Cerebellum 1 and 2 Lecture Notes PDF

Centro Escolar University – School of Medicine NEUROSCIENCE Lecture: Cerebellum 1 and 2 OCTOBER 9, 2023 MD-NEURO | DR. JOHN VINCENT O. ESTRADA...

Centro Escolar University – School of Medicine NEUROSCIENCE Lecture: Cerebellum 1 and 2 OCTOBER 9, 2023 MD-NEURO | DR. JOHN VINCENT O. ESTRADA 3rd SHIFTING OUTLINE I. CEREBELLUM II. LOBES AND FISSURE OF THE CEREBELLUM III. LOBULES IN THE VERMIS AND CEREBELLAR HEMISPHERE IV. STRUCTURE OF THE CEREBRAL CORTEX A. MOLECULAR LAYER B. PURKINJE CELLS C. GRANULAR LAYER V. FUNCTIONAL AREAS OF THE CEREBELLAR CORTEX VI. INTRACEREBELLAR NUCLEI (DEEP CEREBELLAR NUCLEI) A. WHITE MATTER VII. CEREBELLAR CORTICAL MECHANISM VIII. INTRACEREBELLAR NUCLEAR MECHANISMS REVIEW QUESTIONS REFERENCES II. LOBES AND FISSURE OF THE CEREBELLUM I. CEREBELLAR PEDUNCLES It is divided into three main lobes: anterior lobe, II. CEREBELLAR AFFERENT FIBERS middle lobe, and the flocculonodular lobe. A. FROM THE CEREBRAL CORTEX ○ The anterior lobe may be seen on the superior B. FROM THE SPINAL CORD 1 C. FROM THE VESTIBULAR NERVE surface of the cerebellum and is separated from the III. CEREBELLAR EFFERENT FIBERS middle lobe by a wide V-shaped fissure called the primary A. GLUBOSE-EMBOLIFORM RUBRAL PATHWAY fissure. 2 ○ The middle lobe (sometimes called the posterior B. DENTOTHALAMIC NUCLEI PATHWAY C. FASTIGIAL VESTIBULAR PATHWAY lobe), which is the largest part of the cerebellum, is D. FASTIGIAL RETICULAR PATHWAY situated between the primary and uvulonodular fissure. E. THE CEREBELLAR EFFERENT PATHWAYS The flocculonodular lobe is situated posterior to IV. FUNCTIONS OF THE CEREBELLUM V. CLINICAL NOTES3 the A. SIGNS AND SYMPTOMS OF CEREBELLAR uvulonodular fissure. DISEASE REVIEW QUESTIONS ○ A deep horizontal fissure that is found along the REFERENCES margin of the cerebellum separates the superior from the inferior surfaces. I.CEREBELLUM The cerebellum is situated in the posterior cranial fossa and is covered superiorly by the tentorium cerebelli. It is the largest part of the hindbrain and lies posterior to the fourth ventricle, the pons, and the medulla oblongata. It is somewhat ovoid in shape and constricted in its median pa It consists of two cerebellar hemispheres joined by a narrow median vermis. It is collected to the posterior aspect of the brainstem by three symmetrical bundles of nerve fibers called the superior, middle and inferior cerebellar peduncles. BASE, EDANO, FLORENDO, MONTEIRO PASAJOL, K. SORIANO, V.SORIANO 1  II.LOBULES IN THE VERMIS AND CEREBELLAR HEMISPHERE ANTERIOR LOBE Lingula No counterpart Central Lobule Ala Culmen Quadrangular lobule MIDDLE LOBE Declive Lobulus Simplex Folium Superior Semilunar lobule Tuber Inferior Semilunar lobule Pyramid Biventral lobule Uvula Tonsil FLOCCULONODULAR LOBE Nodule Flocculus II.LOBULES IN THE VERMIS AND CEREBELLAR HEMISPHERE A section made through the cerebellum parallel with the median plane divides the folia at right angles, and the cut surface has a branched appearance, called the arbor vitae. BASE, EDANO, FLORENDO, MONTEIRO, PASAJOL, K. SORIANO, V.SORIANO 2  B. PURKINJE CELLS The gray matter of the cortex throughout its extent has a uniform structure. It may be divided into three It is a single layer of large Golgi Type 1 neurons layers: called Purkinje cells. ○ → An external layer (Molecular layer) At the base of the Purkinje cell, the axon arises ○ → A middle layer ( Purkinje cell layer) and passes through the granular layer to enter the white ○ → An internal layer (Granular layer) matter. On entering the white matter, the axon acquires a myelin sheath, and it terminates by synapsing with cells of one of the intracerebellar nuclei. A few of the Purkinje cell axons pass directly to end in the vestibular nuclei of the brainstem. C. GRANULAR LAYER It is packed with small cells called granule cells with densely staining nuclei and scanty cytoplasm Each cell gives rise to four or five dendrites, which make clawlike endings and have synaptic contact with mossy fiber input. The axon of each granule cell passes into the molecular layer, where it bifurcates at a T junction, the branches running parallel to the long axis of the cerebellar folium. These fibers, known as parallel fibers, run at right angles to the dendritic processes of the Purkinje cells. Most of the parallel fibers make synaptic contacts with the spinous processes of the dendrites of the Purkinje cells. Scattered throughout the granular layer are Golgi cells. Their dendrites ramify in the molecular layer, and their axons terminated by splitting up into branches