Anat 6.6 Cerebellum_Deriada

Anatomy 6.6

February 14, 2012 Dr. Maj Deriada

Cerebellum OUTLINE I. CEREBELLUM A. Gross B. Function II. DIVISIONS AND ORGANIZATION A. Lobes (Transverse Division) B. Longitudinal Zones (Sagittal Division) C. Organization III. CEREBELAR CORTEX: CELL LAYERS A. Molecular Layer B. Purkinje Layer C. Granular Layer D. Inner White Matter IV. IMPORTANT SYNAPSES AND CIRCUITRY A. Synaptic Organization B. Patterns of Excitation V. NEURONS AND FIBERS OF THE CEREBELLUM A. Three Highways B. Three Inputs C. Three Outputs VI. CEREBELLAR AFFERENT FIBERS A. From the Cortex B. From the Spinal Cord C. From the Vestibular Nerve VII. CEREBELLAR EFFERENT FIBERS VIII. 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.

 is ovoid in shape with 2 lateral rounded cerebellar hemisphere that pinched in the middle by the vermis  fiber tracts called cerebellar peduncle connecting it to the midbrain or medulla o Superior Cerebellar peduncle (brachium conjunctivum)  midbrain o Middle Cerebellar peduncle (B. Pontis) pons o Inferior (restiform body)  medulla  The medial part is the juxtarestiform body B. FUNCTION  Coordination of voluntary muscle activity [maintaining fine and complex]  Equilibrium  Muscle tonus o [Helps maintain posture and maintain equilibrium while walking and running; execute sequential movement like writing, putting on buttons and brushing teeth and as well as rapidly, alternating and repetitive movement.] o Controls muscular movement ipsilateral or same side of the body unlike 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 will have disorganized, uncoordinated, slow and tremulous movement in the eye and limb movements  There will be problem in muscle tone and posture- either hyper tonus or hypotonus; and when standing or walking he would or stagger or swaying II. DIVISIONS AND ORGANIZATION A. LOBES (Transverse division)  LOBES (transverse division)- divided by a transverse plane: giving rise to Anterior, Posterior and Flocculonodular lobe

References  Snell’s Neuroanatomy  Lansang’s Neuroananatomy Notes  Dr. Deriada’s Slide Lecture Legends Text in Times New Roman are from reference books and 2014B trans Text in Arial Narrow are from the recorded lecture of Dr. Deriada Text 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 Group 3A |Cy, CARA, Cring, Kenji

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

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Anatomic Division

ANTERIOR

POSTERIOR OR MIDDLE (Largest)

FLOCCULONODULAR

Functional Division Phylogenetic Division Gross Location

Spinocerebellum

Cerebrocerebellum

Vestibulocerebellum

Paleocerebellum

Neocerebellum

Archicerebellum (oldest) With a pair of flocculus and at the vermis there is a nodulus (pl. Flocculi and noduli)

Situated anterior to primary fissure and terminates at rostral end of cerebellum

Posterior to the primary fissure and anterior lobe. Limited by the posterolateral fissure

Between anterior and posterior lobe Fissure

Input

Function

Primary Fissurewide v-shape depression or longitudinal fissure that separates anterior and posterior lobe

Posterolateral Fissure- separate posterior lobe from flocculonodular lobe

Spinocerebellar and trigeminocerebella r pathways Stance and gait

Cerebral cortex

Vestibular nuclei

Speech and coordinated movement

Equilibrium (balance, posture and eye movements)

Function

Control of posture, muscle tone, locomotion and equilibrium

spinal cord and limbs [particularly of hands and feet] Thereby responsible for STANCE AND GAIT

Coordination of ipsilateral somatic motor activity Planning of movements Assessment of errors

Damage/ Disease/ Lesion

Ataxiauncoordinated voluntary muscular movements

Wide-based stance Stagger walking

Cerebellar incoordination (asynergia- lack of coordination. Ergo incoordination )

Dysmetria- refers to a lack of coordination of movement typified by the undershoot or overshoot of intended position with the hand, arm, leg, or eye. Inability to judge distance or scale

