Digestion

  1. Vertebrate skeletal muscle 

    1. Introduction to muscle 

      1. Contractile tissue – movement

      2. Motor output – mechanical force

      3. Functions

        1. Locomotion

        2. Manipulation of environment

        3. Blood circulation

        4. Feeding, peristalsis

      4. Skeletal muscle 

        1. Moves skeleton

        2. Attached to bone via tendons: cords of connective tissue

        3. Most abundant tissue in the body

    2. Muscle structure 

      1. Muscle Fiber: long cylindrical cell

        1. Multinucleate – many cells fused

        2. Several distinctive features

          1. T tubles: Infolding of plasma membrane

          2. Sarcoplasmic reticulum: Specialized ER of muscle cells

          3. Myofibrils: longitudinal fibers within cell

            1. Made of 2 types of filaments 

              1. Thin filaments - actin, tropomyosin, troponin complex 

              2. Thick filaments - myosin 

                1. Each has head and tail - head sticks out, tails make filament 

            2. Actin and myosin present in many cells, best organized in muscle cells

            3. Arranged in regular pattern – striped appearance

            4. Sarcomere: contractile unit, overlapping thin and thick filaments

              1. Myofibril = hundreds of sarcomeres end to end

              2. Sarcomere structure

                1. Z line – ends of sarcomere, thin filaments embedded

                2. M line – middle of sarcomere

              3. During contraction – overlap of thin and thick filaments increases

                1. Length of fibers does not change

    3. Sliding filament model 

      1. At Rest

        1. Tropomyosin covers myosin binding sites of actin

      2. Message from Motor Neuron

        1. AP → acetylcholine released

        2. Binds specific receptors → PM depolarization in muscle fiber

        3. If strong enough depolarization → AP in muscle fiber

        4. Problem: large diameter

          1. Axon narrow – AP spreads easily – not so in muscle fibers

          2. Solution: t tubules

          3. AP travels along PM, down T tubules, depolarizes SR, Ca2+ released

      3. Contraction 

        1. Ca2+ binds troponin – exposes myosin binding sites on actin

        2. Contraction cycle

          1. High E state at rest

          2. Tropomyosin shifts, cross-bridge forms

          3. Power stroke

          4. Cross-bridge breaks, low E state

          5. ATP hydrolysis

  2. Other types of muscles 

    1. Cardiac muscle 

      1. Walls of heart

      2. Striated, branched cells

      3. Unique functionality – contract simultaneously, independently

      4. Intercalated discs

    2. Smooth muscle 

      1. Wall of digestive tract, bladder, uterus blood vessels

      2. Not attached to bone, not striated, no T tubules, no well-developed SR

      3. Less efficient, slower contractions and relaxation

  3. Skeleton 

    1. 3 functions 

      1. Support, protect internal organs, movement 

    2. 3 types of skeletons 

      1. Hydrostatic skeleton: fluid-filled cavity

        1. Closed, fluid under pressure

        2. Cnidarians, nematodes, annelids

      2. Exoskeleton

        1. External, non-living – does not grow

        2. Arthropods – chitin – protection and movement

        3. Mollusks – CaCO3 – just protection

      3. Endoskeleton

        1. Internal, living – able to grow

        2. Echinoderms and chordates

        3. 2 types – cartilage, bone

          1. Cartilage

            1. Flexible skeletal tissue

            2. Composed of chondrocytes, collagen fibers, lipoprotein material

          2. Bone

            1. Rigid skeletal tissue

            2. Consists of collagen, hydroxyapatite (mostly CaPO4), CaCO3

            3. Highly dynamic tissue, NOT inert