that synapse with the dendrites of the granular cells. V.FUNCTIONAL AREAS OF CEREBELLAR CORTEX The vermis influences the movements of the long axis of the body, namely the neck, shoulders, thorax, abdomen, and hips. Immediately lateral to the vermis is the intermediate zone of the cerebellar hemisphere, which has been shown to control the muscles of the distal part of the limbs, especially the hands and feet. Lateral zone of each cerebellar hemisphere appears to be concerned with the planning of consequential movements of the entire body and is involved with the conscious assessment of movement errors. A. MOLECULAR LAYER It contains two types of neurons: ○ the outer stellate cell ○ the inner basket cell These neurons are scattered among dendritic arborizations and numerous thin axons that run parallel to the long axis of the folia. BASE, EDANO, FLORENDO, MONTEIRO, PASAJOL, K. SORIANO, V.SORIANO 3  VI.INTERCEREBELLAR NUCLEI (DEEP CEREBELLAR NUCLEI) They are embedded in the white matter on each side of the midline. From lateral to medial are the dentate nucleus, emboliform nucleus, globose nucleus, and fastigial nucleus. ○ Dentate nucleus largest of the intracerebellar nuclei Has the shape of a crumpled bag with the opening facing medially ○ Emboliform nucleus It is ovoid and is situated medial to the dentate nucleus ○ Globose nucleus It consists of one or more rounded cell groups that lie medial to the emboliform nucleus ○ Fastigial nucleus It lies near the midline in the vermis and close to VII.CEREBELLAR CORTICAL MECHANISM the roof of the fourth ventricle. The intracerebellar nuclei are composed of large The climbing fibers and the mossy fibers multipolar neurons; the axons form the cerebellar outflow constitute the two main lines of input to the cerebellar in the superior and inferior cerebellar peduncles. cortex and are excitatory to the purkinje cells ○ The climbing fibers are the terminal fibers of the olivocerebellar tracts. ○ The mossy fibers are the terminal fibers of all other cerebellar afferent tracts. They have multiple branches and exert a much more diffuse excitatory effect. ○ A single mossy fiber may stimulate thousands of purkinje cells through the granular cells. The stellate cells, basket cells, and Golgi cells serve as inhibitory interneurons. ○ It is believed that they not only limit the area of cortex excited, but also influence the degree of purkinje cell excitation produced by the climbing and mossy fiber input. ○ By this means, fluctuating inhibitory impulses are transmitted by the purkinje cells to the intracerebellar nuclei, which in turn modify muscular activity through the motor control areas of the brainstem and cerebral cortex. ○ It is thus seen that the purkinje cells form the A.WHITEMATTER center of a functional unit of the cerebellar cortex. It is made up of the three groups of fibers: (1) intrinsic, (2) afferent, (3) efferent. ○ The intrinsic fibers do not leave the cerebellum but connect different regions of the organ, some on the same side and some connecting both sides. ○ The afferent fibers enter the cerebellum mainly through the inferior and middle cerebellar peduncles where they proceed to the cerebellar cortex. ○ The efferent fibers constitute the output of the cerebellum and commence as the axons of the purkinje cells of the cerebellar cortex. The great majority of the purkinje cell axons synapse with the neurons of the intracerebellar nuclei, and the axons of the neurons then leave the cerebellum Fibers from the dentate, emboliform, and globose nuclei leave the cerebellum through the superior cerebellar peduncle. Fibers from the fastigial nucleus leave through the inferior cerebellar peduncle. BASE, EDANO, FLORENDO, MONTEIRO, PASAJOL, K. SORIANO, V.SORIANO 4  VII.INTRACEREBELLAR CORTICAL MECHANISM The deep cerebellar nuclei (intracerebellar nuclei) receive afferent nervous information from two sources. ○ The inhibitory axons from the purkinje cells of the overlying cortex ○ The excitatory axons that are branches of the afferent climbing and mossy fibers that passing to the overlying cortex In this manner, a given sensory input to FIGURE 1. Three cerebellar peduncles connecting the the cerebellum sends excitatory information to cerebellum to the rest of the central nervous system. the nuclei which a short time later receives cortical processed inhibitory information from the II. CEREBELLAR PEDUNCLES purkinje cells. Efferent information from the deep A. FROM THE CEREBRAL CORTEX CORTICOPONTOCEREBELLAR PATHWAY cerebellar nuclei leaves the cerebellum to be The corticopontine fiber arise