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Capítulo 12 Tejido Nervioso II Biol 3791 UPR – Aguadilla
JA Cardé, Ph. D. © 2015 Pearson Education, Inc.
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An Introduction to the Nervous System
Learning Outcomes 12-1 Describe the anatomical and functional divisions of the nervous system. 12-2 Sketch and label the structure of a typical neuron, describe the functions of each component, and classify neurons on the basis of their structure and function. 12-3 Describe the locations and functions of the various types of neuroglia. © 2015 Pearson Education, Inc.
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An Introduction to the Nervous System
Learning Outcomes 12-4 Explain how the resting membrane potential is created and maintained. 12-5 Describe the events involved in the generation and propagation of an action potential. 12-6 Discuss the factors that affect the speed with which action potentials are propagated. © 2015 Pearson Education, Inc.
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An Introduction to the Nervous System
Learning Outcomes 12-7 Describe the structure of a synapse, and explain the mechanism involved in synaptic activity. 12-8 Describe the major types of neurotransmitters and neuromodulators, and discuss their effects on postsynaptic membranes. 12-9 Discuss the interactions that enable information processing to occur in neural tissue. © 2015 Pearson Education, Inc.
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12-3 Neuroglia Neuroglia Half the volume of the nervous system
Many types of neuroglia in CNS and PNS © 2015 Pearson Education, Inc.
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12-3 Neuroglia Four Types of Neuroglia in the CNS Ependymal cells
Cells with highly branched processes; contact neuroglia directly Astrocytes Large cell bodies with many processes Oligodendrocytes Smaller cell bodies with fewer processes Microglia Smallest and least numerous neuroglia with many fine-branched processes © 2015 Pearson Education, Inc.
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Figure 12-5 An Introduction to Neuroglia (Part 1 of 2).
are found in Central Nervous System contains Ependymal cells Astrocytes Oligodendrocytes Microglia Line ventricles (brain) and central canal (spinal cord); assist in producing, circulating, and monitoring cerebrospinal fluid Maintain blood–brain barrier; provide structural support; regulate ion, nutrient, and dissolved gas concentrations; absorb and recycle neurotransmitters; form scar tissue after injury Myelinate CNS axons; provide structural framework Remove cell debris, wastes, and pathogens by phagocytosis
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12-3 Neuroglia Ependymal Cells Form epithelium called ependyma
Line central canal of spinal cord and ventricles of brain Secrete cerebrospinal fluid (CSF) Have cilia or microvilli that circulate CSF Monitor CSF Contain stem cells for repair © 2015 Pearson Education, Inc.
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Figure 12-6a Neuroglia in the CNS.
Light micrograph showing the ependyma of the central canal of the spinal cord Ependymal cells Central canal Gray matter White matter Gray matter Central canal of spinal cord LM × 450
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12-3 Neuroglia Astrocytes Maintain blood–brain barrier (isolates CNS)
Create three-dimensional framework for CNS Repair damaged neural tissue Guide neuron development Control interstitial environment © 2015 Pearson Education, Inc.
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12-3 Neuroglia Oligodendrocytes Myelination
Increases speed of action potentials Myelin insulates myelinated axons Makes nerves appear white © 2015 Pearson Education, Inc.
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12-3 Neuroglia Oligodendrocytes Nodes and internodes
Internodes – myelinated segments of axon Nodes (also called nodes of Ranvier) Gaps between internodes Where axons may branch © 2015 Pearson Education, Inc.
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12-3 Neuroglia Myelination White matter Gray matter
Regions of CNS with many myelinated nerves Gray matter Unmyelinated areas of CNS © 2015 Pearson Education, Inc.
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12-3 Neuroglia Microglia Migrate through neural tissue
Clean up cellular debris, waste products, and pathogens © 2015 Pearson Education, Inc.
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Figure 12-6b Neuroglia in the CNS (Part 1 of 2).
Gray matter White matter CENTRAL CANAL Ependymal cells Gray matter Neurons Microglial cell
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Figure 12-6b Neuroglia in the CNS (Part 2 of 2).
