A&P 2 Chapter 12

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Nervous System
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1. Sense organs receive information about changes in the body and the external environment, and transmits coded messages to the spinal cord and the brain
2.Brain and spinal cord processes this information,relates it to past experiences, and determine what response is appropriate to the circumstances
3. Brain and spinal cord issue commands to muscles and gland cells to carry out such a response
Motor (efferent) divisioncarries signals from the CNS to gland and muscle cells that carry out the body's responseEffectorscells and organs that respond to commands from the CNSSomatic Motor Divisioncarries signal to skeletal muscles output produces muscular contraction as well as somatic reflexesSomatic Reflexesinvoluntary muscle contractionsVisceral Motor Division (Autonomic Nervous System)carries signals to glands.cardiac muscle,and smooth muscle involuntary and responses of this system and its receptors are visceral reflexesSympathetic Divisiontends to arouse the body for action accelerates heart beat and respiration,while inhibiting digestive and urinary systemsParasympathetic Divisiontends to have calming effect slows heart rate and breathing stimulates digestive and urinary systemsUniversal Properties of NeuronsExcitability Conductivity SecretionExcitabilityrespond to environmental changes called stimuliConductivityneurons respond to stimuli by producing electrical signals that are quickly conducted to other cells at distant locationsSecretionwhen electrical signals reaches end of nerve fiber, a chemical neurotransmitter is secreted that crosses the gap and stimulates the next cellWhat are the functional classes of neurons?Sensory (afferent) neurons Inter-neurons (association) neurons Motor (efferent) neuronSensory (afferent) neuronsspecialized to detect stimuli transmit information about them to the CNS begin in almost every organ in the body and end in CNS afferent- conducting signals toward the CNSInter-neurons (association) neuronslie entirely within the CNS receive signals from many neurons and carry out the integrative function process,store,and retrieve information and make decisions that determine how the body will respond to stimuli90% of all neurons areinterneuronsMotor (efferent) neuronssend signals out to muscles and gland cells (the effectors) motor because most of them lead to muscles efferent neurons conduct signals away from the CNSSomathe control center of the neuron cell body performs life functions of the cellDendritesmany,receive information, thick branchesAxon Hillocktrigger zone, site of action potential development if it will occurAxon (nerve fiber)only one, output structure of neuronSynaptic Knobportion of the cell that communicates with the next cellAxon collateralsbranches of an axon specialized for rapid conduction of nerve signals to points distal to the somaTerminal arborizationextensive complex of fine branches of the distal axon ending in a synaptic knobMultipolar Neuronmost common,most neurons in the brain and spinal cord,one axon and multiple dendritesBipolar Neuronone axon,one dendrite olfactory cells,retina,inner earUnipolar Neuronsingle process leading away from the soma sensory from skin and organs to spinal cordAnaxonic Neuronmany dendrites but no axon help in visual processesAxonal transporttwo way passage of proteins,organelles,and other material along an axonAnterograde Transportdown the axon, away from somaRetrograde Transportup the axon, toward the somaMicrotubulesguide materials along the axonWhat is the motor protein in anterograde transport?KinesineWhat is the motor protein in retrograde transport?DyneinFast axonal transportoccurs at a rate of 20-400 mm/dayFast anterograde transportup to 400 mm/day organelles,enzymes,synaptic vesicles and small moleculesFast retrograde transportfor recycled materials and pathogens-rabies,herpes simplex,tetanus,polio virusesSlow axonal transport or axoplasmic flow0.5 to 10 mm/day always anterograde moves enzymes, cytoskeletal components,and new axoplasm down the axon during repair and regeneration of damaged axons damaged nerve fibers regenerate at a speed governed by slow axonal transportNeuroglia or Glial Cellssupport and protect the neurons bind neurons together and form framework for nervous tissueOligodendrocytesform myelin sheath in CNS each arm-like process wraps around a nerve fiber forming an insulating later that speeds up signal conductionEpendymal CellsLines internal cavities of the brain Cuboidal epithelium with cilia on apical surface secretes and circulates CSFMicrogliasmall,wandering macrophages formed from white blood cells called monocytes thought