from the nerve cells distributed to the remainder of the brain and in the lobes of the cerebral cortex and descend through spinal cord. the corona radiata and internal capsule and terminate upon the pontine nuclei. The pontine nuclei give rise to transverse fibers of the pons, which cross the midline and enter the opposite cerebellar hemisphere as the middle cerebellar peduncle. CEREBRO-OLIVOCEREBELLAR PATHWAY The cortico-olivary fibers rise from nerve cells in the lobes of the cerebral cortex and descend through the corona radiata and internal capsule to terminate bilaterally upon the inferior olivary nuclei. The inferior olivary nuclei give rise to fibers that cross the midline and enter the opposite cerebellar hemisphere through the inferior cerebellar peduncle. These fibers terminate as the climbing fibers in the cerebellar cortex.. CEREBRORETICULOCEREBELLAR PATHWAY The cortico-reticular fibers arise from nerve cells from many areas of the cerebral cortex, particularly the sensorimotor areas. They descend to terminate in the reticular formation on the same side and on the opposite side in the pons and medulla. I. CEREBELLAR PEDUNCLES The cells in the reticular formation give rise to the They are made up of afferent and efferent fibers. reticulocerebellar fibers that enter the cerebellar The superior cerebellar peduncles connect the hemisphere on the same side through the inferior and cerebellum to the midbrain. middle cerebellar peduncles. The middle cerebellar peduncles connect the cerebellum to the pons The inferior cerebellar peduncles connect the cerebellum to the medulla oblongata BASE, EDANO, FLORENDO, MONTEIRO, PASAJOL, K. SORIANO, V.SORIANO 5  C. FROM THE VESTIBULAR NERVE The vestibular nerve receives information from the internal ear concerning position relative to gravity from the utricle and saccule, and motion from the semicircular canals. The vestibular nerve sends many afferent fibers directly to the cerebellum through the inferior cerebellar peduncle on the same side. Other vestibular afferent fibers pass first to the vestibular nuclei in the brainstem, where they synapse and are relayed to the cerebellum. They enter the cerebellum through the inferior cerebellar peduncle on the same side. All the afferent fibers from the internal ear terminate as mossy fibers in the flocculonodular lobe of the cerebellum. FIGURE 2. Cerebellar afferent fibers from the cerebral cortex. The cerebellar peduncles are shown as ovoid dotted lines. This connection between the cerebrum and the cerebellum is important in the control of voluntary movement. Information regarding the initiation of movement in the cerebral cortex is probably transmitted to the cerebellum so that the movement can be monitored and appropriate adjustments in the muscle activity can be made B. FROM THE SPINAL CORD ANTERIOR SPINOCEREBELLAR TRACT POSTERIOR SPINOCEREBELLAR TRACT CUNEOCEREBELLAR TRACT III. CEREBELLAR EFFERENT FIBERS The entire output of the cerebellar cortex is through the axons of the Purkinje cells Most of the axons of the Purkinje cells end by synapsing on the neurons of the deep cerebellar nuclei. The axons of the neurons that form the deep cerebellar nuclei constitute the efferent outflow from cerebellum. BASE, EDANO, FLORENDO, MONTEIRO, PASAJOL, K. SORIANO, V.SORIANO 6  projecting on the neurons of the lateral vestibular nucleus on both sides. 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. D. FASTIGIAL RETICULAR PATHWAY The axons of neurons in the fastigial nucleus travel through the inferior cerebellar peduncle and end by synapsing with neurons of the reticular formation. Axons of these neurons influence spinal segmental neuron influence spinal segmental motor activity through the reticular tract. E. THE CEREBELLAR EFFERENT PATHWAYS PATHWAY FUNCTION ORIGIN DESTINATI ON Globose- Influences Globose Via the emboliform the ipsilateral Nucleus rubro spinal - motor tract to FIGURE 3. Cellular organization of the cerebellar cortex. Note the activity ipsilateral afferent and efferent fibers. rubral motor neurons in the spinal A. GLUBOSE-EMBOLIFORM RUBRAL PATHWAY cord Axons of the neurons in the globose and emboliform nuclei travel through the superior cerebellar Dentothala Influences Dentate Via peduncle and cross the midline to the opposite side in the mic the ipsilateral corticospin motor al tract to decussation of the superior cerebellar peduncle. activity ipsilateral The fibers end up by synapsing with cells of the motor contralateral red nucleus, which gives rise to axons of the neurons in rubrospinal tract. the spinal This