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Chapter 2

Chapter 2: Structure and Function of the Nervous System

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PSYC 211
Yogita Chudasama

ary Intro: brain moves muscles, behavior = NS 1 function. Sensory neuron: detect change in ext/int enviro, info to CNS. Motor neuron: CNS, muscle contraction/gland secretion. Interneuron: within CNS. Locals: circuits w/ nearby neurons, analyze small info. Relays connect local circuits in 1 region w/ other regions. Through connections, neuron circuits perform essential functions. CNS: brain / cord. PNS: nerves / sensory organs. Cells of Nervous System  Neurons (basic structure) process/transmit info o Soma: body, has nucleus, machinery for life processes, shape varies o Dendrites: recipients of messages across synapse (junction btwn terminal buttons, 1-way) o Axon: myelinated, carries info (electrochem action potential from axon to button). multipolar: 1 axon, many dendrites. Bipolar: 1 axon, 1 dendrite at opp ends, sensory. Unipolar: 1 stalk leaves soma2 branches, transmit sense info, skin. CNS communicates w/ body via nerves (bundles of fibers wrapped in membrane) attached to brain / spinal cord o Terminal buttons: bud at end of axon, forms synapse, sends info to other neuron. Secrete NT: chemical that excites/inhibits receiving cell, det if action potential occurs.  Neurons (internal structure): SEE PAGE 33 o membrane: defines cell boundary, double lipid layer, embedded protein molecules o nucleus: central, nucleolus (makes ribosomes, [small proteins, produce proteins translated from mRNA], chromosomes [long strands of DNA w/ genetic info]. When active, genes (functional unit of chromosome) cause mRNA production, receives copy of info stored at location, leaves membrane, attaches to ribosomes, causing production of particular protein). o Proteins as enzymes: control chem reaction, combine/break; catalysts. Genome: sequence of nucleotide bases on chromosomes, info for protein. “Junk” DNA does not have info, but correlates w/ complexity. ncRNA: functions, spliceosomes, attach/modify proteins that regulate gene expression. o Cytoplasm: viscous substance in cell interior, contains organelles.  Mitochondria: energy from nutrients, double membrane, wrinkles = cristae (break down nutrients via enzymes). ATP breakdown liberates energy for metabolism.  ER: storage, channel for transporting chem. Parallel membrane layers. Rough: ribosomes make protein. Smooth: segregation of molecules in various processes, produces lipids. Golgi: smooth ER, makes complex molecules, wrap/pack. Secretion via exotycosis. Produces lysosomes: small sacs w/ enzymes to break down substances not needed by cell, recycled/excreted.  Cytoskeleton: matrix, gives neuron shape, made of 3 types of protein strands (microtubules thickest, bundles of 13 protein filaments around hollow core, involved in transport)  Axoplasmic support: substances propelled along microtubules of axon. Anterograde: move from somabuttons, via kinesin. Retrograde: buttonssoma, via dynein protein, slower.  Support Cells: neurons are ½ CNS, high metabolism but can’t store nutrients, need constant supply. o Glia: most important = neuroglia, glue CNS, buffer/insulate neurons, surround/hold, control nutrient supply and chem to exchange messages, clean  Astrocyte: physical support, clean, make chem, control chem composition, establish structure for interneuron communication, nourish. Processes wrapped around vessels or neuron parts (soma/dendrite). Supply nutrients from capillaries, break down to lactate, to cytoplasm of astrocytes to mitochondria, faster than glucose. Store glycogen. Hold neuron in place, surround/ isolate synapse to limit NT dispersion. Glide w/ pseudopodia, engulf/eat debris via phagocytosis.  Oligodendrocytes: support axon, make myelin sheath: insulate, 80-20% lipid-protein, uncoated = node. Makes 50 myelin segments w/ paddle processes wrapped around axon to make myelin. MS: immune attacks myelin, axons can’t conduct messagesneuro symptoms over time/space  Microglia: phagocytes, protect brain from invading microorganisms, inflammatory. o Schwann cells: each segment of myelin in PNS has 1 Schwann wrapped many times around axon. Differ from CNS oligodendrocytes DIFFERENCES IN REGROWTH PG 40  Blood-Brain Barrier: semipermeable; CNS has no gaps in capillaries, substances can’t leave, come in via proteins. Regulates extracellular composition, important for message transmission, keeps bad chem out. Not uniform in NS, some areas permeable: area postrema: weak barrier in medulla, poison detectedvomiting Interim Summary Neuron Comm.: action potential: membrane alterations, movement btwn axon/fluid, exchange currents.  overview: stim sense neuron dendrites axon spinal cord buttons release NT, excite interneuron axoninterneuron buttons release NT, excite motor neuronaxonjoins nerve, travel to muscle; motor neuron buttons release NT, contraction. Brain inhibits excitation: axon from brain neuroncord, buttons form synapses w/ inhibitory interneuronexcited, release inhibitory NT, dec. motor activity  Measuring electrical potential of axons: Electrodes: conductors, path for electricity in/out, one simple wire + microelectrode into axon, records potential w/o damage. Axon neg charged -70 mV: membrane /resting potential (stored source of electric energy). Oscilloscope: records voltages as f(t). Pos charge applied insidedepolarization: reduction to 0 of potential from resting. Action potential: brief electric impulse, basis for conduction of info along axon, rapid reversal of potential: hyperpolarization. Threshold of excitation: value of membrane potential that must be reached to produce action potential.  membrane potential: electrical charge is result of balance between two opposing forces 1. diffusion: molecules distribute selves evenly, highlow concentration. In motion, prop to T. 2. electrostatic pressure: attraction/repulsion of ions, hilo electrolytesinto ions w/ opp charge 3. extra/intracellular fluid: D+E balance from dif. ionspotential. Organic A- only intracellular. K+ mostly intracellular, diffusion pushes out, electrostatic (+ outside) pushes in. Na/Cl mostly extracellular (sea). Cl- mostly out, diffusion pushes in, electrostatic pushes out. Na+ pushed in by diffusion, attracted to neg charge, but Na/K pump pushes out - consists of protein in membrane, driven by energy from ATP–molecules are Na/K transporters, exchange Na for K, push 3 Na out for every 2 K in. Transporters keep intracellular Na+ low b/c membrane not very permeable; also transport K+ in, to which membrane more permeable. Transporters use 40% neuron energy.  Action potential: inc in permeability to Na, goes intransient inc in permeability to K+, goes out. Protein molecule makes opening lets ions in/out, make ion channels w/ pores
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