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Ovid: Clinical Neuroanatomy

Authors: Snell, Richard S. Title: Clinical Neuroanatomy, 7th Edition Copyright ©2010 Lippincott Williams & Wilkins > Table of Contents > Chapter 6 – The Cerebellum and Its Connections Chapter 6 The Cerebellum and Its Connections A 56-year-old woman was examined by a neurologist for a variety of complaints, including an irregular swaying gait and a tendency to drift to the right when walking. Her family recently noticed that she had difficulty in keeping her balance when standing still, and she found that standing with her feet apart helped her keep her balance. On examination, it was apparent that she had diminished tone of the muscles of her right upper limb, as seen when the elbow and wrist joints were passively flexed and extended. Similar evidence was found in the right lower limb. When asked to stretch out her arms in front of her and hold them in position, she demonstrated obvious signs of right-sided tremor. When asked to touch the tip of her nose with the left index finger, she performed the movement without any difficulty, but when she repeated the movement with her right index finger, she either missed her nose or hit it due to the irregularly contracting muscles. When she was asked to quickly pronate and supinate the forearms, the movements were normal on the left side but jerky and slow on the right side. A mild papilledema of both eyes was found. No other abnormal signs were demonstrated. The right-sided hypotonia, static tremor, and intention tremor associated with voluntary movements, right-sided dysdiadochokinesia, and the history were characteristic of right-sided cerebellar disease. A computed tomography scan revealed a tumor in the right cerebellar hemisphere. Understanding the structure and the nervous connections of the cerebellum and, in particular, knowing that the right cerebellar hemisphere influences voluntary muscle tone on the same side of the body enable the neurologist to make an accurate diagnosis and institute treatment. P.231 Chapter Objectives

  • To review the structure and functions of the cerebellum

The cerebellum plays a very important role in the control of posture and voluntary movements. It unconsciously influences the smooth contraction of voluntary muscles and carefully coordinates their actions, together with the relaxation of their antagonists. It is suggested that the reader commit the functions of the connections of the cerebellum to the remainder of the central nervous system to memory, as this will greatly assist in the retention of the material. In this chapter, great emphasis is placed on the fact that each cerebellar hemisphere controls muscular movements on the same side of the body and that the cerebellum has no direct pathway to the lower motor neurons but exerts its control via the cerebral cortex and the brainstem. Gross Appearance of the 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 (Fig. 6-1). The cerebellum is somewhat ovoid in shape and constricted in its median part. It consists of two cerebellar hemispheres joined by a narrow median vermis. The cerebellum is connected to the posterior aspect of the brainstem by three symmetrical bundles of nerve fibers called the superior, middle, and inferior cerebellar peduncles (see Atlas Plates 1, 2, 3 and 5, 6, 7, 8). The cerebellum is divided into three main lobes: the anterior lobe, the middle lobe, and the flocculonodular lobe. The anterior lobe may be seen on the superior surface of the cerebellum and is separated from the middle lobe by a wide V-shaped fissure called the primary fissure (Figs. 6-2 and 6-3). The middle lobe (sometimes called the posterior lobe), which is the largest part of the cerebellum, is situated between the primary and uvulonodular fissures. The flocculonodular lobe is situated posterior to the uvulonodular fissure (Fig. 6-3). A deep horizontal fissure that is found along the margin of the cerebellum separates the superior from the inferior surfaces; it is of no morphologic or functional significance (Figs. 6-2 and 6-3). Structure of the Cerebellum The cerebellum is composed of an outer covering of gray matter called the cortex and inner white matter. Embedded in the white matter of each hemisphere are three masses of gray matter forming the intracerebellar nuclei. Structure of the Cerebellar Cortex The cerebellar cortex can be regarded as a large sheet with folds lying in the coronal or transverse plane. Each fold or folium contains a core of white matter covered superficially by gray matter (Fig. 6-1). 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 (Fig. 6-1). The gray matter of the cortex throughout its extent has a uniform structure. It may be divided into three layers: (1) an external layer, the molecular layer; (2) a middle layer, the Purkinje cell layer; and (3) an internal layer, the granular layer (Figs. 6-4 and 6-5). Molecular Layer The molecular layer contains two types of neurons: the outer stellate cell and the inner basket cell (Fig. 6-4). These neurons are scattered among dendritic arborizations and numerous thin axons that run parallel to the long axis of the folia. Neuroglial cells are found between these structures. Purkinje Cell Layer The Purkinje cells are large Golgi type I neurons. They are flask shaped and are arranged in a single layer (Figs. 6-4 and 6-5). In a plane transverse to the folium, the dendrites of these cells are seen to pass into the molecular layer, where they undergo profuse branching (Figs. 6-4 and 6-5). The primary and secondary branches are smooth, and subsequent branches are covered by short, thick dendritic spines. It has been shown that the spines form synaptic contacts with the parallel fibers derived from the granule cell axons. At the base of the Purkinje cell, the axon arises and passes through the granular layer to enter the white 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. Collateral branches of the Purkinje axon make synaptic contacts with the dendrites of basket and stellate cells of the granular layer in the same area or in distant folia. A few of the Purkinje cell axons pass directly to end in the vestibular nuclei of the brainstem. Granular Layer The granular layer is packed with small cells with densely staining nuclei and scanty cytoplasm (Figs. 6-4 and 6-5). Each cell gives rise to four or five dendrites, which make P.232 P.233 clawlike endings and have synaptic contact with mossy fiber input (see p. 236). 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 (Fig. 6-4). 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. Neuroglial cells are found throughout this layer. Scattered throughout the granular layer are Golgi cells (Fig. 6-4). Their dendrites ramify in the molecular layer, and their axons terminate by splitting up into branches that synapse with the dendrites of the granular cells (Fig. 6-5).

Figure 6-1 Sagittal section through the brainstem and the vermis of the cerebellum.
Figure 6-2 The cerebellum. A: Superior view. B: Inferior view.
Figure 6-3 A: Flattened view of the cerebellar cortex showing the main cerebellar lobes, lobules, and fissures. B: Relationship between the diagram in (A) and the cerebellum.

