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PSpsy290 jan 22Y290 January 22.docx

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Junchul Kim

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PSY290 January 22, 2013 Neurophysiology Neurons – functional unit of the nervous system How neurons communicate with each other? Today - Learn basics abut physiological properties of the neuron - Resting membrane potential important* nd - 2 part learn about how neurons comm. With each other by generating ap and how travel down axon and how captured by post synaptic neuron - And finally - What type of nts are found in the system Resting potential - Remember is voltage difference exist across membrane voltage differes inside and outside the cell and this difference is membrane potential and can be measured microelectrode tiny glass needle into the cell - Single neuron and big one containing medium to stay in healthy state and two electreode one referecen outside and recording one both out no difference voltage is tiny need to a,plify need device amplifier to read it and shows the value of voltage difference - As poke inside neuron can detect the difference this is moment enter cell and poke inside can pick up difference Resting potential - Membrane potential of neuron when at rest - Inside is neg respect to outside - Around -70mv depending what type of neuron may differ and when see and detect voltage difference membrane of neuron is polarized - Rmp how cells generate voltage difference - Why iiinside negative How ions distributed - Ion distribution - Inside and outside - 4 major ions - Na k cl and negative proteins - Na con is greater outside then inside by 10times - All negat ions are balanced with positive chard (switched on slide) - All neutralized and balanced how can trigger voltage difference - Ions cannot pass lipid bilayer hydrophobic hate ionic molecules can pass through protein ion channels - Ion channels channel pass lipid bilayer and ion channel has selectivity - One k channel is always open and leak ions through channel leaky k channel – k pass regulary - Na channels closed at resting not a lot of movement at rest - Main driving force of resting potential is not na but k ions How does movement Yoda - Two forces - Con gradient and elect Two forces - Ions will diffuse from areas of high conc to low - Es pressure same charge repel each other different charge attract K ions - K ions diffuse through leaky k channel not lipid bilayer - Along con gradient - Everytime k ions leave exit cell outside more ositve and inside more negative - How more neg - When k leave leave neg charged ions protein behind and balance Is broken - Voltage difference introduce second force es force - Two forces opp of k ions - Con leave and es pull back into neuron tug of war - Enough time two forces balanced and reach equilibrium - No net movement of k ions two forces are equal - No net movement is called equilibrium and membrane potential is equilibrium potential - Can calculate this using Nernst equation - Not have to memeorize Nernst - Conc k inside and outside - Arrive at equilibrium potenitial for k is -80mv Next - Resting pot not same as equilibrium - Bc other contributing factors - Ion for na closed steady leak and ion channels differ - K ions contributing factor for rmp but other players determine variation - From -60 to -70 Nak pump - Nak pump is protein pump - Use energy to pump out sodium and in k consume atp 3 na for 2 k constantly use energy - Why brain needs so much energy constantly pump out sodium and in k and gradient later used to generate signal Recap - K ions are major contributing factor for generating rmp and when two forcs baalced reach equailbrium called equ potential Today 2 - Ap is a neural signal nerve system use to convey information from cells Can change - Membrane potential change when stimulate neurons - Change - 0 when not poke into neuron in drop to -60 - Two graphs are synched - Upper tells experimental manipulation - Injection positive or negative ions – can introduce ions experiemntall - Inject – ions current is negative and next is positive current - - ions in two cases see potential decreases or increase negative - Opp inject + current then membrane potential become more positive or less negative - Change is graded more injection more change observe Next - As reach threshold is usually -40mv all of sudden membrane potential increase to +40 and this spike is called ap – change freq of ap if inject more - Coreraltion freq ap and current injection you do - Each indi ap look the same what changes is frequency - Real nerve system what can induce neg or pos ions What can change - Na is higherrr outside k higheeer inside - Na es and con na same way force sodium ions move inside cell - Ion channel remain close so not a lot of movement - Become permeable rush of na into cell what happens in ap - Na rush in due to boh forces and results in reversal mebran potential negative to positive and this is ap - Why permeable next - Sodium channel closed at rest na opens when membrane potential reaches threshold - Na channel allow entry na ion into cell - Critical compneent of ap generation - What causes change in membrane potential - Once mp reaches na channel open - To reach it introduce change in membrane potential Why look like this - Stereotypical shape - 5 stages - More negative then resting Voltage - Voltage of k and na - Remember these 2 – ion channel respond to voltage change The ap - Resting pot - K leaky in or out - Blue thing is volt na channel resting closed - Voltage gated k - 3 ion channels 1 leaky two voltage - Reach threshold - The vltage na channel open and na rush into neuron resulting in rising phase - Rising membrane potential limited by ion flow of potassium as it rises k is closed k responds and opens and result k ions leave cell bc k ions inside higher in then out along ion concentration gradient - Makes mebran potential negative open and close of k is slower then na channels have dip - If k channel remain open drop further if closed fast no dip - Close is slow have hyperpoloariztion stage - As k voltage close then membrane to resting potential stage Refractory period - During ap firing not initiate another firing - Refracted to ap – abs and relative - Abs spike and relative longer Recap - Threshold mebran potential reach to generate ap -40mv - And all or none reposnse of ap not reach threshold not trigger ap - Once reached always fire - Always same value when reach peak wha changes is ap - Refractory cant produce ap abs and relative - Relaive needs more Where ap initiated - Axon hillock specialized compartment for generation of ap – where ap is generated - Votage gated na channels highly enriched in axon hillock and along axon - Soma and dendrites do but more cone in axon hillock Communicate - From axon to gap to psn receive signal - Traveling ap along axon Important - Ap propagates without losing magnitude - Electrodes stimulating electrode to inject current – experimental membrane manipulation - Not lose amplitude its all or none response Hwo travel - Bc new axon potential generated in each successive spot - Ap rush of na voltage gated ion channels - Key i
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