to performe complete check up on the brain tissue several times a dayAstrocytesform supportive framework of nervous tissue have extensions that form the blood brain barrier convert blood glucose to lactate to nourish neurons regulate chemical composition of tissue fluid absorbing excess neurotransmitters and ionsAstrocytosis or Sclerosiswhen a neuron is damaged,astrocytes form hardened scar tissue and fill space formerly occupied by the neeuronSchwann Cellsenvelope nerve fibers in PNS produces myelin sheath assist in the regeneration of damaged fibersSatellite Cellssurround the neurosomas in ganglia of the PNS provide electrical insulation around the soma regulate the chemical environment of the neuronsTumorsmasses of rapidly dividing cellsBrain tumors arise frommeninges (protective membranes of CNS) most come from glial cells that are mitotically active throughout life by metastasis from non-neuronal tumors in other organsGliomasgrow rapidly and highly malignant treatment consists of radiation or surgeryDoes the blood brain barrier decrease effectiveness of chemotherapy/yesMyelin Sheathan insulating layer around a nerve fiber formed by oligodendrocytes in CNS and Schwann cells in PNSMyelinationproduction of the myelin sheath 14th week of fetal dev. complete in late adolescence dietary fat is important to nervous system dev.Myelin in PNSSchwann cells spiral repeatedly around a single nerve fiber lays down as many as a hundred layers of its own membrane no cytoplasm between the membranesNeurilemmathick outermost coil of myelin sheath contains nucleus and most of its cytoplasmEndoneuriumeternal to neurilemma is basal lamina and a thin layer of fibrous connective tissueMyelin Sheath in CNSoligodendrocytes reach out to myelinate several nerve fibers in the immediate vicinity does not have any neurilemma or endoneuriumNodes of Ranviergap between segmentsInternodesmyelin covered segments from one gap to the nextInitial segmentshort section of nerve fiber between the axon hillock and the first glial cellTrigger zonethe axon and the initial segment play an important role in initiating a nerve signalSpeed at which nerve signal travels along a nerve fiber depends on what two factors/diameter of fiber and presence or absence of myelinSlow signals of Nerve Fibersupply the stomach and dilate pupil where speed is less of an issueFast signals of Nerve Fibersupple skeletal muscles and transport sensory signals for vision and balanceMultiple sclerosis and Tay-Sachs is a disease of themyelin sheathMultiple sclerosisoligodendrocytes and myelin sheaths in the CNS deteriorate myeline replaced by hardened scar tissue nerve conduction is disrupted cause may be autoimmune triggered by virus can mimic alot of things,double vision,20-40Tay Sachsa hereditary disorder of infants of eastern European Jewish ancestry abnormal accumulation of glycolipid called GM2 in the myelin sheath fatal before age 4Regeneration of a damaged peripheral nerve fiber can occur ifits soma is intact at least one neurilemma remainsRegeneration tubeformed by Schwann cells,basal lamina, and the neurilemma near the injury guides sprout back to the original target cells and reestablishes synaptic contactCan regeneration of damaged nerve fibers in the CNS occur?NO, IT CANNOT OCCUR AT ALLElectrophysiologycellular mechanisms for producing electrical potentials and currents basis for neural communication and muscle contractionElectrical potentiala difference in the concentration of charged particles between one point and anotherElectrical currenta flow of charged particles from one point to the anotherIn the body, currents aremovement of ions,such as sodium and potassium through gated channels in the plasma membraneLiving cells are polarized or not polarized?polarizedResting membrane potentialcharge difference across the plasma membrane -70mv in resting, unstimulated neuronWhy does resting membrane potential exist?it exists because of unequal electrolyte distribution between ECF and ICFRMP results from the combined effect of three factors1. Ions diffuse down their concentration gradient 2. Plasma membrane is selectively permeable and allows some ions to pass easier than others 3. Electrical attraction of cations (positive charge) and anions (negative charge) to each otherWhat ion has the greatest influence on RMP?potassium (K+) about 40x as concentrated in the ICF as in the ECF leaks out until electrical charge of cytoplasmic anions attracts it back in and equilibrium is reachedSodium in RMPmembrane is less permeable to high concentration of sodium found outside the cell has a hard time about 12x as concentrated in the ECF as in the ICFLocal Potentials*disturbances in membrane potential when a neuron is stimulated *short range change in voltageNeuron response begins _________, spreads through the __________, travels down the _____________, and ends at the __________________dendrite,soma,axon,synaptic knobWhen a neuron is stimulated by chemicals, light, heat or mechanical disturbance in a local potential...