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Posts Tagged ‘CNS’

INTERNAL STRUCTURE Transverse sections of the pons Transverse sections (Fig. 19.9, Fig. 19.11) reveal that the pons consists of a dorsal tegmentum, which is a continuation of the medulla (excluding the pyramids), and a ventral (basilar) part. The latter contains bundles of longitudinal descending fibres, some of which continue into the pyramids, while others end […]

INTERNAL ORGANIZATION In transverse section, the spinal cord is incompletely divided into symmetrical halves by a dorsal (posterior) median septum and a ventral (anterior) median sulcus (Fig. 18.1). It consists of an outer layer of white matter and an inner core of grey matter; their relative sizes and configuration vary according to level. The amount […]

AUTONOMIC NERVOUS SYSTEM The autonomic nervous system represents the visceral component of the nervous system. It consists of neurones located within both the CNS and PNS which are concerned with the control of the internal environment, through the innervation of secretory glands, cardiac and smooth muscle. Its functions are, however, closely integrated with those of […]

CRANIAL NERVES Cranial nerves are the means by which the brain receives information from, and controls the activities of, the head and neck and to a lesser extent the thoracic and abdominal viscera. The component fibres, their route of exit from the cranial cavity, their subsequent peripheral course and the distribution and functions of the […]

OVERVIEW OF ASCENDING SENSORY PATHWAYS Sensory modalities are conventionally described as being either special senses or general senses. The special senses are olfaction, vision, taste, hearing and vestibular function. Afferent information is encoded by highly specialized sense organs and transmitted to the brain in cranial nerves I, II, VII, VIII and IX (Ch. 25). The […]

PERIPHERAL NERVOUS SYSTEM The PNS is composed mainly of spinal nerves, cranial nerves, their ganglia and their ramifications which carry afferent and efferent neurones between the CNS and the rest of the body. It also includes the peripheral part of the autonomic nervous system, notably the sympathetic trunks and ganglia, and the enteric nervous system […]

Section 3 – NEUROANATOMY CHAPTER 15 – Overview of the nervous system The human nervous system is the most complex product of biological evolution. The constantly changing patterns of activity of its billions of interactive units represent the fundamental physical basis of every aspect of human behaviour and experience. Many thousands of scientists and clinicians around the world, whether […]

PARASYMPATHETIC NERVOUS SYSTEM Preganglionic parasympathetic neurone cell bodies are located in certain cranial nerve nuclei of the brain stem (see Fig. 19.1) and in the grey matter of the second to fourth sacral segments of the spinal cord. Efferent fibres, which are myelinated, emerge from the CNS only in cranial nerves III, VII, IX and […]

ENTERIC NERVOUS SYSTEM AND INTRINSIC NEURONES Many peripheral autonomic ganglia contain neurones derived from the neural crest during embryonic development that are anatomically distinct from classical sympathetic and parasympathetic neurones. Connections between these intrinsic neurones allow them to sustain and modulate visceral activities by local reflex mechanisms. The enteric nervous system consists of many millions […]

VISCERAL AFFERENT PATHWAYS General visceral afferent fibres from the viscera and blood vessels accompany their efferent counterparts, and are the peripheral processes of unipolar cell bodies located in some cranial nerve and dorsal root ganglia. They are contained in the vagus, glossopharyngeal, and possibly other cranial nerves; the second to fourth sacral spinal nerves, distributed […]

EMBRYONIC CELL POPULATIONS AT THE START OF ORGANOGENESIS The developmental processes operating in the embryo between stages 5 and 9 enabled the construction of the bi- and tri-laminar embryonic disc, the intraembryonic coelom and new proliferative epithelia. From the end of stage 10, a range of local epithelial and mesenchymal populations now interact to produce […]

PHAGOCYTES AND ANTIGEN-PRESENTING CELLS Macrophages and neutrophils (see above) are specialized phagocytes. Certain dendritic cells (see Fig. 4.12), e.g. Langerhans cells of the skin and other stratified squamous epithelia, are ‘professional’ antigen-presenting cells (APCs): they take up foreign material by endocytosis and macropinocytosis, and are uniquely capable of efficiently activating naïve as well as mature […]

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