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Fundamentals of the Nervous System

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 of the body Sensory input (to brain) Sensors External or internal info Integration

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Fundamentals of the Nervous System

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  1. Fundamentals of the Nervous System Chapter 11 Dr Tamily Weissman, Department of Molecular and Cellular Biology, Harvard University

  2. Functions of the Nervous System • Master controller and communicator of the body • Sensory input (to brain) • Sensors • External or internal info • Integration • Immediate context • Experience • Motor output (from brain) • Effector organs • Muscle or gland response See yellow light Process options Foot to brake or gas

  3. Human Nervous System Divisions Info in & out Integration & command

  4. Neuroglia • CNS • Astrocytes • Maintaining blood-brain barrier • Guide growing neurons • Microglia • Remove cellular debris and foreign material • Ependymal cells • Circulate and produce CSF • Oligodendrocytes • Produce multiple myelin sheaths • PNS • 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

  5. Neurons • Structural unit of the nervous system • Cell body (soma) • Nissl bodies (rough ER) • Nucleivsganglia • Processes • Dendrites • Input; dendritic spines; graded potentials • Axons • Axon hillock (trigger zone) • Myelin sheath and nodes of Ranvier • Axon terminals (secretory region) • Lack Nissl bodies and Golgi • Anterograde and retrograde transport • Axolemmaand axoplasm • Tractsvsnerves • Whitevsgray matter http://www.pspnperak.edu.my/biologit5/Abd%20Razak%20b.%20Yaacob/Portfolio/BBM/Audio/saraf/Neuron%208.gif http://www.mind.ilstu.edu/curriculum/neurons_intro/imgs/neuron_types.gif

  6. Classification of Neurons • Structural classification • Multipolar: 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 classification • Sensory (afferent): message to CNS • Motor (efferent): message from CNS • Interneurons (Sensory Neuron) http://www.unisanet.unisa.edu.au/Resources/101766/Online%20Brain%20Development%20course/Pics/Photo%201g.gif

  7. Neurophysiology • Resting membrane potential • Positive charge outside, negative charge inside • Polarity creates potential energy • Measured in millivolts (mV) • -70 mV in the plasma membrane of neurons • Flow of charge (ions) is the current • K+ flows out more readily than Na+ flows in • Na+/K+ pump maintains concentrations of Na + (3 out) and K + (2 in) • Plasma membrane provides resistance • Ohm’s law: current = (voltage/resistance) • More volts (potential difference) = more movement • Greater resistance = less movement

  8. Ion Channels • Proteins spanning PM controlling flow • Leak channels • Gated channels • Chemical (ligand) respond to NT • Voltage respond to change in polarization • Mechanical respond to physical change/deformation • Ions move down an electrochemical gradient • Charge • Concentration

  9. Graded Potentials • Short lived and local • Depolarizations or hyperpolarizations • Decrease in magnitude w/distance = decremental • Varies with strength of stimuli • Point of stimulus only place ions can pass • (+) ions toward (-) areas and (-) ions to (+) areas • Inside (+) ions move from stimuli site to neighboring (-) areas • Outside (+) ions move toward stimuli site

  10. Action Potentials • Rapid reversal of membrane potential • All-or-nothing • Graded until threshold reached • Magnitude independent of strength • Intensity coded by frequency • Carry information • Depolarization • Positive feedback maintains • Repolarization • Hyperpolarization • Returning electrical conditions • Na+/K+ pump • Returns ionic conditions • Refractory periods • Absolutevsrelative

  11. Propagation of an AP • Stimuli site is depolarized and local ion movement disperses the signal (graded) • Origin enters a refractory period • Local changes can produce another AP • Depolarization followed by repolarization • Myelinated axons allow conduction spread and regeneration • Saltatory conduction at nodes of Ranvier • Axon diameter • Larger = faster • Degree of myelination • w/o = continuous conduction; AP immediately = slow • w/ = prevents leaks; faster change Unmyleinated Myleinated

  12. Synapses • Types • Presynaptic neuron sends • Postsynaptic neuron receives • Classification • Axodendritic • Axosomatic • Axoaxonic • Function • Electrical 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

  13. Transmission at a Synapse • AP opens Ca2+ channels in presynaptic neuron • Ca2+ influx causes synaptic vesicle fusion and NT exocytoic release • NT 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

  14. Neurotransmitter Classes • Acetylcholine (ACh): skeletal muscles (excitatory); acetylcholinesterase (AChE) • Biogenic amines • Dopamine (DA): movement (both) • Norepinephrine (NE) & epinephrine (Epi): feel good NT’s (both) • Common pathway from AA tyrosine • Serotonin (5-HT): mood, sleep, appetite & anger (inhibitory); AA tryptophan • Histamine: immune response & wakefulness (both); AA histidine • Amino acids • GABA (inhibitory) • Glutamate (excitatory) • Neuropeptides • Endorphins and enkephalins: natural opiates (inhibitory) • Substance P: perception of pain (excitatory) • Dissolved gases • NO: synthesized on demand; relaxation of smooth muscle (Viagra)

  15. Nervous System Disorders • Polio: destroys motor neurons in CNS • Rabies: inflames the brain • Multiple sclerosis: destruction of myelin slows AP conduction, axons unaffected • Tay-Sachs: harmful accumulation of lipids in brain tissue • Shingles: viral infection in skin sensory neurons • Numbing and prickling: slowed blood flow to areas impair nerve impulses

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