Lecture 15- Cerebellum.pdf

Cerebellum Dr. Kelly C. S. Roballo [email protected] VCOM-Main Building Room 341 Learning Objectives 1. Describe three functional divisions of the cerebellum, detailing the input and output connections of each. Be able to differentiate the functions of each and their integration with lateral an...

Cerebellum Dr. Kelly C. S. Roballo [email protected] VCOM-Main Building Room 341 Learning Objectives 1. Describe three functional divisions of the cerebellum, detailing the input and output connections of each. Be able to differentiate the functions of each and their integration with lateral and medial motor systems. 2. Describe the nuclei of the cerebellum and their functions. 3. Identify each cerebellar peduncles and their functions. 4. Designate the intra-cerebellar tracts and the tracts that enter and exit the cerebellum. 5. Compare and contrast knowledge about the effect of the cerebellum on the body’s movements. Chapter 9 basic clinical neuroscience Chapter 15 Blumenfeld Cerebellum & Posterior Fossa Blumenfeld, Neuroanatomy through Clinical Cases Cerebellum Dorsal View Dorsal View Ventral View Blumenfeld, Neuroanatomy throughClinical Cases Cerebellum Gross anatomy and blood supply of the cerebellum, seen from above (A), behind (B), below (C), in front (D), and hemisected (E). The primary fissure, marking the division between the anterior and posterior lobes, is indicated by blue arrows. The horizontal fissure, which prominently subdivides the posterior lobe, is indicated by green arrows. Nolte’s The Human Brain AICA, Anterior inferior cerebellar artery; F, flocculus; I, M, and S, inferior, middle, and superior cerebellar peduncles; PICA, posterior inferior cerebellar artery; SCA, superior cerebellar artery; T, tonsil; V, vermis. In the hemisected view (E), the depth of many of the cerebellar fissures is apparent; these are used to divide the vermis into a number of lobules. Vermal lobules I and II are thin plates of cerebellar tissue (the lingula) that cover the roof of the rostral fourth ventricle; vermal lobule X is the nodulus. Three Peduncles Convey the Inputs and Outputs of Each Half of the Cerebellum Posterior (A) and lateral (B) views of the severed cerebellar peduncles. (C) Diffusion tensor image of a lateral view of the brainstem, showing the courses and an overview of the contents of the cerebellar peduncles. CST, Corticospinal tract; IC, inferior colliculus; ICP, inferior cerebellar peduncle; MCP, middle cerebellar peduncle; Pi, pineal gland; SC, superior colliculus; SCP, superior cerebellar peduncle; T, thalamus. Nolte’s The Human Brain Cerebellum has no direct connections to lower motor neurons Blumenfeld, Neuroanatomy throughClinical Cases Cerebellar lesions result in a characteristic type of irregular uncoordinated movement, ataxia Lesions can be localized easily: 1. Ataxia is ipsilateral to the side of a cerebellar lesion 2. Midline lesions of the cerebellar vermis or flocculonodular lobes mainly cause unsteady gait (truncal ataxia) and eye movement abnormalities 3. Lesions lateral to the cerebellar vermis mainly cause ataxia of the limbs (appendicular ataxia- ATAXIA OF LIMBS) Deep Cerebellar Nuclei Dentate nuclei: receive projections from the lateral cerebellar hemispheres (active just before voluntary movements) Emboliform & globose nuclei: receive inputs from the intermediate part (active during and in relation to the movement) Fastigial nuclei: receive inputs from the vermis Blumenfeld, Neuroanatomy throughClinical Cases Cerebellar Input & Output Pathways INPUT-1: Mossy fibers, ascend through the cerebellar white matter and form excitatory synapses on granule cells Granule cells’ axons form parallel fibers, each of these fibers form excitatory synapses with numerous Purkinje Cells. n All output from the cerebellar cortex is carried by the axons of Purkinje cells Purkinje cells form inhibitory synapses onto deep cerebellar nuclei and vestibular nuclei Blumenfeld, Neuroanatomy throughClinical Cases Cerebellar Input & Output Pathways n INPUT-2: Climbing fibers arise from neurons in the contralateral inferior olivary nucleus. They wrap around the cell body and proximal dendritic tree of Purkinje