*opens the sodium gates and allows sodium to rush into the cell *sodium inflow neutralizes some of the internal negative charge *voltage measured across the membrane drifts toward 0 *Depolarization *sodium diffuses for short distance on the inside of the plasma membrane producing a current that travels towards the cell's trigger zoneLocal Potential 4 Characteristics*Graded *Decremental *Reversible *Either excitatory or inhibitoryAction Potential*more dramatic change produced by voltage regulated ion gates in the plasma membrane *rapid up and down shift in the membrane voltageA action potential can only occur ifthere is a high enough density of voltage regulated gatesSoma in action potentialcant generate a action potentialWhere is the action potential generated?at the trigger zoneThresholdcritical voltage to which local potentials must rise to open the voltage regulated gates -70 to -55mvSpikewhen threshold is reached,neuron fires and produces an action potential more and more sodium channels open in the trigger zone in a positive feedback cycle creating a rapid rise in membrane voltageWhich one: Local potential or action potential follows a All or None Lawaction potentialNondecrementaldo not get weaker with distanceRefractory Periodthe period of resistance to stimulationWhat are two phases of the refractory period?Absolute refractory period Relative refractory periodAbsolute refractory periodno stimulus of any strength will trigger an AP for as long as sodium gates are openRelative refractory periodonly an especially strong stimulus will trigger a new AP *potassium gates are still open and any affect of incoming sodium is opposed by the outgoing potassiumSignal conduction in Unmyelinated Fibers*nerve signal must reach end of the axon *unmyelinated fibers have voltage regulated ion gates along its entire length *AP from the trigger zone causes Na+ to enter the axon and diffuse *depolarization excites voltage regulated gates *sodium and potassium pumps open and close producing a new AP, repetition, chain reaction continues to the end of the axonWhat is needed for Action potentials to occur/voltage gated channels!!!!!!!!!!!!!Saltatory conduction in myelinated fibersthe nerve signal seems to jump from node to nodeWhich one is faster: Myelinated fibers or Unmyelinated fibersmyelinated fibers in saltatory conductionA neuron can have how many synapses?an enormous amount of synapses1st neuron in the signal pathpresynaptic neuron releases neurotransmitter2nd neuron in the signal pathpostsynaptic neuron responds to the neurotransmitterPresynaptic neuron may synapse with a dendrite,soma,or axon of postsynaptic neuron to formaxodendritic, axosomatic, or axoaxonic synapsesIn cerebellum of brain,one neuron can have as many as __________________ synapses100,000Synaptic Cleft*gap between neurons discovered by Ramon y CajalChemical synapses*neurons communicate by releasing chemicals demonstrated by Otto Loewi in 1921What was the first known neurotransmitter?acetycholine, it was first named vausstoffe ( Loewi flooded exposed hearts of two frogs with saline,stimulated vagus nerve of first frog and heart slowed,removed saline and found that it slowed the heart of the second frog)What are the advantages of quick transmission in electrical synapses?no delay for release and binding of neurotransmitter cardiac and smooth muscle and some neuronsWhat are the disadvantages of electrical synapses?*they cannot integrate information and make decisions *ability is reserved for the chemical synapses in which neurons communicate by releasing neurotransmittersWhat are gap junctions?*they join adjacent cells *ions diffuse through the gap junctions from one cell to the next *allow some cells to communicate more rapidly than chemical synapsesSynaptic knob of presynaptic neuron contains _____________ containing _______________synaptic vesicles,neurotransmitterPostsynaptic neuron membrane contains ___________ that function as __________ and ___________________________________proteins,receptors and ligand-regulated ion gates4 major categories of neurotransmittersacetylcholine amino acid neurotransmitters monoamines neuropeptidesWhy does a particular neurotransmitter have one effect at a synapse for one neuron and a different effect at a synapse for a different neuron?the type of receptor governs the effect that the neurotransmitter has on the target cell not the neurotransmitterFunction of neurotransmitters at synapse*they are synthesized by the presynaptic neuron *they are released in response to stimulation *they bind to specific receptors on the postsynaptic cell *they alter the physiology of that cellEffects of Neurotransmitters*a given neurotransmitter does not have the same effect everywhere in the body *multiple receptor types exist for a particular neurotransmitter *receptor governs the effect the neurotransmitter has on the target cellHow are neurotransmitters diverse in their action?