Y khoa, dược - The nervous system

25The Nervous System25-2Learning Outcomes25.1 Explain the difference between the central nervous system and the peripheral nervous system.25.2 Describe the functions of the nervous system.25.3 Describe the structure of a neuron.25.4 Describe the function of a nerve impulse and how a nerve impulse is created.25-3Learning Outcomes (cont.)25.5 Describe the structure and function of a synapse. 25.6 Describe the function of the blood-brain barrier.25.7 Describe the structure and functions of meninges.25.8 Describe the structure and functions of the spinal cord.25-4Learning Outcomes (cont.)25.9 Describe the location and function of cerebrospinal fluid.25.10 Define reflex and list the parts of a reflex arc.25.11 List the major divisions of the brain and give the general functions of each.25.12 Explain the functions of the cranial and spinal nerves.25-5Learning Outcomes (cont.)25.13 Describe the differences between the somatic nervous system and autonomic nervous system.25.14 Explain the two divisions of the autonomic nervous system.25.15 Describe the causes, signs and symptoms, and treatments of various diseases and disorders of the nervous system. 25-6Introduction Highly complex system of two partsCentral nervous system (CNS)Peripheral nervous system (PNS)Controls all other organ systems and is important for maintaining balance within those systemsDisorders are numerous and often difficult to diagnose and treat25-7General Functions of the NSCNSBrainSpinal cordPNSPeripheral nervesTwo sectionsSomatic nervous system (SNS)Skeletal or voluntary musclesAutonomic nervous system (ANS)Automatic functions25-8General Functions (cont.)Three types of neuronsAfferent or sensory nervesSensory information from environment or inside body to CNS for interpretationEfferent or motor nervesImpulses from CNS to PNS to allow for movement or actionInterneurons Interpretive neurons between afferent and efferent nerves in the CNS25-9Apply Your KnowledgeMatch the following:___ Somatic nervous system A. Motor nerves___ Autonomic nervous system B. Governs skeletal or voluntary  muscles___ Afferent nerves C. Governs respiratory and GI systems___ Efferent nerves D. Go-betweens or interpreters___ Interneurons E. Sensory nervesCAEDBANSWER:Correct!25-10Neuron Structure Functional cells of NSTransmit electrochemical messages called nerve impulses to Other neurons Effectors (muscles or glands) 25-11Neuron Structure (cont.)Neurons lose their ability to divide If destroyed, not replacedNeuralgiaSupport cells for neurons that can divideAstrocytes – anchor blood vessels to nervesMicroglia – act as phagocytesOligodendrocytes – assist with production of myelin sheath25-12Neuron Structure (cont.)Neurons have a cell body and processes called nerve fibers that extend from the cell body. Dendrites – short Receive nerve impulses for the neuronAxons – long Send nerve impulses away from the cell body25-13Neuron Structure (cont.)White matter – axons with myelin sheath Schwann cellsWrap around some axonsCell membranes contain myelinMyelin insulates axons and enables axons to send nerve impulses more quicklyGray matter – axons without myelin sheath Schwann cellsAxonDendrites25-14Apply Your KnowledgeTrue or False:___ Effectors are neurons.___ Neurons can reproduce.___ Astrocytes anchor blood vessels to nerve cells.___ Microglia act as phagocytes.___ Oligodendrocytes are reproductive cells.___ Repolarization is the return to the resting state.FTTFTFANSWER:They are the muscles or glands.Neurons cannot reproduce.They take part in myelin production.GOOD JOB!25-15Nerve Impulse Membrane potential Neuron cell membrane at rest is in a polarized stateInside of cell membrane is negativeOutside of cell membrane is positive due to more Na+ and K+ As Na+ and K+ move into the cell, the membrane becomes depolarizedInside becomes more positiveAction potential (nerve impulse) is created Repolarization occurs when K+ and later Na+ move to the outside of the cell membraneReturn of the cell to polarized (resting) state25-16Nerve Impulse (cont.)Impulse travels down axon to synaptic knob Vesicles or small sacs in synaptic knob Produce chemicals called neurotransmittersNeurotransmitters