Anat 6.6 Cerebellum_Deriada

8/17/2019 Anat 6.6 Cerebellum_Deriada

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Anatomy 6.6 February 14, 2012

Cerebellum Dr. Maj Deriada

Group 3A |Cy, CARA, Cring, Kenji Page 1 of 11

OUTLINEI. CEREBELLUM

A. GrossB. Function

II. DIVISIONS AND ORGANIZATION

A.

Lobes (Transverse Division)B. Longitudinal Zones (Sagittal Division)C. Organization

III. CEREBELAR CORTEX: CELL LAYERSA. Molecular LayerB. Purkinje LayerC. Granular LayerD. Inner White Matter

IV. IMPORTANT SYNAPSES AND CIRCUITRYA. Synaptic OrganizationB. Patterns of Excitation

V. NEURONS AND FIBERS OF THE CEREBELLUMA. Three HighwaysB. Three Inputs

C.

Three OutputsVI. CEREBELLAR AFFERENT FIBERSA. From the CortexB. From the Spinal CordC. From the Vestibular Nerve

VII. CEREBELLAR EFFERENT FIBERSVIII. SUMMARY (CEREBELLAR CORTICAL CIRCUITRY)IX. CLINICAL CORRELATIONS

Objectives: Name the major lobes of the cerebellum and give the function of each

lobe. Describe the division of the cerebellum into a midline vermis and lateral

cerebellar hemispheres. Describe the histology of the cerebellar cortex. Name the deep cerebellar nuclei and their general connections. Name the types of afferent fibers to the cerebellar cortex and identify

their source. Name the afferent fibers from the cerebellar cortex. Trace the various circuitries within the cerebellar cortex. Name the cerebellar peduncles and the fiber tracts (afferent and efferent)

that constitute them. Describe the cerebellar connections of the vestibular system.

References Snell’s Neuroanatomy Lansang’s Neuroananatomy Notes Dr. Deriada’s Slide Lecture

LegendsText in Times New Roman are from reference books and 2014B trans

Text in Arial Narrow are from the recorded lecture of Dr. DeriadaText in Calibri are from the powerpoint presentation of the lectures

I. CEREBELLUM

A. GROSS

Located in the posterior cranial fossa roof over by a vault of dura matter separating from occipital lobe of

cerebrum (tentorium cerebelli) lies posterior to the pons and medulla oblongata

is ovoid in shape with 2 lateral rounded cerebellar hemisphere thpinched in the middle by the vermis

fiber tracts called cerebellar peduncle connecting it to the midbrainmedulla

o Superior Cerebellar peduncle (brachium conjunctivum)midbrain

o Middle Cerebellar peduncle (B. Pontis) ponso Inferior (restiform body) medulla

The medial part is the juxtarestiform body

B. FUNCTION

Coordination of voluntary muscle activity [maintaining fine ancomplex]

Equilibrium Muscle tonus

o [Helps maintain posture and maintain equilibrium while walking running; execute sequential movement like writing, putting buttons and brushing teeth and as well as rapidly, alternating anrepetitive movement.]

o Controls muscular movement ipsilateral or same side of the bounlike cerebrum

The cerebellum has no direct PW to the LMN’s Exerts its control via the cerebral cortex and the brainstem Does not initiate movement; regulation A person with lesion on the cerebellum WILL NOT be paralyzed but

have disorganized, uncoordinated, slow and tremulous movement in teye and limb movements

There will be problem in muscle tone and posture- either hyper tonushypotonus; and when standing or walking he would or stagger or swayin

II. DIVISIONS AND ORGANIZATION

A. LOBES (Transverse division) LOBES (transverse division)- divided by a transverse plane: givingrise to Anterior, Posterior and Flocculonodular lobe

Fig. 1 Cerebellar Lobes in Transverse View. Take note of the fissures.


