Cerebellum: Ataxia Lecture Notes PDF

The Cerebellum : Ataxia DR. DOHA AL-AFIFI Objectives At the end of this lecture the student will be able to: Understand the anatomy of the Cerebellum. Describe the function of the Cerebellum. Describe the lesion of the Cerebellum. The cerebellum The cerebellum is the large, bilater...

The Cerebellum : Ataxia DR. DOHA AL-AFIFI Objectives At the end of this lecture the student will be able to: Understand the anatomy of the Cerebellum. Describe the function of the Cerebellum. Describe the lesion of the Cerebellum. The cerebellum The cerebellum is the large, bilaterally symmetric “little brain” in the posterior cranial fossa. Through its afferent and efferent connections, the cerebellum influences the timing and force of contractions of voluntary muscles that result in smooth, coordinated movements. The cerebellum is divided sagittalLy into three areas and horizontally into three lobes. The cerebellum is connected to the brainstem by three pairs of peduncles (Superior, middle and inferior) cerebellar peduncles., Its cortex is composed of three layers, its output occurs through three nuclei, and three cerebellar syndromes can be identified.  The surface of the cerebellum is thrown into numerous parallel folds, the folia, oriented in the transverse plane. In the sagittal plane, the cerebellum consists of a median part, the vermis, and lateral expansions of the vermis, the hemispheres. Cutting the cerebellum in cross section will reveal a tree-like appearance (arbor vitae or ‘tree of life’), marked by four deep grey cerebellar nuclei. Cerebellar Peduncles Three pairs of cerebellar peduncles, containing input and output fibers, connect the cerebellum and brainstem The superior cerebellar peduncle, connects the cerebellum to the mid brain. Its most abundant and most important components are output fibers (efferent). The middle cerebellar peduncle, is the largest peduncle and connects the basilar part of the pons to the cerebellum. Its fibers are entirely input (afferent). The inferior cerebellar peduncle arches dorsally from the dorsolateral surface of the medulla and connect the medulla to the cerebellum. Its composition is chiefly input fibers, although it does contain some output fibers (afferent and efferent). Function of the cerebellum peduncles Connect the brain stem to cerebellum. Send in and out signals to and from cerebellum Anatomically Two deep fissures separated the cerebellum hemisphere in to three lobes: Anterior lobe Posterior lobe Flocculonodular lobe: Flocculus and nodule Primary fissures : separated the anterior lobe and posterior lobe. Posterolateral fissures : separated the Posterior lobe and flocculonodular lobe. Zones There are three cerebellar zones. In the midline of the cerebellum is the vermis (the intermediate zone). Lateral to the intermediate zone are the lateral hemispheres on either side.  Histologically Grey matter: Is found on the surface of the cerebellum and form (Cerebellar cortex) White matter : Is found underneath the cerebellar cortex. Cerebellar nuclei are embedded within the White matter.  Histology and connectivity of The Cerebellar Cortex Histology The cortex has three layers, which from external to internal are: 1. The molecular layer, 2. The Purkinje cell layer, 3. The granular layer, The cerebellar Cortex The cerebellar cortex receives information from many parts of the nervous system, both central and peripheral. Hence, the cerebellum has numerous afferent connections; in fact, it is said to have 40 times as many afferent fibers as efferent. The cerebellar cortex is dissimilar to the cerebral cortex in many ways, the most important of which are: 1- None of its activity contributes directly to consciousness. 2. Its hemispheres possess ipsilateral representation of the body parts, whereas the motor areas of the cerebral hemispheres possess contralateral representation. Connectivity There are two major types of input fibers to the cerebellar cortex: The mossy fibers. The climbing fibers Cerebellar Output All output from cerebellum originate from the cerebellar deep nuclei. Thus, a lesion to the cerebellar nuclei has the same effect as a complete lesion of entire cerebellum. It is important to know the inputs, outputs and anatomical relationships between the different cerebellar and the subdivision of the cerebellum. Functionally  Flocculonodular Lobe flocculonodular lobe is most inferior and lies posterior to the posterolateral fissure. The flocculonodular lobe is the most ancient part of the cerebellum, and it receives its major input from the vestibular apparatus; Hence, it is referred to as the archicerebellum or the vestibulocerebellum. Folocculonodular Lobe Flocculonodular Lobe The Anterior Lobe The anterior lobe is most superior and lies anterior to the primary fissure. It appeared somewhat later in evolution than the vestibulocerebellum, and its main input is from the limbs via their spinal connections; hence, the anterior lobe is called the paleocerebellum or the spinocerebellum. The Anterior Lobe The Anterior Lobe Syndrome Gait Ataxia Patients with Anterior lobe syndrome Suffer from: Loss of coordination mainly in lower limps, they have marked gait instability. And walk As if drunk. The Posterior Lobe Is the largest part of the cerebellum, the posterior lobe. It is the newest part and has very strong connections with the cerebral cortex; hence, it is called the neocerebellum or the cerebrocerebellum. Function of the posterior Lobe Posterior Lobe Syndrome Function of the cerebellum