Anatomy and Physiology - Nervous Tissue - Quick Guides

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Study GuideAnatomy and Physiology–Nervous Tissue1.Neuroglia (Glial Cells)Neuroglia, orglia, are special cells thatsupport, protect, and help neurons function properly.Unlike neurons, glial cells do not mainly focus on sending nerve impulses. Instead, they act like the“helper team” of the nervous system.Neuroglia are found in both:•theCNS(Central Nervous System: brain and spinal cord)•thePNS(Peripheral Nervous System: nerves outside the CNS)1.1Neuroglia in the CNS (4 Types)1. AstrocytesAstrocytes have many branching extensions, giving them astar-shapedappearance.Main function:•maintain theion balancearound neurons•control exchange of materials betweenblood vessels and neurons2. OligodendrocytesOligodendrocytes have fewer processes than astrocytes.Main function:•wrap their cytoplasmic processes around neurons to form amyelin sheathThemyelin sheathacts as an insulating layer that helps nerve signals travel faster.3. MicrogliaMicroglia act like immune-defense cells in the CNS.

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Study GuideMain function:•they arephagocytic macrophages•they protect by engulfing:omicroorganismsodamaged cellsocellular debris4. Ependymal CellsEpendymal cells form a lining inside the CNS.Main features:•they line thefluid-filled cavitiesof the brain and spinal cord•many areciliated, helping with movement of fluid1.2Neuroglia in the PNS (2 Types)1. Schwann Cells (Neurolemmocytes)Schwann cells wrap around axons in the PNS.Main function:•form amyelin sheatharound axons•provide the same role in the PNS thatoligodendrocytesprovide in the CNS2. Satellite CellsSatellite cells are found inganglia(clusters of neuron cell bodies in the PNS).Main function:•surround and support thecell bodies of neurons

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Study Guide2.Quiz: Neuroglia1. QuestionGlial cells that form a myelin sheath around axons in the CNS are called __________.Answer Choices• microglia• astrocytes• oligodendrocytesCorrect AnsweroligodendrocytesWhy This Is CorrectIn thecentral nervous system (CNS),oligodendrocytesform themyelin sheatharound neuronaxons.Myelin acts like insulation and helps signals travel faster.2. QuestionWhich glial cells act as phagocytes to protect CNS neurons?Answer Choices• microglia• astrocytes• oligodendrocytesCorrect Answermicroglia

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Study GuideWhy This Is CorrectMicrogliaare the “immune cells” of the CNS.They act asphagocytes, meaning they clean up debris and destroy pathogens to protect neurons.3. QuestionWhich statement is true?Answer Choices• Neurolemmocytes form a myelin sheath around axons in the PNS, and oligodendrocytes form amyelin sheath around axons in the CNS.• Astrocytes form a myelin sheath around axons in both the PNS and CNS.• Schwann cells are the same as oligodendrocytes, and both act as phagocytic cells.Correct AnswerNeurolemmocytes form a myelin sheath around axons in the PNS, and oligodendrocytes form amyelin sheath around axons in the CNS.Why This Is Correct•Neurolemmocytes (Schwann cells)= myelin in thePNS•Oligodendrocytes= myelin in theCNSAstrocytes do not make myelin, and Schwann cells are not the same as oligodendrocytes.4. QuestionWhich glial cell is found in the peripheral nervous system (PNS)?Answer Choices• ependymal cells• neurolemmocytes (Schwann cells)• oligodendrocytes

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Study GuideCorrect Answerneurolemmocytes (Schwann cells)Why This Is CorrectNeurolemmocytes (Schwann cells)are found in thePNSand help form the myelin sheath aroundaxons outside the brain and spinal cord.5. QuestionThe myelin sheath wraps around the __________ of a neuron to provide insulation.Answer Choices• axon• soma• dendriteCorrect AnsweraxonWhy This Is CorrectThemyelin sheathcovers theaxon, helping electrical signals travel faster and protecting the nervefiber.3.MyelinationMyelinationis the process of forming amyelin sheath, which is a fatty insulating covering around anaxon.This insulation helps nerve impulses travelfasterand more efficiently, and it also prevents signalsfrom interfering with nearby neurons.Myelination happens differently in the:

