Snell's Clinical Neuroanatomy

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CHAPTER 7 Cerebellum and Its Connections

Key Concepts

Cerebellum • The cerebellum is composed of an outer covering of gray matter (cortex) and inner white matter. Embedded in the white matter of each hemisphere are three masses of gray matter forming the four intracerebellar nuclei. • The gray matter of the cortex is divided into three layers: molecular, Purkinje, and granular layers. • Basket and stellate cells are found in the molecular layer and are scattered throughout the dendritic arborizations of the Purkinje cells, whose cell bodies are found within the Purkinje layer. • Granule cells (and Golgi cells) are found throughout the granular layer and have synaptic contact with mossy fiber input (cerebellar afferent tracts). The axon of each granule cell branches and runs parallel to the long axis of the cerebellar folium. • Climbing fibers are terminal fibers of the olivocere bellar tracts. A single Purkinje neuron makes synap tic contact with only one climbing fiber. • Mossy fibers are the terminal fibers of all other cerebellar afferent tracts. Each mossy fiber commu nicates with thousands of Purkinje cells through the granule cells.

Cerebellar Afferent Fibers • The cerebellum receives three afferent pathways from the cerebrum and is important for monitoring and control of voluntary movements. • The cerebellum also receives three afferent pathways from the spinal cord, all of which supply the cerebellum with muscle and joint information of the limb and trunk. Cerebellar Efferent Fibers • Cerebellar output is through Purkinje cell axons, most of which synapse on the neurons of the deep cerebellar nuclei. • Efferent fibers from the deep nuclei connect with the red nucleus (globose-emboliform-rubral), thalamus (dentatothalamic), vestibular complex (fastigial ves tibular), and reticular formation (fastigial reticular). Cerebellar Functions • The cerebellum functions as a coordinator of pre cise movements by continually comparing the out put of the motor area of the cerebral cortex with the proprioceptive information received from the site of muscle action and making necessary adjustments.

Clinical Problem Solving

1. A 10-year-old female is taken to a neurologist because her parents notice that her gait is becom ing awkward. Six months previously, the child had mentioned that she felt her right arm is clumsy, and she had inadvertently knocked a teapot off the table. More recently, her family notices that her hand movements are becoming jerky and awkward; this is particularly obvious when she is eating with a knife and fork. The mother comments that her daughter has had problems with her right foot since birth and that she had a clubfoot. She also has scoliosis and is attending an orthopedic surgeon for treatment. The mother said she is particularly worried about her daughter because two other members of the family had similar signs and symptoms. On physical examination, the child is found to have a lurching gait with a tendency to reel over to the right. Intention tremor is present in the right arm and the right leg. When the strength of the limb

muscles is tested, those of the right leg are found to be weaker than those of the left. The muscles of the right arm and right lower leg are also hypotonic. She has severe pes cavus of the right foot and a slight pes cavus of the left foot. Kyphoscoliosis of the upper part of the thoracic vertebral column is also present. On examination of her sensory system, she is found to have loss of muscle joint sense and vibra tory sense of both legs. She also has loss of two-point discrimination of the skin of both legs. Her knee jerk reflexes are found to be exaggerated, but her ankle jerk reflexes are absent. The biceps and triceps jerk reflexes of both arms are normal. She has bilateral Babinski responses. Slight nystagmus is present in both eyes. Using your knowledge of neuroanat omy, explain the symptoms and signs listed for this patient. Did the disease process involve more than one area of the central nervous system? Explain.

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