Functional Areas of the Cerebellar Cortex Clinical observations by neurologists and neurosurgeons and the experimental use of the positron emission tomography scan have shown that it is possible to divide up the cerebellar cortex into three functional areas. The cortex of the vermis influences the movements of the long axis of the body, namely, the neck, the shoulders, the thorax, the abdomen, and the hips (Fig. 6-6). Immediately lateral to the vermis is a so-called intermediate zone of the cerebellar hemisphere. This area has been shown to control the muscles of the distal parts of the limbs, especially the hands and feet (Fig. 6-6). The lateral zone of each cerebellar hemisphere appears to be concerned with the planning of sequential movements of the entire body and is involved with the conscious assessment of movement errors. Intracerebellar Nuclei Four masses of gray matter are embedded in the white matter of the cerebellum on each side of the midline (Fig. 6-7). From lateral to medial, these nuclei are the dentate, the emboliform, the globose, and the fastigial. P.234

Figure 6-4 Cellular organization of the cerebellar cortex. Note the afferent and efferent fibers.
Figure 6-5 Photomicrograph of a cross section of a cerebellar folium, showing the three layers of the cerebellar cortex.

P.235

Figure 6-6 Somatosensory projection areas in the cerebellar cortex.

The dentate nucleus is the largest of the cerebellar nuclei. It has the shape of a crumpled bag with the opening facing medially (Fig. 6-7). The interior of the bag is filled with white matter made up of efferent fibers that leave the nucleus through the opening to form a large part of the superior cerebellar peduncle. The emboliform nucleus is ovoid and is situated medial to the dentate nucleus, partially covering its hilus (Fig. 6-7). The globose nucleus consists of one or more rounded cell groups that lie medial to the emboliform nucleus (Fig. 6-7).

Figure 6-7 Position of the intracerebellar nuclei.

The fastigial nucleus lies near the midline in the vermis and close to the roof of the fourth ventricle; it is larger than the globose nucleus (Fig. 6-7). The intracerebellar nuclei are composed of large, multipolar neurons with simple branching dendrites. The axons form the cerebellar outflow in the superior and inferior cerebellar peduncles. White Matter There is a small amount of white matter in the vermis; it closely resembles the trunk and branches of a tree and thus is termed the arbor vitae (Fig. 6-1). There is a large amount of white matter in each cerebellar hemisphere. The white matter is made up of three groups of fibers: (1) intrinsic, (2) afferent, and (3) efferent. The intrinsic fibers do not leave the cerebellum but connect different regions of the organ. Some interconnect folia of the cerebellar cortex and vermis on the same side; others connect the two cerebellar hemispheres together. The afferent fibers form the greater part of the white matter and proceed to the cerebellar cortex. They enter the cerebellum mainly through the inferior and middle cerebellar peduncles. 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 pass to and synapse with the neurons of the cerebellar nuclei (fastigial, globose, emboliform, and dentate). The axons of the neurons then leave the cerebellum. A few Purkinje cell axons in the flocculonodular lobe and in parts of the vermis bypass the cerebellar nuclei and leave the cerebellum without synapsing. Fibers from the dentate, emboliform, and globose nuclei leave the cerebellum through the superior cerebellar P.236 peduncle. Fibers from the fastigial nucleus leave through the inferior cerebellar peduncle. Cerebellar Cortical Mechanisms As a result of extensive cytological and physiological research, certain basic mechanisms have been attributed to the cerebellar cortex. The climbing and the mossy fibers constitute the two main lines of input to the cortex and are excitatory to the Purkinje cells (Fig. 6-8). The climbing fibers are the terminal fibers of the olivocerebellar tracts (Fig. 6-8). They are so named because they ascend through the layers of the cortex like a vine on a tree. They pass through the granular layer of the cortex and terminate in the molecular layer by dividing repeatedly. Each climbing fiber wraps around and makes a large number of synaptic contacts with the dendrites of a Purkinje cell. A single Purkinje neuron makes synaptic contact with only one climbing fiber. However, one climbing fiber makes contact with 1 to 10 Purkinje neurons. A few side branches leave each climbing fiber and synapse with the stellate cells and basket cells.

Figure 6-8 Functional organization of the cerebellar cortex. The arrows indicate the direction taken by the nervous impulses.

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 granule cells (Fig. 6-8). What then is the function of the remaining cells of the cerebellar cortex, namely, the stellate, basket, and Golgi cells? Neurophysiologic research, using microelectrodes, would indicate that they serve as inhibitory interneurons. It is believed that they not only limit the area of cortex excited but 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 center of a functional unit of the cerebellar cortex. Intracerebellar Nuclear Mechanisms The deep cerebellar nuclei receive afferent nervous information from two sources: (1) the inhibitory axons from the Purkinje cells of the overlying cortex and (2) the excitatory axons that are branches of the afferent climbing and mossy P.237fibers that are passing to the overlying cortex. In this manner, a given sensory input to the cerebellum sends excitatory information to the nuclei, which a short time later receive cortical processed inhibitory information from the Purkinje cells. Efferent information from the deep cerebellar nuclei leaves the cerebellum to be distributed to the remainder of the brain and spinal cord. Cerebellar Cortical Neurotransmitters Pharmacologic research has suggested that the excitatory climbing and mossy afferent fibers use glutamate (gamma-aminobutyric acid [GABA]) as the excitatory transmitter on the dendrites of the Purkinje cells. Further research has indicated that other afferent fibers entering the cortex liberate norepinephrine and serotonin at their endings that possibly modify the action of the glutamate on the Purkinje cells. Cerebellar Peduncles The cerebellum is linked to other parts of the central nervous system by numerous efferent and afferent fibers that are grouped together on each side into three large bundles, or peduncles (Fig. 6-9). The superior cerebellar peduncles connect the cerebellum to the midbrain, the middle cerebellar peduncles connect the cerebellum to the pons, and the inferior cerebellar peduncles connect the cerebellum to the medulla oblongata.

Figure 6-9 Three cerebellar peduncles connecting the cerebellum to the rest of the central nervous system.

Cerebellar Afferent Fibers Cerebellar Afferent Fibers From the Cerebral Cortex The cerebral cortex sends information to the cerebellum by three pathways: (1) the corticopontocerebellar pathway, (2) the cerebro-olivocerebellar pathway, and (3) the cerebroreticulocerebellar pathway. Corticopontocerebellar Pathway The corticopontine fibers arise from nerve cells in the frontal, parietal, temporal, and occipital lobes of the cerebral cortex and descend through the corona radiata and internal capsule and terminate on the pontine nuclei (Fig. 6-10). The pontine nuclei give rise to the transverse fibers of the pons, which cross the midline and enter the opposite cerebellar P.238 hemisphere as the middle cerebellar peduncle (see Figs. 5-13, 5-14 and 5-15).

Figure 6-10 Cerebellar afferent fibers from the cerebral cortex. The cerebellar peduncles are shown as ovoid dotted lines.