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Study GuidePNS (Peripheral Nervous System)CNS (Central Nervous System)3.1Myelination in the PNS (Schwann Cells)In thePNS, the myelin sheath is formed bySchwann cells.How Schwann cells form myelinEach Schwann cell wraps around an axonmany times.This creates a thick, multilayered insulation called themyelin sheath.NeurilemmaThe final outer wrap of the Schwann cell membrane is called theneurilemma.Unlike the tight myelin layers, the neurilemma is looser and contains:•the Schwann cell’snucleus•cytoplasm•organelles3.2Nodes of Ranvier (Neurofibral Nodes)The myelin sheath is not continuous along the entire axon.Small gaps occur between Schwann cells, leaving uninsulated areas called:•nodes of Ranvier(also called neurofibral nodes)3.3Saltatory Conduction (“Jumping” Signals)Because myelin insulates the axon, the nerve impulse cannot travel smoothly along the entiresurface.Instead:•electrical current moves through the inside of the axon•action potentials happen only at thenodes of Ranvier

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Study GuideThis makes the signal appear to “jump” from node to node.This fast method is calledsaltatory conduction.Why Myelin is UsefulThe myelin sheath helps by:•speeding up impulse conduction•insulating nearby nerve fibers•preventing one nerve impulse from crossing over to a neighboring axon3.4Myelination in the CNS (Oligodendrocytes)In theCNS, myelin is formed byoligodendrocytes, not Schwann cells.How oligodendrocytes form myelinAn oligodendrocyte sends out a process that wraps around an axon to form myelin.One important difference from the PNS:A single oligodendrocyte can myelinatemany axons, usingmultiple processes.White Matter vs Gray MatterThe brain and spinal cord havewhite matterandgraymatter, based on the presence of myelin.White MatterWhite matter contains:myelinated axonsThe white color comes from themyelin sheath.

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Study GuideGray MatterGray matter contains:•neuroncell bodies•dendrites•axon terminals•unmyelinated axons•neurogliaGray matter is where most processing and neuron communication occurs.4.Quiz: Myelination1. QuestionWhich of the following best describes saltatory conduction?Answer Choices• An impulse moves from one neurofibril node to the next neurofibril node along the length of an axon.• An impulse moves from one Schwann cell to the next Schwann cell along the length of the axon.• An impulse moves from the axon of one neuron, across the synapse, and to the dendrite of the nextneuron.Correct AnswerAn impulse moves from one neurofibril node to the next neurofibril node along the length of anaxon.Why This Is CorrectSaltatory conductionmeans the nerve impulse “jumps” from onenode (node of Ranvier)to thenext.This makes conductionmuch fasterthan traveling continuously down the whole axon.

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Study Guide2. QuestionThe neurofibril nodes are areas of the axon that __________.Answer Choices• consist of nuclei for the neuron• are covered by the neurolemmocytes• are not covered by the neurolemmocytesCorrect Answerare not covered by the neurolemmocytesWhy This Is CorrectNeurofibril nodes (nodes of Ranvier) are gaps in the myelin sheath.They are the spots where the axon isnot coveredby Schwann cells, allowing the impulse to “jump”node to node.3. QuestionIf a neurolemmocyte makes 10 wraps around an axon, the nucleus of the neurolemmocyte can befound in wrap number __________.Answer Choices• 1• 5• 10Correct Answer1Why This Is CorrectThe nucleus and cytoplasm of the Schwann cell stay in theoutermost layer(the first wrap).The inner wraps become mostly myelin, which is tightly packed and doesn’t contain the nucleus.

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Study Guide5.Transmission of Nerve ImpulsesA nerve impulse travels along a neuron because ofelectrical changes across the neuron’s cellmembrane.These changes happen when ions move in and out of the neuron.The neuron’s membrane acts like an electrical barrier, and when it is not being stimulated, it stays in aspecial charged condition calledpolarization.5.1Polarization and Resting Membrane PotentialAnunstimulated neuronispolarized, meaning:•the outside and inside of the membrane have different electrical charges•the inside isnegativecompared to the outsideThis charge difference is maintained mainly by ion concentration differences:•moresodium ions (Na⁺)are keptoutsidethe cell•morepotassium ions (K⁺)are keptinsidethe cell5.2Ion Leakage and the Na⁺/K⁺PumpEven at rest, Na⁺and K⁺constantly “leak” across the membrane throughleakage channels.To fix this leakage and maintain the proper ion balance, the membrane usesNa⁺/K⁺pumps.These pumps actively restore:•Na⁺back to the outside•K⁺back to the inside5.3Why the Inside Stays More NegativeThe most important reason for theresting membrane potentialis that:the resting membrane is much more permeable toK⁺than toNa⁺.

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