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Group 3A |Cy, CARA, Cring, Kenji Page 2 of11

AnatomicDivision

ANTERIOR POSTERIOR ORMIDDLE(Largest)

FLOCCULONODULAR

FunctionalDivision

Spinocerebellum Cerebrocerebellum Vestibulocerebellum

PhylogeneticDivision

Paleocerebellum Neocerebellum Archicerebellum(oldest)

Gross Location Situated anterior toprimary fissure andterminates at rostralend of cerebellum

Posterior to theprimary fissure andanterior lobe.Limited by theposterolateral fissure

With a pair of flocculusand at the vermis thereis a nodulus (pl. Flocculiand noduli)

Between anterior and

posterior lobeFissure Primary Fissure-

wide v-shapedepression orlongitudinal fissurethat separatesanterior and posteriorlobe

PosterolateralFissure- separateposterior lobe fromflocculonodular lobe

Input Spinocerebellarandtrigeminocerebellar pathways

Cerebral cortex Vestibular nuclei

Function Stance and gait Speech andcoordinatedmovement

Equilibrium (balance,posture and eyemovements)

Three fissures of cerebellum:

1. Primary Fissure2. Posterolateral or Uvulonodular Fissure3. Horizontal Fissure- no significance and demarcates the superior

and inferior surfaces of the cerebellum

TONSILS ON THE NEOCEREBELLUMIn the neocerebellum there is a pair of tonsils (located at both side of the midline).When ICP increase like of tumor may cause herniation through the foramenmagnum because it immediately lies to it, compressing the brainstem which isessential for breathing and blood pressure

B. LONGITUDINAL ZONES (Sagittal Division)

Section made through the cerebellum parallel to the median planedivides the folia at right angles and the cut surface has a branched

appearance called Arbor vitae.

This gives rise to the functional areas of the cerebellar cortex

VERMIS INTERMEDIATE LATERAL

Medial LateralSynonymous

termVERMALFLOCCULONODULAR ZONE

PARAVERMAL

Direction ofprojection

fibers

To spinal cord

[efferent fibers:fastigialnucleus synapse axon tovestibularnuclei SC long axis of thebody]

To cerebralhemisphere[includes anteriorlobe and the anteriorpart of vermis]

[singals/ informationfrom cereberalcortext to emboliformand globose nuclei ornucleus interposidus

axonsterminated

contralateral rednucleus crossingthe other side of thespinal cord]

[MOSTLYPOSTERIOR part]

[cerebral cortex dendate nuclei thalamus motorcortex pontinenuclei and anteriorhorn of spinalcord]

Function Control ofposture, muscletone,locomotion andequilibrium

spinal cord andlimbs [particularlyof hands and feet]

Therebyresponsible forSTANCE AND GAIT

Coordination ofipsilateralsomatic motoractivity

Planning ofmovements

Assessment oferrors

Damage/Disease/Lesion

Ataxia-uncoordinatedvoluntarymuscularmovements

Wide-based stanceStagger walking Cerebellarincoordination(asynergia- lackof coordination.Ergoincoordination )

Dysmetria- refersto a lack ofcoordination ofmovement typified

by the undershootor overshoot ofintended positionwith the hand, arm,leg, or eye.Inability to judgedistance or scale

Past-pointing

Tremors

Dysdiadochokinesis- inability toperform regular/rapidlyalternatingmovementsReboundphenomenon

Fig. 2 Cerebellar Zones.

C. Organization Outer layer of gray matter- cortex Inner core of white matter

o Fold in cerebellum or folia would contain outer cortex and inner cwhite matter

Deep in the white matter are four pairs of masses of gray matteror the intracerebellar nuclei:

o Large, multipolar neurons; simple branching dendrites; andAxons


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1. Dentate nucleus - largest, most lateral2. Emboliform nucleus - ovoid and situated medial to dentate3. Globose nucleus - small, rounded in pairs or single4. Fastigial nucleus - the most medial on the sides of midline

The collection of globose and emboliform nucleus forms asINTERPOSED NUCLEI or NUCLEUS INTERPOSIDUS

Fig. 3 Location of the Nucleus Interpositus

III. CEREBELAR CORTEX: CELL LAYERSThe cerebellar cortex can be regarded as a large sheet with foldslying in the coronal plane. Each fold or folium contains a core ofwhite matter covered superficially by gray matter. The gray matter of the cortex throughout its extent has a

uniform structure. It may be divided into 3 layers:1. Molecular layer External

2. Purkinje cell layer Middle

3. Granular layer Internal

Fig.4 Cerebellar cortex layers.

