Chapter 7 The Muscular System

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Chapter 7The Muscular System
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INTRODUCTION

• Muscular tissue enables the body and its parts to
  move
• Three types of muscle tissue exist in body (see
  Chapter 3)
• Movement caused by muscle cells (called fibers)
  shortening, or contracting
• Muscle movement occurs when chemical energy
  (obtained from food) is converted into mechanical
  energy

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MUSCLE TISSUE

• Types of muscle tissue (Figure 7-1)
• Skeletal musclealso called striated or voluntary
  muscle
• Microscope reveals crosswise stripes or
  striations
• Contractions can be voluntarily controlled
• Cardiac musclecomposes bulk of heart
• Cardiac muscle fibers branch frequently
• Characterized by unique dark bands called
  intercalated disks
• Interconnected nature of cardiac muscle fibers
  allows heart to contract efficiently as a unit

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MUSCLE TISSUE

• Types of muscle tissue (cont.)
• Nonstriated muscle, or involuntary musclealso
  called smooth or visceral muscle
• Lacks cross stripes or striations when seen under
  a microscope appears smooth
• Found in walls of hollow visceral structures such
  as digestive tract, blood vessels, and ureters
• Contractions not under voluntary control
  movement caused by contraction is involuntary
• Functionall muscle fibers specialize in
  contraction (shortening)

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STRUCTURE OF SKELETAL MUSCLE

• Compositionmainly striated muscle fibers and
  connective tissue
• Most skeletal muscles extend from one bone across
  a joint to another bone
• Parts of a skeletal muscle
• Originattachment to the bone that remains
  relatively stationary or fixed when movement at
  the joint occurs
• Insertionpoint of attachment to the bone that
  moves when a muscle contracts
• Bodymain part of the muscle
• Muscles attach to bone by tendonsstrong cords of
  fibrous connective tissue some tendons enclosed
  in synovial-lined tubes and are lubricated by
  synovial fluid tubes called tendon sheaths
• Bursaesmall synovial-lined sacs containing a
  small amount of synovial fluid located between
  some tendons and underlying bones

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STRUCTURE OF SKELETAL MUSCLE

• Microscopic structure (Figure 7-3)
• Contractile cells called fibersgrouped into
  bundles
• Fibers contain thick myofilaments (containing the
  protein myosin) and thin myofilaments (composed
  of actin)
• Basic functional (contractile) unit called
  sarcomere
• Sarcomeres separated from each other by dark
  bands called Z lines
• Sliding filament model explains mechanism of
  contraction
• Thick and thin myofilaments slide past each other
  as a muscle contracts
• Contraction requires calcium and energy-rich ATP
  molecules

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FUNCTIONS OF SKELETAL MUSCLE

• Movement
• Muscles produce movement as a muscle contracts,
  it pulls the insertion bone closer to the origin
  bone movement occurs at the joint between the
  origin and the insertion
• Groups of muscles usually contract to produce a
  single movement
• Prime movermuscle whose contraction is mainly
  responsible for producing a given movement
• Synergistmuscle whose contractions help the
  prime mover produce a given movement
• Antagonistmuscle whose actions oppose the action
  of a prime mover in any given movement

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FUNCTIONS OF SKELETAL MUSCLE

• Posture
• A specialized type of muscle contraction, called
  tonic contraction, enables us to maintain body
  position
• In tonic contraction, only a few of a muscles
  fibers shorten at one time
• Tonic contractions produce no movement of body
  parts
• Tonic contractions maintain muscle tone called
  posture
• Good posture reduces strain on muscles, tendons,
  ligaments, and bones
• Poor posture causes fatigue and may lead to
  deformity

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FUNCTIONS OF SKELETAL MUSCLE

• Heat production
• Survival depends on the bodys ability to
  maintain a constant body temperature
• Feveran elevated body temperatureoften a sign
  of illness
• Hypothermiaa reduced body temperature
• Contraction of muscle fibers produces most of the
  heat required to maintain normal body temperature

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FATIGUE

• Reduced strength of muscle contraction
• Caused by repeated muscle stimulation without
  adequate periods of rest
• Repeated muscular contraction depletes cellular
  ATP stores and outstrips the ability of the blood
  supply to replenish oxygen and nutrients

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FATIGUE

• Contraction in the absence of adequate oxygen
  produces lactic acid, which contributes to muscle
  soreness
• Oxygen debtterm used to describe the metabolic
  effort required to burn excess lactic acid that
  may accumulate during prolonged periods of
  exercise the body is attempting to return the
  cells energy and oxygen reserves to pre-exercise
  levels