Cerebro-olivocerebellar Pathway The cortico-olivary fibers arise from nerve cells in the frontal, parietal, temporal, and occipital lobes of the cerebral cortex and descend through the corona radiata and internal capsule to terminate bilaterally on the inferior olivary nuclei (Fig. 6-10). 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 corticoreticular 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 (Fig. 6-10). The cells in the reticular formation give rise to the reticulocerebellar fibers that enter the cerebellar hemisphere on the same side through the inferior and middle cerebellar peduncles. 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. Cerebellar Afferent Fibers From the Spinal Cord The spinal cord sends information to the cerebellum from somatosensory receptors by three pathways: (1) the anterior spinocerebellar tract, (2) the posterior spinocerebellar tract, and (3) the cuneocerebellar tract. P.239 Anterior Spinocerebellar Tract The axons entering the spinal cord from the posterior root ganglion terminate by synapsing with the neurons in the nucleus dorsalis (Clarke’s column) at the base of the posterior gray column. Most of the axons of these neurons cross to the opposite side and ascend as the anterior spinocerebellar tract in the contralateral white column; some of the axons ascend as the anterior spinocerebellar tract in the lateral white column of the same side (Fig. 6-11). The fibers enter the cerebellum through the superior cerebellar peduncle and terminate as mossy fibers in the cerebellar cortex. Collateral branches that end in the deep cerebellar nuclei are also given off. It is believed that those fibers that cross over to the opposite side in the spinal cord cross back within the cerebellum.

Figure 6-11 Cerebellar afferent fibers from the spinal cord and internal ear. The cerebellar peduncles are shown as ovoid dotted lines.

The anterior spinocerebellar tract is found at all segments of the spinal cord, and its fibers convey muscle joint information from the muscle spindles, tendon organs, and joint receptors of the upper and lower limbs. It is also believed that the cerebellum receives information from the skin and superficial fascia by this tract. Posterior Spinocerebellar Tract The axons entering the spinal cord from the posterior root ganglion enter the posterior gray column and terminate by P.240 synapsing on the neurons at the base of the posterior gray column. These neurons are known collectively as the nucleus dorsalis (Clarke’s column). The axons of these neurons enter the posterolateral part of the lateral white column on the same side and ascend as the posterior spinocerebellar tract to the medulla oblongata (Fig. 6-11). Here, the tract enters the cerebellum through the inferior cerebellar peduncle and terminates as mossy fibers in the cerebellar cortex. Collateral branches that end in the deep cerebellar nuclei are also given off. The posterior spinocerebellar tract receives muscle joint information from the muscle spindles, tendon organs, and joint receptors of the trunk and lower limbs.

Table 6-1 The Afferent Cerebellar Pathways
Pathway Function Origin Destination
Corticopontocerebellar Conveys control from cerebral cortex Frontal, parietal, temporal, and occipital lobes Via pontine nuclei and mossy fibers to cerebellar cortex
Cerebro-olivocerebellar Conveys control from cerebral cortex Frontal, parietal, temporal, and occipital lobes Via inferior olivary nuclei and climbing fibers to cerebellar cortex
Cerebroreticulocerebellar Conveys control from cerebral cortex Sensorimotor areas Via reticular formation
Anterior spinocerebellar Conveys information from muscles and joints Muscle spindles, tendon organs, and joint receptors Via mossy fibers to cerebellar cortex
Posterior spinocerebellar Conveys information from muscles and joints Muscle spindles, tendon organs, and joint receptors Via mossy fibers to cerebellar cortex
Cuneocerebellar Conveys information from muscles and joints of upper limb Muscle spindles, tendon organs, and joint receptors Via mossy fibers to cerebellar cortex
Vestibular nerve Conveys information of head position and movement Utricle, saccule, and semicircular canals Via mossy fibers to cortex of flocculonodular lobe
Other afferents Conveys information from midbrain Red nucleus, tectum Cerebellar cortex

Cuneocerebellar Tract These fibers originate in the nucleus cuneatus of the medulla oblongata and enter the cerebellar hemisphere on the same side through the inferior cerebellar peduncle (Fig. 6-10). The fibers terminate as mossy fibers in the cerebellar cortex. Collateral branches that end in the deep cerebellar nuclei are also given off. The cuneocerebellar tract receives muscle joint information from the muscle spindles, tendon organs, and joint receptors of the upper limb and upper part of the thorax. Cerebellar Afferent Fibers From the Vestibular Nerve The vestibular nerve receives information from the inner ear concerning motion from the semicircular canals and position relative to gravity from the utricle and saccule. 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 (Fig. 6-11). They enter the cerebellum through the inferior cerebellar peduncle on the same side. All the afferent fibers from the inner ear terminate as mossy fibers in the flocculonodular lobe of the cerebellum. Other Afferent Fibers In addition, the cerebellum receives small bundles of afferent fibers from the red nucleus and the tectum. The afferent cerebellar pathways are summarized in Table 6-1. 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 (Fig. 6-4). The axons of the neurons that form the cerebellar nuclei constitute the efferent outflow from the cerebellum. A few Purkinje cell axons pass directly out of the cerebellum to the lateral vestibular nucleus. The efferent fibers from the cerebellum connect with the red nucleus, thalamus, vestibular complex, and reticular formation. P.241

Figure 6-12 Cerebellar efferent fibers. The cerebellar peduncles are shown as ovoid dotted lines.

Globose-Emboliform-Rubral Pathway Axons of neurons in the globose and emboliform nuclei travel through the superior cerebellar peduncle and cross the midline to the opposite side in the decussation of the superior cerebellar peduncles (Fig. 6-12). The fibers end by synapsing with cells of the contralateral red nucleus, which give rise to axons of the rubrospinal tract (Fig. 6-12). Thus, it is seen that this pathway crosses twice, once in the decussation of the superior cerebellar peduncle and again in the rubrospinal tract close to its origin. By this means, the globose and emboliform nuclei influence motor activity on the same side of the body. Dentothalamic Pathway Axons of neurons in the dentate nucleus travel through the superior cerebellar peduncle and cross the midline to the opposite side in the decussation of the superior cerebellar peduncle (Fig. 6-12). The fibers end by synapsing with cells in the contralateral ventrolateral nucleus of the thalamus. The axons of the thalamic neurons ascend through the internal capsule and corona radiata and terminate in the primary motor area of the cerebral cortex. By this pathway, the dentate nucleus can influence motor activity by acting on the motor neurons of the opposite cerebral cortex; impulses from the motor cortex are transmitted to P.242spinal segmental levels through the corticospinal tract. Remember that most of the fibers of the corticospinal tract cross to the opposite side in the decussation of the pyramids or later at the spinal segmental levels. Thus, the dentate nucleus is able to coordinate muscle activity on the same side of the body. Fastigial Vestibular Pathway The axons of neurons in the fastigial nucleus travel through the inferior cerebellar peduncle and end by projecting on the neurons of the lateral vestibular nucleus on both sides (Fig. 6-12). Remember that some Purkinje cell axons project directly to the lateral vestibular nucleus. 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. 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 (Fig. 6-12). Axons of these neurons influence spinal segmental motor activity through the reticulospinal tract. The efferent cerebellar pathways are summarized in Table 6-2.

