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 muscles to 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 Lecture Motor 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 unit o Large Powerful Actions Smaller muscles 10 fibers motor unit o 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 fibers 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 Parallel Muscles o Muscle fascicles run parallel to axis of muscle o Tendon on both ends o Rope like o Longer fibers able to shorten more faster Pennate Muscles o Fascicles attach to tendons at an angle o Shorter fibers than parallel muscles o Compact lots of fibers in parallel o Resemble a feather o 3 subtypes Unipennate Bipennate Multipennate Convergent Muscles o Origin of muscle is long broad o Muscle fascicles converge onto tendon at insertion o FAN SHAPED o Relationship to other muscle types o More fibers than parallel o 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 Muscles o Fascicles arranged as a ring o Sphincter muscles when contracted the muscle constricts an orifice opening keeping it closed Muscles 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 flexion o Agonist prime mover brachialis muscle is the primary muscle of elbow flexion o Antagonists triceps brachii muscle reverses the movement and extends elbow o Synergists brachialis biceps brachii and brachioradialis muscles work together to flex elbow o Fixators e g muscles of scapula stabilize the shoulder to isolate elbow flexion Direct short dense regular CT fibers connect muscle to bone periosteum Indirect 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 bone Cardiac 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 discs Structures 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 attached Inherent 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 beat Smooth 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 layers o Circular layer closest to lumen of organ o Longitudinal layer wraps around circular layer o Layers differ in orientation of cells typically perpendicular to each other Smooth Muscle Cells Intermediate filaments anchor actin myosin Like all muscle cells contraction involves myosin actin fibers rowing past each other