PHIS 206 1st EditionLecture 11Outline of Last Lecture I. 3 Categories of MusclesII. Skeletal MuscleIII. Muscle PhysiologyIV. Muscle Cell ContractionsV. Muscles Are Elastic Muscle Types Outline of Current Lecture I. Muscle Mechanics―Skeletal MusclesII. Smooth MusclesIII. Cardiac MusclesIV. Atrial and VentricularV. Mechanism of Stimulation―Cardiac MuscleVI. Cardiac CycleCurrent LectureI. Muscle Mechanics―Skeletal Muscles-Brief shock administered = brief contraction = shock-Tetanic stimulus: no relaxation between stimuli -Long contractions: deliver a tetanic stimulus-Muscles contract and do not relax for anything above 60 s/cycle-Vary strength of contraction how many muscle cells contracting simultaneously strength goes up by increasing # of muscle cellso motor neurons spread out and innervate more that 1 muscle cello in some muscles, selectively stimulate very few muscle cells-Motor unit: 1 motor neuron and all of the muscle cells it innervates so all cells simultaneously contract fine movements = smaller motor units-SUMMARY: can vary duration of contraction and strength of stimulus in skeletal musclesII. Smooth Muscles-No striations because myosin and actin are organized in all directions/irregular-Can contract in several planes (shorter, narrower, etc…)-Rate of contraction is slower and less forceful because of the irregular elements-Can propagate action potentials from 1 cell to another (CANNOT for SKELETAL)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. conductive cells if stimulated, everything (wave of contraction) will contract/relax at the same time-Smooth muscles will relax if waste product increase and O2 production decreasesIII. Cardiac Muscles-hybrid between skeletal and smooth-is striated and cylindrical (like SKELETAL muscle)-action potential can propagate in 1 direction (like SMOOTH muscle) NOTE: Smooth muscles, however, can propagate action potentials in ALL directions.-3 Basic Types1.) Atrial2.) Ventricular3.) Conductive-In any tissue, a group of cells that are connected so that they can transmit action potentials to each other: syncytium IV. Atrial and Ventricular-Similarities look like striated muscle cells contractile generate action potentials-DifferencesDuration of plateau (refractory period: atrial 150 millisec v. ventricular 300 millisec)atrial: maximum rate of contraction is ≈ 360/minuteventricular: maxium rate of contraction is ≈ 180/minuteatrial: contracts with more frequency, longer refractory periodV. Mechanism of Stimulation―Cardiac Muscle-same as routine of skeletal muscle (sarcolemma, sarcoplasm, etc…)-rhythmic contraction b/c of rather “leaky” cells different parts of heart have different levels of leakinesso Drift rapidly if more leaky: higher frequencies to reach thresholdso Drift slowly if less leaky: lower frequencies to reach thresholdsVI. Cardiac Cycle: from one end of the contraction to another-left ventricular pumps blood to everywhere except lungs-2 Gross Phases1.) Systole: heart contracting2.) Diastole: heart resting-Sino-Atrial (S-A) Node: most “leaky”; generates action potentials more frequently than any other parts of the heart 90 millisec for cycle from S-A node to entire atrial and
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