A. Molecular Layer

Contains two types of neurons: (1) outer: stellate cell (2) inner:basket cell that are scattered among dendritic arborizationsand numerous thin axons running parallel to the folia.

Neuroglial cells are found in between

B. Purkinje Cell Layer

Purkinje cells - large, flask-shaped Golgi type 1 neuron arrangedin a single layer

The cell body of the purkinje cells lie in the purkinje cell layerwhile the dendrites pass into the molecular layer where theyundergo profuse branching

The primary and secondary branches of the dendrites aresmooth

Dendritic spines- short and thick spines that cover thesubsequent branches which form synaptic contacts with theparallel fibers derived from granule cell axons

Axons of the purkinje cells will project into the granular layerand will acquire myelin sheath and terminate by synapsing with

the cells of one of the intracerebellar nuclei which will form thecerebellar peduncle.

Collateral branches synapse with dendrites of the basket andstellate cells.

Some pass directly to the end in the vestibular nuclei of thebrainstem. They by-pass the intracerebellar nuclei.

The axons of these cells are the ENTIRE OUTPUT FIBERS of thecerebellar cortex.

Purkinje cells form the center of a functional unit of thecerebellar cortex

C. Granular Layer

Found between purkinje cell layer and the cerebellar white matter . Packed small cells with densely staining nuclei and scanty

cytoplasm It has three structures. Each give rise to 4-5 dendrites whichmake claw-like endings synapsing with mossy fiber output1. Granule cells- smallest neurons in the body2. Golgi Cells- scattered throughout and dendrites reach

molecular layer3. Cerebellar glomeruli/cerebellar island

Cerebellar glomeruli are capped by glial cells which contain:1. Mossy fiber rosette2. Terminals of golgi type II axons3. Dendrites terminal of granular cell

Dendrites synapse with mossy fiber output Axons pass into the molecular layer where it bifurcates in a T-

junction forming parallel fibers that run at right angles and

synapse with dendritic processes of the purkinje cells Neuroglial cells are found throughout

Fig. 5 Photomicrograph of a cross-section of the folia showing the layers ofthe cerebellar cortex

IV. INNER WHITE MATTERThere is a large amount of white matter in each cerebellarhemisphere. The white matter is made up of three groups offibers: (1) intrinsic, (2) afferent, and (3) efferent

Intrinsic fibers- located in the cerebellum but connect differentregions of the organ. Within in the cerebellum only.


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Afferent fibers- form the greater part of the white mattercoming from the cerebral cortex and proceed to cerebellarcortex; enter the cerebellum mainly to inferior and middlecerebellar peduncle.**MIDDLE CEREBELLAR PEDUNCLE ONLY CONTAINS AFFERENTFIBERS.

Efferent fiber- OUTPUT of cerebellum; commence as the axonsof the Purkinje cell and synapse with deep cerebellar nuclei.** most of purkinje cell axons in flocculonodular lobe and vermisefferent fibers leave cerebellum via juxtarestiform body w/o

synapsing in any cerebellar nucleiV. IMPORTANT SYNAPSES AND CIRCUITRY

A. SYNAPTIC ORGANIZATION PURKINJIE CELLS

- Output cells of the cortex inhibit neurons of theunderlying deep cerebellar nuclei.

- The inhibitory control of Purkinje cells over theexcitability of the deep cerebellar nuclei is a key aspectof cerebellar function.