Three fissures of cerebellum: 1. Primary Fissure 2. Posterolateral or Uvulonodular Fissure 3. Horizontal Fissure- no significance and demarcates the superior and inferior surfaces of the cerebellum

Past-pointing Tremors

TONSILS ON THE NEOCEREBELLUM

Dysdiadochokine sis- inability to perform regular/ rapidly alternating movements Rebound phenomenon

In 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 foramen magnum because it immediately lies to it, compressing the brainstem which is essential for breathing and blood pressure

B. LONGITUDINAL ZONES (Sagittal Division) Section made through the cerebellum parallel to the median plane divides 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 Synonymous term Direction of projection fibers

INTERMEDIATE

Medial  VERMAL PARAVERMAL FLOCCULONOD ULAR ZONE To spinal cord To cerebral hemisphere [efferent fibers: [includes anterior fastigial lobe and the anterior nucleussynaps part of vermis] eaxon to vestibular [singals/ information nucleiSC from cereberal long axis of the cortext to emboliform body] and globose nuclei or nucleus interposidus axons terminated contralateral red nucleus  crossing the other side of the spinal cord]

Group 3A |Cy, CARA, Cring, Kenji

LATERAL 

Lateral

[MOSTLY POSTERIOR part] [cerebral cortex dendate nuclei  thalamus motor cortex pontine nuclei and anterior horn of spinal cord]

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 core white matter  Deep in the white matter are four pairs of masses of gray matter or the intracerebellar nuclei: o Large, multipolar neurons; simple branching dendrites; and Axons

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1. 2. 3. 4.

Dentate nucleus- largest, most lateral Emboliform nucleus- ovoid and situated medial to dentate Globose nucleus- small, rounded in pairs or single Fastigial nucleus- the most medial on the sides of midline The collection of globose and emboliform nucleus forms as INTERPOSED NUCLEI or NUCLEUS INTERPOSIDUS

Fig. 3 Location of the Nucleus Interpositus

III. CEREBELAR CORTEX: CELL LAYERS The cerebellar cortex can be regarded as a large sheet with folds lying in the coronal plane. Each fold or folium contains a core of white 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



The cell body of the purkinje cells lie in the purkinje cell layer while the dendrites pass into the molecular layer where they undergo profuse branching  The primary and secondary branches of the dendrites are smooth  Dendritic spines- short and thick spines that cover the subsequent branches which form synaptic contacts with the parallel fibers derived from granule cell axons  Axons of the purkinje cells will project into the granular layer and will acquire myelin sheath and terminate by synapsing with the cells of one of the intracerebellar nuclei which will form the cerebellar peduncle.  Collateral branches synapse with dendrites of the basket and stellate cells.  Some pass directly to the end in the vestibular nuclei of the brainstem. They by-pass the intracerebellar nuclei.  The axons of these cells are the ENTIRE OUTPUT FIBERS of the cerebellar cortex.  Purkinje cells form the center of a functional unit of the cerebellar 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 which make claw-like endings synapsing with mossy fiber output 1. Granule cells- smallest neurons in the body 2. Golgi Cells- scattered throughout and dendrites reach molecular layer 3. Cerebellar glomeruli/cerebellar island  Cerebellar glomeruli are capped by glial cells which contain: 1. Mossy fiber rosette 2. Terminals of golgi type II axons 3. Dendrites terminal of granular cell  Dendrites synapse with mossy fiber output  Axons pass into the molecular layer where it bifurcates in a Tjunction forming parallel fibers that run at right angles and synapse with dendritic processes of the purkinje cells  Neuroglial cells are found throughout

Fig.4 Cerebellar cortex layers.

A. Molecular Layer  

B. Purkinje Cell Layer 

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

Contains two types of neurons: (1) outer: stellate cell (2) inner: basket cell that are scattered among dendritic arborizations and numerous thin axons running parallel to the folia. Neuroglial cells are found in between

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

Group 3A |Cy, CARA, Cring, Kenji



IV. INNER WHITE MATTER There is a large amount of white matter in each cerebellar hemisphere. The white matter is made up of three groups of fibers: (1) intrinsic, (2) afferent, and (3) efferent Intrinsic fibers- located in the cerebellum but connect different regions of the organ. Within in the cerebellum only.