*some are excitatory *some are inhibitory *the effect of some depends on what kind of receptor the postsynaptic cell has *some open ligand regulated ion gates *some act through second messenger systemsList 2 different neurotransmitters that are present in the excitatory synapse and provide the name of the neurotransmitter that is present in the inhibitory synapse*Excitatory- acetylcholine and norepinephrine *Inhibitory- GabaWhat are the three kinds of synapses with different modes of action?*Excitatory cholinergic synapse *Inhibitory gaba-ergic synapse *Excitatory adrenergic synapseSynaptic Delaytime from the arrival of a signal at the axon terminal of a presynaptic cell to the beginning of an action potential in the postsynaptic cell .5msec for all the complex sequence of events to occurCholinergic Synapseemploys acetylcholine as its neurotransmitter ACh excites some postsynaptic cells (skeletal muscles) Inhibit othersExcitatory action of Excitatory Cholinergic Synapse1. Nerve signal approaching the synapse, opens the voltage regulated calcium gates in synaptic knob 2. Calcium enters the knob 3. Calcium triggers exocytosis of synaptic vesicles releasing ACh 4. Empty vesicles drop back into the cytoplasm to be refilled with ACh 5.Reserve poll of synaptic vesicles move to the active sites and release their ACh 6.ACh diffuses across the synaptic cleft, binds to ligand regulated gates on the postsynaptic neuron 7.As sodium enters the cell it spreads out along the inside of the plasmam memnrane and depolarized it producing a local potential called the postsynaptic potention 8.If it is strong enough and persistent enough, it opens voltage regulated ion gates in the trigger zone causing the postsynaptic neuron to fireInhibitory GABA-ergic Synapse Steps1. GABA-ergic synapse employs y-aminobutyric acid as its neurotransmitter 2.Nerve signals triggers release of GABA into synaptic cleft 3. GABA receptors are chloride channels 4.Chlorine enters the cell and makes the inside more negative than the resting membrane potential 5.Postsynaptic neuron is inhibited, and less likely to fireExcitatory Adrenergic Synapse1. Employs the neurotransmitter norepinephrine (NE) also called noradrenaline 2.NE and other monoamines,and neuropeptides act through the second messenger system using cyclic AMP 3.Receptor is not an ion gate,but a transmembrane protein associated with a G protein 4. Unstimulated NE receptor is bound to a G protein binding of NE to the receptor causes the G protein to dissociate from it 5.G protein binds to adenylate cyclase and activates this enzyme 6. Induces the conversion of ATP to cyclic AMP 7. Cyclic AMP can induce several alternative effects in the cellWhich synapse is the slowest to respond? A.Excitatory Adrenergic Synapse B.Inhibitory GABA-ergic Synapse C.Excitatory Cholinergic SynapseA. Excitatory Adrenergic SynapseWhat is the advantage of Excitatory Adrenergic Synapse?Excitatory Adrenergic Synapse has Enzyme Amplification which is a single molecule of NE that can produce vast numbers of product molecules in the cellCessation (ending) of the Signal*Stop adding neurotransmitterWhat are the three ways to remove the neurotransmitter which is already there? Part of cessation of the signal1. Diffusion 2. Reuptake 3. Degradation in the synaptic cleftDiffusion*neurotransmitter escapes the synapse into the nearby ECF *Astrocytes in CNS absorb it and return it to neuronsReuptake*synaptic knob reabsorbs amino acids and monoamines by endocytosis *break neurotransmitters down with monoamine oxidase enzymeDegradation in the synaptic cleft*enzyme acetylcholinesterase in synaptic cleft degrades ACh into acetate and chlorine *chlorine reabsorbed by synaptic knobDo action potentials degrade?NOOOOOWhy we have neural integration?