Cerebellum.pptx

THE THE CEREBELLUM CEREBELLUM INTRODUCTION INTRODUCTION The cerebellum or “little brain” is the part of the brain located directly behind the cerebrum. It lies between the back of the medulla oblongata and the infero-posterior part of the cerebral hemispheres. It typically consists of...

THE THE CEREBELLUM CEREBELLUM INTRODUCTION INTRODUCTION The cerebellum or “little brain” is the part of the brain located directly behind the cerebrum. It lies between the back of the medulla oblongata and the infero-posterior part of the cerebral hemispheres. It typically consists of two hemispheres connected by a thin central region (the vermis), and it serves to control and coordinate muscular activity and maintain balance.  INTRODUCTION INTRODUCTION  It is the largest part of the hindbrain, accounting for about 10% of the total brain volume, but over 50% of the total number of neurons in the brain.  In adults, the weight ratio between cerebellum and cerebrum is 1:10. In infants, it is 1:20. INTRODUCTION INTRODUCTION INTRODUCTION INTRODUCTION LOCATION LOCATION  It is found in the posterior cranial fossa, occupying most of it.  It lies behind the pons and medulla, separated from them by the cavity of the fourth ventricle.  It lies below the posterior aspect of the cerebrum.  It is separated from the cerebrum by the tentorium cerebelli. ANATOMY OF THE CEREBELLUM ANATOMY OF THE CEREBELLUM  The cerebellum consists of a part lying near the midline called the vermis and two lateral hemispheres. The two hemispheres are separated by a deep depression called the vallecular.  It has two surfaces, superior and inferior.  The surface of the cerebellum is marked by a series of fissures that subdivide the surface of the cerebellum into narrow leaf-like bands or folia.  Sections of the cerebellum cut at right angles to this axis have a characteristic tree-like appearance to which the term arbor-vitae (tree of life) is applied. ANATOMY ANATOMYOF OFTHE THECEREBELLUM CEREBELLUM Some of the fissures on the surface of the cerebellum divide the cerebellum into lobes within which smaller lobules may be recognized. The deepest fissures in the cerebellum are:  The primary fissure  The posterolateral fissure  The horizontal fissure, which  The part anterior to the primary fissure is the anterior lobe. The part between the two fissures is the posterior lobe. The posterior lobe extends on both superior and inferior surfaces.  The remaining part is the flocculonodular lobe, present in the inferior surface of the cerebellum.  ANATOMY ANATOMYOF OFTHE THECEREBELLUM CEREBELLUM Proceeding from above downwards, it consists of the lingula, central lobule, and culmen (in the anterior lobe); the declive, folium, tuber, pyramid, and uvula (in the middle lobe); and the nodule (in the flocculonodular lobe). SUBDIVISIONS SUBDIVISIONSOF OFCEREBELLUM CEREBELLUM  Archicerebellum: It is the oldest part of cerebellum. It consists of flocculonodular lobe and lingula. It is concerned with the maintenance of body equilibrium.  Paleocerebellum: It consists of anterior lobe (except lingula), pyramids and uvula of the posterior lobe. It is concerned with maintenance of muscle tone and finer control of movements.  Neocerebellum: It is the most recent part of cerebellum to develop. It consists of posterior lobe except pyramids and uvula. It is responsible for fine co-ordination of voluntary movements. GREY MATTER OF CEREBELLUM GREY MATTER OF CEREBELLUM The grey matter of cerebellum is represented by;  The cerebellar cortex and  The intracerebellar nuclei. STRUCTURE OF CEREBELLAR CORTEX STRUCTURE OF CEREBELLAR CORTEX Most of the grey matter of the cerebellum is arranged as a thin layer covering the central core of white matter. This layer is the cerebellar cortex. It is divided into three layers:  Molecular layer (most superficial)  Purkinje cell layer  Granular layer, which rests on white matter. General organization of the cerebellar cortex. A single folium has been sectioned vertically, both in its longitudinal axis (right side of the diagram) and transversely. The two asterisks on the left face indicate recurrent collateral branches of Purkinje cell axons. STRUCTURE STRUCTUREOF OFCEREBELLAR CEREBELLARCORTEX CORTEX The neurons of the cerebellar cortex are of five main types:  Purkinje cells, forming the layer named after them.  Granule cells, forming the granular layer.  Outer (external) stellate cells lying in molecular layer.  Basket cells, lying in the molecular layer.  Golgi cells, present in the granular layer. POSITION OF INTRACEREBELLAR NUCLEI  WHITE WHITEMATTER MATTEROF OFCEREBELLUM CEREBELLUM  The central core of each cerebellar hemisphere is formed by the white matter. The peduncles are continued into this white matter.  The white matter of the two sides is connected by a thin lamina of fibres that are closely related to the fourth ventricle.  The upper part of this lamina forms the superior medullary velum, and its lower part forms two crescentic sheets called inferior medullary vela.  Both these take part in the formation of the roof of the fourth ventricle.  WHITE WHITEMATTER MATTEROF OFCEREBELLUM CEREBELLUM The white matter consists of two types of fibres— intrinsic and extrinsic.  Intrinsic fibres: remain confined within the cerebellum and connect different regions of the cerebellum.  Projection fibres connect cerebellar cortex to the cerebellar nuclei.  Association fibres interconnect different parts of the cerebellar cortex.  