Nerve周围神经解剖

1、1会计学Nerve周围神经解剖周围神经解剖Morphology categoriesFunctional Categories(1). Classifications99% of neurons are interneuronsNeurites:Neurons can be classified by the number of neurites (axons and dendrites) that extend from the cell body .Cells can be unipolar, bipolar, or multipolar. Dendrites:Dendritic tree

2、s can vary widely between neurons. In the cerebral cortex, there are two types: pyramidal cells and stellate cells. Cells can also be classified by whether the dendrites have spines or not. Those that do are called spiny and those that dont are called aspinous. Pyramidal cells are spiny, while stell

3、ate cells can be spiny or aspinous.Connections:Neurons can be classified based on their connections to different tissue types in the body. Neurons that have connections to sensory surfaces, such as the skin, are primary sensory neurons. Neurons that form synapses with muscles are motorneurons. Howev

4、er, most neurons form connections with other neurons - these are the interneurons.Axon Length:Neurons can be differentiated based on how long of an axon they have. Neurons with very long axons that extend from on area of the brain to another are the Golgi Type I, while those with short, local circui

5、t axons are the Golgi Type II.Neurotransmitter:Aside from neuron morphology, neurons can also be classified based on their chemistry - the neurotransmitter(s) they release. For example, neurons that release acetylcholine are called cholinergic neuron.Nucleus: large, euchromatic, prominent nucleolus,

6、 usually center of somaNissl bodies: clumps of RERGolgi complex and mitochondriaNeurofilaments and microtubulesInclusions: melanin (rare)Cell membrane has specialized receptive areas, the subsynaptic membranes of synapses. Perikaryon (Cell Body) In gray matter and ganglia(2)StructuresNissl bodies: b

7、asophil, concentration of granular ER. In cell body and dendrites Neurofilaments: a variety of intermediate filament - are bundle into neurofibrils visible after silver impregnations in the cytoplasm.Skeleton and transportationinputs from over 200,000 other cells Purkinje cell of cerebellumMembrane

8、is the axolemma（轴膜）轴膜）, at its terminal/synapse which holds vesicles. May or may not be myelinated around the axolemma, sometimes recurrent back to near the soma. Has mitochondria, neurofilaments, microtubules, travelling vesicles, and, in some neurons, secretion droplets, in the axoplasm. Can be me

9、ter longContains axoplasm flowing from the axon hillock（轴丘）轴丘）.The initial segments,the triggering of the action potential retrograde transportationanterograde transportationTargettissueAxon transportationIn this image, used to quantify synapses, the proteins associated with synapses appear as blue

10、and red dots. Axodendritic synapseAxosomatic synapseAxoaxonic synapseStructure of synapseTypes of synapseLM:the axon terminal form bulbous swelling or terminal bouton.cleftreceptors1.presynaptic element presynaptic membranesynaptic vesicles with neurotransmitter, e.g., serotonin, acetylcholine, dopa

11、mine, etc. dense projectionsynapsin Imitochondria,SER, microtubule,microfilament.2.synaptic cleft 15-30nm3.postsynaptic element receptorAction potentials travel down the axon of the neuron to its end, the axon terminal(synaptic knob).The synaptic knob opens Ca2+ channels in the plasma membrane. The

12、influx of Ca2+ triggers the exocytosis of some of the vesicles. Their neurotransmitter is released into the synaptic cleft. The neurotransmitter molecules bind to receptors (ion channels) on the postsynaptic membrane.The Synapse Nerve cells coounicate with electrical impulses called nerve impulses.

13、A nerve impulse travels out from the nerve cell along a long extension called an axon. Eventually the impulse reaches the tip end of the axon, usually positioned very close to another neuron or to a muscle cell or gland. Axons, however, do not actually make direct contact with other neurons or with

14、large tissue. Instead, a narrow gap, 10 to 20 nanometers across, separates the axon tip and the target neuron or tissue. This junction of an axon with another cell is called a synapse. The membrane on the near (axon) side of the synapse is called the presynaptic membrane; the membrane on the far (re

15、ceiving) side of the synapse is called the postsynaptic membrane Figure 1 A synapse between two neurons.This micrograph clearly shows the space between the presynaptic and postsynaptic membranes, which is called the synaptic cleft.Events at the synapse.(a) When a nerve impulse reaches the end of an

16、axon, it releases a neurotransmitter into the synaptic space. The neurotransmitter molecules diffuse across the synapse and bind to receptors on the postsynaptic cell, a neuron in this case, passing the signal to that cell. Enzymes destroy the neurotransmitter molecules to prevent continuous stimula

17、tion of the postsynaptic cell. (b) A transmission electron micrograph of the tip of an axon filled with synaptic vesicles.(a) Many different axons synapse with the cell body of the postsynaptic neuron illustrated here. The summed influence of their input determines whether or not an action potential

18、 will be realized and a nerve impulse will be sent down the axon extending below. (b) Micrograph of a neuronal cell body with numerous synapses.4. NeurogliaFUNCTIONS OF NEUROGLIA(1) Structural support (especially the astrocytes in the CNS)(2) Participation in the blood-brain-barrier (astrocytes)(3)

19、Formation of the myelin sheath of axons(4) Isolation of junctional surfaces of synapses(5) Repair processes following damage or injury to nerves.pediclesLane Phalen, a multiple sclerosis sufferer, with her service dog. The dog helps her with daily activities that have become difficult because of MS.