Table 6-2 The Efferent Cerebellar Pathwaysa
Pathway Function Origin Destination
Globose-emboliform-rubral Influences ipsilateral motor activity Globose and emboliform nuclei To contralateral red nucleus, then via crossed rubrospinal tract to ipsilateral motor neurons in spinal cord
Dentothalamic Influences ipsilateral motor activity Dentate nucleus To contralateral ventrolateral nucleus of thalamus, then to contralateral motor cerebral cortex; corticospinal tract crosses midline and controls ipsilateral motor neurons in spinal cord
Fastigial vestibular Influences ipsilateral extensor muscle tone Fastigial nucleus Mainly to ipsilateral and to contralateral lateral vestibular nuclei; vestibulospinal tract to ipsilateral motor neurons in spinal cord
Fastigial reticular Influences ipsilateral muscle tone Fastigial nucleus To neurons of reticular formation; reticulospinal tract to ipsilateral motor neurons to spinal cord
aNote that each cerebellar hemisphere influences the voluntary muscle tone on the same side of the body.

Functions of the Cerebellum The cerebellum receives afferent information concerning voluntary movement from the cerebral cortex and from the muscles, tendons, and joints. It also receives information concerning balance from the vestibular nerve and possibly concerning sight through the tectocerebellar tract. All this information is fed into the cerebellar cortical circuitry by the mossy fibers and the climbing fibers and converges on the Purkinje cells (Fig. 6-8). The axons of the Purkinje cells project with few exceptions on the deep cerebellar nuclei. The output of the vermis projects to the fastigial nucleus, the intermediate regions of the cortex project to the globose and emboliform nuclei, and the output of the lateral part of the cerebellar hemisphere projects to the dentate nucleus. A few Purkinje cell axons pass directly out of the cerebellum and end on the lateral vestibular nucleus in the brainstem. It is now generally believed that the Purkinje axons exert an inhibitory influence on the neurons of the cerebellar nuclei and the lateral vestibular nuclei. The cerebellar output is conducted to the sites of origin of the descending pathways that influence motor activity at the segmental spinal level. In this respect, the cerebellum has no direct neuronal connections with the lower motor P.243 neurons but exerts its influence indirectly through the cerebral cortex and brainstem.

Figure 6-13 Cerebellum serving as a comparator.

Physiologists have postulated that the cerebellum functions as a coordinator of precise movements by continually comparing the output of the motor area of the cerebral cortex with the proprioceptive information received from the site of muscle action; it is then able to bring about the necessary adjustments by influencing the activity of the lower motor neurons (Fig. 6-13). This is accomplished by controlling the timing and sequence of firing of the alpha and gamma motor neurons. It is also believed that the cerebellum can send back information to the motor cerebral cortex to inhibit the agonist muscles and stimulate the antagonist muscles, thus limiting the extent of voluntary movement. P.244 Clinical Notes General Considerations Each cerebellar hemisphere is connected by nervous pathways principally with the same side of the body; thus, a lesion in one cerebellar hemisphere gives rise to signs and symptoms that are limited to the same side of the body. The main connections of the cerebellum are summarized in Figure 6-14. The essential function of the cerebellum is to coordinate, by synergistic action, all reflex and voluntary muscular activity. Thus, it graduates and harmonizes muscle tone and maintains normal body posture. It permits voluntary movements, such as walking, to take place smoothly with precision and economy of effort. It must be understood that although the cerebellum plays an important role in skeletal muscle activity, it is not able to initiate muscle movement. Signs and Symptoms of Cerebellar Disease While the importance of the cerebellum in the maintenance of muscle tone and the coordination of muscle movement has been emphasized, it should be remembered that the symptoms and signs of acute lesions differ from those produced by chronic lesions. Acute lesions produce sudden, severe symptoms and signs, but there is considerable clinical evidence to show that patients can recover completely from large cerebellar injuries. This suggests that other areas of the central nervous system can compensate for loss of cerebellar function. Chronic lesions, such as slowly enlarging tumors, produce symptoms and signs that are much less severe than those of acute lesions. The reason for this may be that other areas of the central nervous system have time to compensate for loss of cerebellar function. The following symptoms and signs are characteristic of cerebellar dysfunction. Hypotonia The muscles lose resilience to palpation. There is diminished resistance to passive movements of joints. Shaking the limb produces excessive movements at the terminal joints. The condition is attributable to loss of cerebellar influence on the simple stretch reflex. Postural Changes and Alteration of Gait The head is often rotated and flexed, and the shoulder on the side of the lesion is lower than on the normal side. The patient assumes a wide base when he or she stands and is often stiff legged to compensate for loss of muscle tone. When the individual walks, he or she lurches and staggers toward the affected side.

Figure 6-14 Some of the main connections of the cerebellum. The cerebellar peduncles are shown as ovoid dashed lines.