cells, forming powerful excitatory synapses n A single climbing fiber will branch to supply about 10 Purkinje cells; however each Purkinje cell is excited by just one climbing fiber Regions of the cerebral cortex that project to the cerebellum. The cortical projections to the cerebellum are mainly from the sensory association cortex of the parietal lobe and motor association areas of the frontal lobe. Somatotopic maps of the body surface in the cerebellum. The spinocerebellum contains two maps of the body. Blumenfeld, Neuroanatomy through Clinical Cases Cell Layers of Cerebellar Cortex Blumenfeld, Neuroanatomy through Clinical Cases n n n Mossy fibers excite granule cells, which excite the inhibitory Purkinje cells. Climbing fibers excite Purkinje cells directly Purkinje cells have fanlike dendritic trees, parallel fibers pass through these, then basket cell axons pass perpendicular to the parallel fibers Convergent inputs onto the Purkinje cell from parallel fibers and local circuit neurons. The output of the Purkinje cells is to the deep cerebellar nuclei. Excitatory and inhibitory connections in the cerebellar cortex and deep cerebellar nuclei. The excitatory input from mossy fibers and climbing fibers to Purkinje cells and deep nuclear cells is basically the same. Additional convergent input onto the Purkinje cell from local circuit neurons (basket and stellate cells) and other Purkinje cells establishes a basis for the comparison of ongoing movement and sensory feedback derived from it. The Purkinje cell output to the deep cerebellar nuclear cell thus generates an error correction signal that can modify movements already begun. The climbing fibers modify the efficacy of the parallel fiber-Purkinje cell connection, producing long-term changes in cerebellar output. Purves Neuroscience, 2nd Ed. All axons projecting upward are excitatory All axons projecting downward are inhibitory The outputs of the deep cerebellar nuclei are excitatory Blumenfeld, Neuroanatomy through Clinical Cases Activity of Purkinje cells (A) and deep cerebellar nuclear cells (B) at rest (upper traces) and during movement of the wrist (lower traces) The lines below the action potential records show changes in muscle tension, recorded by electromyography. The durations of the wrist movements are indicated by the colored blocks. Both types of cells are tonically active at rest and change their frequency of firing as movements occur. The neurons respond selectively to various aspects of movement, including extension or contraction of specific muscles, the position of the joints, and the direction of the next movement that will occur. All this information is therefore encoded by changes in the firing frequency of Purkinje cells and deep cerebellar nuclear cells. VENTROLATERAL NUCLEUS OF THE THALAMUS!! Blumenfeld, Neuroanatomy through Clinical Cases Three Peduncles Convey the Inputs and Outputs of Each Half of the Cerebellum Cerebellar peduncles in axial sections. Nolte’s The Human Brain (B) Axial section showing the middle cerebellar peduncle connecting the cerebellum and basal pons. The inferior cerebellar peduncle is cut in cross section just below the level at which it enters the cerebellum. (C) Axial section slightly superior to (B), showing the superior cerebellar peduncles leaving the cerebellum, entering the brainstem, and decussating in the midbrain. Am, amygdala; C, cerebral peduncle; Ca, caudate nucleus; Fl, flocculus; H, hypothalamus; HC, hippocampus; NA, nucleus accumbens; Put, putamen; S, substantia nigra; V, vermis. Outputs from the lateral cerebellar hemisphere via the dentate nucleus n Lateral cerebellar hemispheres involved in motor planning Blumenfeld, Neuroanatomy through Clinical Cases Output from the intermediate cerebellar hemisphere n Intermediate hemisphere involved in the control of ongoing movements of the distal extremities Blumenfeld, Neuroanatomy through Clinical Cases Outputs from the cerebellar vermis & flocculonodular lobe n Cerebellar vermis influences mainly proximal trunk movements and flocculonodular lobes influence vestibulo-ocular control Blumenfeld, Neuroanatomy through Clinical Cases Blumenfeld, Neuroanatomy through Clinical Cases