*they allow the processing of information,storage of information and decision making *chemical synapses are the decision making devices of the nervous system *the more synapses a neuron has,the greater its information-processing capabilitiesNeural integrationthe ability of your neurons to process information,store and recall it,and make decisionsWhat is neural integration based on?postsynaptic potentials produced b neurotransmittersExcitatory postsynaptic potentials (EPSP)any voltage change in the direction of threshold that makes a neuron more likely to fire usually results from sodium flowing int o the cell canceling some of the negative charge on the inside of the membraneWhat are the excitatory brain neurotransmitters that produce EPSP?glutamate and aspartateInhibitory postsynaptic potentials (IPSP)any voltage change,more negative tan threshold makes a neuron less likely to fire neurotransmitter hyperpolarizes the postsynaptic cell and makes it more negative than the RMP making less like ly fire produced by neurotransmitters that open ligand regulated chloride gatesWhat produces IPSPs and are they inhibitory or excitatory?glycine and GABA and they are inhibitoryACh excites ____________________ but inhibits _______________ due to the different type of receptorsskeletal muscle,cardiac muscleNeuron's respond depends onwhether the net input is excitatory or inhibitorySummationthe process of adding up postsynaptic potentials and responding to their net effect occurs in the trigger zoneThe balance between _________ and __________ enables the nervous system to make decisionsEPSPs and IPSPsTemporal Summationoccurs when a single synapse generates EPSPs so quickly that each is generated before the previous one fades *allows EPSPs to add up over time to a threshold voltage that triggers an action potentialSpatial Summationoccurs when EPSPs from several different synapses add up to threshold at an axon hillock *several synapses admit enough sodium to reach threshold *presynaptic neurons cooperate to induce the postsynaptic neuron to fireFacillitationa process in which one neuron enhances the effect of another one *combined effort of several neurons facilitates firing of postsynaptic neuronPresynaptic Inhibitionprocess in which one presynaptic neuron suppresses another one (remove action) *opposite of facillitaion *releases inhibitory GABA *prevents voltage gated calcium channels from opening in synaptic knob and presynaptic neuron reals less or no neurotransmitterNeural Codingthe way in which the nervous system converts information to a meaningful pattern of action potentialsQualitative Information depends onwhich neurons fireLabeled line codeeach nerve fiber to the brain leads from a receptor that specifically recognizes a particular stimulus type - light,sound,temperature,etc.Quantitative Information depends oninformation about the intensity of a stimulus is encoded in two ways *excitement of sensitive,low threshold fibers gives way to excitement of less sensitive high threshold fibers as intensity of stimuli increases *another depends on the fact that the more strongly a neuron is stimulated,the more frequently it fires CNS can judge stimulus strength from the firing frequency of afferent neuronsNeural poolsneurons function in large groups, each of which consists of millions of interneurons concerned with a particular body functionExample of neural poolthe control of the rhythm of breathing or the moving of the limbs rhythmically when walkingDischarge zone of an input neuronthat neuron acting alone can make the postsynaptic cells fireFacilitated zone of an input neuronit synapses with still other neurons in the pool *fewer synapses on each of them *able to stimulate those neurons to fire only with the assistance of other input neuronsDiverging Circuitone nerve fiber branches and synapses with several postsynaptic cells one neuron may produce output through hundreds of neuronsConverging Circuitinput from many different nerve fibers can be funneled to one neuron or neural pool opposite of diverging circuitReverberating Circuitneurons stimulate each other in linear sequence but one cell re stimulates the first cell to start the process all over *diaphragm and intercostal muscleParallel after discharge circuitsinput neuron diverges to stimulate several chains of neuronsAlzheimer Diseasememory loss for recent events,moody,combative,lose ability to talk,walk,and eatAlzheimer Disease show deficiencies ofacetycholine and nerve growth factorWhen is Alzheimer Disease diagnosis confirmed?autopsy atrophy of gyri (folds) in cerebral cortex neurofibrillary tangles and senile plaques formation of beta amyloid protein from breakdown product of plasma membraneIs Alzheimer Disease genetics implicated?yesParkinson Diseaseprogressive loss of motor function beginning in 50s or 60s, no recoveryParkinson Disease is the degeneration ofdopamine-releasing neurons *dopamine normally prevents excessive activity in motor centers *involuntary muscle contractions,pill rolling motion, facial rigidity,slurred speechParkinson Disease treatmentdrugs and physical therapy dopamine precursor crosses brain barrier bad side effects on heart and liver MAO inhibitor slows neural degeneration surgical technique to relieve tremors