101_11AI-neuro3_Er_signal

101_11AI-neuro3_Er_signal - previous lectures: functions of...

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topic set #3: need for electrical signals basis of resting potentials previous lectures: functions of the nervous system structural organization receptor cells, interneurons, spiking neurons afferent & efferent neurons cerebrospinal, interstitial, & extracellular fluids now: how does the nervous system function? npb101-w2011-ishida neurons can… thus, neurons have… rest leak channels transduce stimulus energy into electrical signals stimulus-gated channels generate a spike voltage-gated Na & K channels release neurotransmitter onto other neurons & onto other tissues (muscle, etc) voltage-gated Ca channels respond to input from other neurons transmitter-gated channels transduce stimuli process signals produce involuntary responses generate & control behavior extract information & intellectual activity overall functions afferent & efferent signals receptor ending, dendrite, axon, terminal, polarity, rest, response, neurotransmitter today & next week 4 cells “responding” 1 2 3 4 summary formation of extracellular fluid in periphery & in CNS
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Na + K + sodium ion infux potassium ion eFfux signals… due to movement of ions across nerve cell membrane where do these ions come from? diet, extracellular fluid, intracellular fluid how do ions move across membranes? what structures allow ions to move across membranes? what decides the direction of this movement? electrical & chemical forces how does this produce a useful signal? ! start here today npb101-w2011-ishida problem to solve: 1) this is a “collection of cells”. 2) it is watching a flashing light (somewhere in space) 3) when light impinges on cell A , this cell can ‘report’ this event -- it can produce a response. cell B (alone) can not. 4) question: how can cell A tell cell B when the light flashes? A B two details: 1) as soon as possible, B wants to know when a flash occurs. 2) B wants to know even if the light flashes frequently. solution: 1) A must generate a signal that can reach B quickly reliably . 2) this signal must be brief - the response to one flash must end before the next flash starts.
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requirements of the signal: 1) it must travel quickly from A to B . 2) it must be brief . 3) it must be repeatable . 4) it must be able to reach cell B without loss of information. solution #1: 1) the signal can not be a chemical : a) diffusion over long distances would be too slow . b) when the chemical diffuses to cell B, what would prevent it from reaching other cells? c) after each flash, how would the chemical be removed from the extracellular fluid? solution #2: 1) an electrical signal could satisfy job description #1. because charge spreads much faster than diffusion .
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101_11AI-neuro3_Er_signal - previous lectures: functions of...

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