Nervous system 1

1. Nervous system1 Department of Anatomy Luzhou Medical College Edited by professor Xiao

2. Brain 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. Cranial nerves Spinal cord Spinal nerves Nervous system as a whole

3. Nervous system Introduction • 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.

4. 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”.

5. 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）.

6. Microtubule Smooth granular Endoplasmic reticulum Rough granular Endoplasmic reticulum Myelin sheath Schwann’s cell Lysosomes Lipofuscin脂褐质

7. Nervous system Introduction The structures of the neuron • 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).

8. 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. engage in 从事于

9. Nervous system Introduction 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.

10. 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 neurotransmitter substances.

11. Nervous system Introduction Axoplasmic transport Because the axoplasm does not contain RNA, proteins synthesis cannot take place in the axon. All axonal proteins, therefore, must come from the cell body, and products are transported by a perpetual（永久的）axoplasmic motion, some organelles, structural protein and neurotransmitters contained within cytoplasm are carried by axoplasmic flow which moves in both directions and with varying velocity. The anterograde transport, moving from the cell body to the nerve terminals, has two types of rate: one is the slow transport, which is bulk flow（总体流动）of axoplasm carrying mitochondria, lysosomes（溶酶体）and vesicles; the other is a rapid transport which moves the membrane-bound vesicles, and other material.

12. Nervous system Introduction Axoplasmic transport • The retrograde transports, moving from the synaptic terminal to the cell body, provide a feedback passage. Some pinocytotic（胞饮的）material uptaken by an axonal terminals or distal dendrites are carried to the cell body for utilization or lysosomal degradation. The axoplasmic transport can be used experimentally to determine neuronal connectivity（连通性）by an axon-tracing technique and gas a clinic implication as centripetal（向心力）transport of neurotoxic（神经毒素）and infective agents, which may be responsible for some disease.

13. Nervous system Introduction Axoplasmic transport • The dendrites constitute protoplasmic(原浆) extensions of the cell body. The main or primary dendrites arises from the cell body and then branch repeatedly in a tree-like manner to form a complex dendrites tree. Further, the dendrites are studded（颗粒状的）with a large members of thorn（棘）like process, dendrite spines or gemmulus（芽）, which are structures specialized for synoptic contact. In this manner the dendrites greatly increase the receptive surface area（接收面积）of the whole neuron and thus enhance（增加）the scope（机会） for its being influenced by other neurons. To a large extend, the diversity（多样性）among neurons depends on the complexity, configurations and position of the dendrites.

14. Nervous system Introduction Classification of the neuron Bipolar neuron neuron pseudounipolar neuron According to the number Of their processes Multipolar neuron Sensory neuron Afferent neuron functionally neuron Motor neuron Efferent neuron Association neuron Intermediate neuron Small neuron Medium From 10～200um Large

15. dendrite nucleus Nissl body Bipolar neuron Axon hillock Multipolar neuron axon pseudounipolar neuron

16. Nervous system Introduction nervous fibers The longer processes of the neuron enveloped by the myelin sheath and the neurilemma are termed nerve fibers. The myelinated fibers are surrounded by a myelin sheath and neurilemma. The unmyelinated fibers are not, however, insulated（绝缘的）by a myelin sheath. Oligodendrocytes form myelin in the central nervous system while Schwann cells form myelin in peripheral nerves.

17. Nervous system Introduction Synapses (Ⅰ) Within the nervous system impulses are conducted from One part to another along a chain of neurons. The terminal arborizations of the axon of one neuron ramify in close contact with the cell body or dentrites, less frequently with axonic terminals of many others. concept of the synapse Concept Of the synapses Structures of the synapses Each synapse involves the close apposition of a presynaptic element with a postSynaptic element from which it is separated by a synaptic cleft. The presynaptic element contains numerous synaptic vesicles in which the chemical substance neurotransmitter is present.

18. Mitochondria Synaptic vesicle Synaptic cleft Presynaptic membrane Postsynapse membrane

19. Nervous system Introduction Synapses (Ⅱ) When an impulse arrives at the presynaptic element, the neurotransmitter Diffuses across the synaptic cleft and binds to receptor molecules in the postsynaptic membrane. As a result, the postsynaptic neuron is activated and impulse is conducted from one neuron to the others. The “chemical synapse” involving the release the transmitter substance is the most common type in the mammalian nervous system. The axon of lower motor neuron project through peripheral nerves to Muscle cells and terminate at a specialized portion of the muscle membrane Which are called neuromuscular junctions or motor end plates. The fibers Innervating the voluntary muscles of the body and limbs are the axon of large multipolar nerve cells located in anterior horn of the gray matter of The spinal cord. It has been estimated that each of these motor neurons Receives synaptic connections from the terminal axonal ramifications of Up to 1000 other nerve cells.

20. Nervous system Introduction • Ⅱ.The neuroglia • Neuroglia cells outnumber neurons in the central nervous system • 10:1. These cells appear to play a number of important roles, • including myelin formation, guidance of developing neurons, • maintenace of extracellular K+levels, and reuptake of transmitters • after synaptic activity. • The astrocytes • Astrocytes have many radiating processes, some of which end at • Nerve cells and others at capillaries. They are neuroectodermal in • Origin and may assist in the transfer of nutrients and metabolic • Products between the neurons and the blood.

21. Nervous system Introduction 2. The oligodendrocytes Oligodendrocytes are smaller and have fewer branching processes; they tend to lay in rows between nerve fibers and are concerned with the production and nourishment of myelin sheaths especially those surround axons in the central nervous system. They are neuroectodermal in origin. 3. The microglia Microglia are diminutive cells, which permeate the entire central nervous system. They are modified macrophages and form part Of the reticulo-endothelial system and are probably mesodermal In origin.

22. Nervous system Introduction Ⅲ. The reflex and reflex arc Reflexes are subconscious stimulus-esponse mechanism. The reflex arc, a linkage of afferent and efferent neurons, is defined as the entire neural pathway that is involved in a reflex. Several structures are involved in the reflex arc. These include the receptor whose stimulation initiates an impulse; the afferent neuron, which transmits the impulse through a peripheral nerve to the central nervous system

23. where the nerve synapses with a lower motor neuron or an interneuron up to one or more interneurons which relay the impulse to the efferent neurons; the efferent neuron which passes outward in the nerve and delivers the impulse to the effector and an effector. The interruption of this reflex arc at any point abolishes the response.

24. Nervous system Introduction In the CNS, the part of aggregations of nerve cell bodies Embedded in a network of delicate nerve processes is Known as gray matter, it has a gray color during the Fresh condition. Gray matter Terminology The cortex is the outmost layer of gray matter in the Cerebral hemispheres or in the cerebellum. The cell Bodies in the cortex are arranged in more or less well- Defined laminae or layers. Cortex Nerve cells with common shape, function and connections within the CNS are grouped together into nucleus. Nucleus Nerve cells with the same shape, function and connections Outside the CNS often are grouped together into ganglion. Ganglion

25. Nervous system Introduction In the CNS, the part that contains mainly bundles of nerve fibers is white matter and the white color is due To a rich content of fatty myelin sheath. Terminology White matter The medullary substance is a central core of white matter beneath the cortex of the cerebrum and cerebellum. Medullary substance In the CNS, a distinct collection of nerve with common origins, destinations and functions is referred to fasciculus, or tract. A funiculus is a collection of tracts having different origins, destinations and functions Funiculus (fasciculus) In the peripheral nervous system, the nerve fibers are grouped into bundles to form the nerve trunk called nerve. Most of nerves have a whitish appearance because of their myelin content. Nerve

26. 专业单词复习 Imagination 想像力 Versatility 多功能性 Potential capabilities 濽能 Efficiency 效率 Self-programming nature 自我谋略天性 Integration 整合 Coded information 编码信息 Chromatin 染色质 Nucleolus 核仁 Organelles 细胞器 Lysosomes 溶酶体 Mitochondria 线粒体 Lipofuscin 脂褐质

27. Neuromelanin （神经黑色素） • Catecholamine （儿茶酚胺） • Axoplasm （轴索原浆 • Axolemma （轴膜） • Lysosomes （溶酶体） • Pinocytotic （胞饮的） • Neurotoxic （神经毒素） • Protoplasmic (原浆) • Microtubule • Rough granular endoplasmic reticulum • Smooth granular endoplasmic reticulum • Myelin sheath