Muscular System

• Skeletal muscle

  Attached to bones, or, for some facial muscles, to skin
• Cardiac muscle

  Walls of the heart
• Smooth muscle

  Mostly in walls of hollow visceral organs (other than the heart)
• Skeletal muscle cells

  • Single, very long, cylindrical, multinucleate cells with very obvious striations
• Cardiac muscle cells

  • Branching chain cells; uninucleate, striations, intercalated discs
• Smooth muscle cells

  • Single, fusiform, uninucleate; no striations
• Connective tissue components

  • Skeletal: Epimysium, perimysium, and endomysium
  • Cardiac: Endomysium attached to the fibrous skeleton of the heart
  • Smooth: Endomysium
• Regulation of contraction

  • Skeletal: Voluntary; via nervous system control
  • Cardiac: Involuntary; the heart has a pacemaker; also nervous system controls; hormones
  • Smooth: Involuntary; nervous system controls; hormones, chemicals, stretch
• Speed of contraction

  • Skeletal: Slow to fast
  • Cardiac: Slow
  • Smooth: Very slow
• Rhythmic contraction

  • Skeletal: No
  • Cardiac: Yes
  • Smooth: Yes, in some
• Muscle Functions

  • Produce movement
  • Maintain posture and body position
  • Stabilize joints
  • Generate heat
• Muscles perform other important functions as well. Smooth muscles form valves that regulate the passage of substances through internal body openings, dilate and constrict the pupils of our eyes, and make up the arrector pili muscles that cause our hairs to stand on end. Skeletal muscles form valves that are under voluntary control, and they enclose and protect fragile internal organs.
• Myofibrils

  Long ribbonlike organelles that nearly fill the cytoplasm
• Striations

  Alternating light (I) bands and dark (A) bands along the length of the perfectly aligned myofibrils
• Sarcomeres

  The structural and functional units of skeletal muscle
• Thick filaments

  Made mostly of bundled molecules of the protein myosin, also contain ATPase enzymes
• Thin filaments

  Composed of the contractile protein actin, plus some regulatory proteins
• Sarcoplasmic reticulum (SR)

  A specialized smooth endoplasmic reticulum that stores calcium and releases it on demand when the muscle fiber is stimulated to contract
• Motor unit

  Composed of one neuron and all the skeletal muscle cell it stimulates
• Skeletal Muscle Activity

  1. Nerve impulse reaches axonal terminal

  2. Neurotransmitter (acetylcholine) is released

  3. Acetylcholine diffuses across synaptic cleft and attaches to receptors

  4. Sarcolemma becomes temporarily permeable to sodium ions

  5. Electrical current (action potential) is generated
• Types of Body Movements

  • Flexion
  • Extension
  • Rotation
  • Abduction
  • Adduction
  • Circumduction
  • Pronation
  • Supination
  • Inversion
  • Eversion
  • Dorsiflexion
  • Plantar flexion
• Prime mover

  Muscle that has the major responsibility for causing a particular movement
• Antagonists

  Muscles that oppose or reverse a movement
• Synergists

  Help prime movers by producing the same movement or be reducing undesirable or unnecessary movement
• Fixators


  Specialized synergists that hold a bone still or stabilize the origin of a prime mover so all the tension can be used to move the insertion bone
• Head and Neck Muscles

  • Frontalis
  • Occipitalis
  • Orbicularis Oculi
  • Orbicularis Oris
  • Buccinator
• Prime mover


  A muscle that provides the main force to move a bone
• Tension


  The force exerted by a muscle to move a bone
• The prime mover uses all the tension to move the insertion bone
• Gross Anatomy of Skeletal Muscles

  • Head and Neck Muscles
  • Trunk Muscles
  • Muscles of the Upper Limb
  • Muscles of the Lower Limb
• Frontalis


  Muscle that covers the frontal bone, runs from the cranial aponeurosis to the skin of the eyebrows, allows you to raise your eyebrows and wrinkle your forehead
• Occipitalis


  Small muscle that covers the posterior aspect of the skull and pulls the scalp posteriorly
• Orbicularis Oculi


  Circular muscle around the eyes that allows you to close your eyes, squint, blink, and wink
• Orbicularis Oris


  Circular muscle of the lips that closes the mouth and protrudes the lips
• Buccinator


  Muscle that runs horizontally across the cheek, flattens the cheek (as in whistling or blowing a trumpet), also helps hold food between the teeth during chewing
• Zygomaticus


  Muscle that extends from the corner of the mouth to the cheekbone, raises the corners of the mouth (the "smiling" muscle)
• Masseter


  Muscle that covers the angle of the lower jaw, closes the jaw by elevating the mandible
• Temporalis


  Fan-shaped muscle overlying the temporal bone that inserts into the mandible and acts as a synergist of the masseter in closing the jaw
• Platysma


  Single sheetlike muscle that covers the anterolateral neck, pulls the corners of the mouth inferiorly, producing a downward sag of the mouth
• Sternocleidomastoid


  Two-headed muscle, flexes the neck, rotates the face toward the shoulder on the opposite side and tilts the head to its own side