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Neurons and Nervous Systems
- 2. 2 Neurons & Nervous SyNeurons & Nervous Sy OutlineOutline EVOLUTION OF THE NERVOUS SYSTEMEVOLUTION OF THE NERVOUS SYSTEM Gradual increase in the complexity of the nervous systemGradual increase in the complexity of the nervous system All vertebrates have a well-developed brainAll vertebrates have a well-developed brain NERVOUS TISSUENERVOUS TISSUE NeuronsNeurons Nerve impulseNerve impulse BRAIN AND SPINAL CORDBRAIN AND SPINAL CORD Spinal cordSpinal cord CerebrumCerebrum Sensory inputSensory input Motor controlMotor control HomeostasisHomeostasis Limbic systemLimbic system PERIPHERAL NERVOUS SYSTEMPERIPHERAL NERVOUS SYSTEM NervesNerves Somatic systemSomatic system Autonomic systemAutonomic system
- 3. 3 Neurons & Nervous SyNeurons & Nervous Sy Invertebrate Nervous OrganizationInvertebrate Nervous Organization HydrasHydras Nerve net composed of neurons in contactNerve net composed of neurons in contact with one anotherwith one another Also in contact with contractileAlso in contact with contractile epitheliomuscular cellsepitheliomuscular cells PlanariansPlanarians Ladderlike nervous systemLadderlike nervous system Cephalization - a concentration of gangliaCephalization - a concentration of ganglia and sensory receptors in the headand sensory receptors in the head Annelids, Arthropods and MolluscsAnnelids, Arthropods and Molluscs Complex animalsComplex animals True nervous systemsTrue nervous systems
- 4. 4Evolution of the Nervous System
- 5. 5 Neurons & Nervous SyNeurons & Nervous Sy Vertebrate Nervous OrganizationVertebrate Nervous Organization Central nervous systemCentral nervous system Develops from an embryonic dorsalDevelops from an embryonic dorsal tubular nerve cordtubular nerve cord Cephalization and bilateral symmetryCephalization and bilateral symmetry result in several paired sensory receptorsresult in several paired sensory receptors Vertebrate brain is organized into threeVertebrate brain is organized into three areasareas HindbrainHindbrain MidbrainMidbrain Forebrain
- 6. 6 Neurons & Nervous SyNeurons & Nervous Sy Human Nervous SystemHuman Nervous System Nervous system has three specificNervous system has three specific functionsfunctions Receiving sensory inputReceiving sensory input Performing integrationPerforming integration Generating motor outputGenerating motor output
- 7. 7Organization of the Human Nervous System
- 8. 8 Neurons & Nervous SyNeurons & Nervous Sy Human Nervous SystemHuman Nervous System Central nervous system (CNS)Central nervous system (CNS) Includes the brain and spinal cordIncludes the brain and spinal cord Lies in the midline of the bodyLies in the midline of the body The peripheral nervous system (PNS)The peripheral nervous system (PNS) Contains cranial nerves and spinal nervesContains cranial nerves and spinal nerves thatthat Gather info from sensors and conductGather info from sensors and conduct decisions to effectorsdecisions to effectors Lies outside the CNSLies outside the CNS
- 9. 9 Neurons & Nervous SyNeurons & Nervous Sy Nervous TissueNervous Tissue NeuronsNeurons Cell body contains nucleusCell body contains nucleus Dendrites receive signals from sensoryDendrites receive signals from sensory receptorsreceptors Axon conducts nerve impulsesAxon conducts nerve impulses Covered by myelin sheathCovered by myelin sheath Any long axon is also called a nerve fiberAny long axon is also called a nerve fiber
- 10. 10 Neurons & Nervous SyNeurons & Nervous Sy Types of NeuronsTypes of Neurons Motor NeuronsMotor Neurons Accept nerve impulses from the CNSAccept nerve impulses from the CNS Transmit them to muscles or glandsTransmit them to muscles or glands Sensory NeuronsSensory Neurons Accept impulses from sensory receptorsAccept impulses from sensory receptors Transmit them to the CNSTransmit them to the CNS InterneuronsInterneurons Convey nerve impulses between variousConvey nerve impulses between various parts of the CNSparts of the CNS
- 11. 11Neuron Anatomy
- 12. 12 Neurons & Nervous SyNeurons & Nervous Sy Nerve Impulses:Nerve Impulses: Resting PotentialResting Potential Resting PotentialResting Potential The membrane potential (voltage) whenThe membrane potential (voltage) when the axon is not conducting an impulsethe axon is not conducting an impulse The inside of a neuron is more negativeThe inside of a neuron is more negative than the outside -65 mVthan the outside -65 mV Due in part to the action of the sodium-Due in part to the action of the sodium- potassium pumppotassium pump
- 13. 13 Neurons & Nervous SyNeurons & Nervous Sy Action PotentialAction Potential An action potential is generated only afterAn action potential is generated only after a stimulus larger than the thresholda stimulus larger than the threshold Gated channel proteinsGated channel proteins Suddenly allows sodium to pass throughSuddenly allows sodium to pass through the membranethe membrane Another allows potassium to pass throughAnother allows potassium to pass through other directionother direction