Disturbances of Voluntary Movement (Ataxia) The muscles contract irregularly and weakly. Tremor occurs when fine movements, such as buttoning clothes, writing, and shaving, are attempted. Muscle groups fail to work harmoniously, and there is decomposition of movement. When the patient is asked to touch the tip of the nose with the index finger, the movements are not properly coordinated, and the finger either passes the nose (past-pointing) or hits the nose. A similar test can be performed on the lower limbs by asking the patient to place the heel of one foot on the shin of the opposite leg. Dysdiadochokinesia Dysdiadochokinesia is the inability to perform alternating movements regularly and rapidly. Ask the patient to pronate and supinate the forearms rapidly. On the side of the cerebellar lesion, the movements are slow, jerky, and incomplete. Disturbances of Reflexes Movement produced by tendon reflexes tends to continue for a longer period of time than normal. The pendular knee jerk, for example, occurs following tapping of the patellar tendon. Normally, the movement occurs and is self-limited by the stretch reflexes of the agonists and antagonists. In cerebellar disease, because of loss of influence on the stretch reflexes, the movement continues as a series of flexion and extension movements at the knee joint; that is, the leg moves like a pendulum. Disturbances of Ocular Movement Nystagmus, which is essentially an ataxia of the ocular muscles, is a rhythmical oscillation of the eyes. It is more easily demonstrated when the eyes are deviated in a horizontal direction. This rhythmic oscillation of the eyes may be of the same rate in both directions (pendular nystagmus) or quicker in one direction than in the other (jerk nystagmus). In the latter situation, the movements are referred to as the slow phase away from the visual object, followed by a quick phase back toward the target. The quick phase is used to describe the form of nystagmus. For example, a patient is said to have a nystagmus to the left if the quick phase is to the left and the slow phase is to the right. The movement of nystagmus may be confined to one plane and may be horizontal or vertical, or it may be in many planes when it is referred to as rotatory nystagmus. The posture of the eye muscles depends mainly on the normal functioning of two sets of afferent pathways. The first is the visual pathway whereby the eye views the object of interest, and the second pathway is much more complicated and involves the labyrinths, the vestibular nuclei, and the cerebellum. Disorders of Speech Dysarthria occurs in cerebellar disease because of ataxia of the muscles of the larynx. Articulation is jerky, and the syllables often are separated from one another. Speech tends to be explosive, and the syllables often are slurred. In cerebellar lesions, paralysis and sensory changes are not present. Although muscle hypotonia and incoordination may be present, the disorder is not limited to specific muscles or muscle groups; rather, an entire extremity or the entire half of the body is involved. If both cerebellar hemispheres are involved, then the entire body may show disturbances of muscle action. Even though the muscular contractions may be weak and the patient may be easily fatigued, there is no atrophy. Cerebellar Syndromes Vermis Syndrome The most common cause of vermis syndrome is a medulloblastoma of the vermis in children. Involvement of the flocculonodular lobe results in signs and symptoms related to the vestibular system. Since the vermis is unpaired and influences midline structures, muscle incoordination involves the head and trunk and not the limbs. There is a tendency to fall forward or backward. There is difficulty in holding the head steady and in an upright position. There also may be difficulty in holding the trunk erect. Cerebellar Hemisphere Syndrome Tumors of one cerebellar hemisphere may be the cause of cerebellar hemisphere syndrome. The symptoms and signs are usually unilateral and involve muscles on the side of the diseased cerebellar hemisphere. Movements of the limbs, especially the arms, are disturbed. Swaying and falling to the side of the lesion often occur. Dysarthria and nystagmus are also common findings. Disorders of the lateral part of the cerebellar hemispheres produce delays in initiating movements and inability to move all limb segments together in a coordinated manner but show a tendency to move one joint at a time. Common Diseases Involving the Cerebellum One of the most common diseases affecting cerebellar function is acute alcohol poisoning. This occurs as the result of alcohol acting on GABA receptors on the cerebellar neurons. The following frequently involve the cerebellum: congenital agenesis or hypoplasia, trauma, infections, tumors, multiple sclerosis, vascular disorders such as thrombosis of the cerebellar arteries, and poisoning with heavy metals. The many manifestations of cerebellar disease can be reduced to two basic defects: hypotonia and loss of influence of the cerebellum on the activities of the cerebral cortex. P.245 P.246 Clinical Problem Solving 1. A 10-year-old girl was taken to a neurologist because her parents had noticed that her gait was becoming awkward. Six months previously, the child had complained that she felt her right arm was clumsy, and she had inadvertently knocked a teapot off the table. More recently, her family had noticed that her hand movements were becoming jerky and awkward; this was particularly obvious when she was eating with a knife and fork. The mother commented that her daughter had had problems with her right foot since birth and that she had a clubfoot. She also had scoliosis and was attending an orthopedic surgeon for treatment. The mother said she was particularly worried about her daughter because two other members of the family had similar signs and symptoms. On physical examination, the child was found to have a lurching gait with a tendency to reel over to the right. Intention tremor was present in the right arm and the right leg. When the strength of the limb muscles was tested, those of the right leg were found to be weaker than those of the left leg. The muscles of the right arm and right lower leg were also hypotonic. She had 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 also was present. On examination of her sensory system, she was found to have loss of muscle joint sense and vibratory sense of both legs. She also had loss of two-point discrimination of the skin of both legs. Her knee jerks were found to be exaggerated, but her ankle jerks were absent. The biceps and triceps jerks of both arms were normal. She had bilateral Babinski responses. Slight nystagmus was present in both eyes. Using your knowledge of neuroanatomy, explain the symptoms and signs listed for this patient. Did the disease process involve more than one area of the central nervous system? Explain. View Answer1. This 10-year-old girl had the symptoms and signs of Friedreich ataxia, an inherited degenerative disease of the cerebellum and posterior and lateral parts of the spinal cord. Degeneration of the cerebellum was revealed by the altered gait, clumsy movements of the right arm, tendency to fall to the right, intention tremor of the right arm and leg, hypotonicity of the right arm and right leg, and nystagmus of both eyes. Involvement of the fasciculus gracilis was evidenced by loss of vibratory sense, loss of two-point discrimination, and loss of muscle joint sense of the lower limbs. Corticospinal tract degeneration resulted in weakness of the legs and the presence of the Babinski plantar response. The exaggerated knee jerks were due to involvement of the upper motor neurons other than the corticospinal tract. The loss of the ankle jerks was due to the interruption of the reflex arcs at spinal levels S1-2 by the degenerative process. The clubfoot and scoliosis can be attributed to altered tone of the muscles of the leg and trunk over a period of many years. 