EXCITATORY1. Mossy fibers: enter the cerebellum from the spinal cord,

pontine nuclei, vestibular ganglia and nuclei, trigeminalnuclei, and reticular formation nucleio Glutamate (except those from the pedunculopontine

nucleus and some of the vestibular nuclei – Ach)2. Climbing fibers: originate exclusively in the inferior olive

o Glutamate and Aspartate (excite the purkinje celldendrites on which they synapse)

o GABA:inhibit the deep cerebellar nuclei Inhibitory : noradrenergic (locus ceruleus superior

cerebellar peduncle), dopaminergic (substantia nigra& ventral mesencephalic tegmentum nucleusinterpositus and dentate nuclei), and serotonergic(raphe nuclei all parts of the cerebelar nuclei andcortex

OTHER CELLS: INHIBITORY1. Basket cells

o Inhibit the Purkinje neurons; synapse with climbingfibers and purkinje dendrites

2. Stellate cellso inhibit the Purkinje neurons; synapse with climbing

fibers and purkinje dendriteso Golgi – inhibits granule cell

B. PATTERNS OF EXCITATION Both mossy and climbing fibers input produce excitatory effects

in both the deep cerebellar nuclei and cortex 1. Mossy fiber input: indirectly – activates the granule cells

(through their axonal processes, the parallel fibers) and theiraxonso Ends of all other afferent cerebellar tracts (except the

olivocerebellar tract)o Have multiple brancheso Exert much more diffuse excitatory effecto A single mossy fiber can stimulate thousands of Purkinje

cells through the granule cells

o Terminate at the granular layer to form the cerebellarisland

o 1 mossy fiber: 20 granule cell dendriteso 1 mossy fiber synapse with golgi neurons

A. Granule cells excite purkinje, basket, stellateand golgi type ii

B. Basket & stellate inhibit purkinje and golgi typeii

C. Golgi type ii inhibit granule cells D. Purkinje cells, the only route for all information

exiting from the cerebellar cortex, inhibit thedeep cerebellar and vestibular nuclei.Consequently, within it, only the granule cellscause excitation.

MOSSY FIBERS CIRCUITRY:*(+) = excitatory synapses *(-) = inhibitory synapseso Mossy fiber (+) Granule cell axon (Parallel

fiber) to (+) Golgi cell axon to (-) Granulecell

o Mossy fiber (+) Granule cell axon (Parallelfiber) to (+) :

2. Climbing fiber input: directlyo Directly synapse with the dendrites of Purkinje cells

(molecular layer) o Terminal fibers of the olivocerebellar tractso Pass through the granular layer of the cortex and

terminate in the molecular layer by dividing repeatedly (T- junction forming parallel fibers that run at right angles tothe dendritic processes of the purkinje cells)

o One climbing fiber makes contact with 1 to 10 Purkinjeneurons

o Synapse with cells: (collaterals) Purkinje Golgi Type II Basket cells Stellate cells

CLIMBING FIBERS CIRCUITRY:Climbing fiber (+) Dendrites of Purkinje cell axon to (-) Dentate nucleus

o Dendrite of Purkinje cell Axon to (-) Deepcerebellar nuclei

o Dendrite of Basket cell Axon to (-) Purkinje cell ataxon hillock

o Dendrite of Stellate cell Axon to (-) Purkinje cell

*Purkinje Cell = Functional Unit Sole output neuron of the cerebellar cortex

It will accept excitatory impulses but in return, as it formsit axon, its output is inhibitory. Where modulation and regulation of impulses occur


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Fig. 6 Perpendicular arrangement of parallel fibers to purkinje cells

Fig. 7 Cerebellar Cortex Circuitry

*Excitatory climbing and mossy fibers use GLUTAMATE as excitatorytransmitter on the dendrites of the Purkinje cells. Other afferent

fibers entering the cortex liberate NOREPINEPHRINE ANDSEROTONIN at their endings that possibly modify the action of theglutamate on the Purkinje cells.