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



A.

o

Afferent fibers- form the greater part of the white matter coming from the cerebral cortex and proceed to cerebellar cortex; enter the cerebellum mainly to inferior and middle cerebellar peduncle. **MIDDLE CEREBELLAR PEDUNCLE ONLY CONTAINS AFFERENT FIBERS. Efferent fiber- OUTPUT of cerebellum; commence as the axons of the Purkinje cell and synapse with deep cerebellar nuclei. ** most of purkinje cell axons in flocculonodular lobe and vermis efferent fibers leave cerebellum via juxtarestiform body w/o synapsing in any cerebellar nuclei V. IMPORTANT SYNAPSES AND CIRCUITRY

o o

SYNAPTIC ORGANIZATION 





PURKINJIE CELLS Output cells of the cortex inhibit neurons of the underlying deep cerebellar nuclei. The inhibitory control of Purkinje cells over the excitability of the deep cerebellar nuclei is a key aspect of cerebellar function. EXCITATORY 1. Mossy fibers: enter the cerebellum from the spinal cord, pontine nuclei, vestibular ganglia and nuclei, trigeminal nuclei, and reticular formation nuclei o 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 cell dendrites on which they synapse) o GABA: inhibit the deep cerebellar nuclei  Inhibitory: noradrenergic (locus ceruleus  superior cerebellar peduncle), dopaminergic (substantia nigra & ventral mesencephalic tegmentum  nucleus interpositus and dentate nuclei), and serotonergic (raphe nuclei  all parts of the cerebelar nuclei and cortex OTHER CELLS: INHIBITORY 1. Basket cells o Inhibit the Purkinje neurons; synapse with climbing fibers and purkinje dendrites 2. Stellate cells o inhibit the Purkinje neurons; synapse with climbing fibers and purkinje dendrites o 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 Mossy fiber input: indirectly – activates the granule cells (through their axonal processes, the parallel fibers) and their axons o Ends of all other afferent cerebellar tracts (except the olivocerebellar tract) o Have multiple branches o Exert much more diffuse excitatory effect o A single mossy fiber can stimulate thousands of Purkinje cells through the granule cells

1.

Group 3A |Cy, CARA, Cring, Kenji

Terminate at the granular layer to form the cerebellar island 1 mossy fiber: 20 granule cell dendrites 1 mossy fiber synapse with golgi neurons A. Granule cells excite purkinje, basket, stellate and golgi type ii B. Basket & stellate inhibit purkinje and golgi type ii C. Golgi type ii inhibit granule cells D. Purkinje cells, the only route for all information exiting from the cerebellar cortex, inhibit the deep cerebellar and vestibular nuclei. Consequently, within it, only the granule cells cause excitation.

MOSSY FIBERS CIRCUITRY: *(+) = excitatory synapses *(-) = inhibitory synapses o Mossy fiber (+)  Granule cell  axon (Parallel fiber) to (+)  Golgi cell  axon to (-)  Granule cell o Mossy fiber (+)  Granule cell  axon (Parallel fiber) to (+) : 2.

Climbing fiber input: directly o Directly synapse with the dendrites of Purkinje cells (molecular layer) o Terminal fibers of the olivocerebellar tracts o Pass through the granular layer of the cortex and terminate in the molecular layer by dividing repeatedly (Tjunction forming parallel fibers that run at right angles to the dendritic processes of the purkinje cells) o One climbing fiber makes contact with 1 to 10 Purkinje neurons 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 (-)  Deep cerebellar nuclei o Dendrite of Basket cell  Axon to (-) Purkinje cell at axon 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 forms it axon, its output is inhibitory.  Where modulation and regulation of impulses occur

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Small granules Cells

Granular layer

Golgi Type II cells

Granular layer

climbing fibers Granular layer and synapse with axons of Golgi type II and mossy fibers

Molecular layer and synapse with mossy fibers

nuclei to inhibit them Molecular layer and bifurcates to form parallel fibers. They synapse with dendrites of purkinje, basket, stellate and golgi type II cells Granular layer and synapse with mossy fiber and small granule dendrites

VI. CEREBELLAR CORTEX CIRCUITRY A.

THREE HGHWAYS

1.

