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. 8/22/2019 Cerebellum

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 %. 8/22/2019 Cerebellum

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 8/22/2019 Cerebellum

Functional divisions Floculonodular lobe- is also known as vestibulo-cerebellum. [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. 8/22/2019 Cerebellum

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. 8/22/2019 Cerebellum

Input to Cerebellum. Cortico-ponto-cerebellar pathway Olivocerebellar tract Vestibuocerebellar tract Dorsal spinocerebellar tract Ventral spinocerebellar Spinoreticular pathway 8/22/2019 Cerebellum

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. 8/22/2019 Cerebellum

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. 8/22/2019 Cerebellum

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 8/22/2019 Cerebellum

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. 8/22/2019 Cerebellum

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. 8/22/2019 Cerebellum

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: 8/22/2019 Cerebellum

Atxia Drunken gait, Slurred or scanning speech, Dysmetria [past pointing], Intention tremor, Rebound phenomenon- no brakes, Adiadiadochokinsia., Decomposition of movement. 8/22/2019 Cerebellum