chapter 17 - muscle system

• muscle twitch: tension production
• muscle twitch is measured comparing contraction period where tension increases through crossbridge cycling and relaxation period where tension decreases as Ca2+ pumped back into sarcoplasmic reticulum over time
• muscle tension can be altered because of:

  1. frequency of stimuli
  2. number of cross bridges
• variation in muscle fibers

  1. type I fibers ("dark meat")
  2. slow twitch
  3. low myosin ATPase activity
  4. maintained extended periods of contractions
  5. largely oxidative metabolism to produce sustained ATP
  6. well developed blood supply, myoglobin, mitochondria (darker red)
  7. type II fibers ("white meat")
  8. fast twitch
  9. high myosin ATPase activity
  10. quickly fatigued (but powerful)
  11. largely anaerobic metabolism to produce sustained ATP
  12. smaller blood supply, less myoglobin and mitochondria (white)
• type I fibers have slow oxidative fibers
• type II fibers subtypes:

  1. fast oxidative glycolytic fibers
  2. fast oxidative fibers
  3. fast glycolytic fibers
• motor units: single motor neurons with multiple axon branching

  • stimulate on average 150 fibers
  • fibers within a motor unit are the same type (fast or slow)
  • multiple motor units in a given muscle
• 1. cellular level
  2. sarcomeres contract transmitting tension to sarcolemma & endomysium
  3. tissue level
  4. tension generated by individual muscle fibers in fascicles transmitted to perimysium
  5. organ level
  6. tension in perimysiums transmitted to epimysium, continuous tendons with insertions & origins in bones
  7. system level
  8. coordinated contraction of muscle groups
• motor unit activation

  1. recruitment
  2. more motor units recruited as required
  3. muscle tone
  4. alternating motor unit contractions to maintain muscle tone
  5. hypotonia vs. hypertonia
  6. shivering
  7. random motor unit contractions to generate heat
  8. brief normal hypertonia
• types of muscle contraction:

  1. isotonic concentric: force generated by muscle greater than load, muscle shortens
  2. isotonic eccentric: force generated by muscle is less than load, muscle lengthens
  3. isometric: length of muscle does not change
• muscle shapes:

  1. parallel
  2. convergent
  3. unipennate
  4. bipennate
  5. multipennate
  6. circular
  7. spiral
  8. fusiform
• muscles are named based on:

  1. shape/appearance
  2. size
  3. structural characteristics (number)
  4. location
  5. body region
  6. muscle fiber orientation
  7. action
• skeletal muscle functions

  1. locomotion (contraction, across articulations)
  2. breathing (diaphragm, intercostals)
  3. swallowing initiation
  4. sound modulation (stapedius in middle ear)
  5. voluntary control over defecation and urination
  6. shivering
• functional groups of muscles: take cooperation of several individual muscles working as group to perform movement (Action); roles of different muscles in group

  • agonists (prime movers): provide most force for given muscle action
  • antagonists: usually on opposite side of bones & joint where they meet; opposite action of agonist
  • synergists: aid agonists by supplying supplemental force, minimizing unwanted movement; help stabilize joints; provide for more efficient movement
  • fixators: provide stabilizing force that anchors bone; provides movement efficiency & protection from injury
• lever system:

  1. load or resistance
  2. applied force that moves load
  3. pivot point (fulcrum)
• changing configuration of components of lever system leads to lever classes:

  1. first-class lever: fulcrum sits between load and applied force; load moved in opposite direction than applied force
  2. second-class lever: fulcrum is at one end of lever, applied force is near other end; load is somewhere in between; load moved in same direction as applied force
  3. third-class lever: fulcrum and applied force are close to one another at same end of lever; load is near other end; load moved in same direction as applied force
• myoplasticity: changes in muscle structure as result of changes in function related to physical training

  • majority of mature skeletal muscle fiber nuclei are amitotic (do not undergo mitosis)
  • satellite cells (small population of unspecialized cells) do retain mitotic ability; can help repair injured skeletal muscle
  • therefore, changes in response to training are within muscle fibers; do not involve changes in number of muscle fibers
• endurance training:

  • large increase in frequency of motor unit activation and moderate increase in production (more repetitions with lighter weight)
  • causes primarily biochemical changes, most dramatically in type I fibers, but even in type II:
  • increased oxidative enzymes, and mitochondria (associated proteins)
  • increased fatigue resistance
  • more efficient use of fatty acids and non-glucose fuels for ATP production
  • increases in blood vessel network supplying muscle
• resistance or strength training:

