<aside> 💡 Primary Tissue 4: Muscle Structure and Function

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1. Outline the characteristics of structure and function of muscle cells.

   1. Muscles divided into smaller subunits, allowing for selective contraction
      1. alters contraction for different scenarios
   2. Muscles not only contract but also provide tension
      1. More motor units = more complex function
   3. Muscle characteristics:
      1. Sarcomere
         1. Functional (contractile) units in cardiac and skeletal muscle
         2. Assembly between two z-discs
      2. Sarcoplasmic reticulum
         1. Membrane bound structure similar to ER
         2. Stores Ca++
      3. T-Tubules
         1. Invagination of sarcolemma
         2. Sarcolemma extensions penetrating the centre of skeletal and cardiac muscle cells.
         3. Conducts signals from sarcolemma to sarcoplasmic reticulum
         4. fIled with interstitial fluid for fast travel of APs throughtout cell
      4. Gap junctions
         1. Cardiac muscles electrically connected via gap junctions
         2. Allows contractions to spread throughout heart
         3. Essential for coordinated contraction
      5. Focal densities
         1. Anchor/attachment points on plasma membrane for actin/myosin microfilaments
         2. Smooth muscle
         3. Similar to Z-discs
      6. Skeletal muscle triad

         1. 1 Central T-tubule + 2 terminal cisternae of sarcoplasmic reticulum on either side

            

         2. Control contractions - way of coordinating activation of sarcomere simultaneously

      7. Fasicles
         1. Bundles of muscle fibres in skeletal muscle
      8. connective tissue
         1. blood supply, organization, and connection to surrounding tissue
            1. Endomysium
               1. Surrounds muscle fibre
               2. Reticular
                  1. Nerve, blood supply
            2. Perimysium
               1. surrounds fasicle
               2. Irregular dense CT
                  1. Organizes movement
            3. Epimysium
               1. surrounds whole muscle
               2. Helps anchor muscle through integration with tendons and ligaments
               3. Dense irregular CT
   4. Functions
      1. Skeletal
         1. Voluntary movement of bones across joints
      2. Cardiac
         1. Myogenic contraction of heart
      3. Smooth
         1. Autonomic movement of visceral organs, especially those with hollow lumens: GIT, vagina, lungs

2. Describe the structural specializations/classifications of muscle cells.

   1. Cardiac

      

      1. Sarcomeres increase contractility; result in striations
      2. More T-tubules, irregular arrangement allow quicker, widespread depolarization
      3. Intercalated discs and gap junctions allow faster, coordinated depolarization
      4. Branched structure allows faster/coordinated depolarization
      5. Mono/binucleated, no regenerative capabilities
      6. Myogenic, involuntary
      7. Short
      8. Not fatigable
      9. Strong connections between cells = intercalated discs - cells fuse together and contraction spreads from one cell to another
         1. Desmosomes - rigid connections to withstand contractions
         2. Gap junctions - spreads depolarization (action potential)

      

      

      

   2. Smooth Muscle

      

      

      

      1. Visceral control by ANS (involuntary); maintains homeostasis

      2. Associated with visceral organs

      3. Cells: spindle shape

      4. 1 central nucleus, elongated

      5. No sarcomeres or myofibrils (not striated)

      6. Only muscle fibers

      7. Arranged in layers (circular/longitudinal), not fascicles

         1. Circular = inner

         2. Longitudinal = outer

            

      8. Slow

      9. High regeneration

      10. No-TT, less SR

      11. Focal densities (dense plaques): anchor points on plasma membrane for actin/myosin microfilaments

   3. Skeletal

3. Identify and recall the locations of the different types of muscle within the body.

4. Describe the structure of the contractile unit of skeletal muscle – the “sarcomere”