2. Two physicians were talking in the street when one turned to the other and said, “Look at that man over there. Look at the way he is walking. He is not swinging his right arm at all; it is just hanging down by his side. I wonder if he has a cerebellar lesion.” Does a person with a unilateral cerebellar hemisphere tumor tend to hold the arm limply at the side when he walks? View Answer2. Yes. A person who has a unilateral lesion involving one cerebellar hemisphere demonstrates absence of coordination between different groups of muscles on the same side of the body. This disturbance affects not only agonists and antagonists in a single joint movement but also all associated muscle activity. For example, a normal person when walking swings his or her arms at both sides; with cerebellar disease, this activity would be lost on the side of the lesion. 3. A 37-year-old man visited his physician because he had noticed clumsiness of his right arm. The symptoms had started 6 months previously and were getting worse. He also noticed that his right hand had a tremor when he attempted fine movements or tried to insert a key in a lock. When he walked, he noticed that now and again he tended to reel over to the right, “as if he had too much alcohol to drink.” On physical examination, the face was tilted slightly to the left, and the right shoulder was held lower than the left. Passive movements of the arms and legs revealed hypotonia and looseness on the right side. When asked to walk heel to toe along a straight line on the floor, the patient swayed over to the right side. When he was asked to touch his nose with his right index finger, the right hand displayed tremor, and the finger tended to overshoot the target. Speech was normal, and nystagmus was not present. Using your knowledge of neuroanatomy, explain each sign and symptom. Is the lesion of the cerebellum likely to be in the midline or to one side? View Answer3. This man, at operation, was found to have an astrocytoma of the right cerebellar hemisphere. This fact explains the occurrence of unilateral symptoms and signs. The lesion was on the right side, and the clumsiness, tremor, muscle incoordination, and hypotonia occurred on the right side of the body. The progressive worsening of the clinical condition could be explained on the basis that more and more of the cerebellum was becoming destroyed as the tumor rapidly expanded. The flaccidity of the muscles of the right arm and leg was due to hypotonia, that is, a removal of the influence of the cerebellum on the simple stretch reflex involving the muscle spindles and tendon organs. The clumsiness, tremor, and overshooting on the finger-nose test were caused by the lack of cerebellar influence on the process of coordination between different groups of muscles. The falling to the right side, the tilting of the head, and the drooping of the right shoulder were due to loss of muscle tone and fatigue. 4. A 4-½-year-old boy was taken to a neurologist because his mother was concerned about his attacks of vomiting on waking in the morning and his tendency to be unsteady on standing up. The mother also noticed that the child walked with an unsteady gait and often fell backward. On physical examination, the child tended to stand with the legs well apart—that is, broad based. The head was larger than normal for his age, and the suture lines of the skull could be easily felt. A retinal examination with an ophthalmoscope showed severe papilledema in both eyes. The muscles of the upper and lower limbs showed some degree of hypotonia. Nystagmus was not present, and the child showed no tendency to fall to one side or the other when asked to walk. Using your knowledge of neuroanatomy, explain the symptoms and signs. Is the lesion in the cerebellum likely to be in the midline or to one side? View Answer4. The diagnosis was medulloblastoma of the brain in the region of the roof of the fourth ventricle, with involvement of the vermis of the cerebellum. The child died 9 months later after extensive deep x-ray therapy. The sudden onset of vomiting, the increased size of the head beyond normal limits, the sutural separation, and the severe bilateral papilledema could all be accounted for by the 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, indicate a tumor involving the vermis. The presence of bilateral hypotonia, especially during the later stages, was due to involvement of both cerebellar 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. During a ward round, a third-year student was asked to explain the phenomenon of nystagmus. How would you have answered that question? Why do patients with cerebellar disease exhibit nystagmus? View Answer5. Nystagmus, an involuntary oscillation of the eyeball, may occur physiologically, as when a person watches rapidly moving objects, or by rapid rotation 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 between the agonists and antagonists involved in the eyeball movement. For full understanding of the different forms of nystagmus, a textbook of neurology should be consulted. Also see page 245. 6. What is the essential difference between the symptoms and signs of acute and chronic lesions of the cerebellum? Explain these differences. View Answer6. Acute lesions, such as those resulting from a thrombosis 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, and this can be explained by the fact that the cerebellum influences muscular activity not directly, but indirectly, through the vestibular nuclei, reticular formation, red nucleus, tectum, and corpus striatum and the cerebral cortex; it may be that these other areas of the central nervous system take over this function. In chronic lesions, the symptoms and signs are much less severe, and there is enough time to allow the other areas of the central nervous system to compensate for loss of cerebellar function. P.247 P.248 P.249 Review Questions 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 appearance 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. View Answer1. A is correct. The cerebellum is separated from the occipital lobes of the cerebral hemisphere by the tentorium cerebelli (see p. 428). B. The cerebellum lies posterior to the medulla oblongata (see Fig. 6-1). C. The anterior lobe is separated from the middle (posterior) lobe by the primary fissure (see Fig. 6-3). D. The flocculonodular lobe is separated from the middle (posterior) lobe by the uvulonodular fissure (see Fig. 6-3). E. The fourth ventricle lies anterior to the cerebellum (see Fig. 6-1). 2. The following general statements concern the cerebellum: (a) The cerebellum greatly influences the activity of smooth muscle. (b) The cerebellum has no influence on the skeletal muscles supplied by the cranial nerves. (c) Each cerebellar hemisphere controls the tone of skeletal muscle 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. View Answer2. C is correct. Each cerebellar hemisphere controls the tone of skeletal muscles supplied by spinal nerves on the same side of the body (see p. 243). A. The cerebellum has no effect on the activity of smooth muscle. B. The cerebellum has the same influence on the skeletal muscle supplied by cranial nerves as on that supplied by spinal nerves. D. The important Purkinje cells are Golgi type I neurons. E. The Purkinje cells exert an inhibitory influence on the intracerebellar nuclei (see p. 236). 