- 14. 14Resting and Action Potential of the Axonal Membrane
- 15. 15 Neurons & Nervous SyNeurons & Nervous Sy Propagation of Action PotentialsPropagation of Action Potentials In myelinated fibers, an action potentialIn myelinated fibers, an action potential at one node causes an action potentialat one node causes an action potential at the next nodeat the next node Saltatory (jumping) ConductionSaltatory (jumping) Conduction Conduction of a nerve impulse is an all-Conduction of a nerve impulse is an all- or-nothing eventor-nothing event Intensity of signal is determined by howIntensity of signal is determined by how many impulses are generated within amany impulses are generated within a given time spangiven time span
- 16. 16 Neurons & Nervous SyNeurons & Nervous Sy Transmission Across a SynapseTransmission Across a Synapse A synapse is a region where neuronsA synapse is a region where neurons nearly touchnearly touch Small gap between neurons is theSmall gap between neurons is the synaptic cleftsynaptic cleft Transmission across a synapse is carriedTransmission across a synapse is carried out by neurotransmittersout by neurotransmitters Sudden rise in calcium at end of oneSudden rise in calcium at end of one neuronneuron Stimulates synaptic vesicles to mergeStimulates synaptic vesicles to merge with the presynaptic membranewith the presynaptic membrane Neurotransmitter molecules are releasedNeurotransmitter molecules are released
- 18. 18 Neurons & Nervous SyNeurons & Nervous Sy Synaptic IntegrationSynaptic Integration A single neuron is on the receiving end ofA single neuron is on the receiving end of Many excitatory signals, andMany excitatory signals, and Many inhibitory signalsMany inhibitory signals IntegrationIntegration The summing of signals fromThe summing of signals from Excitatory signals, andExcitatory signals, and Inhibitory signalsInhibitory signals
- 20. 20 Neurons & Nervous SyNeurons & Nervous Sy CNS: Brain and Spinal CordCNS: Brain and Spinal Cord Spinal cord and brain are wrapped inSpinal cord and brain are wrapped in three protective membranes, meningesthree protective membranes, meninges Spaces between meninges are filled withSpaces between meninges are filled with cerebrospinal fluidcerebrospinal fluid Fluid is continuous with that of centralFluid is continuous with that of central canal of spinal cord and the ventricles ofcanal of spinal cord and the ventricles of the brainthe brain
- 21. 21 Neurons & Nervous SyNeurons & Nervous Sy Spinal CordSpinal Cord The spinal cord has two main functionsThe spinal cord has two main functions Center for many reflex actionsCenter for many reflex actions Means of communication between theMeans of communication between the brain and spinal nervesbrain and spinal nerves The spinal cord is composed of grayThe spinal cord is composed of gray matter and white mattermatter and white matter Cell bodies and short unmyelinated fibersCell bodies and short unmyelinated fibers give the gray matter its colorgive the gray matter its color Myelinated long fibers of interneuronsMyelinated long fibers of interneurons running in tracts give white matter itsrunning in tracts give white matter its colorcolor
- 22. 22 Neurons & Nervous SyNeurons & Nervous Sy The BrainThe Brain Cerebrum is the largest portion of theCerebrum is the largest portion of the brain in humansbrain in humans Communicates with, and coordinates theCommunicates with, and coordinates the activities of, the other parts of the brainactivities of, the other parts of the brain Longitudinal fissure divides into left andLongitudinal fissure divides into left and right cerebral hemispheresright cerebral hemispheres
- 24. 24 Neurons & Nervous SyNeurons & Nervous Sy Cerebral CortexCerebral Cortex A thin but highly convoluted outer layer ofA thin but highly convoluted outer layer of gray mattergray matter Covers the cerebral hemispheresCovers the cerebral hemispheres Contains motor areas and sensory areasContains motor areas and sensory areas as well as association areasas well as association areas Primary motor area is in the frontal lobePrimary motor area is in the frontal lobe just ventral to central sulcusjust ventral to central sulcus Primary somatosensory area is just dorsalPrimary somatosensory area is just dorsal to central sulcusto central sulcus
- 25. 25The Lobes of a Cerebral Hemisphere
- 26. 26 Neurons & Nervous SyNeurons & Nervous Sy CerebrumCerebrum Rest of cerebrum is composed of whiteRest of cerebrum is composed of white mattermatter Descending tracts communicate withDescending tracts communicate with lower brain centerslower brain centers Ascending tracts send sensoryAscending tracts send sensory information to primary somatosensoryinformation to primary somatosensory areaarea Basal nucleiBasal nuclei Integrate motor commandsIntegrate motor commands Ensure that the proper muscle groups areEnsure that the proper muscle groups are
