nullNervous system1Nervous system1Department of Anatomy
Luzhou Medical College Edited by professor Xiaonull 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. BrainSpinal cordCranial
nervesSpinal
nervesNervous system as a wholenullThe nervous system possesses(拥有) particular importance in all organs and systems of human body. It modulates(调整)the different cells, tissues and organs, to complete certain activities or response(反射)
exterior stimulus(外界刺激) for the benefit of organism (机体)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(精心的详尽的) sensory system.
Nervous system Introduction nullReceptor 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 nullThe 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.(神经胶质)
The neuron(神经元)
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 nullRough granular
Endoplasmic
reticulum Smooth granular
Endoplasmic reticulumMicrotubuleSchwann’s cellMyelin sheathLysosomesLipofuscin脂褐质dendritenullEach neuron possesses a nucleated cell body and two types of processes(突起), an neuron, which conducts impulse away from the cell body, and one or more dendrites(树突) that conducts impulses towards the cell body. Both of these processes show marked morphological(形态学的) difference. The cell body serves as metabolic (代谢的)center of the entire unit and consists of a large, pale (灰白的)nucleus(胞核) and cytoplasm(细胞浆) ( perikaryon). Nervous system Introduction The structures of
the neuronnullThe 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(蛋白质合成). The organelles(细胞器) contained within the cytoplasm(细胞质 你) 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
nullThe 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 neuronnullThe 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.Nervous system Introduction The structures of
the neuronnull 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.Nervous system Introduction Axoplasmic transportnullThe 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.Nervous system Introduction Axoplasmic transportnullThe 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.Nervous system Introduction Axoplasmic transportnullNervous system Introduction Classification of the neuronneuronBipolar neuron pseudounipolar neuronMultipolar neuronAccording to the number
Of their processesneuronSensory neuronMotor neuron Association neuronAfferent neuronEfferent neuronIntermediate neuronfunctionallyneuronSmall Medium Large From 10~200umnullBipolar neuronpseudounipolar neuronMultipolar neurondendritenucleusaxonNissl bodyAxon hillocknullNervous system Introduction nervous fibersThe 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.nullNervous system Introduction Synapses concept
of the
synapseWithin 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
synapsesStructures of the synapsesEach 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. (Ⅰ)nullPresynaptic membranePostsynapse membraneSynaptic cleftSynaptic vesicleMitochondria nullNervous 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. nullNervous 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. nullNervous 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.nullNervous system IntroductionⅢ. 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 systemnullwhere 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.
nullNervous system Introduction Terminology Gray matterIn 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.Cortex 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.Nucleus Nerve cells with common shape, function and connections
within the CNS are grouped together into nucleus.Ganglion Nerve cells with the same shape, function and connections
Outside the CNS often are grouped together into ganglion.nullNervous system Introduction Terminology White matterIn 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.Medullary
substanceThe medullary substance is a central core of white
matter beneath the cortex of the cerebrum and
cerebellum. Funiculus
(fasciculus)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 functionsNerve 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.null 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nullNeuromelanin (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