are released by synaptic knobAllow impulse transmission to postsynaptic structuresDendritesCell bodiesAxons of other neurons25-17Nerve Impulse (cont.)Functions of neurotransmittersCause muscles to contract or relaxCause glands to secrete products Activate or inhibit neurons25-18Apply Your KnowledgeWhat is the function of neurotransmitters?ANSWER: Neurotransmitters cause muscles to contract or relax, cause glands to secret products, activate neurons to send nerve impulses, or inhibit neurons from sending them.Right!25-19Central Nervous SystemIncludes the spinal cord and brain Blood-brain barrierProtects layers of the membranes of the CNSFormed by tight capillariesPrevents unwanted substances from entering the CNS tissuesInflammation can make more permeable25-20Central Nervous System (cont.)Meninges –protect brain and spinal cordDura mater Tough outer layerArachnoid mater Middle layer (web-like)Pia mater Innermost and most delicateDirectly on top of brain and spinal cordHolds blood vessels on the surface of these structures25-21Central Nervous System (cont.)Epidural space Above dura materSubdural spaceBelow dura materSubarachnoid space Between arachnoid mater and pia materContains cerebrospinal fluid (CSF) Cushions CNS25-22Spinal CordSlender structure continuous with the brain Descends into the vertebral canal and ends around the level of the first or second lumbar vertebra31 spinal segments: 8 cervical segments 12 thoracic segments 5 lumbar segments 5 sacral segments1 coccygeal segment  25-23Spinal Cord (cont.)Cervical enlargementMotor neurons that controlmuscles of the armsLumbar enlargementMotor neurons that control muscles of the legs25-24Spinal Cord (cont.)Gray matter Inner tissue with darker color Contains neuron cell bodies and their dendritesDivisions are called hornsCentral canal runs down the entire length of the spinal cord through the center of the gray matter Spinal Cord/Nerve25-25Spinal Cord (cont.)White matter Outer tissue Contains myelinated axonsDivisions are called columns (funiculi)Columns contain groups of axons called nerve tracts Spinal Cord/NerveSpinal Cord/Nerve25-26Previous SlideSpinal Cord (cont.)25-27Spinal Cord (cont.)One function of the spinal cord is to carry sensory information to and from the brain Ascending tracts Carry sensory information up to the brainDescending tracts Carry motor information down from the brain to muscles and glands 25-28Spinal Cord (cont.)Reflexes Another function of the spinal cord is to participate in reflexes Reflex – a predictable, automatic response to stimuli Receptor Sensory NeuronsEffectorsMotor NeuronsInterneurons 25-29BrainFour sectionsCerebrumDiencephalonBrain stemCerebellum25-30CerebrumLargest sectionTwo cerebral hemispheres Connected by a thick bundle of nerve fibers called the corpus callosumLongitudinal fissure between hemispheresSulci – grooves on surfaceGyri or convolutions – bumps of brain matter between sulciBrain25-31Cerebrum (cont.)LobesFrontal Motor areas for voluntary body movementsParietal Somatosensory – interprets sensationsTemporal Auditory – interprets sounds Occipital Interprets what a person seesFrontalParietalOccipitalTemporal25-32Cerebrum (cont.)CortexOuter layer – gray matterContains about 75% of all neuronsInner layer – white matterFunctionsInterpret sensory informationInitiate body movementsStores memories and creates emotionsVentriclesInterconnected cavities within the brainFilled with CSF25-33DiencephalonBetween the cerebral hemispheres superior to the brain stem Thalamus Relay station for sensory information going to the cerebral cortex for interpretationHypothalamus Maintains homeostasis by regulating vital activitiesBrain25-34Brain StemConnects the cerebrum to the spinal cordMidbrain Just beneath diencephalonControls both visual and auditory reflexesPons Rounded bulge on underside of brain stemBetween midbrain and medulla oblongataRegulates respiration Medulla oblongata Inferior portion of brain stemDirectly connected to spinal cordControls many vital activities, such as heart rate, blood pressure, and breathingBrain25-35CerebellumLocationInferior to the occipital lobes of the cerebrumPosterior to the pons and medulla oblongataCoordinates Complex