MUSCULAR

• Functions of the muscular system

  • Movement
  • Maintain posture
  • Respiration
  • Production of body heat
  • Communication
  • Heart beat
  • Contraction of organs and vessels
• Types of Muscles


  • Skeletal
  • Smooth
  • Cardiac
• General Properties of Muscle Tissues

  • Excitability: response to stimulus
  • Contractility: ability to shorten
  • Extensibility: ability to stretch
  • Elasticity: ability to recoil

  
• Clinical Significance of Muscles

  • Muscles are sites for the introduction of drugs
  • Muscles are efficiently used in lifting & moving clients (body mechanics)
• Skeletal Muscle Characteristics


  • Makes up 40% of body weight
  • Named because attached to bones (skeleton)
  • Many nuclei per cell (near periphery)
  • Striated
  • Longest of muscle types

  
• Skeletal Muscle Structures- Connective Tissue Coverings

  • Epimysium: connective tissue that surrounds entire skeletal muscle (outside)
  • Muscle fasciculus: bundle of muscle fibers
  • Perimysium: connective tissue around each muscle fasciculus
  • Muscle fiber: skeletal muscle cells, many nuclei
  • Endomysium: connective tissue that surrounds each muscle fiber

  
• Skeletal Muscle Structures- Muscle Fiber Structure

  • Sarcolemma: cell membrane, contains T-tubules
  • Sarcoplasm: cytoplasm of muscle fiber (cell)
  • Myofibril: thread-like proteins that make up muscle fibers
  • Myofilament: proteins that make up myofibrils, e.g. actin and myosin
  • Sarcoplasmic reticulum: stores and releases Ca2+
  • Sarcomere- basis for muscle contraction theory known as sliding filament theory

  
• Skeletal Muscle Structures- Actin and Myosin Myofilaments


  • Actin: thin myofilament, resemble 2 strands of pearls
  • Myosin: thick myofilament, resemble golf clubs

  
• Skeletal Muscle Structures: Sarcomeres


  • Sarcomere: contractile unit, contains actin and myosin
  • Z disk: protein fibers that form attachment site for actin
  • H zone: center of sarcomere, contains only myosin
  • I band: contains only actin
  • A band: where actin and myosin overlap
  • M line: where myosin are anchored

  
• Excitability of Muscle Fibers

  Action Potential: "electricity", stimulus that causes rapid depolarization and repolarization, causes muscle to contract

  
• Depolarization


  Change in charges, inside becomes more + and outside more -, Na+ channels open
• Repolarization


  Na+ channels close, change back to resting potential
• Sodium-Potassium Pump


  Pumps Na+ out of cell and transports K+ into cell, restores balance
• Nerve Supply and Muscle Fiber Stimulation

  • Motor neuron: nerve cells that carry action potentials to muscle fibers
  • Neuromuscular junction (synapse): where nerve cell and muscle fiber meet
  • Presynaptic terminal: end of nerve cell (axon)
  • Synaptic cleft: space between presynpatic terminal and postsynaptic membrane
  • Postsynaptic membrane: muscle fiber membrane
• Nerve Supply and Muscle Fiber Stimulation (continued)

  • Synaptic vesicle: in presynaptic terminal, store and release neurotransmitters
  • Neurotransmitter: chemicals that stimulate or inhibit a muscle fiber, e.g. Acetylcholine
• Steps in a Muscle Contraction (Sliding Filament Theory)

  1. Action potential travels down motor neuron to presynaptic terminal causing Ca2+ channels to open

  2. Ca2+ causes synaptic vesicles to release acetylcholine into synaptic cleft

  3. Acetylcholine binds to receptor sites on Na+ channels, Na+ channels open, and Na+ rushes into postsynaptic terminal (depolarization)

  4. Na+ causes sarcolemma and t-tubules to increase the permeability of sarcoplasmic reticulum which releases stored calcium

  5. Ca2+ binds to troponin which is attached to actin

  6. Ca2+ binding to troponin causes tropomyosin to move exposing attachment sites for myosin

  7. Myosin heads bind to actin

  8. ATP is released from myosin heads and heads bend toward center of sarcomere

  9. Bending forces actin to slide over myosin

  10. 10. Acetylcholinesterase (enzyme breaks down acetylcholine) is released, Na+ channels close, and muscle contraction stops