Gray matter White matter Myelinated axons Internode Myelin (cut) Oligodendrocyte Astrocyte Axon Axolemma White matter Node Unmyelinated axon Basement membrane Capillary b A diagrammatic view of neural tissue in the CNS, showing relationships between neuroglia and neurons
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12-3 Neuroglia Neuroglia of the Peripheral Nervous System Ganglia
Masses of neuron cell bodies Surrounded by neuroglia Found in the PNS © 2015 Pearson Education, Inc.
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Figure 12-5 An Introduction to Neuroglia (Part 2 of 2).
are found in Peripheral Nervous System contains Satellite cells Schwann cells Surround neuron cell bodies in ganglia; regulate O2, CO2, nutrient, and neurotransmitter levels around neurons in ganglia Surround all axons in PNS; responsible for myelination of peripheral axons; participate in repair process after injury
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12-3 Neuroglia Neuroglia of the Peripheral Nervous System
Satellite cells Also called amphicytes Surround ganglia Regulate environment around neuron © 2015 Pearson Education, Inc.
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12-3 Neuroglia Neuroglia of the Peripheral Nervous System
Schwann cells Also called neurilemma cells Form myelin sheath (neurilemma) around peripheral axons One Schwann cell sheaths one segment of axon Many Schwann cells sheath entire axon © 2015 Pearson Education, Inc.
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segment (unmyelinated)
Figure 12-7a Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath (Part 1 of 2). Axon hillock Nucleus Myelinated internode Initial segment (unmyelinated) Dendrite Nodes Axon Axolemma Myelin covering internode A myelinated axon, showing the organization of Schwann cells along the length of the axon. a
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Figure 12-7a Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath (Part 2 of 2).
Schwann cell nucleus Myelin covering internode Neurilemma Axon Myelin sheath TEM × 20,600 A myelinated axon, showing the organization of Schwann cells along the length of the axon. a
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Figure 12-7b Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath (Part 1 of 2).
Schwann cell nucleus Neurilemma Axons Schwann cell #3 nucleus Axons b The enclosing of a group of unmyelinated axons by a single Schwann cell. A series of Schwann cells is required to cover the axons along their entire length.
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Figure 12-7b Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath (Part 2 of 2).
Neurilemma Axons Schwann cell #3 nucleus Axons Unmyelinated axons TEM × 27,625 The enclosing of a group of unmyelinated axons by a single Schwann cell. A series of Schwann cells is required to cover the axons along their entire length. b
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Figure 12-7c Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath.
A Schwann cell first surrounds a portion of the axon within a groove of its cytoplasm. 2 The Schwann cell then begins to rotate around the axon. 3 As the Schwann cell rotates, myelin is wound around the axon in multiple layers, forming a tightly packed membrane Schwann cell Myelin Axon Schwann cell cytoplasm c Stages in the formation of a myelin sheath by a single Schwann cell along a portion of a single axon.
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12-3 Neuroglia Neurons and Neuroglia Neurons perform:
All communication, information processing, and control functions of the nervous system Neuroglia preserve: Physical and biochemical structure of neural tissue Neuroglia are essential to: Survival and function of neurons © 2015 Pearson Education, Inc.
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12-3 Neuroglia Neural Responses to Injuries Wallerian degeneration
Axon distal to injury degenerates Schwann cells Form path for new growth Wrap new axon in myelin © 2015 Pearson Education, Inc.
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12-3 Neuroglia Nerve Regeneration in CNS
Limited by chemicals released by astrocytes that: Block growth Produce scar tissue © 2015 Pearson Education, Inc.
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Figure 12-8 Peripheral Nerve Regeneration after Injury (Part 1 of 4).
Fragmentation of axon and myelin occurs in distal stump. Axon Myelin Proximal stump Distal stump
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Figure 12-8 Peripheral Nerve Regeneration after Injury (Part 2 of 4).
Schwann cells form cord, grow into cut, and unite stumps. Macrophages engulf degener-ating axon and myelin. Macrophage Cord of proliferating Schwann cells
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Figure 12-8 Peripheral Nerve Regeneration after Injury (Part 3 of 4).
Axon sends buds into network of Schwann cells and then starts growing along cord of Schwann cells.
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Figure 12-8 Peripheral Nerve Regeneration after Injury (Part 4 of 4).
Axon continues to grow into distal stump and is enclosed by Schwann cells.
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