Cerebellum AN5203 PDF

Neuroanatomy AN5203 The Cerebellum Dr. Moira Jenkins Functions of the Cerebellum • For movement, it’s not enough to cause muscles to contract-need a detailed sequence, precision, and coordination! • Directly regulates and COORDINATES execution of specific movements • Synergistic multijoint moveme...

Neuroanatomy AN5203 The Cerebellum Dr. Moira Jenkins Functions of the Cerebellum • For movement, it’s not enough to cause muscles to contract-need a detailed sequence, precision, and coordination! • Directly regulates and COORDINATES execution of specific movements • Synergistic multijoint movement • Coordination of hand and eye movements • Compares movement intention with performance and makes adjustments • Regulation of muscle tone • Motor learning • Accuracy in rate, range, and direction of movement is from cerebellum • Some connection to the limbic systemCerebellar Cognitive Affective/Schmahmann Syndrome Basic Anatomy “little brain” In the posterior cranial fossa Inferior to the occipital lobe Under the tentorium cerebelli 2 hemispheres; 3 lobes; median vermis somatotopy Anatomy – Lobes of the Cerebellum • The are 2 cerebellar hemispheres and midline vermis • There are 3 lobes anterior posterior flocculonodular • Fissures Primary –between the anterior and posterior lobe Posterolateral – between the posterior and focculonodular lobe Basic Anatomy Gray Matter Cortex • 3 layers of cells in the outer cortex • central gray contain nuclei-only projection out of the cerebellum Folia – the folds on the surface of the cortex increase surface area Arbor vitae- white matter of the cerebellum “tree of life” Afferent and efferent fibers Microanatomy of Cerebellar Cortex The cerebellum has more neurons than all other areas of the brain combined! CORTICAL LAYERS: the cortex is divided into three layers: MOLECULAR - superficial layer PURKINJE - middle layer Granular -deepest layer • Granular (deepest) • Closely packed small neurons; main receptive layer of fibers originating outside cerebellum • Purkinje • Single row of purkinje cells; axons project to deep nuclei • Molecular • Few neuron cell bodies; mostly a synaptic and integrative area St - stellate St CELLS FORMING INTRACORTICAL CIRCUITS • Granule - excitatory (glutamate) • Purkinje - axons are output of cortex; inhibitory (GABA) • Basket - axons around Purkinje cells; inhibitory (GABA) • Golgi - inhibitory (GABA) to mossy fibers • Stellate - most synapse with Purkinje cells; inhib (GABA) Anatomy – Gray Matter Nuclei “Don’t Eat Greasy Foods” The 4 nuclei, from lateral to medial: Dentate - largest Emboliform Globose Interposed Fastigial Axons from these nuclei project to brain stem nuclei and thalamus Cerebellar function depends on input and output to produce the movement accuracy, direction, timing, and force There is input from the cortex, brainstem, and spinal cord Output is to brainstem, thalamus, and cortex Not directly to cord but will influence output down cord Anatomy – Cerebellar Peduncles • The only connections of the cerebellum to the brainstem are the peduncles (stalk), white matter tracts running in and out of cerebellum • Superior Cerebellar Peduncle - midbrain afferent and efferent • Middle Cerebellar Peduncle – pons afferent only largest peduncle • Inferior Cerebellar Peduncle – medulla afferent and efferent Afferent to the Cerebellum INPUT from Cerebral cortex -to pons From pons to cerebellum ka: cerebropontocerebellar projection *this projection has 20x more axons than the corticospinal tract! Middle peduncle-one way and why so large (pontocerebellar fibers) Contralateral fibers from pontine nuclei Olive & other brainstem nuclei Vestibular input Peripheral proprioception (spinal cord tracts) Superior Cerebellar Peduncle Afferents- from spinal cord, VSCT red nucleus Superior colliculus Efferents-to contralateral red nucleus and thalamus VL These efferents form the decussation of the superior cerebellar peduncles In midbrain cross-section slides Middle Cerebellar Peduncle All afferent from pontine nuclei Cortex telling cerebellum “this is the Movment we plan to do” Cerebellum checks movement against Plan and sends info back to brainstem, thalamus, cortex to make adjustments **cerebellum does NOT project down cord Inferior Cerebellar Peduncle Afferents -from spinal cord Dorsal spinocerebellar, Cuneocerebellar, Vestibular nuclei Inferior olivary nucleus (olivocerebellar fibers that Decussate in medulla) Efferentsto reticular formation and vestibular nuclei St - stellate St Input from all other sources, e.g., cord Input from inferior olivary nuclei 2 massive pathways from the contralateral brain stem: olivoand ponto- Anatomy – Functional Divisions of the Cerebellum Functionally the hemispheres are separated into; • Flocculonodular lobe – Vestibulocerebellum • Vermis • Intermediate Zone • Lateral Zone Spinocerebellum - Cerebrocerebullum/pontocerebellum The functional regions of the cerebellum were determined by associating movement disorders with cerebellar lesions ORGANIZATION OF THE CEREBELLUM - Phylogeny (Evolutionary history deduced from comparative anatomy) • Archicerebellum • Flocculonodular lobe • Fish and amphibians • Paleocerebellum • Superior vermis of anterior lobe and inferior vermis of posterior lobe • Amphibians, reptiles, birds • Neocerebellum • Mammals, humans ORGANIZATION OF THE CEREBELLUM - functional • Vestibulocerebellum (flocculonodular lobe) • Afferents from vestibular nuclei • Adjustment of muscle tone in response to vestibular stimuli • Coordinates actions of muscles that maintain balance and posture; participates in other motor responses to vestibular stimuli (e.g., eye movements) • Utilizes MLF, VeSpTract, ReSpTract Fastigial Nuclei Vestibular Nuclei Reticular Formation ORGANIZATION OF THE CEREBELLUM - functional Nuc. Interpositus • Spinocerebellum (vermis and adjacent paravermal/intermediate zones) Red nucleus VL of thalamus • Controls tone and synergy of (RF) collaborating muscles, as appropriate, at any moment for adjusting posture and ongoing automatic movements • Input from cord [spinocerebellar and cuneocerebellar tracts] providing sensory feedback [strong connections], trigeminal nuclei [similar to spinocerebellar tracts], inf. olivary nuc., tectum, RF Fastigial Nuclei Vestibular Nuclei Reticular Formation ORGANIZATION OF THE CEREBELLUM - Functional • Pontocerebellum (lateral parts of hemispheres) aka cerebrocerebellum • Massive connections with cerebral cortex • Ensures a smooth and orderly sequence of muscle contractions and intended precision in force, direction, and extent of voluntary movements, especially in upper extremities • Input ONLY from cerebral cortex via contralateral pontine nuclei (volitional movements anticipated or in progress) Primary and Premotor cortex Dentate Nucleus VL of thalamus (Red nucleus) Inf. Oliv Nuc [loops back to contralat Cerebellum] Regulates body and limb movements (i.e., neck, trunk, proximal parts of arm for balance and posture control during voluntary movements) Regulates balance and eye movements Plans voluntary movements and regulates cortical motor programs Corticopontine tells cerebellum what the cortex told the body to do; cerebellum sends input back to the cortex (feed-forward) saying ‘this is what I want you to do’ Functional Divisions of the Cerebellum A. Vestibulocerebellum controls – equilibrium/balance receives input from semicircular canals, otolithic organs, and superior colliculus adjusts axial muscles to maintain balance and coordination of eye movements. B. Spinocerebellum controls - Adjustment of ongoing movements. Because of its somatosensory inputs and its outputs to descending systems, the spinocerebellum is involved in: 1. Regulation of muscle tone 2. Compensation for small variations in loads encountered during movement 3. Smoothing out oscillations (tremors) 4. Correcting for deviations of intended movement C. Cerebrocerebellum modulates - Planning of limb movements. By virtue of its connections with primary and premotor cortex, the cerebrocerebellum is a center of complex feedback circuits modulating motor commands Damaged this in monkeys – ran into walls PROPRIOCEPTION Receptors: Muscle Spindles, Golgi Tendon Organs, and some touch receptors Subconscious Conscious Subconscious: Cerebellum (Dorsal Columns)  Cortex tracts From individual muscles - enters inferior cerebellar peduncle 1. Posterior spinocerebellar tract (lower limb) 2. Cuneocerebellar tract (upper limb) From muscle groups - enters superior cerebellar peduncle Ventral spinocerebellar tract Disease of the Cerebellum • NOT weakness or spasticity • Ataxia • Intention Tremor • Hypotonia • Broad based stance • Past pointing/Dysmetria • Clumsy gait • Moving trunk from side to side • Scanning speech • Cerebellar damage symptoms : • VANISHED: Vertigo Ataxia Nystagmus Intention tremor Slurred (or Staccato) speech Exagerrated broad based gait Hypotonic reflexes Dysdiadochokinesia Ataxia • Ataxia= the inability to make smooth coordinated movements • Can be seen with other disorders • The primary symptom of cerebellar disease Intention Tremor • Intention Tremor= rhythmic oscillating movement when trying to perform intentional movement • Interferes with voluntary movements • Also called Essential Tremor • Not displayed at rest • Opposite of Parkinson’s tremor • Unable to make the normal adjustments Dysdiadochokinesia • Dysdiadochokinesia DDK= greek, “bad succeeding movements” • the inability to perform rapid alternating movements Disorders of the Cerebellum • Many different signs and symptoms but if one functional area is affected, may have more specific signs • Vestibulocerebellum lesions – Balance and eye coordination eye movements, nystagmus, vertigo • Spinocerebellar lesions - Execution truncal and gait ataxia • Cerebrocerebellar lesions - Planning limb ataxia • Cerebellar cognitive affective syndrome (aka Schmahmann syndrome) • Dysmetria of thought and emotion • A mismatch between reality and perceived reality, and erratic attempts to correct the errors of thought or behavior • autism Cerebrocerebellar Lesion Medial lesions affect medial structures (axial), lateral lesions affect lateral structures (limbs) Alcohol and the Cerebellum • When alcohol is consumed faster than it can be metabolized, the function of most brain structures is altered, especially the cerebellum • Increased GABA inhibition of granule cells • Slurred speech, loss of coordination and balance • Long term alcohol abuse causes cerebellar degeneration same symptoms with possible nystagmus, memory loss confusion, psychosis,