pathway crosses twice, once in the cord decussation of the superior cerebellar peduncle and again in the rubrospinal tract to its origin. Influence the Fastigial Via Fastigial vestibulo By this means, the globose and emboliform Vestibular ipsilateral extensor spinal nuclei influence motor activity on the same side of the muscle tone tract to body. ipsilateral motor B. DENTOTHALAMIC NUCLEI PATHWAY neurons in Axons of neurons in the dentate nuclei travel the spinal through the superior cerebellar peduncle and cross the cord midline to the opposite side in the decussation of the Influence the Fastigial Via Fastigial superior cerebellar peduncle. ipsilateral reticulospin Reticular The fibers end by synapsing with cells in the muscle tone al tract to contralateral ipsilateral ventrolateral of the thalamus motor The axons of the thalamic neurons ascend neurons in through the motor activity by acting upon the motor spinal cord neurons of the opposite cerebral cortex; impulses for the motor cortex are transmitted to segmental segments IV. FUNCTIONS OF THE CEREBELLUM through the corticospinal tract. Functions as coordinator of precise movements Most of the fibers in the corticospinal tract cross by continually comparing the output of the motor area of to the opposite side in the decussation of the pyramid or the cerebellar cortex with the proprioceptive information lateral to the spinal segmental levels. received from the site of muscle action. The dentate nucleus thus is able to coordinate It is able to bring about muscle adjustments by muscle activity on the same side of the body. influencing the activity of the lower motor neurons. It can send back information to the motor C. FASTIGIAL VESTIBULAR PATHWAY cerebral cortex to inhibit the agonist muscles and stimulate The axons of neurons in the fastigial nucleus the antagonist muscle, the limiting extent of voluntary travel through the inferior cerebellar peduncle and end by movement. BASE, EDANO, FLORENDO, MONTEIRO, PASAJOL, K. SORIANO, V.SORIANO 7  V. CLINICAL NOTES ○ In cerebellar lesions, paralysis and sensory Each cerebral hemisphere is connected by changes are not present. nervous pathways principally with the same side of the ○ Even the muscular contractions may be weak body, so that a lesion in one cerebellar hemisphere gives and the patient easily fatigued, there is no atrophy. rise to signs and symptoms that are limited to the same side of the body. IV. REFERENCES The essential function of the cerebellum is to Book coordinate, but synergistic action, all reflex and voluntary Snell, Richard S, Splittgerber Ryan. (2019). Snell's Clinical muscular activity. Neuroanatomy (8TH). Philadelphia: Wolters Kluwer/Lippincott It thus graduates and harmonizes muscle tone Williams & Wilkins and Lecturer’s Powerpoint maintains normal body posture, Estrada, MD, J. V. O., (2023) It permits voluntary movements such as walking Previous Transes to take place smoothly with precision and economy of Dasig Neuroscience Transes effort. A. SIGNS AND SYMPTOMS OF CEREBELLAR DISEASE HYPOTONIA The muscle lose resilience to palpation Diminished resistance to passive movement joints Condition if attributable to loss of cerebellar influence on the simple stretch reflex POSTURAL CHANGES AND ALTERATION OF GAIT Head is often rotated and reflexed and the shoulder on the side of the lesion is lower than on the normal side. Patients assume a wide base when he or she stands. When an individual walks, he or she lurches and staggers towards the affected side. DISTURBANCES OF VOLUNTARY MOVEMENT (ATAXIA) INTENTIONAL TREMORS ○ Occurs when fine movements such as buttoning clothes, writing are attempted. Decomposition of movement occurs because muscle groups fail to work harmoniously DYSDIADOCHOKINESIA ○ This is the inability to perform alternating movements regular and rapidly DISTURBANCES OF REFLEXES PENDULUM KNEE JERK ○ Occurs following tapping of the patellar tendon in which the movement continues as a series of flexion movements of the knee joint; that is, the leg moves like pendulum DISTURBANCES OF OCULAR MOVEMENT NYSTAGMUS ○ It is an ataxia of the ocular muscle in which there is rhythmical oscillation on the eye. ○ The rhythmic oscillation of the eyes may be of the same rate in both direction (pendular nystagmus) or quicker in one direction than in other (jerk nystagmus) DISORDERS OF SPEECH DYSARTHRIA ○ Articulation is jerky and the syllables often are separated from one another. ○ Speech tends to be explosive and the syllables often are slurred. BASE, EDANO, FLORENDO, MONTEIRO, PASAJOL, K. SORIANO, V.SORIANO 8