fundamentals of the nervous system
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Fundamentals of the Nervous System. Chapter 11. Dr Tamily Weissman, Department of Molecular and Cellular Biology, Harvard University. Functions of the Nervous System. Master controller and communicator for the body Sensory input (to brain) Sensors External or internal info Integration - PowerPoint PPT PresentationTRANSCRIPT
Functions of the Nervous SystemMaster controller and communicator for
the body
Sensory input (to brain)Sensors External or internal info
IntegrationImmediate contextExperience
Motor output (from brain)Effector organsMuscle or gland response
See yellow light
Foot to brake or gas
Process options
NeurogliaCNS
Astrocytes Most abundant & versatile Exchange b/w blood & neurons;
migration; environment controlMicroglia
Immune cells of CNSEpendymal cells
Circulate CSF & cushioningOligodendrocytes
Produce multiple myelin sheathsPNS
Schwann cells Produce a single myelin sheath
Satellite cells Similar to astrocytes
http://images.google.com/imgres?imgurl=http://www.dmacc.edu/instructors/rbwollaston/Nervous_system/neuroglia_of_CNS.gif&imgrefurl=http://www.dmacc.edu/instructors/rbwollaston/Chapter_8_Nervous_System.htm&usg=__2YxucQKrJmUKtfkBty-PZGw_y1A=&h=386&w=371&sz=9&hl=en&start=1&sig2=zDo9CPoP08kpEikUtueyXw&um=1&tbnid=7Kr6pqq0qPkVQM:&tbnh=123&tbnw=118&prev=/images%3Fq%3Dneuroglia%26hl%3Den%26sa%3DG%26um%3D1&ei=NGVTSvmkE8yjmQels_CgCQ
Neurons
http://www.mind.ilstu.edu/curriculum/neurons_intro/imgs/neuron_types.gif
http://www.pspnperak.edu.my/biologit5/Abd%20Razak%20b.%20Yaacob/Portfolio/BBM/Audio/saraf/Neuron%208.gif
Structural unit of the nervous system
Cell body (soma) Nissl bodies (rough ER) Nuclei vs ganglia
Processes Dendrites
Input; dendritic spines; graded potentials
Axons Axon hillock (trigger zone) Myelin sheath and nodes of Ranvier Axon terminals (secretory region) and Lack Nissl bodies and Golgi
Anterograde and retrograde transport Axolemma and axoplasm
Tracts vs nervesWhite vs gray matter
Classification of NeuronsStructural
classificationMultipolar: 3+
processes; 99% of all neurons, major in CNS
Bipolar: 2 processes; rare, located in sense organs
Unipolar : short, divided process (peripheral and central processes); mainly in PNS
Functional classificationSensory (afferent):
message to CNSMotor (efferent):
message from CNS Interneurons
http://www.unisanet.unisa.edu.au/Resources/101766/Online%20Brain%20Development%20course/Pics/Photo%201g.gif
NeurophysiologyResting membrane potential
Positive charge outside, negative charge inside
Separation of charges creates PE Measured in millivolts (mV) -70 mV in the plasma membrane of neurons
Cell said to be polarizedFlow of charge (ions) is the current
K+ flows out, Cl- flows in more readily than Na+ inNa+/K+ pump maintains negative intracellular
environmentPlasma membrane provide resistance
Ohm’s law: current = (voltage/resistance) More volts (potential difference) = more movement Greater resistance = less movement
Ion ChannelsProteins spanning PM controlling flow
Leak channelsGated channels
Chemical respond to NT Voltage respond to potential change Mechanical respond to physical change/deformation
Ions move down an electrochemical gradientConcentration Charge
Graded PotentialsShort lived and localDepolarizations or hyperpolarizationsDecrease in magnitude w/distance,
decrementalVaries with strength of stimuli
Point of stimulus only place ions can pass (+) ions toward (-) areas and (-) ions to (+) areasInside (+) ions move from stimuli site to
neighboring (-) areasOutside (+) ions move toward stimuli site
Action PotentialsRapid reversal of membrane
potentialAll-or-nothing
Graded until threshold reachedMagnitude independent of strength
Carry informationDepolarization
Positive feedback maintainsRepolarization Hyperpolarization
Returning electrical conditionsNa+/K+ pump
Returns ionic conditionsRefractory periods
Absolute vs relative
Propagation of an APLocal currents depolarize membrane
at stimuli site and disperseOrigin enters a refractory period
Local changes can produce another APMyelinated axons allow speed
conduction and allow regenerationSaltatory conduction
at nodes of RanvierAxon diameter
Larger = fasterDegree of myelination
w/o = continuousconduction; AP immediately= slow
w/ = prevents leaks; fasterchange
SynapsesTypes
Presynaptic neuron sendsPostsynaptic neuron receives
ClassificationAxodendriticAxosomaticAxoaxonic
FunctionElectrical synapses allow ion
flow b/w gap junctions Electrical only
Chemical synapses release and receive NT’s b/w pre- and postsynaptic neurons Electrical chemical electrical
Transmission at a SynapseAP opens Ca2+ channels
in presynaptic neuronCa2+ influx causes
synaptic vesicle fusion and NT exocytoic release
Binds to postsynaptic neuron Postsynaptic ion
channels change EPSP or IPSP
Temporal summation Spatial summation
Actions of NT in synaptic cleft ended Degradation Reuptake Diffusion
http://anthropologynet.files.wordpress.com/2008/01/neuron-synapse.png
Neurotransmitter ClassesAcetylcholine (Ach): skeletal muscles (excitatory)Biogenic amines
Dopamine (DA): movement (both)Norepinephrine (NE) & epinephrine (Epi): feel good NT’s
(both)Serotonin (5-HT): mood, sleep, appetite & anger (inhibitory)Histamine: immune response & wakefulness (both)
Amino acidsGABA (inhibitory)Glutamate (excitatory)
PeptidesEndorphins and enkephalins: natural opiates (inhibitory)Substance P: perception of pain (excitatory)
Dissolved gasesNO: synthesized on demand; relaxation of smooth muscle
(Viagra)
Nervous System DisordersPolio: destroys motor neurons in CNSRabies: inflames the brainMultiple sclerosis: destruction of myelin
slows AP conduction, axons unaffectedTay-Sachs: harmful accumulation in brain
tissueShingles: viral infection in skin sensory
neuronsNumbing and prickling: slowed blood flow
to areas impair nerve impulses