Nervous system1,Department of Anatomy Luzhou Medical College,Edited by professor Xiao,Nervous system Introduction The nervous system is composed of two parts, the central nervous system and peripheral nervous system. The former is represented by the brain and spinal cord; while the latter consists of the spinal and cranial nerves. The autonomic nervous system, often considered as a separate functional entity, is a part central and a part peripheral.,Brain,Spinal cord,Cranial nerves,Spinal nerves,Nervous system as a whole,The nervous system possesses particular importance in all organs and systems of human body. It modulates the different cells, tissues and organs, to complete certain activities or response exterior stimulus for the benefit of organism as a whole. The brain is commonly regarded as the organ solely concerned with thought, memory and consciousness. All information we have concerning the world about us is conveyed centrally to the brain by an elaborate sensory system.,Nervous system Introduction,Receptor of many kinds act as transducers which change physical and chemical stimuli in our environment into nerve impulse which the brain can read and give meaning to. Attention, consciousness, emotional experience and sleep are all central neural functions. Such higher functions as memory, imagination(想像力), thought and creative ability are poorly understood（难懂的） but must be related to complex neuronal activity. While the gross features of the human brain are not especially impressive（印象）, its versatility（多功能性）, potential capabilities（濽能）, efficiency（效率）and self-programming nature（自我谋略天性） put it in a class beyond any “electronic brain”.,Nervous system Introduction,The elements of the nervous system The nervous system composed of nervous tissue that consists of billions of nerve cells (neurons) and supported by a special variety of connective tissue known as neuroglia. The neuron The neuron are independent structural unit of the nervous system and are functional specialized for reception, integration（整合）, and transmission of coded information（编码）.,Nervous system Introduction,Rough granular Endoplasmic reticulum,Smooth granular Endoplasmic reticulum,Microtubule,Schwanns cell,Myelin sheath,Lysosomes,Lipofuscin脂褐质,Each neuron possesses a nucleated cell body and two types of processes, an neuron, which conducts impulse away from the cell body, and one or more dendrites that conducts impulses towards the cell body. Both of these processes show marked morphological difference. The cell body serves as metabolic center of the entire unit and consists of a large, pale nucleus and cytoplasm ( perikaryon).,Nervous system Introduction,The structures of the neuron,The nuclear envelope is double-layered membrane with numerous pores（小孔）. The chromatin（染色质） consists mostly of large molecules of deoxyribonucleic acid (DNA). The nucleolus（核仁） occupies a prominent position in the nucleus, which is rich in ribonucleic acid (RNA). As in all cells, the nucleus engages in marked degree of protein synthesis. The organelles（细胞器） contained within the cytoplasm are common to other cells in the body, but there is abundant granular endoplasmic reticulum that constitutes the Nissl body, a protein synthesis apparatus.,Nervous system Introduction,engage in 从事于,The structures of the neuron,The microtubules and neurofilaments in the cytoplasm extend throughout the cell body and processes and constitute the cytoskeleton of the neuron, which are involved in the maintenance of the shape of neuron and facilitate（易于） transfer of substance between the cells body and cell processes. The neuron also contains abundant lysosomes（溶酶体）, and mitochondria（线粒体） for energy metabolism. There are lipofuscin（脂褐质 ） granules ( prominently in some large adult neuron) which are byproducts of metablism, and the neuromelanin（神经黑色素）granules in the substantia nigra and locus ceruleus which are the waste product of catecholamine（儿茶酚胺） synthesis probably.,Nervous system Introduction,The structures of the neuron,The axon is a slender process. It may arise from the conical region of the cell body called axon hillock, or from the base of one of the main dendrites. The axon gives rise to several side branches or collaterals, usually oriented perpendicular（垂直的） to the main axon process. Distally, the axon breaks up into fine branches that end in swollen button called button terminal or axon terminal. The latter comes into contact with other neurons to form synapse, or with muscle to cause muscle contraction, or with the gland to cause secretion. The plasmic membrane of the axon is known as axolemma（轴膜） and the interior of axon called axoplasm（轴索原浆）. The axoplasm differs from the cytoplasm of the dendrites by complete absence of the Nissl body. Components of the axoplasm consist of agranular endoplasmic reticulum, mitochondria, microtubules and neurofilments. The terminal segments of axon comprises numerous synaptic vesicles that contain neurot