Site of stimulation any stimulus that opens a gated

This preview shows page 4 - 6 out of 7 pages.

site of stimulation; any stimulus that opens a gated channel produces a graded potentialResting state:opening Na+channel produces graded potential: resting membrane exposed tochemicalNa+channel opens & Na+enter the celltransmembrane potentialdepolarizationoccursDepolarization -a shift in transmembrane potential toward 0 mV: movement of Na+throughchannel produceslocal current; depolarizes nearby plasma membrane (graded potential);change in potential is proportional to stimulusRepolarization :when the stimulus is removed, transmembrane potential returns to normalHyperpolarization:the negativity of resting potential; result of opening a K+channel; oppositeeffect of opening a Na+channel; positive ions move out, not into cellEffects of graded potentials:cell dendrites/cell bodies: trigger specific functions, e.g., exocytosis ofsecretions & motor end plate releases ACh into synaptic cleftAPs:propagated changes in transmembrane potential; affect an entire excitable membrane & linkgraded potentials at cell body with motor end plate actionsInitiating the APInitial stimulusa graded depolarization of axon hillock large enough (10 - 15 mV) to changeresting potential; (-70 mV) to threshold level of voltage-gated Na+channels (–60 to –55 mV)All-or-none principle -if a stimulus exceeds threshold amount the AP is the same no matterhow large the stimulus; AP is either triggered, or notFour Steps in the Generation of APsStep 1: Depolarization to thresholdStep 2: Activation of Na+channels -rapid depolarization & Na+ions rush into cytoplasm; innermembrane changes from negative to positiveStep 3: Inactivation of Na+channels, activation of K+channels -at +30 mV inactivation gatesclose (Na+channel inactivation) & K+channels open & repolarization beginsStep 4: Return to normal permeability -K+channels begin to close: when membrane reachesnormal resting potential (–70 mV); K+channels finish closing: membrane is hyperpolarized to -90mV; transmembrane potential returns to resting level: AP is overRefractory Periodis the time period from beginning of AP to return to resting state during whichmembrane will not respond normally to additional stimuliAbsolute refractory period:Na+channels open or inactivated & no AP possibleRelative refractory period:membrane potential near normal; very large stimulus can4
initiate APPowering the Na+-K+Exchange Pumpto maintain concentration gradients of Na+& K+over time- requires energy (1 ATP per 2K+/3 Na+exchange); no ATP - neurons stop functioningPropagation of APs Propagationmoves APs generated in axon hillock along entire length ofaxon; a series of repeated actions, not passive flowTwo methods of propagating APs1.Continuous Propagationof APs along anunmyelinatedaxon; affects one segment of axonat a timeSteps in a propagationStep 1:AP in segment 1: depolarizes membrane to +30 mV; local currentStep 2:Depolarizes second segment to threshold: second segment develops APStep 3:First segment enters refractory periodStep 4:

Upload your study docs or become a

Course Hero member to access this document

Upload your study docs or become a

Course Hero member to access this document

End of preview. Want to read all 7 pages?

Upload your study docs or become a

Course Hero member to access this document

Term
Fall
Professor
WATSON

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture