Properties of the living organism. Interaction between living organism and the environment. Processing informations. Definitions

Transcription

1 thermodynamcs energy materal Interacton between lvng organsm and the envronment Propertes of the lvng organsm Separaton from the envroment: Strctly controlled energy and materal transport. Changng n the envroment: accomodaton Open system: free materal and energy exchange. Condton: nformaton from the envronment, rght and fast processng and adequate response. Processng nformatons Defntons nformaton processng answer stmulus: any effects on the organsm (sgnal and nose) outer stmulus from the envroment (e.g. lght, sound etc.) nner stmulus: from the organsm (glucose concentraton, ph of the blood etc.) 1

2 Smple responses n plants Fast moton n plants phototropsm geotropsm Senstve plant Smple responses n anmals Anmals and the human bengs nsuln producton Moton (requres fast processes) Chemcal system : hormones melann producton More complex and faster system: nerves and muscles 2

3 Membranes n the cell Restng potental cell Role of the cell : separaton and controlled nteracton to the envroment observaton In restng state about -30 és -90 mv voltage may be measured between the extraand ntracellular space. Inner s: formaton of ntracellular spaces (compartments). Several base processes take place on the. electrodes extracellular space Intracellular space Typcal on dstrbutons Dffuson of the ons observaton The on concentratons are dfferent on the two sdes of the. Dffuson of neutral partcles. In the case of charged partcles the electrc work must be taken nto the consderaton! Intensve quantty: chemcal potental Intensve quantty: electrochemcal potental Intracellular space (mm/l) Squd gant axon Na + K + Cl Extracellular space(mm/l) Squd gant axon Na + K + Cl equlbrum: z: no. of charges F: Faraday constant. : electrc potental e zf Nernst-equaton Frog muscle Rat muscle Frog muscle Rat muscle e e 1 2 RT zf ln c c 1 2 3

4 Dffuson through the Donnan-equlbrum Use the permeablty constant as characterstc quantty! p = D/d ntal state Intal condtons: There are non permeable ons. Electrc neutralty both sdes (the sum of charges s zero) - + D dffuson constant d thckness of the c(1) c(2) moble ons (permeable ), fnal state equlbrum. 0 equlbrum: c(1) = c(2) Rght soluton? = 0!!! electrc blayer Rato of concentratons (extracell./ntracell.) Ion Na + K + Cl - squd frog rat Calculated potentals on the base of Nernst-equaton for dfferent ons and the measured potental (mv) -potental (meas.) Na + K + Cl - Squd gant axon Frog muscle Rat muscle Sgnfcant dfferences between the measured and calculated values! Man dfference n the case of Na +. 4

5 Typcal values for the heart Calculated potental on Extracell. space (mm) Intracell. space (mm) rato (extra/ntra) Na K Cl on Na + K + Cl - Ca 2+ Membrane potental (mv) (37-85) Ca Donnan-equlbrum In the case of the phenomenon descrbed by Donnan constant potental dfference may be observed between two sdes of the. There are moble and mmoble ons. In the case of equlbrum the electrochemcal potental s same. Concluson On the base of the measured values there s no Donnan-equlbrum between two sdes of the. (The concentraton dfference of the Na + s too hgh for example!) The bologcal system s not n equlbrum! Passve process (dffuson) may change the state to the equlbrum. Actve (energy consumpton) processes are necessary to keep steady state. 5

6 The role of actve transport Charge and materal transport exst, the concentraton were not constant, e.g. slow nflow of Na + nto the cell. 3 Na + on and 2 K + exchange extracellular space Na-K pump Dfferent, energy consumer mechansms, socolled pumps ensure the steady state. (e.g. Na + -K + pump, Na + -Ca ++ etc.) requres ATP! ctoplasm extracellular space ctoplasm Ion flow n the The base of the transport-model neutral partcles J pc J flux p permeablty constant c- concentraton gradent (sngle) charged partcles J pc c J flux p permeablty constant c- concentraton gradent F Faraday constant T temperature potental dfference R - gas constant F RT The s n rest but there s no equlbrum between two sdes. The potental s constant the net on flow through the s zero. The potental gradent n the s constant d/dx = const. 6

7 Goldman-Hodgkn-Katz (GHK) potental equaton Smplfed GHK equaton condton of steady state: (the net flux s zero) J k k 0 RT pc ln F pc e Na Na c c e K K (p = relatve permeablty constant, compared to the K + ) RT F ln p p Na Na c c e Na Na p p K K c c e K K p p Cl Cl c c Cl e Cl p (calc.) (mv) (meas.) (mv) Squd gant axon 0, p permeablty constant of an on e extracellular space ntracellular space Frog muscle 0, Electrc model of the Accordng to the man ons ntracellular space extracellular space The model descrbng the restng potental and the on current: model for restng potental C represents the capacty, R - characterzes the resstance aganst the flow of the gven on, E voltage source representng the potental 7

8 Changng of the potental Changng the potental The defnton of the stmulus: changng of the potental transmts the nformaton. stmulus experment detecton Changng of the restng potental s due to the specfc on flow though the. Depolarzaton, hyperpolarzaton Depolarzaton (example) stmulus response hyperpolarzaton depolarzaton exponental ncreasng and decreasng. har cells n the ear: Mechancal effect - depolarzaton. 8

9 Hyperpolarzaton Synaps (example) rod n dark rods n the eye: photochemcal effect results the hyperpolarzaton of the. rod n lght vescules synaptc space postsynaptc presynaptc nerve cell dark current actvated transducn closed on channel A possble mechansm: the released acetyl cholne bondng to the receptor opens an on-channel. Propagaton of the changng along the Extenson of the electrc model: cable model extracellular space place of the local changng exponental decreasng ntracellular space R e - longtudnal resstance of the extracellular space. R - longtudnal resstance of the ntracellular space. These elements connect to each other the dfferent parts of the. 9