Fig. 6 Perpendicular arrangement of parallel fibers to purkinje cells

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 nucleus o 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 the decussation of the superior cerebellar peduncle

2. Fig. 7 Cerebellar Cortex Circuitry *Excitatory climbing and mossy fibers use GLUTAMATE as excitatory transmitter on the dendrites of the Purkinje cells. Other afferent fibers entering the cortex liberate NOREPINEPHRINE AND SEROTONIN at their endings that possibly modify the action of the glutamate on the Purkinje cells.



3.

V. NEURONS AND FIBERS OF THE CEREBELLUM Afferent fibers a. Climbing Fibers -arise ONLY from olivocerebellar afferent pathway from inferior 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 stimulation produced by climbing and mossy fiber input  Efferent Fibers: neuron location and synapses Neuron Purkinje Fibers

Cell body Location Purkinje layer

Dendrites Location

Axons Location

Molecular layer synapsing with parallel fiber/axons of granule cell and

Granular layer extending to white matter and synapse with deep cerebellar

Group 3A |Cy, CARA, Cring, Kenji

B.

Middle Cerebellar Peduncle  Pons (Brachiobodies)  Afferent ONLY: o Pontocerebellar Tract (Cross tract / Contralateral) Inferior Peduncle  Medulla (Lentiform bodies)  Mainly afferent  Afferent: o Dorsal Spinocerebellar Tract o Cuneocerebellar Tract o Reticulocerebelllar Tract o Olivocerebellar Tract (important) o Trigeminocerebellar Fibers (some) o Vestibulocerebellar Fibers  Efferent: o Fastigiobulbar Tract  Juxtarestiform body to Vestibular Nuclei

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.

C.

Flocculonodular Cortex

Vestibular Nuclei

Inferior (juxtarestiform) Inferior (juxtarestiform)

THREE OUTPUTS 1.

2.

3.



More Mossy Fibers  From the pons, which are carrying information from the cerebral cortex

Fastigial Nuclei  Concerned with balance; sends information mainly to the vestibular and reticular nuclei (Medial)  Receives purkinje cell output from the vermal zone, send efferent fibers to the reticular and vestibular nuclei of the brainstem  project into the spinal cord  control of posture and balance Interposed Nuclei  Same as dentate nucleus; Globose + Emboliform  Receives input from purkinje cell in the paravermal and vermal zone  magnocellular division of the red nucleus  rubrospinal tract  crosses midline and descend into the SC. – locomotion and coordinated movements of the extremities Dentate Nuclei  Concerned more with voluntary movement and send axons mainly to the thalamus and red nucleus (lateral & biggest)

OTHER EFFERENTS

o Lateral zone  Lateral part of the posterior lobe  send purkinje cell axon  dentate and interposed nucleus  Fibers from the dentate nucleus terminate in the parvocellular division of the red nucleus  rubro-olivary tract  descend ipsilaterally  terminate in the inferior olivary complex  feedback to the dentate and lateral zone 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 Dentate Nucleus -voluntary mov’t Nucleus Interpositus Fastigial Nucleus -balance and sends info

TERMINATION VL Thalamic nucleus Red nucleus Reticular Formation VL thalamic nucleus Red nucleus Reticular Formation Vestibular Nuclei

Reticular Formation

Group 3A |Cy, CARA, Cring, Kenji

VI. CEREBELLAR AFFERENT FIBERS 





From the Cerebral Cortex o Important in the control of voluntary movement; initiation of movement 1. 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 and lower limbs 1. Anterior spinocerebellar tract 2. Posterior spinocerebellar tract 3. Cuneocerebellar tract From the Vestibular Nerve (Vestibulocerebellar) o From the vestibular nerve to flocculonodular lobe o Receive information from the inner ear: motion (semicircular canal) and position (utricle and saccule)

A. From the Cerebral Cortex 

Corticopontocerebellar Pathway o 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 internal capsule o Terminate on the pontine nuclei (corticopontine fibers) o The pontine nuclei give rise to the transverse fibers of the pons

PEDUNCLE USED Superior

Superior

Superior (Uncinate fasciculus) Inferior (juxtarestiform) Superior (Uncinate fasciculus)

o Neurons project its axons from pontine nuclei to contralateral cerebellar cortex which cross the midline and enter the opposite cerebellar hemisphere as the middle cerebellar peduncle.