3. The following statements concern the structure of the cerebellum: (a) The cerebellum consists of two cerebellar hemispheres joined by a narrow median vermis. (b) The inferior surface of the cerebellum shows a deep groove formed by the superior surface of the vermis. (c) The inferior cerebellar peduncles join the cerebellum 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, called the arbor vitae. View Answer3. A is correct. The cerebellum consists of two cerebellar hemispheres joined by a narrow median vermis (see Fig. 6-2). B. The inferior surface of the cerebellum shows a deep groove formed by the inferior surface of the vermis (see Fig. 6-2). C. The inferior cerebellar peduncle joins the cerebellum to the medulla oblongata (see Fig. 6-9). D. The gray matter of the cerebellum is found in the cortex and in the three masses forming the intracerebellar nuclei (see p. 233). E. The white matter and folia of the cortex have a branched appearance on the cut surface, called the arbor vitae (see Fig. 6-1). 4. The following statements concern the structure of the cerebellar cortex: (a) The cortex is folded by many vertical fissures into folia. (b) The structure of the cortex differs widely in different parts of the cerebellum. (c) The Purkinje cells are found in the most superficial layer of the cortex. (d) The Golgi cells are found in the most superficial layer of the cerebellar cortex. (e) The axons of the Purkinje cells form the efferent fibers from the cerebellar cortex. View Answer4. E is correct. The axons of the Purkinje cells form the efferent fibers from the cerebellar cortex (see p. 231). A. The cerebellar cortex is folded by many transverse fissures into folia (see Fig. 6-1). B. The structure of the cortex is identical in different parts of the cerebellum. C. The Purkinje cells are found in the middle layer of the cerebellar cortex (see Fig. 6-4). D. The Golgi cells are found in the deepest (granular) layer of the cerebellar cortex (see Fig. 6-4). 5. The following statements concern the intracerebellar nuclei: (a) The nuclei are found within the superficial layers of the white matter. (b) The nuclei are located in the walls of the fourth ventricle. (c) The nuclei are composed of many small unipolar neurons. (d) The axons of the nuclei form the main cerebellar outflow. (e) From medial to lateral, the nuclei are named as follows: dentate, emboliform, globose, and fastigial. View Answer5. D is correct. The axons from the neurons of the intracerebellar nuclei form the main cerebellar outflow (see p. 237). A. The intracerebellar nuclei are deeply embedded in the white matter (see Fig. 6-7). B. The nuclei are located posterior to the roof of the fourth ventricle (see Fig. 6-7). C. The nuclei are composed of large multipolar neurons. E. From medial to lateral, the nuclei are named as follows: fastigial, globose, emboliform, and dentate (see Fig. 6-7). 6. The following statements concern the cerebellar peduncles: (a) In the superior cerebellar peduncle, most of the fibers are afferent and arise from the neurons of the spinal cord. (b) The anterior spinocerebellar tract enters the cerebellum through the superior cerebellar peduncle. (c) The inferior cerebellar peduncle is made up exclusively of fibers that pass from the inferior olivary nuclei to the middle lobe of the cerebellar hemisphere. (d) The middle cerebellar peduncle is formed of fibers that arise from the dentate nuclei. (e) The cerebellar peduncles are surface structures that are difficult to see even by brain dissection. View Answer6. B is correct. The anterior spinocerebellar tract enters the cerebellum through the superior cerebellar peduncle (see Fig. 6-11). A. In the superior cerebellar peduncle, most of the fibers are efferent and arise from the neurons of the intracerebellar nuclei (see Fig. 6-12). C. The inferior cerebellar peduncle contains afferent fibers of the posterior spinocerebellar tract, the cuneocerebellar tract, the vestibular nucleus, and the olivocerebellar tract (see Figs. 6-10 and 6-11). In addition, there are the efferent fibers from the cerebellum, including the fastigial vestibular pathway and the fastigial reticular pathway (see Fig. 6-12). D. The middle cerebellar peduncle is formed of fibers that arise from the pontine nuclei (see Fig. 6-10); there are also fibers that connect the cerebellar hemispheres of the two sides together (see Fig. 6-12). E. The cerebellar peduncles are surface structures and are easily seen on dissection. 7. The following statements concern the afferent fibers entering the cerebellum: (a) The mossy fibers end by making synaptic contacts with the dendrites of the Purkinje cells. (b) The fibers enter the cerebellum mainly through the internal and external arcuate fibers. (c) The climbing and mossy fibers constitute the two main lines of input to the cerebellar cortex. (d) The afferent fibers are inhibitory to the Purkinje cells. (e) The afferent fibers to the cerebellum are nonmyelinated. View Answer7. C is correct. The climbing and mossy fibers of the cerebellum constitute the two main lines of input to the cerebellar cortex (see p. 236). A. The mossy fibers end by making synaptic contacts with the dendrites of the granular cells and the Golgi cells (see Fig. 6-8). B. The afferent fibers enter the cerebellum through the superior, inferior, and middle cerebellar peduncles. D. The afferent fibers are excitatory to the Purkinje cells (see p. 236). E. The afferent fibers to the cerebellum are myelinated. 8. The following statements concern the functions of the cerebellum: (a) The cerebellum influences the actions of muscle tendons. (b) The cerebellum controls voluntary movement by coordinating the force and extent of contraction of different muscles. (c) The cerebellum stimulates the contraction of antagonistic muscles. (d) The cerebellum directly influences skeletal muscle activity without the assistance of the cerebral cortex. (e) The cerebellum coordinates the peristaltic waves seen in intestinal muscle. View Answer8. B is correct. The cerebellum controls voluntary movement by coordinating the force and extent of contraction of different muscles (see p. 242). A. The cerebellum influences the actions of muscles not tendons. C. The cerebellum inhibits the contraction of antagonistic muscles. D. The cerebellum indirectly influences skeletal muscle activity with the assistance of the cerebral cortex (see p. 242). E. The cerebellum has no effect on the control of smooth muscle in the wall of the intestine. 9. The following statements concern the cerebellum: (a) The afferent climbing fibers make single synaptic contacts with individual Purkinje cells. (b) The afferent mossy fibers may stimulate many Purkinje cells by first stimulating the stellate cells. (c) The neurons of the intracerebellar nuclei send axons without interruption to the opposite cerebral hemisphere. (d) The output of the cerebellar nuclei influences muscle activity so that movements can progress in an orderly sequence from one movement to the next. (e) Past pointing is caused by the failure of the cerebral cortex to inhibit the cerebellum after the movement has begun. View Answer9. D is correct. The output of the cerebellar nuclei influences muscle activity so that movements can progress in an orderly sequence from one movement to the next. A. The afferent climbing fibers make multiple synaptic contacts with 1 to 10 Purkinje cells. B. The afferent mossy fibers may stimulate many Purkinje cells by first stimulating the granular cells (see p. 236). C. The neurons of the intracerebellar nuclei send axons to the ventrolateral nucleus of the thalamus, where they are relayed to the cerebral cortex (see Fig. 6-12). E. Past pointing is caused by the failure of the cerebellum to inhibit the cerebral cortex after the movement has begun. 