20、 (Reproduced by permission of AP/Wide World Photos) Ependymal CellsLine ventricles of CNSCuboidal shapeSome are ciliated#Smaller axons unmyelinated.#Larger axons Myelinated by Schwann cells or oligodendrocytesThe long process of axon or dendrite enveloped by glia cellThe Schwann cells plasmalemma wi

21、nds and wraps around the axon.The layers of membrans unite and form mylin.The membrane propagates the action potential. insulatornodes of Ranvier. internodeMyelin sheath around the axolemma is interrupted at regular intervals to leave the axolemma bare at nodes of Ranvier.EM reveals myelin to have l

22、amellae with alternate dark and light lines, apparently concentric around the axon.Schmidt-Lanterman clefts: In each internode of myeline sheath, Schwann cell cytoplasm penetrates ,separations of the myelin lamellae, constituting the incisures of Schmidt-Lantermann, perhaps giving the myelin some fl

23、exibility and aiding molecular turnover.Nerve fibersNerve bundlesnervePeripheral NerveEpineuriumPerineuriumEndoneuriumEpineurium: several layers of fibroblasts with collagen in betweenNerve bundleEndoneurium: reticular fibers, fibroblasts and collagenPerineurium: 2-3 layers of fibroblast-like cells

24、with some collagenFree nerve endingsMeissners corpuscles: tactile mechanoreceptors found in dermal papilla. Pacinian corpuscles: mechanoreceptors common in the dermis of thick skin. Neuromuscular spindle6. Nerve EndingsEfferent nerve endings (motor)Afferent nerve endings (sensory)Motor unitUnencapsu

25、lated endingsEncapsulated endingsFree nerve endings: sensory endings in deep layers of epidermis and papillary layer of dermis; responsive to pain, temperature, movement (associated with hair follicles). Tactile (Meissner) corpuscle: ovoid, a stack of flattened cells (modified Schwann cells) intertw

26、ined with nerve endings and surrounded by a CT capsule; papillary layer of the skin (e.g., fingertips); responsive to touch; Lamellar (Pacinian) corpuscle: big, round or oval, the nerve ending and concentric layers of flat cells; hypodermis, mucous membranes; responsive to pressure; Muscle spindle:

27、a double tapered object, lying between and among myofibers, is an important proprioceptor, the device for body position, tactile input, joint movement, etc., to determine how much tension is being generated by the myofibers; to then report that back to the CNS. Neuromuscular junctionMotor end plates

28、 or neuromuscular junctions are specialized structures at the ends of motor axons and are the sites of innervation of skeletal muscle fibers. Motor unit: A single motor nerve and all the muscle fibers it innervates.(a) The sarcolemma is depressed into a trough and invaginates into many small seconda

29、ry synaptic clefts. It has ACh receptors. (b) The swollen ending of the axon lies in the trough. (c) The axon terminal has Mt, and vesicles(d) Schwann cells cover the axon and its terminal bag. For a long time it was believed that only the young brain can undergo such structural changes. However, re

30、cent findings have shown that the adult brain can also grow, reorganize and form new connection between neurons. Thus, the research on neuroplasticity points to the brain as a growing organ that responds structurally not only to the demands of the external environment, but also to internally generat

31、ed states, including aspects of consciousness. Neuronal plasticity the ability of neurons in the brain to change in response to experience, has been one of the most exciting discoveries in neuroscience. Neural stem cell(NSC)Step One - Neural Stem CellsNeural stem cells (NSC) are cells that can matur

32、e into any type of cell and can continually renew themselves.Step Two - Progenitor CellsProgenitor cells do not themselves perform active neurological functions but are “reserve” cells that become activated when mature nerve tissue is damaged. The progenitor cells can develop into mature active cell

33、s in order to repair or replace the damaged tissue. Progenitor cells include:GRP: Glial-Restricted PrecursorsNRP: Neuron Restricted PrecursorsO-2A/OPC: Oligodendrocyte-Type-2 AstrocytesStep Three - Mature Nerve CellsAstrocytes Neurons are the primary nerve cells in the nervous system that process an

34、d transmit information via electrical signals.OligodendrocytesAlzheimers disease (AD): also known simply as Alzheimers, is a neurodegenerative disease characterized by progressive cognitive deterioration together with declining activities of daily living and neuropsychiatric symptoms or behavioral c

35、hanges. The most striking early symptom is loss of short-term memory (amnesia), which usually manifests as minor forgetfulness that becomes steadily more pronounced with illness progression, with relative preservation of older memories. As the disorder progresses, cognitive (intellectual) impairment

36、 extends to the domains of language (aphasia), skilled movements (apraxia), recognition (agnosia), and functions such as decision-making and planning get impaired. President Reagan Objectives for Nervous Tissues1. to classify the neurons by characteristics of form and function.2. to describe the for

37、m and function of the structures found within typical nerve cell bodies.3. to describe the form and function of typical nerve cell processes (e.g., axons and dendrites).4. to define and/or describe the form and function of Synapses and neuroglial cells.5. to compare and contrast myelination of peripheral versus central nervous tissues.6. to describe the organization and structure of peripheral nerves. Membrane is the axolemma（轴膜）轴膜）, at its terminal/synapse which holds vesicles. Ma