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Homeo UIC 3
Homeostasis uic 3rd set of slides
| Question | Answer |
|---|---|
| neuronal signaling controls/integrates | organim functions |
| action potentials | propagate signals along axons, info encoded by its frequency are communicated to other neurons at synapses |
| axon hillock | initiates atp (start of axon) |
| dendritic spines | receive incoming signals from other neurons onto dendrites |
| axon terminals | make synaptic contacts with target cells |
| every output can have up to how many inputs | 10000 |
| vesicles contain | neurotransmitter that will be releaed into the post synaptic space |
| presynaptic terminal | site of neuronal output -very close alligned with post synaptic part -rapid action -2-3 mSec -used for fast response, very local |
| endocrine cell | broadcast signaling, hormone via chemical signal, into blood, whole body response, slow but massive ex: insuline glucose into cells |
| neuroglia | nerve glue- make up half mammilian brain volume very important |
| astrocytes | metabolic intermediates between blood capillaries and neurones -take up and release neurotransmitters and ions -involved in development |
| microglial cells | mediat immune response of neural tissue |
| ensheathing cells | on peritheral axons(schwann cells) and CNS (Oligodendrocytes -increase velocity of nerve impulse propagation |
| resting potential | negative in all cells known bc voltometer shows -65 in squid axon |
| a current pulse changes membrane potential | + ions depolarize it - ions polarize it |
| time course of depolarization isnt instantaneous bc | the membrane acts as a capacitor storing charge separated across the membrane -delay |
| cell membranes exhibit | resistance and capacitance in parallel which together dictate the time constant for a change in membrane potential |
| t | how long it takes to reach 2/3 of ap time constant |
| how far in axon current can be seen | distance changes potential p alot of ions injected leak out smaller further away |
| lambda | membrane length constant steepness of the drop from original |
| passive spread depends on | resistance to current movement along interior and resistance to urrent flow across membrane through channels lambda = Rm/Ri |
| selective permeability to K+ | determines the resting membrane potential |
| slow leak of K+ | causes a local charge separation at the membrane |
| how to lower Ri | make axon really big, can transport more easily through axoplasm |
| chemical gradient of Na and K | maintained by Na K atpase pump |
| Na ecg | goes into cell |
| K ecg | goes out of cell |
| Gradients | very steep gradient for Na, intermediate for K and close to equilibrium for Cl |
| Cl- | a little less inside cell than outside |
| nerst equation def | describes relationship btw ion concentrations difference and membrane potential at equilibrium for a permeating ion |
| neutral P | very dependent on K, so very close to reversal potential of K |
| Permeability to K | is highest in membrane so Vm is slightly closer to Ek(-75mV) |
| Vm is slightly less than Ek | bc Na counteracts resting membrane potential bc its Ena is (+55) |
| determine Em | (membrane potential) by relative permeabilities to K and Na Em approaches Ek |
| Em | Em= -70, Ek=-90, ENa=+55 |
| Once the membrane is depolarized above a threshold potential | an action potential of fixed size is generated( all or none phenomenon) |
| voltage threshold | once goes over this ap starts, below this nothing starts |
| positive feedback loop | action potential generation is an exampe initiaal depolarization--open voltage gated Na chanels--increase Na flow--further membrane depolarization--opening of more channels |
| electrically separate and test channel | patch-clamp technique |
| na channels open when | membrane depolarizes |
| na channels close | after 1ms |
| K channels | exibit delayed opening |
| whoearly current dependos on | sodium ion concentratioons |
| tea blocks | current flow through K channels |
| voltage gated na K channels | the P loop btw helices 5 and 6 confers ion selectivity (draws in Na+) slightly -P -the 4th alpha helix confers voltage sensitivity (opens channel) - |
| K channels fromed | by interaction of 4 separate but identical subunits |
| why dont action potentials travel along both directions in the axon | bc na channel deactivation, lingering K channel activation, increaded membrane permeability results in decreased memb resistance so local currents cause less depolarization |
| conduction velocity is | determined by lenght constant and time constant |
| large diameter axons | increase ap conduction velocity ( increasing length constant by reducikng Ri) |
Created by:
ddrag
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