Cerebellum Prof K Sivapalan Cerebellum It has a

Cerebellum. Prof. K. Sivapalan

Cerebellum • It has a central structure called vermis and lateral structures known as cerebella hemispheres. • It is connected to brain stem by superior, middle and inferior peduncles. • It is situated above the fourth ventricle. • 150 g. 9/21/2021 Cerebellum 2

Cerebellum- structure • Anatomically, anterior, posterior and flocculonodular lobes. • Hemispheres are extensively folded and fissured than cerebral cortex • Weight is 10 % of the cerebral cortex but surface area is 75 %. 9/21/2021 Cerebellum 3

Evolution of Cerebellum • Developed in fish with vestibular apparatus • With quatrupedal locomotion anterior lobes became connected to spinal cord • Erect posture and skilled movements resulted in linkages between posterior lobe and cerebral cortex 9/21/2021 Cerebellum 4

Functional divisions • Floculonodular lobe- is also known as vestibulocerebellum. [oldest] • Rest of the vermis and medial portions of the hemispheres are known as spinocerebellum • Lateral portions of the hemispheres are Neocerebellum- [gratest in humans]. Also known as cerebrocerebellum. 9/21/2021 Cerebellum 5

Function of cerebellum. • Floculonodular lobe is concerned with equilibrium and vestibulo-occular reflex. • Spinocerebellum receives proprioceptive impulses from the body and the motor plan from the motor cortex. • It compares the plan with performances and smoothes and coordinates ongoing movements by influencing the descending pathways. • Vermis projects to brainstem areas concerned with axial and proximal muscles. • Medial hemispheres project to brainstem areas concerned with distal limb muscles. • Neocerebellum- interacts with motor cortex in planning and programming of movements. • Cerebellum is important for learning motor activities. 9/21/2021 Cerebellum 6

Input to Cerebellum. • Cortico-pontocerebellar pathway • Olivocerebellar tract • Vestibuocerebellar tract • Dorsal spinocerebellar tract • Ventral spinocerebellar • Spinoreticular pathway 9/21/2021 Cerebellum 7

Information reaching cerebellum. • Cortico-ponto-cerebellar pathway originates in motor, premotor and sensory cortex. • They synapse in the pontine nuclei and goes to opposite lateral cerebellar hemisphere. • Olivocerebellar tract- from inferior olive to all parts of cerebellum. • Olive gets fibers from motor cortex, basal ganglia, widespread areas of reticular formation, and spinal cord. • Vestibuocerebellar tract originates in vestibular apparatus, vestibular nuclei in brain stem, and goes to floculor nodular lobe and fastigial nucleus of the cerebellum. 9/21/2021 Cerebellum 8

Information reaching cerebellum • Reticulocerebellar fibers from brain stem reticular formation terminate in midline cerebellar areas. • Dorsal spinocerebellar tract terminates in spinocerebellum of the same side. • These fibers come from muscle spindles, Golgi tendon organs, large tactile receptors in the skin, and joint receptors. • Dorsal column nuclei and spinoreticular pathway also project. • These appraise cerebellum of muscle contraction, degree of tension in tendons, position and rate of movement, and the forces acting on the surface of the body. • Ventral spinocerebellar tract terminates in both sides of the cerebellum. • These are activated by impulses coming to the anterior horn cells through corticospinal, rubrospinal tracts and internal motor patern generators in the cord. • It appraises of the motor impulses to anterior horn cell. 9/21/2021 Cerebellum 9

Output from cerebellum. • Cortical output is through Purkinje cell which is inhibitory to the nuclei. • The output goes from the nuclei. • Midline structures project to medullary and pontile regions • Intermediate zone to venterolateral and venteroanterior nuclei of thalamus and cerebral cortex • Fibers from lateral zone to venterolateral and venteroanterior thalamus and to cerebral cortex 9/21/2021 Cerebellum 10

Output from cerebellum • Midline structures project to medullary and pontile regions of the brain stem for control of equilibriumn and the postural attitudes of the body. • Intermediate zone projects to venterolateral and venteroanterior nuclei of thalamus and to cerebral cortex. • In addition, they project to midline structures of the thalamus and through basal ganglia to red nucleus and reticularformation of upper brainstem. • These control the reciprocal movements of the agonist and antoganist muscles of distal limbs. • Lateral zone projects to venterolateral and venteroanterior thalamus and to cerebral cortex. This coordinates sequential motor activities. 9/21/2021 Cerebellum 11

Function of cerebellum. • Floculonodular lobe is concerned with equilibrium and vestibulo-occular reflex. • Spinocerebellum receives proprioceptive impulses from the body and the motor plan from the motor cortex. • It compares the plan with performances and smoothes and coordinates ongoing movements by influencing the descending pathways. • Vermis projects to brainstem areas concerned with axial and proximal muscles. • Medial hemispheres project to brainstem areas concerned with distal limb muscles. • Neocerebellum- interacts with motor cortex in planning and programming of movements. • Cerebellum is important for learning motor activities. 9/21/2021 Cerebellum 12

Effects of Cerebella lesions. • Floculonodular lobe lesion- staggering walk in animals and children, abolition of motion sickness. • Cerebella hemisphere lesions give no signs at rest. • Hypotonia- reduced or absent muscle tone. • Atxia- in-coordination due to error in rate, range, force, and direction of movement manifesting as: 9/21/2021 Cerebellum 13

Atxia • • Drunken gait, Slurred or scanning speech, Dysmetria [past pointing], Intention tremor, Rebound phenomenon- no brakes, Adiadiadochokinsia. , Decomposition of movement. 9/21/2021 Cerebellum 14