Minagar Cerebellar Disease, An Issue of Neurologic Clinics,

1. Auflage 2015
ISBN: 978-0-323-32661-2
Verlag: Elsevier Health Care - Major Reference Works
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, Band Volume 32-4, 100 Seiten

Reihe: The Clinics: Radiology

Cerebellar Disease, An Issue of Neurologic Clinics,

Autoren/Hrsg.

Minagar, Alireza

Leseproben

The Human Cerebellum
A Review of Physiologic Neuroanatomy
Tina Roostaei, MD, MPHab1, Arash Nazeri, MDabc1, Mohammad Ali Sahraian, MDad*[e-mail] and Alireza Minagar, MDe,     aMS Research Center, Neuroscience Institute, Sina Hospital, Tehran University of Medical Sciences, Hassan Abad Square, Tehran 1136746911, Iran; bInterdisciplinary Neuroscience Research Program, Tehran University of Medical Sciences, Poursina Street, Tehran 1417863181, Iran; cKimel Family Translational Imaging-Genetics Research Laboratory, Centre for Addiction and Mental Health, University of Toronto, 250 College Street, Toronto ON M5T 1R8, Canada; dDepartment of Neurology, Sina Hospital, Tehran University of Medical Sciences, Tehran 1136746911, Iran; eDepartment of Neurology, Louisiana State University-Health, 1501 Kings Highway, Shreveport, LA 71103, USA *Corresponding author. MS Research Center, Neuroscience Institute, Sina Hospital, Hassan Abad Square, Tehran, Iran. The cerebellum resides in the posterior cranial fossa dorsal to the brainstem and has diverse connections to the cerebrum, brain stem, and spinal cord. It is anatomically and physiologically divided into distinct functional compartments and is composed of highly regular arrays of neuronal units, each sharing the same basic cerebellar microcircuitry. Its circuitry is critically involved in motor control and motor learning, and its role in nonmotor cognitive and affective functions is becoming increasingly recognized. This article describes the cerebellar gross and histologic neuroanatomy in relation to its function, and the relevance of cerebellar circuitry and firing patterns to motor learning. Keywords Cerebellar lobules Cerebellar circuitry Compartmentalization Plasticity Cerebellar connections Key points
• Based on the afferent/efferent connections and functions, the cerebellum can be subdivided into the vestibulocerebellum, spinocerebellum, and cerebrocerebellum. • Traditionally, the cerebellum is viewed as a brain region entirely devoted to motor control and learning; however, recent studies suggest that cerebellum is also engaged in cognitive and affective tasks. • The cerebellar cortex is a 3-layered structure with stereotypical circuitry and distribution of cell types. • The cerebellum consists of myriads of functional units (modules) that function independent of each of other. The cerebellum (Latin for “little brain”) is approximately one-tenth of the cerebrum in size and weight and is situated in the posterior cranial fossa. It is connected directly or indirectly to a variety of structures, including brainstem, spine, and diverse cerebral subcortical and cortical regions. The cerebellum contains almost 80% of the total brain neurons1 and is composed of highly regular arrays of neuronal units, each sharing the same basic cerebellar microcircuitry. Its circuitry is classically viewed to be involved in motor control and motor learning. The cerebellum does not contribute to movement initiation, and thus its damage is not associated with paralysis. However, coordinated, precise, and smooth execution of voluntary movements and their adaptive modification rely on an intact cerebellum. Moreover, there is an increasing recognition of the cerebellum’s role in nonmotor cognitive and affective functions. In recent years, novel tools and resources have emerged that can spur new lines of research in cerebellar anatomy and physiology (Box 1).2,3 Box 1   Toolboxes and resources for studying the cerebellum • Healthy aging, normal development, and various central nervous system disorders are associated with cerebellar atrophy and/or volume changes. Tools dedicated to investigating these cerebellar volume differences were recently developed (eg, spatially unbiased atlas template of the cerebellum and brainstem [SUIT],15,16 multiple automatically generated templates of different brains [MAGeT-Brain]17,18). These methods could be used to automatically generate volumetric