Commissural fibres connect the two cerebellar hemispheres. WHITE WHITEMATTER MATTEROF OFCEREBELLUM CEREBELLUM  Extrinsic fibres: Extrinsic fibres connect the cerebellum with other parts of the central nervous system.  The fibres entering or leaving the cerebellum pass through three thick bundles called the cerebellar peduncles: superior, middle, and inferior. Afferent Fibres Entering the Cerebellar Cortex  The afferent fibres to the cerebellar cortex are of two different types:  Mossy fibres  Climbing fibres Efferent Fibres  The efferent fibres from the cerebellar cortex are axons of Purkinje cells, which terminate in the cerebellar (central) nuclei.  Some efferents from the flocculonodular lobe bypass the cerebellar nuclei and terminate in the brainstem nuclei.  Axons of the Purkinje cells are inhibitory to cerebellar nuclei. CONNECTIONS BETWEEN CEREBELLUM AND CONNECTIONS BETWEEN CEREBELLUM AND SPINAL SPINALCORD CORD  Direct pathways from spinal cord to cerebellum:  Ventraland dorsal spinocerebellar tract  Cuneocerebellar tract  Indirect pathways from spinal cord to cerebellum:  These are as follows:  Spino-olivocerebellar  Spinoreticulocerebellar  Spinovestibulocerebellar  Spinotectocerebellar pathways. CONNECTIONS BETWEEN CEREBELLUM AND CONNECTIONS BETWEEN CEREBELLUM AND SPINAL SPINALCORD CORD  Cerebellospinal pathways: The cerebellum influences the spinal cord through the following pathways:  Cerebellorubrospinal  Cerebellovestibulospinal  Cerebelloreticulospinal  Cerebellotectospinal  Cerebellothalamocorticospinal CONNECTIONS BETWEEN CEREBELLUM CONNECTIONS BETWEEN CEREBELLUM AND ANDCEREBRAL CEREBRALCORTEX CORTEX  Corticocerebellar pathways  „Corticopontocerebellar pathway  „Cortico-olivocerebellar  Corticoreticulocerebellar  Corticorubrocerebellar  „Corticotectocerebellar Some of the impulses may reach these intermediary centres through the corpus striatum.  Cerebellocortical pathways CEREBELLAR CEREBELLARPENDUNCLES PENDUNCLES  Superior cerebellar peduncle: connects cerebellum to midbrain  Middle cerebellar peduncle: connects cerebellum to pons  Inferior cerebellar peduncle: connects cerebellum to medulla oblongata FUNCTION FUNCTIONOF OFTHE THECEREBELLUM CEREBELLUM  The cerebellum plays an essential role in the control of movement.  The cerebellar cortex is also important for learning of movements (for example, in learning to write).  Through its vestibular and spinal connections, the cerebellum is responsible for maintaining the equilibrium of the body.  These functions are possible because the cerebellum constantly receives proprioceptive information regarding the state of contraction of muscles and of the position of various joints.  It receives information from the eyes, the ears, the vestibular apparatus, the reticular formation, and the cerebral cortex. BOOD BOODSUPPLY SUPPLYOF OFTHE THECEREBELLUM CEREBELLUM  The cerebellum is supplied by three pairs of cerebellar arteries:  Superior cerebellar artery: A branch of basilar artery supplies the superior surface of the cerebellum.  Anterior inferior cerebellar artery: A branch of basilar artery supplies the anterior part of the inferior surface of the cerebellum.  Posterior inferior cerebellar artery: A branch of vertebral artery supplies the posterior part of the inferior surface of the cerebellum.  CLINICAL CLINICALIMPORTANCE IMPORTANCE DISTURBANCE IN TONE AND POSTURE 1. ATONIA AND HYPOTONIA :  Atonia is the loss of tone.  Hypotonia is the reduction of the tone. 2. ATTTITUDE : Attitude of the body changes with cerebellar lesions:  Rotation of head toward opposite side.  Lowering of shoulder on the same side. 3. DEVIATION MOVEMENT : It is the lateral deviation of arms when both the arms are stretched and held in front of the body. CLINICAL IMPORTANCE CLINICAL IMPORTANCE DISTURBANCE IN EQUILIBRIUM  While standing :  The legs are spread during standing, providing a broad base and body sways side to side with oscillation of head.  While moving i.e. gait :  Gait means the manner of walking. In cerebellar lesion a reeling and drunken like gait is observed.  CLINICAL CLINICALIMPORTANCE IMPORTANCE  DISTURBANCE IN MOVEMENT ATAXIA :  Refers to a lack of voluntary coordination of movements.  Tremors occurs when fine movement are attempted. ASTHENIA :  It refers to the weakness of muscles and loss of muscles strength. ASYNERGIA :  It is the lack of coordination between different group of muscles. DYSMETRIA :  It is inability to check the exact strength and duration of muscular contractions required for voluntary action,i.e. inability to direct or limit motion.  While reaching for an object, the arm may overshoot (hypermetria) or it may fall short of the object (hypometria). DYSARTHRIA :  Incoordination of various muscles and structures involved in speech. Speech is explosive and slurred.  CLINICAL CLINICALIMPORTANCE IMPORTANCE  NYSTAGMUS : This is ataxia of ocular muscles leading to rhythmical oscillation of the eyes. The eyes exhibit a to-and-fro motion.  DYSDIADOCHOKINESIA Inability to perform alternating movements regularly and rapidly, e.g pronation and supination.  DISTURBANCES OF REFLEXES Movements produced by tendon reflexes lasts longer than normal. Pendular knee jerk (flexion and extension at the knee joint continues) occurs following tapping of the patellar tendon for example.  CLINICAL CLINICALIMPORTANCE IMPORTANCE 1. Vermis syndrome -signs and symptoms relate to vestibular system -muscle incoordination involves the head and trunk -patient tends to fall forwards or backwards -head cannot be held steady  Trunk cannot be held erect 2. Cerebellar Hemisphere syndrome -limb movement affected -Swaying to affected side -dysarthria, nystagmus are common