input from exactly one climbing fiber; but this single fiber "climbs" the dendrites of the Purkinje cell, winding around them and making a large number of synapses as it goes.
8. PARALLEL FIBER
9. INFERIOR OLIVA
NUCLEUS 0. D L
NUCLEI 1. Purkinje cell
2. granule cell
3. basket cell
4. Golgi cell
5. stellate cell
6. climbing fiber
7. mossy fiber
8. parallel fiber
9. inferior olivary nucleus
10. deep cerebellar nuclei
The Purkinje cells are central neurons (everything else converges on them)
They consist of= A large dendritic tree in the molecular layer,
which is elaborately branched and fan-shaped (branches are all in one plane) and has dendritic spines at the sites of synapses.
A large cell body. An axon which forms the efferent pathway from
the cerebellum , and sends collaterals in the granular layer.
GABA is the main neurotransmitter.
The Granule cells:
Very numerous: 3-7 million / mm3 Very small (7mm), closely packed neurons. Heterochromatic nuclei, scanty cytoplasm. Small dendritic tree in granule layer.
An unmyelinated axon. Directed to molecular layer (centrifugal). *Splits in T-shape manner to form parallel fibre.
Parallel fibers run longitudinally along folia Cross dendrites of many Purkinje cells. Have glutamate as neurotransmitter.
Cerebellar Neurons are Stimulatory or Inhibitory to Purkinje Cells.
Climbing fibres are strongly excitatory. Mossy fibres stimulate granule cells. Parallel fibres of granule cells stimulate several
Purkinje cells simultaneously. Basket cells strongly inhibit Purkinje cells. Stellate cells inhibit Purkinje cell dendrites. Golgi Type II cells inhibit directly the mossy fibre input.
Main neurotransmitter= L-glutamate. Afferents reaching Purkinje through (Mossy/Climbing fibres) :Excitatory.
Purkinje cells =GABAergic. Golgi cells= -do- Stellate cells = -do- Basket cells = -do-
NEUROCHEMISTRY
Embedded within the white matter—which is known as the arbor vitae (Tree of Life) in the cerebellum due to its branched, treelike appearance—are four deep cerebellar nuclei:
From lateral to medial, they are the dentate, emboliform, globose, and fastigial.
Dentate n.
Emboliform n. Globose n.
Fastigial n.
These nuclei receive inhibitory (GABAergic) inputs from Purkinje cells in the cerebellar cortex and
excitatory (glutamatergic) inputs from mossy fibre pathways.
Most output fibers of the cerebellum originate from these nuclei.
The fastigial nucleus assists stance & gait & controls muscles only in the modes of sitting,standing & walking.
The nucleus interposed assists segmental reflexes & speeds the initiation of movement triggered by somatosensory cues.
The dentate nucleus assists in tasks requiring fine dextirity.
EACH NUCLEUS CONTROLS A DIFF.TYPE OF MOVEMENT AS FOLLOWS:
The cerebellum follows the trend of "threes", with three major input and output peduncles (fiber bundles). These are
the superior (brachium conjunctivum), middle (brachium pontis), and inferior (restiform body) cerebellar
peduncles.
Peduncle Description
SUPERIOR
some afferent fibers from the anterior spinocerebellar pass to the anterior cerebellar lobe via this peduncle. Thus, the superior cerebellar peduncle is the major output pathway of the cerebellum. Most of the efferent fibers originate within the dentate nu.which in turn project to various midbrain structures including the red nucleus, the ventral lat./ventral ant. nucleus of the thalamus, and the medulla. The dentatorubrothalamo cortical& cerebellothalamocortical pathways are two major pathways that pass through this peduncle and are important in motor planning.
MIDDLE
This is composed entirely of afferent fibers originating within the pontine nuclei as part of the massive corticoponto cerebellar tract.These fibers descend from the sensory and motor areas of the cerebral neocortex and make the middle cerebellar peduncle the largest of the three cerebellar peduncles.
INFERIOR
Proprioceptive information from the body is carried to the cerebellum via the dorsal spinocerebellar tract. This tract passes through the inferior cerebellar peduncle and synapses within the paleocerebellum. Vestibular information projects onto the archicerebellum.The climbing fibers of the inferior olive run through the inferior cerebellar peduncle.This peduncle also carries information from the Purkinje cells to the vestibular nuclei in the dorsal brainstem located at the junction between the pons and medulla.
Tracts or fiber bundles Distribution
Inferior cerebellar peduncle
Afferent paths Olivocerebellar tract
Lateral hemispheres and cerebellar
nucleus
Paraolivocerebellar tract Vermis, paravermis. and cerebellar
nucleus
Vestibulocerebellar tract Fastigial nucleus, flocculonodular lobe, and uvula
Reticulocerebellar tract Spinal region of cerebellar vermis
Posterior spinocerebellar tract Hind limb region of cerebellar cortex
Trigeminocerebellar tract Dentate and emboliform nucleus
Cuneocerebellar tract Forelimb and upper trunk region of cerebellar cortex
Anterior exterior arcuate fibers Flocculus
Arcuatocerebellar fibers (striae medullares) Flocculus
Efferent paths Cerebellovestibular tract Vestibular nucleus
Cerebelloreticular tract Pontine and medullary reticular nucleus
CEREBELLAR CONNECTIONS--
Middle cerebellar peduncle
Afferent paths Pontocerebellar tract Neocerebellar cortex
Superior cerebellar peduncle
Afferent paths
Anterior spinocerebellar tract Hind limb region of cerebellar cortex
Tectocerebellar tract Intermediate vermis and lobulus
simplex
Trigeminocerebellar tract
Efferent paths
Dentatorubral fibers Red nucleus
Dentatothalamic fibers Ventral intermediate (VI) and ventral
anterior (VA) nucleus of thalamus
Fastigioreticular fibers Reticular nucleus of midbrain, pons,
and medulla oblongata
CONT.
Afferent connection
MAIN CONNECTIONS OF THE VESTIBULOCEREBELLUM
Floculonodular
Lobe
Vermis
FASTIGIAL NUCLEUS
VESTIBULAR NUCLEUS
Vestibular Organ
lower motor neuron LMN
ARCHICEREBELLUM
vestibulospinal tractMLF
RED NUCLEUS
MAIN CONNECTIONS OF THE PALEOCEREBELLUM
RED NUCLEUSNUCLEUS
INTERPOSITUS
ANTERIOR LOBE
PARAVERMAL ZONE
PALEOCEREBELLUM
Inferior OlivryNucleusLower
motor neuronSPINAL CORD
Rubrospinal tract
spinocerebellar tract
MAIN CONNECTIONS OF THE NEOCEREBELLUM
CEREBRAL CORTEX THALAMUS
PontineNucleus
Lower motor neuron
LMN
DENTATENUCLEUS
POSTERIOR LOBE
CEREBELLAR HEMISPHERE
NEOCEREBELLUM
Pyramidal tract
CEREBELLUM AND AUTOMATIC MOTOR CONTROL
CEREBELLUM
MOTOR CORTEX
RED NUCLEUS
VESTIBULAR
NUCLEUS
RETICULAR FORMATION
LOWER MOTOR NEURONProprioceptor
s
Corticonuclear Connections
A zone ---------- fastigial nucleus medial vestibular nucleus B zone ---------- lateral vestibular nucleus
C1, C3 zone --- emboliform nucleus C2 ---------------- globose nucleus
D1 ---------------- parvocellular portion of dentate nucleus D2 ---------------- magnocellular portion of dentate nucleus
VOOGD ORIGINALLY DESCRIBED 4 ZONES, FROM MEDIAL TO LATERAL--
1. vermis
2. paravermal region
3. cerebella hemisphere
4. nodulus
5. flocculus
6. fastigial nucleus
7. globose nucleus
8. emboliform nucleus
9. dentate nucleus
10. medial vestibular
nucleus
11. lateral vestibular
nucleus
The inferior olivary nucleus or inferior olive comprises 3 major divisions –
the principal olive (PO), the dorsal accessory olive (DAO) and the medial accessory olive (MAO). Different divisions of the olive project to
different cortical zones. The inferior olive is the only source of climbing fibre inputs to the cerebellum. Inputs from all other sources are as mossy fibres.
Olivocerebellar Connections
Caudal portion of medial and dorsal accessory olivary nucleus ----------------- vermis of cerebellar cortex (A and B) fastigial nucleus vestibular nucleus
Rostral portion of medial and dorsal accessory olivary nucleus ----------------- paravermal region (C1, C2, C3) nucleus interpositus
Principal Inferior Olivary Nucleus ----------------- cerebellar hemisphere (D1, D2) dentate nucleus
Caudal portion
Rostral portion
Principal inferior olivary nucleusmedial and dorsal accessory olivary nucleus
The posterior inferior cerebellar artery (PICA): supplies-
Lat.medullary tegmentum, inferior cerebellar peduncle The ipsilat.portion of the inferior vermis & the inferior surface of the cerebellar
hemisphere. The medial br. of the PICA supplies the
medial cerebellum & the dorsolat. Medulla oblongata.
The lateral br.supplies the inferoposterolat. aspect of the cerebellum.
