Snell's Clinical Neuroanatomy

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CHAPTER 7 Cerebellum and Its Connections

rapid rise in intracranial pressure owing to the rapid increase in size of the tumor. The broad based, unsteady gait and the tendency to fall backward (or forward), and not to one side, indi cate a tumor involving the vermis. The presence of bilateral hypotonia, especially during the later stages, was due to involvement of both cerebel lar hemispheres. At autopsy, the tumor was found to have invaded the fourth ventricle extensively, and there was evidence of internal hydrocephalus because the cerebrospinal fluid had been unable to escape through the foramina in the roof of the fourth ventricle. 5. Nystagmus, an involuntary oscillation of the eye ball, may occur physiologically, as when a person watches rapidly moving objects, or by rapid rota tion of the body. It commonly occurs in diseases of the nervous system, eye, and inner ear. In cerebellar disease, nystagmus is due to ataxia of the muscles moving the eyeball. There is lack of coordination Directions: Each of the numbered items in this section is followed by answers. Select the ONE lettered answer that is CORRECT. 1. The following statements concern the gross appear ance of the cerebellum: (a) It is separated from the occipital lobes of the cerebral hemispheres by the tentorium cerebelli. (b) It lies anterior to the medulla oblongata and the pons. (c) The anterior lobe is separated from the middle (posterior) lobe by the uvulonodular fissure. (d) The flocculonodular lobe is separated from the middle (posterior) lobe by the horizontal fissure. (e) The third ventricle lies anterior to the cerebellum. 2. The following general statements concern the cere bellum: (a) It greatly influences the activity of smooth muscle. (b) It has no influence on the skeletal muscles sup plied by the cranial nerves. (c) Each cerebellar hemisphere controls the tone of skeletal muscles supplied by spinal nerves on the same side of the body. (d) The important Purkinje cells are Golgi type II neurons. (e) The Purkinje cells exert a stimulatory influence on the intracerebellar nuclei. 3. The following statements concern the structure of the cerebellum: (a) It consists of two cerebellar hemispheres joined by a narrow median vermis. Review Questions

between the agonists and antagonists involved in the eyeball movement. For full understanding of the different forms of nystagmus, a textbook of neurol ogy should be consulted (also see p. 214). 6. Acute lesions, such as those resulting from a throm bosis of a cerebellar artery or a rapidly growing tumor, produce sudden severe symptoms and signs because of the sudden withdrawal of the influence of the cerebellum on muscular activity. Patients can recover quickly from large cerebellar injuries, because the cerebellum influences mus cular activity not directly, but indirectly, through the vestibular nuclei, reticular formation, red nucleus, tectum, corpus striatum, and the cere bral cortex; it may be that these other areas of the central nervous system (CNS) take over this func tion. In chronic lesions, the symptoms and signs are much less severe, and there is enough time to allow other CNS areas to compensate for loss of cerebellar function. (b) The inferior surface shows a deep groove formed by the superior surface of the vermis. (c) The inferior cerebellar peduncles join the cere bellum to the pons. (d) The gray matter is confined to the cerebellar cortex. (e) The gray matter of folia of the dentate nucleus has a branched appearance on the cut surface, the arbor vitae. 4. The following statements concern the structure of the cerebellar cortex: (a) It is folded by many vertical fissures into folia. (b) It differs widely in different parts of the cere bellum. (c) Purkinje cells are found in the most superficial layer. (d) Golgi cells are found in the most superficial layer. (e) Axons of the Purkinje cells form the efferent fibers from the cerebellar cortex. 5. The following statements concern the intracerebel lar nuclei: (a) They are found within the superficial layers of the white matter. (b) They are located in the walls of the fourth ventricle. (c) They are composed of many small unipolar neurons. (d) The axons of the nuclei form the main cerebellar outflow. (e) From medial to lateral, they are named dentate, emboliform, globose, and fastigial.

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