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

Cerebro-olivocerebellar Pathway o Descend through the corona radiata and internal capsule to terminate bilaterally on the inferior olivary nuclei. o The inferior olivary nuclei give rise to fibers that cross the midline and enter the opposite cerebellar hemisphere 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 Pathway o Descend to terminate in the reticular formation on the same side and on the opposite side in the pons and medulla o Cells in the reticular formation give rise to the reticulocerebellar fibers that enter the cerebellar hemisphere on the same side through the inferior and middle cerebellar peduncles. o Information: motor areas

B. From the Spinal Cord The spinal cord sends information to the cerebellum from somatosensory receptors (like muscles, tendons, joints) 

Anterior Spinocerebellar Tract o Reach the posterior root ganglion

Group 3A |Cy, CARA, Cring, Kenji

o Terminate by synapsing with the neurons in the nucleus dorsalis (Clarke's column) o Nucleus dorsalis located at the base of the posterior gray matter. o Axons of these neurons go to anterolateral part of white matter and ascend to reach brain stem and go through superior cerebellar peduncle o Fibers that cross over to the opposite side in the spinal cord cross back within the cerebellum o Believed that the cerebellum receives information from the skin and superficial fascia by this tract o Involve all segments of spinal cord o Convey muscle-joint information of upper and lower limbs, skin and superficial fascia o Majority of fibers will cross



Posterior Spinocerebellar Tract o From the posterior root ganglion to the posterior gray column o Project fibers in nucleus dorsalis (Clarke's column) o Posterolateral part of white matter cerebellar cortex o Enter cerebellum through inferior cerebellar peduncle on same side then synapse in cerebellar cortex o Collateral branches that end in the deep cerebellar nuclei are also given off o Convey muscle-joint information of trunk and lower limbs



Cuneocerebellar Tract o Originate in the nucleus cuneatus o Enter the cerebellar hemisphere on the same side through the inferior cerebellar peduncle o The fibers terminate as mossy fibers in the cerebellar cortex o Collateral branches that end in the deep cerebellar nuclei

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o

o

Receives muscle joint information from the muscle spindles, tendon organs, and joint receptors of the upper limb and upper part of the thorax Convey muscle-joint information particularly upper Limb and upper part, thorax

C. From the Vestibular Nerve VII. CEREBELLAR EFFERENT FIBERS

 Vestibulocerebellar o receives information from the inner ear o Project axons directly to cerebellum o Directly synapse with neurons in cerebral cortex through inferior cerebellar peduncle o 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 from the red nucleus and the tectum.  Receives information from the inner ear: o Motion - semicricular canal o Position relative to gravity - utricle and saccule.

 Entire output of the cerebellar cortex is through the axons of the Purkinje cells.  Axons of the neurons that form the intracerebellar nuclei constitute the efferent outflow from the cerebellum  Few Purkinje cell axons from the flocculonodular lobe bypass intracerebellar nuclei pass through the juxtarestiform body of the inferior cerebellar peduncle directly synapse with the lateral vestibular nucleus  Efferent fibers from the cerebellum connect with the red nucleus, thalamus, vestibular complex, and reticular formation.

1.

Group 3A |Cy, CARA, Cring, Kenji

Globose-Emboliform-Rubral Pathway  Contained in the intracerebellar nuclei (via Globose and Emboliform or Nucleus interpositus) to the red nucleus/-i.  Axons travel through the superior cerebellar peduncle and cross the midline to the opposite side in the decussation of the superior cerebellar peduncles  Fibers end by synapsing with cells of the contralateral red nucleus, which give rise to axons of the rubrospinal tract

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 Some Purkinje cell axons project directly to the lateral vestibular nucleus.  The neurons of the lateral vestibular nucleus form the vestibulospinal tract.  The fastigial nucleus exerts a facilitatory influence mainly on the ipsilateral extensor muscle tone.

 pathway crosses twice, once in the decussation of the superior cerebellar peduncle and again in the rubrospinal tract 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 primary motor area of the cerebral cortex.  Influence motor activity by acting on the motor neurons of the opposite cerebral cortex  Impulses from the motor cortex are transmitted to spinal segmental levels through the corticospinal tract.  Deccusation of pyramid

4.

