Muscular System Notes Anatomy by bhangrawala06


									                              Muscles and Muscle Tissue
 Muscle: “little mouse”
 Muscles make up about 50% of body mass
 Types of Muscles
    Skeletal
    Smooth
    Cardiac
 Muscle cells = muscle fibers
 Myofilaments = Actin and Myosin
    Myo=muscle, Sarco = flesh
Muscle       Striations/Structure Nuclei         Location      Voluntary/Involuntary
Skeletal     Striations           Multiple, on   Attached to   Voluntary
                                  the sides      or covers the
Cardiac       Branched             One, in the   Heart         Involuntary
              striations,          center
              intercalated disks
Smooth        No striations        One, in the   Organs        Involuntary
 Muscle functions
   Movement- skeletal, smooth, and cardiac all help with movement
   Posture- skeletal
   Stabilizing joints- skeletal
   Generating heat- skeletal
 Functional Characteristics
   Excitability (irritability)- ability to receive and respond to stimulus; ex:
     neurotransmitters, hormones, PH changes
   Contractibility- shorten when stimulated
   Extensibility-stretch when relaxed
   Elasticity- resume resting length
 Skeletal Muscle Structure
   Gross Anatomy:
      Each muscle fiber is surrounded by endomysium (areolar connective tissue)
      Then fibers get bundled into fascicles which are covered with a perimysium
      An epimysium covers the entire unit
      Deep Fascia- fibrous connective tissue that binds muscles together
      Tendons- link muscle to bone
      Each muscle fiber has at least 1 nerve ending
      Each muscle has one artery and one or more veins
      Attachments
          Insertions- moveable bone
          Origin- immoveable bone
          Direct vs Indirect attachments: indirect is most common
   Microscopic anatomy (histology)
      Sarcolemma- plasma membrane of muscle cells- very large cells
    Sarcoplasm- cytoplasm but with more glycogen and myoglobin
    Myoglobin- red pigment that stores oxygen
    Myofibrils- 80% of cell’s volume
    Striations- repeating series of light and dark bands
      Dark bands = A bands
      Light bands = I bands
      A bands have a lighter stripe in the center called the “H-zone”, only seen
         in relaxed muscle
      M-Line = dark line within the H-zone
      I bands have a darker area called the “z-disk” which is a protein sheet that
         anchors thin filaments
      Sarcomere- runs from one z-disk to another z-disk
   Myofilaments
      Thick filaments A band, myosin
      Thin filaments I band, part of A band, actin
      Myosin- protein; has a tail and 2 or more globular heads
          Heads link thick and thin filaments together during contractions
          Heads also have ATP binding site and ATPases
      Actin- polypeptide units have active sites to which myosin cross bridges
         (heads) attach during contraction; actin filaments coil back on themselves
         to form helices
      Tropomyosin- helps to stiffen actin, in relaxed muscle it blocks actin’s
         active site
      Troponin- 3 polypeptide complex
          Helps control myosin/actin interactions
   Intracellular tubules
      Sarcoplasmic reticulum- smooth ER; forms cross channels where A and I
         bands meet, regulates Ca levels in muscle cells
      T Tubules- elongated tube; conduct implses deep within cell; makes sure
         all myofibrils within muscle fibers conract at the same time
 Thick (myosin) : Thin (actin) = 1:2 in skeletal muscle

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