skeletal muscle contractions that are needed for body movementsFine movementsBrain25-36Previous slide25-37Preventing Brain and Spinal Cord InjuriesWear appropriate protective gear for sportsAvoid diving into unknown watersAlways wear seat beltsFollow safety rules on playgroundsChildren should be in car seats appropriate for age and weightKnow how to get help quickly in emergenciesFollow traffic rules and signs while walking, biking, or driving25-38Apply Your KnowledgeMatch the following:___ Meninges A. Carry motor information from brain___ Ascending tracts B. Stores memories and creates emotions___ Descending tracts C. Grooves on the surface of the cerebrum___ Cerebral cortex D. Carry sensory information to the brain___ Hypothalamus E. Predictable, automatic response to stimuli___ Sulci F. Maintains homeostasis___ Cerebellum G. Coordinates skeletal muscle contractions___ Reflexes H. Protects the brain and spinal cordBFCGEDAHAnswer: SUPER!25-39Peripheral Nervous SystemNerves that branch off the CNSPeripheral nervesTwo types:Cranial nerves Spinal nerves25-40Cranial NervesI.   Olfactory nerves Carry smell information to the brain for interpretationII.  Optic nerves Carry visual information to the brain for interpretationIII. Oculomotor nerves Found within the muscles that move the eyeball, eyelid, and irisIV. Trochlear nerves Act in the muscles that move the eyeball.25-41Cranial Nerves (cont.)V.  Trigeminal nerves Carry sensory information from the surface of the eye, the scalp, facial skin, the lining of the gums, and the palate to the brain for interpretationAlso found within the muscles needed for chewingVI. Abducens nerves Act in the muscles that move the eyeball25-42Cranial Nerves (cont.)VII. Facial nerves Found in the muscles of facial expression as well as in the salivary and tear glandsAlso carry sensory information from the tongueVIII. Vestibulocochlear nerves Carry hearing and equilibrium information from the inner ear to the brain for interpretation25-43Cranial Nerves (cont.)IX. Glossopharyngeal nerves Carry sensory information from the throat and tongue to the brain for interpretationAlso act in the muscles of the throatX. Vagus nerves Carry sensory information from the thoracic and abdominal organs to the brain for interpretationAlso found within the muscles in the throat, stomach, intestines, and heart25-44Cranial Nerves (cont.)XI. Accessory nerves Found within the muscles of the throat, neck, back, and voice boxXII. Hypoglossal nerves Found within the muscles of the tongue25-45Spinal NervesPeripheral nerves originating from the spinal cord 31 pairs of spinal nerves8 pairs of cervical nerves (C1 through C8) 12 pairs of thoracic nerves (T1 through T12)5 pairs of lumbar nerves (L1 through L5) 5 pairs of sacral nerves (S1 through S5) 1 pair of coccygeal nerves (C0)Spinal Nerves25-46Spinal Nerves (cont.)Dermatome Skin segment innervated by spinal nerveC1 is not associated with a dermatomeVentral rootAxons of motor neurons onlyDorsal rootAxons of sensory neurons onlyDorsal root ganglion Contains cell bodies of sensory neurons25-47Spinal Nerves (cont.)Main portions of spinal nerves fuse to form nerve plexusesCervical – supply skin and muscles of neckPhrenic nerve originates from this plexus and controls the diaphragmBrachial – control muscles in the armsLumbosacral – lower abdomen, external genitalia, buttocks, thighs, legs, and feetSciatic nerve originates from this plexus and controls muscles of legsSpinal Nerves25-48Previous slide25-49Somatic Nervous System Nerves that connect the CNS to skin and skeletal muscle“Voluntary” nervous system Controls skeletal muscles, which are under voluntary control25-50Autonomic Nervous System Nerves that connect the CNS to organs and other structures “Involuntary” nervous systemMotor neurons located in gangliaNeuron cell bodies outside the CNS 25-51Autonomic Nervous System (cont.) Sympathetic division“Fight or flight” – Prepares body for stressful or emergency situationsNeurons release neurotransmitter norepinephrineIncreases heart and breathing ratesSlows down muscles of the stomach and intestinesDilates pupilsConstricts blood vessels – increases blood pressure25-52Autonomic Nervous System (cont.) Parasympathetic divisionPrepares body for rest and digestingControls most of the body’s organsReleases acetylcholineSlows heart and breathing ratesConstricts pupilsActivates muscles of stomach and intestineNo communication with blood vesselsSympathetic and parasympathetic divisions are antagonistic25-53Apply Your KnowledgeWhat is the difference between the sympathetic and parasympathetic nervous systems?ANSWER: The sympathetic nervous system prepares the body for stress. It releases norepinephrine, causing an increase in heart and respiratory rate, slows down the GI system, and dilates pupils. The sympathetic system also controls constriction of blood vessels.The parasympathetic system prepares the body for resting and digesting. It releases acetylcholine, which slows heart and respiratory rates, constricts pupils, and stimulates the GI system. It has no effect on most blood vessels.Impressive!25-54Neurologic TestingTypical neurologic examinationState of consciousness Reflex activity Speech patterns Motor patterns 25-55Diagnostic ProceduresLumbar punctureMagnetic resonance imaging (MRI)Positron emission tomography (PET) scan Cerebral angiographyComputerized tomography (CT) scan Electroencephalogram (EEG) X-ray25-56Cranial Nerve TestsOlfactory nerves (Cranial nerve I)Have patient smell various substancesCranial nerves III, IV, and VIHave patient track movement of fingerCranial nerve VHave patient clench teeth, feel jaw muscles25-57Cranial Nerve Tests (cont.)Cranial nerve VIICheck patient’s facial expressionCranial nerve XIIHave patient extend his tongue and move it from side to side25-58Reflex TestingAreflexiaAbsence of a reflexHyporeflexiaDecreased reflexHyperreflexiaStronger-than-normal reflex25-59Reflex Testing (cont.) Biceps reflex Absence indicates spinal cord damage in the cervical region Knee reflex Absence may indicate damage to lumbar or femoral nerves Abdominal reflexesUsed to evaluate damage to thoracic spinal nerves25-60Apply Your KnowledgeMatch the following: ___ State of consciousness A. Determines the health of peripheral nerves___ Reflex activity B. Loss of balance,  abnormal posture___ Speech patterns C. Stupor, delirium,  vegetative___ Motor patterns D. Loss of ability to form wordsADBCANSWER:Excellent!25-61Common Diseases and DisordersDisease/DisorderDescriptionAlzheimer’s diseaseProgressive, degenerative disease of the brainAmyotrophic lateral sclerosis (ALS)Lou Gehrig’s diseaseDegeneration of neurons in the spinal cord and brainBell’s palsyWeak or paralyzed facial muscles25-62Common Diseases and Disorders (cont.)Disease/DisorderDescriptionBrain tumors and cancersAbnormal growths Can be primary or secondary tumorsMost common – gliomasEpilepsy and seizuresOccurs as a result of bursts of electrical signals that disrupt normal brain functioningGuillain-Barré SyndromeBody’s immune system attacks the PNS25-63Common Diseases and Disorders (cont.)Disease/DisorderDescriptionHeadachesTension MigrainesClusterEpisodic or chronicWith aura/without auraForm of migraines; occurs in groupsMeningitis Inflammation of meningesMultiple sclerosis (MS)Chronic disease of CNSMyelin is destroyed25-64Common Diseases and Disorders (cont.)Disease/DisorderDescriptionNeuralgiasDisorders causing nerve painParkinson’s diseaseProgressive and degenerative motor system disorderSciaticaDamage to sciatic nerveStrokeBrain cells die because of an inadequate blood flow; “brain attack”25-65Apply Your KnowledgeTrue or false: ___ Alzheimer’s disease is a progressive degenerative disease  of the brain.___ Epilepsy is due to degenerative neurons in the spinal cord and brain.___ Neuralgias are motor system disorders.___ Stroke occurs when brain cells die because of inadequate blood flow.FFTDue to a burst of electrical signals that disrupt brain function. They are group of disorders referred to as nerve pain.TANSWER:Bravo!25-66In Summary25.1 The central nervous system is composed of the brain and spinal cord. The peripheral nervous system consists of the peripheral nerves located throughout the body. The peripheral nervous system is further divided into two distinct systems: the somatic and autonomic nervous systems.25.2 There are three separate types of neurons to carry out the functions of the nervous system. The afferent (sensory) nerves, the efferent (motor) nerves, and the interpretive interneurons that act as “interpreters” between the afferent and efferent nerves.25-67In Summary (cont.)25.3 All neurons are composed of a cell body, the shorter and more numerous dendrites that receive information for the cell body, and the longer axons that bring an impulse from the cell body to the dendrite of the next neuron.25.4 The function of a nerve impulse is the sending of information either from the CNS to the PNS or vice versa. At rest, a neuron is said to be in a polarized state, and when it responds to stimuli, depolarization takes place. Repolarization occurs after the electrical current (impulse) has passed. 25-68In Summary (cont.)25.5 A synapse is the space between the axon of one neuron and the dendrite of the next. At the end of each axon is the synaptic knob, which contains vesicles that produce neurotransmitters. These are released by the synaptic bulb to allow impulse transmission to continue to the next neuron.25.6 The blood-brain barrier is a layer of tightly woven capillaries that protects the delicate tissues of the CNS. This barrier prevents certain substances, such as various waste products and drugs, from easily crossing this barrier and entering the brain tissues25-69In Summary (cont.)25.7 The meninges, a triple-layered membrane protecting the brain and spinal cord, are composed of the following layers: The tough outer layer is the dura mater. The space between the cranium and the dura mater is called the epidural space. Below the dura mater is the subdural space. The middle layer is the arachnoid, and below it is the subarachnoid space, which contains cerebrospinal fluid (CSF). The innermost layer is the pia mater.25-70In Summary (cont.)25.8 The spinal cord is continuous with the brain and consists of 31 spinal segments: 8 cervical 5 sacral 12 thoracic 1 coccygeal 5 lumbar The basic function of the spinal cord is to carry sensory information from the body to the brain and motor information from the brain to the muscles and glands of the body.25-71In Summary (cont.)25.9 Cerebrospinal fluid (CSF) is located within the subarachnoid space of the brain and within the central canal of the spinal cord. It cushions the brain and spinal cord. 25.10 A reflex is a predictable automatic response to a stimulus. A typical reflex flows as follows: Sensory receptors send information (impulse) to the interneurons, which in turn send the information on to the effectors of the motor neurons, producing a response.25-72In Summary (cont.)25.11 The cerebrum is the largest part of the brain and is divided into two hemispheres subdivided into four lobes: frontal, parietal, temporal and occipital. The diencephalon contains the thalamus and hypothalamus. The brain stem consists of three parts: the midbrain, pons, and medulla oblongata. The cerebellum is the final area of the brain.25-73In Summary (cont.)25.12 Twelve cranial nerves carry sensory information: Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Vagus Vestibulocochlear Glossopharyngeal Accessory Hypoglossal  There are 31 pairs of spinal nerves, each except C1 innervating a dermatome. Refer to Figure 25.8 for a map of the spinal nerves.25-74In Summary (cont.)25.13 The somatic nervous system connects the CNS to the skin and skeletal muscle (voluntary functions). The autonomic nervous system connects the CNS to the internal organs (involuntary functions).25.14 The autonomic nervous system is divided into the sympathetic system, which prepares the body for “fight or flight” (stressful) situations, and the parasympathetic system, which is the body’s everyday “resting” system for normal situations.25-75In Summary (cont.)25.15 There are many and varied diseases and disorders related to the nervous system. The signs, symptoms, and treatments of these diseases are as varied as the diseases themselves. Many of the more common diseases are included in the Pathophysiology section at the end of this chapter.25-76Activity of the nervous system improves the capacity for activity, just as exercising a muscle makes it stronger.”~ Dr. Ralph GerardEnd of Chapter 25