measurements of the cerebellum and/or assess local cerebellar volume changes with voxel-wise approaches. Further, specific patterns of cerebellar volume changes/atrophy could be elucidated using these techniques. • Human Connectome Project (http://www.humanconnectome.org/) seeks to explore structural and functional connectivity in the human brain. Advanced high-resolution functional, structural, and diffusion magnetic resonance images of cerebellum along with other structures are provided in this data set.19 • A useful resource for investigators who are interested in patterns of gene expression across cerebellum is transcriptomic databases. In the recent years, spatiotemporal transcriptomic maps of cerebellum have become publically available (cerebellar development transcriptome20 and various datasets in the Allen brain atlas21). The first sections of this review describe neuroanatomy and major physiologic subdivisions and functions of the cerebellum. Next, histology and neural circuitry of the cerebellum along with cerebellar functional units are addressed. Lastly, relevance of cerebellar circuitry and firing patterns to motor learning are discussed. Large-scale neuroanatomy of the cerebellum
The cerebellum is located posterior to the brainstem and the fourth ventricle and is rostrally separated from the cerebrum by an extension of the dura matter called tentorium cerebelli. It consists of 2 lateral hemispheres and a narrow midline zone (ie, the cerebellar vermis, from the Latin for worm), and its surface has many parallel thin transverse folds called folia (Fig. 1). The cerebellum consists of an outer layer of highly convoluted gray matter (cerebellar cortex) surrounding a highly branched body of white matter known as the arbor vitae (Latin for “tree of life”), which in turn surrounds the 3 pairs of deep cerebellar nuclei embedded in the central cerebellar white matter (corpus medullare). From medial to lateral, the deep nuclei are the fastigial, interposed (consisting of globose and emboliform nuclei), and dentate nuclei. Anatomically, the cerebellum is divided into 3 lobes by 2 transverse fissures. The primary fissure separates the anterior from the posterior lobe, and the posterolateral fissure lies between the posterior and flocculonodular lobe. The cerebellum is further subdivided into 10 transverse lobules marked by Roman numerals (lobules I–X) (Fig. 2). Each lobe/lobule encompasses a central portion in the vermis along with the adjacent 2 lateral segments in the hemispheres.
Fig. 1 Cerebellar gross anatomy. (A) Coronal (left) and sagittal (right) views of high-resolution magnetic resonance images of cerebellum with T1/T2 ratio contrast (to enhance white matter/gray matter contrast). (B) Axial (left and right) and coronal (middle) views of the cerebellar peduncles shown in color-coded directional maps (red: left–right, green: anterior–posterior, blue: inferior–superior) modulated by fractional anisotropy estimated from diffusion tensor imaging. (C) Superior (left) and lateral (right) views of 3-dimensional reconstruction of cerebellar surface (spatially unbiased infratentorial and cerebellar template [SUIT] atlas15,16). Lobules IV, V, VI, VIIA (crus I, crus II), VIIB, VIIIA, VIIIB, and IX are shown in different colors. ([A] Adapted from The Human Connectome Project public data. Available at: http://www.humanconnectome.org/. Accessed February 1, 2014.)
Fig. 2 Unfolded view of the cerebellar cortex showing lobes, fissures, lobules, along with cerebellar somatotopy (left cerebellum only). The cerebellum is attached to the brainstem through its 3 pairs of peduncles (inferior, middle, and superior) (see Fig. 1A, B). All efferents and afferents of cerebellum pass through these peduncles to reach their targets (Table 1). The middle cerebellar peduncle is the largest and is composed almost exclusively of pontocerebellar fibers that stem from the contralateral pontine nuclei and relay signals from the cerebral cortex. Lying medial to the middle cerebellar peduncle is the inferior peduncle, which consists of restiform (afferent) and juxtarestiform (mainly efferent) bodies. The superior peduncle is mainly composed of efferent fibers originating from the dentate and interposed nuclei and, to a smaller extent, the fastigial nucleus. Table 1 Major cerebellar afferents and...