10 n relatve unt n relatve unt Electrc propertes: tme constant Electrc propertes: space constant on the base of the exponental answer of the : (responses accordng to the dstance of the place of the stmulus) on the base of the propagaton of the changng along the : (responses accordng to the tme) T = 0 m R C m m Rm R R e R R m the tme, whle the changng decreases or ncreases by factor e. the dstance, where the changng decreases by factor e. R R e Propagaton of the depolarzaton Processes n nerves and muscles r m (W cm 2 ) r (W cm 2 ) (ms) dameter (m) (cm) Squd nerve , ,5 Crawfsh nerve ,25 depolarzaton threshold Frog muscle ,2 Both the tme constant and the space constant depend on the dameter. The value of the space constant shows that these are local phenomena they are not able to propagate too far. a depolarzaton below the threshold (local response) b depolarzaton below the threshold (local response) c depolarzaton above the threshold - acton potental 10

11 Acton potental Ion flow durng acton potental 1 voltage senstve Na + - channels 2 - voltage senstve K + -channels the nflow of the Na + s fast at the begnnng accordng to the non-equlbrum state. 1 2 g = (1/r) conductvty K + channel Propertes of the acton potental depolarzaton repolarzaton depolarza ton threshold The frst step s fast! (slow, long process s not sutable for fast response.) restng potental negatve pot. postve 11

12 Why s t fast? rato of on concentraton (extra/ntracellular space) on Na + K + U (mv) Squd Frog 6.0 0, rat Smple calculaton Let the radus of a cell 20 m! The volume s: ~ l. amount of the K + : ~ mol. surface of the cell: ~ cm 2. capacty of the : ~ F. (specfc capacty: ~1 F/cm 2 ) on the base of restng potental: ~ C ~ mol on. The changng affects only the small envronment of the and transports a small amount of ons. Debye-length and dffuson Electrochemcal potental (rat muscle) the on concentraton close to the Speed of the dffuson d 3Dt example: D ~ 10-9 m 2 /s, t = 0,1 ms d ~ nm (Compare d, the average dstance, to the Debye length!) The dffuson transports the ons far from the. e c2 RT ln zf c 1 Na + e Na ln K + K + e K ln ~ kj/mol ~ kj/mol In rest there s a large thermodynamc force for Na +! e K ln ~ kj/mol After reversng the polarty ths force s hgh for K +! 12

13 Comparson If were equlbrum. (Donnan-equlbrum) Modfed electrc model extracellular space Large force acts on Naons. Fast passve nflow. No energy consumpton. Changng of the potental result the outflow of the K +. Changng of the potental: requres energy and was slower! ntracellular space The trans rsestance s represented by varable resstors, that makes possblechangng the speed of the on flow. Propagaton of the acton potental (AP) t tme dfference exponental decreasng at x the local changng s enough large to produce a new ap. Advantage Shape s ndependent from the stmulus: not senstve to the external effects, noses. It propagates far wthout any attenuaton. depolarzaton threshold speed ~ x/t Such fast process makes possble fast responses. 13

14 Speed of the propagaton Saltatorc propagaton space constant depends on: dameter, R m, R t tme dfference x larger! Larger speed. r m (W cm 2 ) (ms) dameter (m) (cm) depolarzaton threshold (due to the myeln R m s large) Squd Crawfsh frog myeln sheath nodes of Ranver Role of the myeln sheath Speed large space constant: about m/s R m very large, space constant s large too At the nodes of Ranver: R m ~ 50 W cm 2 about 10 4 Na + -channel/m cat n. saphaneus the tme that s necessary to cover 6 cm 14

15 Speed of the propagaton Refracter state fber dameter (m) Speed (m/s) a b g d < No sheath < Rm R R e R R m ncreasng dameter ncreasng R m and decreasng R. absolute relatve absolute: Na-channels are opened, there s no new AP. relatve: only larger stmulus s able to produce new AP. Role of the refracter state When s t not true ntated at the end refracter state propagaton drecton of propagaton ntated at the center the refracter state prevents the back propagaton of the ap. propagaton 15

16 Rectfcaton: synaps Not a whtdrawal? synaptc space vesclues presynaptc nerve postsynaptc neuro-transmtters emtted by the vescules depolarze the postsynaptc and result acton potental after the synapse. The structure makes mpossble the back propagaton. Undrectonal step! remember: speed of the dffuson d 3Dt the dffuson s very fast f the dstance s small! the sze of the synaptc space s about a few 10 nm! the delay s not more than a few hundred s! Electrc synaps Concluson protens konnexonfehérjék 2-3 nm bdrectonal, no rectfcaton. Developed a fast system based on electrc phenomena of the. More characterstcs for the nvertebrates. man: e.g. heart muscle. The charges are ons, so ths system s slower than equpment s used by us. The stmulus (sgnal) s able to propagate far wthout any attenuaton. 16

17 Electrc sgnals on the body surface Dagnostcs Electrocardography (ECG) Electroencephalography (EEG) Electromyography (EMG) Source Geness dpole moment: Elementary dpole moments are summed. d = ql (vector quantty) q charge l dstance between charges d dpole moment analogy: geographc map Electroretnography(ERG) Measurement and ts problems electrodes potental dfference = voltage Problems: Source s an extended, 3D object. Measured on the nody surface. Nose. 17