88%(8)7 out of 8 people found this document helpful
This preview shows page 2 - 4 out of 12 pages.
Due to leaky ion channels and electrogenic ion pumps in membraneoAs membrane potential rises, bursts of APs are createdoThis increases intracellular Ca contraction (strength and duration depend on time course of Ca changes)Can affect frequency or amplitude of contractions, baseline (tonic) tensionRESULTSIncreased contraction: Ach, eserine, atropine, passive stretchDecreased contraction: epinephrineAction Potential Propagation in Peripheral NervesNEURONSCell body (soma), cytosplasmic extensions (dendrites- receive electrical impulses and carry them toward soma), axon (carries impulses away from soma)Ability to carry electrical signals is related to difference in electrical potentialacross surface membrane membrane potential - determined by 2 factors: o(1) Relative concentrations of ions in and around neurono(2) Relative permeability of membrane to ionsoGoldman eqnION CHANNELSVoltage-gated Na and K channels responsible for creating and propagating an action potentialoThreshold value usually 15-30 mV above resting potentialACTION POTENTIALAbove threshold, v-g Na channels open and membrane moves toward equilibrium potential for NaoUpstroke of APV-g K channels are opening simultaneouslyAs Na channels begin to close, membrane pot. moves back towards equil potential for KIncreased K permeability causes membrane to “overshoot”resting membrane potentialoGenerating after-hyperpolarization
V-g K channels close and axon returns to resting membrane potentialGiven neuron does not vary in size of AP, but does vary in frequencyof APDealing w/long nerve so many axonsoDifferent fibers have different diameters different resistances to voltage stimulusoA given stimulus may not be strong enough to initiate an AP in all fibersREFRACTORY PERIODSAbsolute refractory – After depolarization of a section of a membrane, Na channels close and cannot be opened (they are inactivated).oPrevents incoming current of Na from reopening channelsoPrevents backwards propagation of the APoSets upper limit on frequency at which a neuron can generate APsRelative refractory– after absolute, some (but not all) Na channels at rest and can be re-excitedoRequires greater voltage stimulus to activate enough channels for APoIn lab, responses observed were an average of responses from population of neuronsRESULTSObserved CAP, stimulus response; threshold=0.5 V; max=4 VTemporal summation – 2 stimuli; as ISI increased, CAP decreased (log)Refractory period- reached when ISI reduced to 0.5 msConduction velocity= d/t where d=distance between second stimulating and first recording electrode and t=time from onset of stimulus to start of CAPNeuronal Control of Skeletal MuscleSKELETAL MUSCLELargest tissue in vertebrate body; contractions provide voluntary movementMuscle divided into long, cylindrical cells called muscle fiberswhich contain myofibrilso1-2 micrometers in diameter; contain groups of interdigitating thick (myosin) and thin (actin) filaments