V. NEURONS AND FIBERS OF THE CEREBELLUM Afferent fibers

a. Climbing Fibers -arise ONLY from olivocerebellar afferent pathway frominferior olive nucleus into superior cerebellar peduncle

b. Mossy Fibers- Terminal fibers of all other cerebellar afferent fibers

- synapses with golgi neurons- influence the degree of purkinje cell stimulationproduced by climbing and mossy fiber input

Efferent Fibers: neuron location and synapsesNeuron Cell body

LocationDendrites Location Axons Location

PurkinjeFibers

Purkinjelayer

Molecular layersynapsing withparallel fiber/axonsof granule cell and

Granular layerextending to whitematter and synapsewith deep cerebellar

climbing fibers nuclei to inhibit themSmallgranulesCells

Granularlayer

Granular layer andsynapse with axonsof Golgi type II andmossy fibers

Molecular layer andbifurcates to formparallel fibers. Theysynapse with dendritesof purkinje, basket,stellate and golgi type IIcells

GolgiType IIcells

Granularlayer

Molecular layer andsynapse with mossyfibers

Granular layer andsynapse with mossyfiber and small granule

dendrites

VI. CEREBELLAR CORTEX CIRCUITRY

A. THREE HGHWAYS

1. Superior Cerebellar Peduncle Midbrain (Brachosyncytium) Afferent :

o Ventral spinocerebellar Tract (unconscious)o Some trigeminocerebellar Fibers

Efferent (*largest cerebellar efferent bundle):o Projections from the cerebellar cortex originate

from the dentate nucleuso Origin of most efferent fibers from lateral

cerebellar hemisphere (most fibers) to form: Dentatorubral Tract Dentatothalamic Tract Dentatoreticular Tract

NOTE: These tracts cross in the lower midbrain level as thedecussation of the superior cerebellar peduncle

2. Middle Cerebellar Peduncle Pons (Brachiobodies) Afferent ONLY :

o Pontocerebellar Tract (Cross tract / Contralateral)

3. Inferior Peduncle Medulla (Lentiform bodies) Mainly afferent Afferent :

o Dorsal Spinocerebellar Tracto Cuneocerebellar Tracto Reticulocerebelllar Tracto Olivocerebellar Tract (important) o Trigeminocerebellar Fibers (some)o Vestibulocerebellar Fibers

Efferent :o Fastigiobulbar Tract

Juxtarestiform body to Vestibular Nuclei

B. THREE INPUTS

1. Mossy Fibers Spinocerebellar pathways

o Ends in the granular layer

2. Climbing Fibers From the inferior olive Ends in the molecular layer


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3. More Mossy Fibers From the pons, which are carrying information from the

cerebral cortex

C. THREE OUTPUTS1. Fastigial Nuclei

Concerned with balance; sends information mainly tothe vestibular and reticular nuclei (Medial)

Receives purkinje cell output from the vermal zone,send efferent fibers to the reticular and vestibular nucleiof the brainstem project into the spinal cord control of posture and balance

2. Interposed Nuclei Same as dentate nucleus; Globose + Emboliform Receives input from purkinje cell in the paravermal and

vermal zone magnocellular division of the rednucleus rubrospinal tract crosses midline anddescend into the SC. – locomotion and coordinatedmovements of the extremities

3. Dentate Nuclei Concerned more with voluntary movement and send

axons mainly to the thalamus and red nucleus (lateral &biggest)

OTHER EFFERENTSo Lateral zone

Lateral part of the posterior lobe send purkinje cellaxon dentate and interposed nucleus

Fibers from the dentate nucleus terminate in theparvocellular division of the red nucleus rubro-olivarytract descend ipsilaterally terminate in the inferiorolivary complex feedback to the dentate and lateralzone

o Thalamocortical fibers Ventral lateral thalamic nucleus motor regions of the

ipsilateral frontal lobe o Intralaminar nuclei

Prefrontal cortex executive functioning Parietal lobe visuospatial processing Frontal lobe linguistic activity Cingulate and parahippocampal region affective and

motivational phenomena

SOURCE TERMINATION PEDUNCLE USEDDentate Nucleus-voluntary mov’t

VL Thalamic nucleusRed nucleusReticular Formation

Superior

NucleusInterpositus

VL thalamic nucleusRed nucleusReticular Formation

Superior

Fastigial Nucleus-balance andsends info

Vestibular Nuclei Superior(Uncinatefasciculus)Inferior(juxtarestiform)