  • moderate increase in frequency of motor unit activation and a large increase in force production (fewer repetitions with heavier weight)
  • causes primarily anatomical changes; both number of myofibrils and diameter of muscle fibers increase (hypertrophy)
  • with hypertrophy comes decreased proportion of mitochondrial proteins and blood supply to muscle because of fiber enlargement; not because mitochondria or vessels are actually lost
  • can decrease endurance, so balanced program is recommended
• not using your muscles leads to anatomical and biochemical changes including decrease in number of myofibrils and size of fiber and decrease in oxidative enzymes (atrophy)

  • decline in both strength and endurance
  • "use it or lose it"
  • problem for bedridden or those that have lost use of their limbs
• adduction: pulls toward midline

  abduction: pulls away midline
• origin: stationary end of muscle attachment

  insertion: movable end of muscle attachment
• most levers in the human body are third-class levers
• muscle size

  • brevis = short
  • longus = long
  • vastus = wide/large
• muscle location:

  • anterior = toward the front
  • external = toward the outside
  • infra = below
  • intercostal = between the ribs
  • internal = toward the inside
  • posterior = toward the back
  • profundus = deep
  • superficialis = nearer the surface
  • supra = above
• muscle action

  • abductor = pulls away from the midline
  • adductor = pulls towards the midline
  • depressor = pulls down
  • erector = holds erect or straight
  • extensor = increase the angle between bones
  • flexor = decreases the angle between bones
  • levator = raises a body part
  • pronator = turns palm posteriorly
  • supinator = turns palm anteriorly
• body region

  • abdominis = abdominal area
  • brachii = arm area
  • capitis = head area
  • carpi = wrist area
  • cervicis = neck area
  • digitorum/digiti = related to fingers/toes
  • femoris = femur or thigh
  • gluteal = buttocks
  • hallucis = great toe
  • oculi = eye area
  • oris = mouth area
  • pectoralis = chest area
  • pollicis = thumb
• muscle fiber orientation

  • oblique = at an angle
  • orbicular = circular
  • rectus = straight
  • transverse = across/transverse
• muscle heads

  • biceps = two heads
  • quadriceps = four heads
  • triceps = three heads
• muscle shape

  • deltoid = triangular
  • maximus = largest
  • minimus/minimi = smallest
  • minor = small
  • quadratus = rectangular
  • rhomboid = shaped like a rhombus
  • serratus = serrated or jagged
  • trapezius = trapezoidal
• superior rectus muscle:

  • elevates anterior eye, looking up, and turns eye medially
  • origin: common tendinous ring of posterior orbit
  • insertion: superior surface of eye
  • nerve: oculomotor nerve
• inferior rectus muscle:

  • depresses anterior eye, looking down, turns eye medially
  • origin: common tendinous ring of posterior orbit
  • insertion: interior surface of eye
  • nerve: oculomotor nerve
• medial rectus muscle:

  • pulls anterior eye medially, towards nose
  • origin: common tendinous ring of posterior orbit
  • insertion: medial surface of eye
  • nerve: oculomotor nerve
• lateral rectus muscle:

  • pulls anterior eye laterally, toward the temple
  • origin: common tendinous ring of posterior orbit
  • insertion: lateral surface of eye
  • nerve: abducens nerve
• superior oblique muscle:

  • pulls anterior eye inferiorly and laterally, rolls left and down
  • origin: the posterior orbit
  • insertion: superior/lateral surface of eye after passing through the trochlea
  • nerve: trochlear nerve
• inferior oblique muscle:

  • pulls anterior eye superiority and laterally, rolls left and up
  • origin: maxilla just inside the anterior portion of the orbit
  • insertion: inferior/lateral surface of eye
  • nerve: oculomotor nerve
• levator palpebrae superioris muscle:

  • elevates upper eyelid
  • origin: posterior orbit
  • insertion: connective tissue and skin of upper eyelid
  • nerve: oculomotor nerve
• genioglossus muscle:

  • protrudes tongue
  • origin: internal/anterior mandible
  • insertion: majority of muscle blends into the tongue; body of hyoid bone
  • nerve: hypoglossal nerve
• hypoglossus muscle:

  • depresses tongue
  • origin: hyoid bone (greater horn)
  • insertion: posterolateral surface of the tongue
  • nerve: hypoglossal nerve
• styloglossus muscle:

  • retracts and elevates tongue
  • origin: styloid process of temporal bone
  • insertion: lateral/posterior border of tongue
  • nerve: hypoglossal nerve