- 27. 27 Neurons & Nervous SyNeurons & Nervous Sy DiencephalonDiencephalon A region encircling the third ventricleA region encircling the third ventricle Consists of hypothalamus and thalamusConsists of hypothalamus and thalamus Hypothalamus forms floor of the thirdHypothalamus forms floor of the third ventricleventricle Thalamus consists of two masses of grayThalamus consists of two masses of gray matter located in the sides and roof of thematter located in the sides and roof of the third ventriclethird ventricle Pineal glandPineal gland Also located in the diencephalonAlso located in the diencephalon
- 28. 28 Neurons & Nervous SyNeurons & Nervous Sy CerebellumCerebellum Separated from the brain stem by theSeparated from the brain stem by the fourth ventriclefourth ventricle Receives sensory input from the eyes,Receives sensory input from the eyes, ears, joints, and musclesears, joints, and muscles Sends motor impulses out the brain stemSends motor impulses out the brain stem to the skeletal musclesto the skeletal muscles
- 29. 29 Neurons & Nervous SyNeurons & Nervous Sy Brain StemBrain StemContains the midbrain, the pons, and theContains the midbrain, the pons, and the medulla oblangatamedulla oblangata MidbrainMidbrain Acts as a relay station for tracts passingActs as a relay station for tracts passing betweenbetween The cerebrum, andThe cerebrum, and The spinal cord or cerebellumThe spinal cord or cerebellum PonsPons Helps regulate breathing and headHelps regulate breathing and head movementsmovements Medulla oblongataMedulla oblongata Contains reflex centers for vomiting,Contains reflex centers for vomiting, coughing, sneezing, hiccuping, andcoughing, sneezing, hiccuping, and
- 30. 30 Neurons & Nervous SyNeurons & Nervous Sy Limbic SystemLimbic System Complex network of tracts and “nuclei”Complex network of tracts and “nuclei” Incorporates medial portions ofIncorporates medial portions of The cerebral lobes,The cerebral lobes, The subcortical basal nuclei, andThe subcortical basal nuclei, and The dicenephalonThe dicenephalon Integrates higher mental functions andIntegrates higher mental functions and primitive emotionsprimitive emotions HippocampusHippocampus AmygdalaAmygdala
- 32. 32 Neurons & Nervous SyNeurons & Nervous Sy Peripheral Nervous SystemPeripheral Nervous System Somatic systemSomatic system Contains cranial nerves and spinal nervesContains cranial nerves and spinal nerves Gather info from sensors and conduct decisions to effectorsGather info from sensors and conduct decisions to effectors Controls the skeletal musclesControls the skeletal muscles Conscious of its activityConscious of its activity Autonomic systemAutonomic system Controls the smooth muscles, cardiac muscles, and glandsControls the smooth muscles, cardiac muscles, and glands Usually unaware of its actionsUsually unaware of its actions Divided into two divisionsDivided into two divisions Sympathetic divisionSympathetic division Parasympathetic divisionParasympathetic division
- 34. 34A Reflex Arc Showing the Path of a Spinal Reflex
- 35. 35 Neurons & Nervous SyNeurons & Nervous Sy Autonomic SystemAutonomic System Regulates activity of cardiac and smoothRegulates activity of cardiac and smooth muscle, and glandsmuscle, and glands Divided into sympathetic andDivided into sympathetic and parasympathetic divisionsparasympathetic divisions Function automatically and usually in anFunction automatically and usually in an involuntary mannerinvoluntary manner Innervate all internal organsInnervate all internal organs Utilize two neurons and one ganglion forUtilize two neurons and one ganglion for each impulseeach impulse
- 37. 37 Neurons & Nervous SyNeurons & Nervous Sy Sympathetic andSympathetic and Parasympathetic DivisionsParasympathetic Divisions Sympathetic divisionSympathetic division Especially important during fight or flightEspecially important during fight or flight responsesresponses Accelerates heartbeat and dilates bronchiAccelerates heartbeat and dilates bronchi Parasympathetic divisionParasympathetic division Promotes all internal responsesPromotes all internal responses associated with a relaxed stateassociated with a relaxed state Promotes digestion and retards heartbeatPromotes digestion and retards heartbeat
- 38. 38 Neurons & Nervous SyNeurons & Nervous Sy ReviewReview EVOLUTION OF THE NERVOUS SYSTEMEVOLUTION OF THE NERVOUS SYSTEM Gradual increase in the complexity of the nervous systemGradual increase in the complexity of the nervous system All vertebrates have a well-developed brainAll vertebrates have a well-developed brain NERVOUS TISSUENERVOUS TISSUE NeuronsNeurons Nerve impulseNerve impulse BRAIN AND SPINAL CORDBRAIN AND SPINAL CORD Spinal cordSpinal cord CerebrumCerebrum Sensory inputSensory input Motor controlMotor control HomeostasisHomeostasis Limbic systemLimbic system PERIPHERAL NERVOUS SYSTEMPERIPHERAL NERVOUS SYSTEM NervesNerves Somatic systemSomatic system Autonomic systemAutonomic system
- 39. Neurons & Nervous Ending Slide Chapter 39