Reticular Formation Superior(Uncinatefasciculus)

Inferior(juxtarestiform)

FlocculonodularCortex

Vestibular Nuclei Inferior(juxtarestiform)

From the Cerebral Cortexo

Important in the control of voluntary movement;initiation of movement1. Corticopontocerebellar pathway 2. Cerebro-olivocerebellar pathway 3. Cerebroreticulocerebellar pathway

From the Spinal Cord o Receives muscle joint information from muscle spindles,

tendon organs, and joint receptors of the upper andlower limbs

1. Anterior spinocerebellar tract2. Posterior spinocerebellar tract3. Cuneocerebellar tract

From the Vestibular Nerve (Vestibulocerebellar) o From the vestibular nerve to flocculonodular lobeo Receive information from the inner ear: motion(semicircular canal) and position (utricle and saccule)

A. From the Cerebral Cortex

Corticopontocerebellar Pathwayo Information from cerebral cortex particularly primary

motor and sensory areas and associative areas(different lobes of the cerebrum)

o Info descend through the corona radiata and internalcapsule

o Terminate on the pontine nuclei (corticopontine fibers)o The pontine nuclei give rise to the transverse fibers of

the pons

o Neurons project its axons from pontine nuclei tocontralateral cerebellar cortex which cross the midlineand enter the opposite cerebellar hemisphere as themiddle cerebellar peduncle.

VI. CEREBELLAR AFFERENT FIBERS


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Cerebro-olivocerebellar Pathwayo Descend through the corona radiata and internal

capsule to terminate bilaterally on the inferior olivarynuclei.

o The inferior olivary nuclei give rise to fibers that crossthe midline and enter the opposite cerebellarhemisphere through the inferior cerebellar peduncle.

o Information: motor area**Fibers that arise from inferior olivary nuclei terminate as

the climbing fibers in the cerebellar cortex, the rest will

terminate as mossy fibers

Cerebroreticulocerebellar Pathwayo Descend to terminate in the reticular formation on the

same side and on the opposite side in the pons andmedulla

o Cells in the reticular formation give rise to thereticulocerebellar fibers that enter the cerebellarhemisphere on the same side through the inferior andmiddle cerebellar peduncles.

o Information: motor areas

B. From the Spinal Cord

The spinal cord sends information to the cerebellum fromsomatosensory receptors (like muscles, tendons, joints)

Anterior Spinocerebellar Tracto Reach the posterior root ganglion

o Terminate by synapsing with the neurons in the nucleusdorsalis (Clarke's column)

o Nucleus dorsalis located at the base of the posteriorgray matter.

o Axons of these neurons go to anterolateral part of whitematter and ascend to reach brain stem and go throughsuperior cerebellar peduncle

o Fibers that cross over to the opposite side in the spinalcord cross back within the cerebellum

o Believed that the cerebellum receives information from

the skin and superficial fascia by this tracto Involve all segments of spinal cordo Convey muscle-joint information of upper and lower

limbs, skin and superficial fasciao Majority of fibers will cross

Posterior Spinocerebellar Tracto From the posterior root ganglion to the posterior gray

columno Project fibers in nucleus dorsalis (Clarke's column)o Posterolateral part of white matter cerebellar cortexo Enter cerebellum through inferior cerebellar peduncle

on same side then synapse in cerebellar cortexo Collateral branches that end in the deep cerebellar

nuclei are also given offo Convey muscle-joint information of trunk and lower

limbs

Cuneocerebellar Tracto Originate in the nucleus cuneatuso Enter the cerebellar hemisphere on the same side

through the inferior cerebellar peduncleo The fibers terminate as mossy fibers in the cerebellar

cortexo Collateral branches that end in the deep cerebellar

nuclei


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o Receives muscle joint information from the musclespindles, tendon organs, and joint receptors of theupper limb and upper part of the thorax

o Convey muscle-joint information particularly upperLimb and upper part, thorax

C. From the Vestibular Nerve

Vestibulocerebellaro receives information from the inner earo Project axons directly to cerebellumo Directly synapse with neurons in cerebral cortex through

inferior cerebellar peduncleo All the afferent fibers from the inner ear terminate as

mossy fibers in the flocculonodular lobe of the cerebellum.*All afferent fibers terminate in flocculonodular lobe*Other Afferent Fibers

Cerebellum receives small bundles of afferent fibers fromthe red nucleus and the tectum.

Receives information from the inner ear:o Motion - semicricular canalo Position relative to gravity - utricle and saccule.

Entire output of the cerebellar cortex is through the axons ofthe Purkinje cells .

Axons of the neurons that form the intracerebellar nucleiconstitute the efferent outflow from the cerebellum

Few Purkinje cell axons from the flocculonodular lobe by-pass intracerebellar nuclei pass through the juxtarestiformbody of the inferior cerebellar peduncle directly synapsewith the lateral vestibular nucleus

Efferent fibers from the cerebellum connect with the rednucleus, thalamus, vestibular complex, and reticularformation.

1. Globose-Emboliform-Rubral Pathway

Contained in the intracerebellar nuclei (via Globose andEmboliform or Nucleus interpositus) to the red nucleus/-i.

Axons travel through the superior cerebellar peduncle andcross the midline to the opposite side in the decussation ofthe superior cerebellar peduncles

Fibers end by synapsing with cells of the contralateral rednucleus, which give rise to axons of the rubrospinal tract

VII. CEREBELLAR EFFERENT FIBERS


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pathway crosses twice, once in the decussation of thesuperior cerebellar peduncle and again in the rubrospinaltract close to its origin.

influence motor activity on the same side of the body(ipsilateral motor activity)

2. Dentothalamic Pathway Axons travel through the superior cerebellar peduncle Cross the midline to the opposite side in the decussation of

the superior cerebellar peduncle Fibers end by synapsing with cells in the contralateral

ventrolateral nucleus of the thalamus Axons of the thalamic neurons ascend through the internal

capsule and corona radiata and terminate in the primarymotor area of the cerebral cortex.

Influence motor activity by acting on the motor neurons ofthe opposite cerebral cortex

Impulses from the motor cortex are transmitted to spinalsegmental levels through the corticospinal tract.

Deccusation of pyramido Remember that most of the fibers of the corticospinal tract

cross to the opposite side in the decussation of the pyramids orlater at the spinal segmental levels

Influences ipsilateral motor activityo Cerebellum indirectly influences on the same side

3. Fastigial Vestibular Pathway The axons of neurons in the fastigial nucleus travel

through the inferior cerebellar peduncle and end byprojecting on the neurons of the lateral vestibular nucleuson both sides

Some Purkinje cell axons project directly to the lateralvestibular nucleus.

The neurons of the lateral vestibular nucleus form thevestibulospinal tract.

The fastigial nucleus exerts a facilitatory influence mainly onthe ipsilateral extensor muscle tone.

4. Fastigial Reticular Pathway The axons travel through the inferior cerebellar peduncle

and end by synapsing with neurons of the reticularformation.

Axons of these neurons influence spinal segmental motoractivity through the reticulospinal tract. The efferent cerebellar Influences ipsilateral muscle tone


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1. Cortico-ponto-cerebello-dentato-thalamo-cortical Pathway Cerebral cortex -> pontine nuclei via corticopontine fibers Synapses at pontine nuclei –> Crosses then enter cerebellum

via the middle peduncle –> dentate nucleus –> Crosses again atsuperior cerebellar peduncle to thalamus then back to cortex

Double decussation –> at PONTINE LEVEL, SUPERIORCEREBELLAR PEDUNCLE (synapse)

Enter cerebellar cortex through the middle cerebellar peduncle Primary Motor Cortex -> descending motor pathways Thalamus : primary motor cortex

Dentatothalamic fibers project to the VL of the thalamus From motor cortex to loop influences descending motor PW’s Cortex > purkinje cell axons -> dentate nucleus

