EXSS 276 1st Edition Lecture 22 Outline of Last Lecture I. Force ProductionI. Frequency of StimulationII. Energy for Muscle ContractionIII. Muscle FatigueOutline of Current LectureI. Muscle CrampsII. Rigor MortisIII. Cardiac MuscleIV. Smooth Muscle (visceral) Current LectureI. Muscle Crampsa. Definite cause not known; possible causes:i. Feed forward loop between muscle and spinal cordii. Pain or sensory impulses to spinal cord generates feedback response = muscle contraction1. Over-exercised muscle or lack of blood to muscle2. Electrolyte imbalance3. Poor biomechanics (Golgi tendon organs)II. Rigor Mortisa. State of muscular rigidity that begins 3-4 hours after death and lasts about 24 hoursb. After death, calcium ions leak out of SR and allow myosin heads to bind to actinc. Since ATP synthesis has ceased, cross bridges cannot detach from actin until enzymes start to digest decomposing cells III. Cardiac Musclea. Striated, involuntary, autorhythmic because of built in pacemakerb. Similar arrangement of thick and thin filamentsc. Found only in heart walld. Striated, short, quadrangular-shaped branching fiberse. Single centrally located nucleusf. Cells connected by intercalated discs w/ gap junctions g. Gap junctions: send APs h. No epimysium – no overall wrap (only perimysium and endomysium) 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.i. Cardiac vs. skeletal i. Cardiac contractions last longer than skeletal1. Due to prolonged delivery of calcium ions from SR and ECFii. Cardiac muscle fibers contract when stimulated by their own autorhythmic fibers, ~60bpmiii. Cardiac muscle fibers have larger mitochondria to generate ATP aerobically (thus require more oxygen)IV. Smooth Muscle (visceral) a. Attached to hair follicles in skinb. In walls of hollow organs (blood vessels and GI tract)c. Non-striated in appearance; involuntaryd. Small involuntary cells; tapering at endse. Single, oval-shaped, centrally located nucleusf. No sarcomeresg. Sliding of thick and thin filaments generates tensionh. Transferred to intermediate filaments and dense bodies attached to sarcolemmai. Contracts: twists into helix as it shortens, relaxes by untwistingj. Smooth muscle tissue is non-striated and involuntary – 2 types:i. Visceral (single unit) smooth muscle1. In walls of hollow viscera and small BV2. Autorhythmic; fibers contract in unison (gap junctions)3. If one fires, sends to rest of fibers ii. Multiunit smooth muscle1. Individual fibers with own motor neuron ending, fibers operate individually (no gap junctions; not as a unit)2. Found in large arteries, large airways, arrector pili muscles, iris andciliary body k. Physiologyi. Contraction starts slowly, lasts longer1. No t-tubules and little SR2. Calcium must flow in from outsideii. In smooth muscle, regulator protein that binds to calcium ions in cytosol in calmodulin (similar to troponin in striated muscle) – don’t need the nameiii. Calmodulin activates enzyme myosin light chain kinase, which facilitates myosin-actin binding and allows contraction to occur at relatively slow rate l. Tonei. Prolonged presence of calcium in cytosol leads to smooth muscle tone, a state of continued partial contractionii. Stress-relaxation response: smooth muscle fibers can stretch considerablyw/out developing tensioniii. Useful maintaining blood pressure or steady pressure on contents of GI