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1、 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
2、separate functional entity, is a part central and a part peripheral. BrainSpinal cordCranial nervesSpinal nervesNervous system as a wholeRough granularEndoplasmicreticulum Smooth granularEndoplasmic reticulumMicrotubuleSchwanns cellMyelin sheathAxoplasmic transportAxoplasmic transportAxoplasmic tran
3、sportClassification of the neuronneuronBipolar neuron pseudounipolar neuronMultipolar neuronAccording to the numberOf their processesneuronSensory neuronMotor neuron Association neuronAfferent neuronEfferent neuronIntermediate neuronfunctionallyneuronSmall Medium Large From 10200umBipolar neuronpseu
4、dounipolar neuronMultipolar neurondendritenucleusaxonNissl bodyAxon hillock nervous fibersThe longer processes of the neuron enveloped by themyelin sheath and the neurilemma are termed nerve fibers. The myelinated fibers are surrounded by a myelin sheath and neurilemma. The unmyelinated fibers are n
5、ot, however, insulated（绝缘的） by a myelin sheath. Oligodendrocytes form myelin in the central nervoussystem while Schwann cells form myelin in peripheral nerves.Synapses concept of the synapseWithin the nervous system impulses are conducted fromOne part to another along a chain of neurons. The termina
6、l arborizations of the axon of one neuron ramify in closecontact 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
7、 which it is separated by a synaptic cleft. The presynaptic element contains numerous synaptic vesicles in which the chemical substance neurotransmitter is present. ()Presynaptic membranePostsynapse membraneSynaptic cleftSynaptic vesicleMitochondria Synapses ()When an impulse arrives at the presynap
8、tic 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 su
9、bstance 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 membraneWhich are called neuromuscular junctions or motor end plates. The fibersInnervating the volun
10、tary 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 neuronsReceives synaptic connections from the terminal axonal ramifications of Up to 1000 other nerve cells.
11、.The neurogliaNeuroglia cells outnumber neurons in the central nervous system10:1. 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 astro
12、cytes Astrocytes have many radiating processes, some of which end at Nerve cells and others at capillaries. They are neuroectodermal inOrigin and may assist in the transfer of nutrients and metabolic Products between the neurons and the blood. 2. The oligodendrocytesOligodendrocytes are smaller and
13、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 microgliaMicroglia are diminutive cells, whic
14、h permeate the entire central nervous system. They are modified macrophages and form partOf the reticulo-endothelial system and are probably mesodermalIn origin. The reflex and reflex arcReflexes are subconscious stimulus-esponse mechanism. The reflex arc, a linkage of afferent and efferent neurons,
15、 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 systemwhere
16、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 effectorand an effector. The interruption of this reflex arc at any poi
17、nt abolishes the response. Terminology Gray matterIn the CNS, the part of aggregations of nerve cell bodiesEmbedded 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 h
18、emispheres or in the cerebellum. The cellBodies in the cortex are arranged in more or less well-Defined laminae or layers.Nucleus Nerve cells with common shape, function and connectionswithin the CNS are grouped together into nucleus.Ganglion Nerve cells with the same shape, function and connections
19、Outside the CNS often are grouped together into ganglion. Terminology White matterIn the CNS, the part that contains mainly bundles of nerve fibers is white matter and the white color is dueTo a rich content of fatty myelin sheath.Medullary substanceThe medullary substance is a central core of white
20、matter beneath the cortex of the cerebrum and cerebellum. Funiculus(fasciculus)In the CNS, a distinct collection of nerve with commonorigins, destinations and functions is referred to fasciculus, or tract. A funiculus is a collection of tractshaving 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.