Synapses at pontine nuclei Crosses then enter cerebellum via themiddle peduncle Dentate nucleus Crosses again at superior

cerebellar peduncle to thalamus (thereby uncross prior reaching ththalamus- DENTATO-THALAMIC FIBERS) then back to cortex

Double decussation- [refer to the image above: at Pontinelevel, Superior Cerebellar Puduncle (synapse)

2. Vestibulo-archicerebellar Loop 1st pair to develop Balancing: Vestibular sytem Impluses from the vestibular nerve go to flocculonodular lobe

cortex (via vestibulocerebellar projection) and fastigial nucleus

Projections go to the vestibular and reticular nuclei inbrainstem

Exit via vestibulocerebellar peduncle Influences to spinal motor activity occur through the

vestibulospinal tracts

Vestibular nuclei Flocculonodular lobe cortex and fastigialnucleuso Projects to the VESTIBULAR AND RETICULAR nuclei i

brainstem (via juxtarestiform body at Inferior peduncle)o Influence spinal motor activity through the vestibulospinal

tracts

3. Brainstem-nuclei-cerebellar Loop Olivocerebral and Reticulocerebral enters thru the inferior

middle peduncle to the cortex (Lateral/Posterior) then go toPurkinje cells to the Nucleus Interpositus / Dentate Nucleithen to the Red / Reticulospinal then finally the spinal cord

Also follow Double Decussation Dentate Nucleus and Interposed Nucleus

Red Nucleus Reticular Nucleus

Rubrospinal Tract Reticulospinal Tract

Spinal Motor Activity

VIII. FEEDBACK LOOPS


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Lower brainstem nuclei and inferior olivary nucleus Reticulocerebellar and olivocerebellar tract Cerebellarcortex

Cerebellar cortex Purkinje cell axons Cerebellar deepnuclei

Origin:o cerebral cortexo muscles, tendons, and jointso vestibular nerve

Cerebellumo NO DIRECTneuronal connections with LMN’s (indirect) o coordinator of precise movements, bring about the

necessary adjustmentso influence activity of LMN’s Cerebellumo send back information -> inhibit agonist muscleso stimulate antagonist ms. -> limits voluntary movement

IX. CLINICAL CORRELATIONS

A. CEREBELLAR DISORDERS AND SYMPTOMS Hypotonia - decreased muscle tone Postural changes & alteration of gait Ataxia-gross lack of coordination or muscle movements

o Intention tremors – tremor during voluntarymovements

o Decomposition of movement- Pastpointing-Misjudging the location of an

object and pointing too far in the same

direction in which the object was displacedwhen presented monocularly in thedirection of action of a recently paralysedextraocular muscle.

- Heel to shin test Dysdiadochokinesia- inability to perform rapid

opposing/alternating movements Disturbances: Reflexes = Pendular knee reflexes Disturbances of Ocular Movement: Nystagmus-

involuntary eye movement

Dysarthria- difficulty speaking

B. COMMON DISEASES1. Acute Alcohol Poisoning

- Alcohol acting on GABA receptors of thecerebellar neurons

2. Alcohol Cerebellar Degeneration Severe chronic alcoholism with malnutrition Vermal degenerative changes

o Ataxia of gait but with normal speech and musclecoordination of upper extremities

3. Tumors Vermis Syndrome = Medulloblastoma (in Children)

Cerebellar Hemisphere Syndromeo Ataxia is very noticeable

C. ABNORMALITIES IN THE CEREBELLUM1. Neocerebellar Syndrome – Lesion of the lateral

hemispheric zone; asynergia, dysmetria, intention tremor- Asyngeria- Dysmetria- Past-pointing- Intention tumor- Dysdiadochokinesia- Rebound phenomenon- Decomposition of movement-scanning speech

o = Dysarthria

- Ataxia

2. Archicerebellar Syndrome – Damage to theflocculonodular lob and the related vermis; ataxia,uncoordinated gait, vomiting, and nystagmus

VIII. SUMMARY (CEREBELLAR CORTICAL CIRCUITRY)

Anat 6.6 Cerebellum_Deriada

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