VASCULAR SUPPLY OF THE CEREBELLUM:
The ant.inf.cerebellar artery (AICA) supplies- Ant.petrosal surface of the cerebellar hemisphere, Flocculus, Lower portion of the middle cerebellar peduncle & Lat.pontomedullary tegmentum
The superior cerebellar artery (SCA) supplies- The upper surface of the cerebellar
hemisphere, Ipsilat.portion of the superior vermis, Most of the dentate nucleus, Upper portion of the MCP,SCP & lat.pontine
tegmentum.
Maintenance of Equilibrium - balance, posture, eye movement
Coordination of half-automatic movement of walking and posture maintenace - posture, gait
Adjustment of Muscle Tone
Motor Leaning – Motor Skills
Cognitive Function
CEREBELLUM:FUNCTIONS
BALANCE
MOTOR SKILLS
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ARCHICEREBELUM Floculonodular lobe- Vestibulocerebelum Function:
Maintenance of equilibrium Suppress Vestibulo Ocular Reflex Muscle tone in relation to head posture
Animal ablation Disorder of equilibrium Positional nystagmus
Human: Meduloblastoma Trunkal ataxia Vestibular nystagmus (fast component towards the side of lesion) Positional nystagmus does not fatigue Vertigo
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PALLEO-CEREBELUM Anterior lobe + Vermis Afferent:
Spinocerebellar tract Spino-> olivo->cerebellar Spino -> reticulo -> cerebellar
Efferent Festigio -> vestibulo -> spinal Festigio -> Reticulo -> Spinal
Function Tone control Posture of axial muscle Equilibrium and locomotion
Animal ablation Increased lengthening and
shortening Increased tendon reflex Exagerated postural reflex
(positive supporting reflex) Human
Alcoholic degeneration Cerebellar degeneration Gait ataxia Rarely mild hypotonia,
dysmetria and dysarthria
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NEOCEREBELUM Ablation in Dog and Cat inconstant result Monkey ablation
Hypotonia Clumsiness of ipsilateral limb Dentate nucleus ablation -> more enduring
effect intension tremor
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CEREBELLAR ZONES1. Vermis zone: control posture, tone, locomotion, equilibrium
i. Vestibular connection project to festigial nucleusii. Control position of the head in relation to trunk and extraocular
movments
2. Intermediate zonei. Affrent-
a. proprioceptive from limbb. Sensorimotor cortexc. Collateral from corticospinal tract
ii. Efferent globos and embodiform nucleus ->VL thalamus to motor cortex
iii. Function: Regulation of movment via sensory feedback from the corticospinal muscle
a. Control velocity, force, pattern of movement
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CEREBELLAR ZONES: LATERAL Afferent: motor and sensory association cortex Efferent: Dantate -> thalamus -> motor cortex (open loop) Function: Programing of movement before initiation Animal: coordination of ipsilateral movment Human: Hypotonia- flabby muscle, abnormal posture
(slopping of shoulder) increased excursion of outstretched hand tapping. Hyperflexibility of joint, pendular reflex knee
Cerebellum control separately the activity of alpha and gamma motor neuron
Reduced fusimotor activity from abnormal long loop reflex through precentral cortex
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CEREBELLAR DYSFUNCTION1. Ataxia: Limb, gait and speech2. Speech: Scanning3. Tremor: Postural, intention, limb, trunk and head4. Tone: Hypotonia -> Hyperextensibility, pendular knee jerk,
rebound phenomenon5. Voluntary movement: Dysmetria, dysynergia,
disdidokokinesia6. Gait: ataxic, truncal ataxia7. Head tilt8. Postural abnormality: due to unequal hypotonia of truncal
muscle -> scoliosis, elevation or depression of shoulder, pelvic tilt
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3VOLUNTARY MOVEMENT ABNORMALITY Gorden Holms : Rate, range and force
Dyssynergia: Disruption of the normal smooth control of movement provided by gradual contraction of synergic muscle and relaxation of their antagonist
Voluntary movement- longer to start and longer to stop Prolongation of interval between the command and triphasic
agonist- antagonist and motor sequence Agonist burst may be too long or short or continue into the
antagonist burst -> dysmetria and dysenergia Rebound phenomenon (abnormal check reflex) Dysdiadokokinesia Decomposition of movement
Scanning speech Cogwheel eye moevment
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3VOLUNTARY MOVEMENT ABNORMALITY Dysmetria
Inability of the sensorimotor apparatus to measure distance in the course of movement
Hypometria and hypermetria of the limb and eye Tremor : Postural and intention Ataxia of gait: falling towards the side of lesion Nystagmus:
Gaze paretic (evoked) deviation Downbeat Rebound Sustained horizontal Opsoclonus Skew deviation
Weakness, faitibability and loss of associted movement