  
• ATP and Muscle Contractions

  • ATP is made in mitochondria from aerobic or anaerobic respiration
  • During a muscle contraction, H zone and I band shorten but A band stays the same
  • Striations of skeletal and cardiac muscle are due to sarcomeres (actin and myosin)
  • Rigor mortis: person dies and no ATP is available to release cross-bridges
• Terms


  • Threshold: weakest stimulus needed to produce a response
  • All or None Law: muscle contracts or doesn't (no in between)
  • Twitch: rapid contraction and relaxation of a muscle
  • Tetanus: muscle remains contracted
• Types of Muscle Contractions

  • Isotonic: amount of repetitions increases, Concentric- movement is against gravity, Eccentric- movement is with gravity
  • Isometric: amount of tension increases (weight)
• Slow and Fast Twitch Fibers

  • Slow Twitch Fibers: Contract slowly, Fatigue slowly, Long distance runners, Use aerobic respiration, Energy from fat, Dark meat, Red or dark because of myoglobin
  • Fast Twitch Fibers: Contract quickly, Fatigue quickly, Sprinters, Use anaerobic respiration, Energy from glycogen, White meat
• Humans have both types of fibers, Distribution of fibers is genetically determined, Neither type can be converted but capacity can be increased through intense exercise
• Skeletal Muscle Anatomy


  • Origin: nonmovable end
  • Insertion: movable end
  • Belly: middle
  • Agonist: muscle that accomplishes a certain movement
  • Antagonist: muscles that oppose each other
  • Synergists: muscles that work together
  • Fixator: muscles that hold one bone in place

  
• Nomenclature


  • Location, Shape, Number of origins, Size, Direction, Location of attachment, Type of motion
• Muscles of Head and Neck

  • Occipitofrontalis: raises eyebrows (forehead)
  • Orbicularis oculi: allows blinking (eyes)
  • Orbicularis oris: kissing muscle (mouth)
  • Zygomaticus: smiling muscle (cheek)
  • Masseter: chewing (mastication) muscle
• Thoracic Muscles


  • External intercostals: elevate ribs for inspiration
  • Internal intercostals: depress ribs during forced expiration
  • Diaphragm: moves during quiet breathing
• Abdominal Wall Muscles


  • Rectus abdominis: center of abdomen, compresses abdomen
  • External abdominal oblique: sides of abdomen, compresses abdomen
  • Internal abdominal oblique: compresses abdomen
  • Transverse abdominis: compresses abdomen
• Upper Limb Muscles


  • Trapezius: shoulders and upper back, extends neck and head
  • Pectoralis major: chest, elevates ribs
  • Serratus anterior: between ribs, elevates ribs
  • Deltoid: shoulder, abductor or upper limbs
  • Triceps brachii: 3 heads, extends elbow
  • Biceps brachii: "flexing muscle", flexes elbow and shoulder
  • Brachialis: flexes elbow
  • Latissimus dorsi: lower back, extends shoulder
• Muscles of Hips and Thighs

  • Iliopsoas: flexes hip
  • Gluteus maximus: buttocks, extends hip and abducts thigh
  • Gluteus medius: hip, abducts and rotates thigh
• Muscles of the Upper Leg

  • Quadriceps femoris: 4 thigh muscles, Rectus femoris: front of thigh, extends knee and flexes hip, Vastus lateralis: extends knee, Vastus medialis: extends knee, Vastus intermedius: extends knee
  • Gracilis: adducts thigh and flexes knee
  • Biceps femoris, semimembranosus, semitendinosus: hamstring, back of thigh, flexes knee, rotates leg, extends hip
• Muscles of Lower Leg

  • Tibialis anterior: front of lower leg, inverts foot
  • Gastrocnemius: calf, flexes foot and leg
  • Soleus: attaches to ankle, flexes foot
• Cardiac Muscle Characteristics


  • Heart, 1 centrally located nucleus/cell, Striated, Rich in mitochondria, Intercalated disks: special cell junctions that allow cells to act as a unit
• Smooth Muscle Characteristics


  • Found in organs, 1 centrally located nucleus/cell, Not striated, Less actin and myosin, Under involuntary control