IPHY 3410 1st Edition Lecture 8 Outline of Last Lecture 1) Describe the functions & characteristics of muscle tissue that distinguish it from other types of tissues.2) Name the layers of connective tissue that occur in and around a skeletal muscle.3) Describe and explain the structural and organizational levels of skeletal muscle. Begin with the muscle as an organ followed by the fascicle, muscle fiber, myofibril, and sarcomere, then end with the myofilament.4) List general characteristics of skeletal muscle fibers.5) Explain the sliding filament theory in the simplest form.6) Describe the role of titin in the sarcomere.Outline of Current Lecture 1) Define motor unit.2) Describe the various ways in which muscles attach to their origins and insertions. Explain attachments of musclesto bones through tendons, aponeuroses, and direct and indirect attachments.3) Explain how skeletal muscles are classed into several functional types; give specific muscle examples and describe the functions of prime movers (agonists), antagonists, synergists, and fixators.4) Describe the characteristics of cardiac muscle tissue. Compare its structure and function to skeletal muscle tissue.5) Describe the characteristics of smooth muscle tissue. Compare its structure and function to skeletal muscle tissue.6) Compare and contrast skeletal, cardiac, and smooth muscle tissue. Create a comparison chart for key characteristics such as location, cell shape, type of innervation, and function.Current LectureMotor Unit- A motor unit is a motor neuron and all the muscle fibers it innervates- Muscle (e.g. biceps brachii) = fascicles surrounded by epimysium (CT) o Motor Unit = motor neuron & the fibers it innervates - Fascicle = bundles of fibers, surrounded by perimysium (CT)o Each Fiber surrounded by endomysium (CT)o Fiber = single muscle cell, sarcolemma (= cell plasma membrane) encloses: sarcoplasm & myofibrils (= bundles of myofilaments) Myofilaments (actin, myosin, titin) Sarcomere = smallest functional unit- All fibers innervated by a single motor neuron (motor unit) activated at the same time- Activating more motor units within a muscle increases the force exerted by that muscle- Large muscles ~2000 fibers/motor unito Large Powerful Actions- Smaller muscles ~10 fibers/motor unito Fine motor control- Neuromuscular junction: where neuron stimulates muscle cell Arrangements of Muscle Fascicles- Muscle fibers can be arranged for force, speed, compactness and special functions- Muscle fibers only able to shorten ~ 1/3 of resting length- Muscle force is proportional to cross sectional area of fibersThese 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.- Parallel Muscleso Muscle fascicles run parallel to axis of muscleo Tendon on both endso Rope-likeo Longer fibers, able to shorten more (& faster)- Pennate Muscleso Fascicles attach to tendons at an angleo Shorter fibers than parallel muscleso Compact & lots of fibers in parallelo Resemble a feathero 3 subtypes: Unipennate Bipennate Multipennate- Convergent Muscleso Origin of muscle is long & broado Muscle fascicles converge onto tendon at insertiono FAN SHAPEDo Relationship to other muscle types:o More fibers than parallelo Longer fibers than pennate- Strength of comparably sized muscles:o Parallel (weakest), Convergent, Pennate (strongest)- Speed and range of motion ability of comparably sized muscles:o Parallel (greatest), Convergent, Pennate (least)- Circular Muscleso Fascicles arranged as a ringo Sphincter muscles: when contracted the muscle constricts an orifice (opening) keeping it closedMuscles Attachments- Origin – attachment site that is proximal- Insertion – attachment site that is distal- Action – resulting movement of a muscle contraction- Tendon – denser regular CT that connects muscle to bone- Agonist (prime mover) = muscle that is primarily responsible for a movement- Antagonist = muscle that perform opposite functions- Synergist = muscles that work together to perform an action- Fixator = a synergist that assists by holding a bone firmly in place to allow the prime mover to work more effectively- Example: Elbow flexiono Agonist (prime mover) = brachialis muscle is the primary muscle of elbow flexiono Antagonists = triceps brachii muscle reverses the movement and extends elbow o Synergists = brachialis, biceps brachii and brachioradialis muscles work together to flex elbowo Fixators = e.g. muscles of scapula stabilize the shoulder to isolate elbow flexion- Direct à short, dense regular CT fibers connect muscle to bone (periosteum)- Indirect à long, dense regular CT fibers connect muscle to bone (periosteum)o Ex. Tendon & aponeurosis (= sheet-like tendon)- Tubercles, trochanters, “scars”, bumps = muscle/tendon attachment sites on boneCardiac Muscle: An Overview- Comprises thick muscle of heart wall- Striated- Branched- Most cells are uninucleated, but MAY have 2 large nuclei- Cells have some regenerative ability (recent research has shown that perhaps 1% a year)- Involuntary- Surrounded by endomysium- Connected at intercalated discsStructures of Intercalculated Discs- Gap junctions: allow for coordinated contractions by allowing action potentials to quickly spread from cell to cell- Desmosomes: provide strength, site where intermediate filaments are attachedInherent rhythmicity (automaticity) of cardiac muscle- Cardiac muscle cells (myocytes) initiate their own contraction without stimulation from the nervous system- Note: heart rate is controlled by nervous system, but NS does not initiate heart beatSmooth Muscle: An Overview- Small, spindle shaped cells- Uninucleated- NO striations: contain myofilaments, but not arranged into sarcomeres- Each cell covered by endomysium- Involuntary- Regenerate- Smooth muscle typically arranged into 2 distinct layerso Circular layer = closest to lumen of organo Longitudinal layer = wraps around circular layero Layers differ in orientation of cells; typically perpendicular to each otherSmooth Muscle Cells- Intermediate filaments anchor actin & myosin- Like all muscle cells, contraction involves myosin & actin fibers “rowing” past each