10. The following statements concern the cerebellum: (a) The cerebellar cortex has a different microscopic structure in different individuals. (b) The axons of the Purkinje cells exert an inhibitory influence on the neurons of the deep cerebellar nuclei. (c) Each cerebellar hemisphere principally influences movement on the opposite hand. (d) The part of the cerebellum that lies in the midline is called the flocculus. (e) Intention tremor is a sign of cerebellar disease. View Answer10. E is correct. Intention tremor is a sign of cerebellar disease (see p. 244). A. The cerebellar cortex has the same uniform microscopic structure in different individuals. B. The axons of the Purkinje cells exert a stimulatory influence on the neurons of the deep cerebellar nuclei. C. Each cerebellar hemisphere principally influences movement on the same side of the body. D. The part of the cerebellum that lies in the midline is called the vermis. Directions: Matching Questions. Following thrombosis of the posterior inferior cerebellar artery, a patient presents the numbered signs and symptoms listed below; match the signs and symptoms with the appropriate lettered structures involved. Each lettered option may be selected once, more than once, or not at all. 11. Loss of pain and temperature on the left side of the body View Answer11. C is correct. 12. Nystagmus View Answer12. B is correct: right inferior cerebellar peduncle. 13. Hypotonicity of the muscles on the right with a tendency to fall to the right (a) Right reticulospinal tract (b) Right inferior cerebellar peduncle (c) None of the above View Answer13. B is correct: right inferior cerebellar peduncle. Directions: Match the numbered nerve tracts listed below with the lettered pathways by which they leave the cerebellum. Each lettered option may be selected once, more than once, or not at all. 14. Corticopontocerebellar (a) Superior cerebellar peduncle (b) Corpus callosum (c) Striae medullaris (d) Inferior cerebellar peduncle (e) Middle cerebellar peduncle (f) None of the above View Answer14. E is correct: middle cerebellar peduncle. 15. Cuneocerebellar (a) Superior cerebellar peduncle (b) Corpus callosum (c) Striae medullaris (d) Inferior cerebellar peduncle (e) Middle cerebellar peduncle (f) None of the above View Answer15. D is correct: inferior cerebellar peduncle. 16. Cerebellar reticular (a) Superior cerebellar peduncle (b) Corpus callosum (c) Striae medullaris (d) Inferior cerebellar peduncle (e) Middle cerebellar peduncle (f) None of the above View Answer16. D is correct: inferior cerebellar peduncle. 17. Cerebellar rubral (a) Superior cerebellar peduncle (b) Corpus callosum (c) Striae medullaris (d) Inferior cerebellar peduncle (e) Middle cerebellar peduncle (f) None of the above View Answer17. A is correct: superior cerebellar peduncle. Directions: Each case history is followed by questions. Read the case history, then select the ONE BEST lettered answer. A 45-year-old man, who was an alcoholic, started to develop a lurching, staggering gait even when he was not intoxicated. The condition became slowly worse over a period of several weeks and then appeared to stabilize. Friends noticed that he had difficulty in walking in tandem with another person and tended to become unsteady on turning quickly. 18. A thorough physical examination of this patient revealed the following findings except: (a) The patient exhibited instability of trunk movements and incoordination of leg movements. (b) While standing still, the patient stood with his feet together. (c) He had no evidence of polyneuropathy. (d) The ataxia of the legs was confirmed by performing the heel-to-shin test. (e) Magnetic resonance imaging showed evidence of atrophy of the cerebellar vermis. View Answer18. B is correct. Patients with cerebellar disease frequently exhibit poor muscle tone, and to compensate for this, they stand stiff legged with their feet wide apart. 19. The following additional abnormal signs might have been observed in this patient except: (a) Nystagmus in both eyes (b) Dysarthria (c) Tremor of the left hand when reaching for a cup (d) Paralysis of the right upper arm muscles (e) Dysdiadochokinesia View Answer19. D is correct. Although patients with cerebellar disease display disturbances of voluntary movement, none of the muscles are paralyzed or show atrophy. P.250 Additional Reading Adams, R. D., and Victor, M. Principles of Neurology. New York: McGraw-Hill, 1994. Angevine, J. B., Mancall, E. L., and Yakovlev, P. I. The Human Cerebellum. Boston: Little, Brown, 1961. Arshavsky, Y. I., Gelfand, I. M., and Olovsky, G. N. The cerebellum and control of rhythmical movements. Trends Neurosci. 6:417, 1983. Bloedel, J. R., and Courville, J. Cerebellar afferent systems. In V. B. Brooks (ed.), Handbook of Physiology (sec. 1, vol. II, p. 735). Bethesda, MD: American Physiological Society, 1981. Brodal, P. The Central Nervous System: Structure and Function. New York: Oxford University Press, 1992. Colin, F., Manil, J., and Desclin, J. C. The olivocerebellar system. 1. Delayed and slow inhibitory effects: An overlooked salient feature of cerebellar climbing fibers. Brain Res. 187:3, 1980. Cordo, P., and Harnad, S. Movement Control. New York: Cambridge University Press, 1994. Fields, W. D., and Willis, W. D. Jr. The Cerebellum in Health and Disease. St. Louis: Warren H. Green, 1970. Forssberg, H., and Hirschfeld, H. Movement Disorders in Children. Farmington, CT: S. Karger Publishers Inc., 1992. Gilman, S. The cerebellum: Its role in posture and movement. In M. Swash and C. Kennard (eds.), Scientific Basis of Clinical Neurology (p. 36). Edinburgh: Churchill Livingstone, 1985. Gilman, S. The mechanisms of cerebellar hypotonia. Brain 92:621, 1969. Goetz, C. G. Textbook of Clinical Neurology (2nd ed.). Philadelphia: Saunders, 2003. Guyton, A. C., and Hall, J. E. Textbook of Medical Physiology (11th ed.). Philadelphia: Elsevier Saunders, 2006. Ito, M. The Cerebellum and Neural Control. New York: Raven, 1984. Kennedy, P. R., Ross, H. G., and Brooks, V. B. Participation of the principal olivary nucleus in neurocerebellar control. Exp. Brain Res. 47:95, 1982. Leigh, R. J., and Zee, D. S. The Neurology of Eye Movements (2nd ed.). Philadelphia: Davis, 1991. Lewis, A. J. Mechanisms of Neurological Disease. Boston: Little, Brown, 1976. Llinas, R. R. The cortex of the cerebellum. Sci. Am. 232:56, 1975. Llinas, R. R. Electrophysiology of the cerebellar networks. In V. B. Brooks (ed.), Handbook of Physiology (sec. 1, vol. II, p. 831). Bethesda, MD: American Physiological Society, 1981. Nestler, E. J., Hyman, S. E., and Malenka, R. C. Molecular Neuropharmacology. New York: McGraw-Hill, 2001. Palay, S. L., and Chan-Palay, V. Cortex and organization. In Cerebellar Cortex. Berlin: Springer, 1974. Rowland, L. P. Merritt’s Neurology (10th ed.). Philadelphia: Lippincott Williams & Wilkins, 2000. Schweighofer, N. Doya, K, Kuroda, S. Cerebellar aminergic neuromodulation: Towards a functional understanding. Brain Res. Rev. 44:103, 2004. Standring, S. (ed.). Gray’s Anatomy (39th Br. ed.). London: Elsevier Churchill Livingstone, 2005. Thach, W. T. On the specific role of the cerebellum in motor learning and cognition: Clues from PET activation and lesion studies in humans. Behav. Brain Sci. 19:411–431, 1996. Thach, W. T., Goodkin, H. G., Keating, J. G. Cerebellum and the adaptive coordination of movement. Ann. Rev. Neurosci. 15:403–442, 1992. Thach, W. T., Perry, J. G., Kane, S. A., Goodkin, H. P. Cerebellar nuclei: Rapid alternating movement, motor somatotopy, and a mechanism for the control of muscle synergy. Rev. Neurol. 149:607–628, 1993.

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