Fastigial Reticular Pathway  The axons travel through the inferior cerebellar peduncle and end by synapsing with neurons of the reticular formation.  Axons of these neurons influence spinal segmental motor activity through the reticulospinal tract.  The efferent cerebellar Influences ipsilateral muscle tone

o Remember that most of the fibers of the corticospinal tract cross to the opposite side in the decussation of the pyramids or later at the spinal segmental levels

 Influences ipsilateral motor activity o 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 by projecting on the neurons of the lateral vestibular nucleus on both sides

Group 3A |Cy, CARA, Cring, Kenji

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cerebellar peduncle to thalamus (thereby uncross prior reaching the thalamus- DENTATO-THALAMIC FIBERS) then back to cortex  Double decussation- [refer to the image above: at Pontine level, Superior Cerebellar Puduncle (synapse) 2. Vestibulo-archicerebellar Loop st  1 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 in brainstem  Exit via vestibulocerebellar peduncle  Influences to spinal motor activity occur through the vestibulospinal tracts

VIII. FEEDBACK LOOPS 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 at superior cerebellar peduncle to thalamus then back to cortex  Double decussation –> at PONTINE LEVEL, SUPERIOR CEREBELLAR 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

 Vestibular nuclei  Flocculonodular lobe cortex and fastigial nucleus o Projects to the VESTIBULAR AND RETICULAR nuclei in 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 to Purkinje cells to the Nucleus Interpositus / Dentate Nuclei then to the Red / Reticulospinal then finally the spinal cord  Also follow Double Decussation  Dentate Nucleus and Interposed Nucleus 

Red Nucleus



Rubrospinal Tract Reticulospinal Tract

Reticular Nucleus

Spinal Motor Activity

Synapses at pontine nuclei  Crosses then enter cerebellum via the middle peduncle  Dentate nucleus  Crosses again at superior Group 3A |Cy, CARA, Cring, Kenji

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   





Lower brainstem nuclei and inferior olivary nucleus  Reticulocerebellar and olivocerebellar tract  Cerebellar cortex Cerebellar cortex  Purkinje cell axons  Cerebellar deep nuclei

VIII. SUMMARY (CEREBELLAR CORTICAL CIRCUITRY) 



Origin: o cerebral cortex o muscles, tendons, and joints o vestibular nerve Cerebellum o NO DIRECT neuronal connections with LMN’s (indirect) o coordinator of precise movements, bring about the necessary adjustments o influence activity of LMN’s Cerebellum o send back information -> inhibit agonist muscles o stimulate antagonist ms. -> limits voluntary movement

direction in which the object was displaced when presented monocularly in the direction of action of a recently paralysed extraocular muscle. Heel to shin test Dysdiadochokinesiainability to perform rapid opposing/alternating movements Disturbances: Reflexes = Pendular knee reflexes Disturbances of Ocular Movement: Nystagmusinvoluntary eye movement Dysarthria- difficulty speaking

B.

COMMON DISEASES 1. Acute Alcohol Poisoning Alcohol acting on GABA receptors of the cerebellar neurons 2. Alcohol Cerebellar Degeneration  Severe chronic alcoholism with malnutrition  Vermal degenerative changes o Ataxia of gait but with normal speech and muscle coordination of upper extremities 3. Tumors  Vermis Syndrome = Medulloblastoma (in Children)  Cerebellar Hemisphere Syndrome o Ataxia is very noticeable

C.

ABNORMALITIES IN THE CEREBELLUM 1. 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 the flocculonodular lob and the related vermis; ataxia, uncoordinated gait, vomiting, and nystagmus

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 voluntary movements o Decomposition of movement Pastpointing-Misjudging the location of an object and pointing too far in the same

Group 3A |Cy, CARA, Cring, Kenji

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