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What does Fatigue look like.
http//www.youtube.com/watch?vVbWsQMabczMp756EE
379B0E66FBDplaynext1index21
http//www.youtube.com/watch?vMTn1v5TGK_w
Or is that perseverance?
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ROLE OF OTHER BODY SYSTEMS IN MOVEMENT

• Muscle functioning depends on the functioning of
  many other parts of the body
• Most muscles cause movements by pulling on bones
  across movable joints
• Respiratory, circulatory, nervous, muscular, and
  skeletal systems play essential roles in
  producing normal movements
• Multiple sclerosis, brain hemorrhage, and spinal
  cord injury are examples of how pathological
  conditions in other body organ systems can
  dramatically affect movement

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MOTOR UNIT (Figure 7-4)

• Stimulation of a muscle by a nerve impulse is
  required before a muscle can shorten and produce
  movement
• A motor neuron is the specialized nerve that
  transmits an impulse to a muscle, causing
  contraction
• A neuromuscular junction is the specialized point
  of contact between a nerve ending and the muscle
  fiber it innervates
• A motor unit is the combination of a motor neuron
  with the muscle fiber or fibers it innervates

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MUSCLE STIMULUS

• A muscle will contract only if an applied
  stimulus reaches a certain level of intensity
• A threshold stimulus is the minimal level of
  stimulation required to cause a muscle fiber to
  contract
• Once stimulated by a threshold stimulus, a muscle
  fiber will contract completely, a response called
  all or none

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MUSCLE STIMULUS

• Different muscle fibers in a muscle are
  controlled by different motor units having
  different threshold-stimulus levels
• Although individual muscle fibers always respond
  all or none to a threshold stimulus, the muscle
  as a whole does not
• Different motor units responding to different
  threshold stimuli permit a muscle as a whole to
  execute contractions of graded force

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TYPES OF SKELETAL MUSCLE CONTRACTION

• Twitch and tetanic contractions
• Twitch contractions are laboratory phenomena and
  do not play a significant role in normal muscular
  activity they are a single contraction of muscle
  fibers caused by a single threshold stimulus
• http//www.youtube.com/watch?vpeSWznl5pWIfeature
  related
• Tetanic contractions are sustained and steady
  muscular contractions caused by a series of
  stimuli bombarding a muscle in rapid succession

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TYPES OF SKELETAL MUSCLE CONTRACTION

• Isotonic contractions
• Contraction of a muscle that produces movement at
  a joint because the muscle changes length
• During concentric contractions, the muscle
  shortens insertion end of the muscle to move
  toward the point of origin
• During eccentric contractions, the muscle
  lengthens under tension, thus moving the
  insertion away from the origin
• Most types of body movements such as walking and
  running are produced by isotonic contractions

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TYPES OF SKELETAL MUSCLE CONTRACTION

• Isometric contractions
• Isometric contractions are muscle contractions
  that do not produce movement the muscle as a
  whole does not shorten
• Although no movement occurs during isometric
  contractions, tension within the muscle increases

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EFFECTS OF EXERCISE ON SKELETAL MUSCLES

• Exercise, if regular and properly practiced,
  improves muscle tone and posture, results in more
  efficient heart and lung functioning, and reduces
  fatigue
• Muscles change in relation to the amount of work
  they normally do
• Prolonged inactivity causes disuse atrophy
• Regular exercise increases muscle size, called
  hypertrophy

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EFFECTS OF EXERCISE ON SKELETAL MUSCLES

• Strength training is exercise involving
  contraction of muscles against heavy resistance
• Strength training increases the number of
  myofilaments in each muscle fiber, and as a
  result, the total mass of the muscle increases
• Strength training does not increase the number of
  muscle fibers
• Endurance training is exercise that increases a
  muscles ability to sustain moderate exercise
  over a long period it is sometimes called
  aerobic training
• Endurance training allows more efficient delivery
  of oxygen and nutrients to a muscle via increased
  blood flow
• Endurance training does not usually result in
  muscle hypertrophy

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SKELETAL MUSCLE GROUPS (Table 7-1)

• Muscles of the head and neck (Figure 7-7)
• Facial muscles
• Orbicularis oculi
• Orbicularis oris
• Zygomaticus
• Muscles of mastication
• Masseter
• Temporal
• Sternocleidomastoidflexes head
• Trapeziuselevates shoulders and extends head

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SKELETAL MUSCLE GROUPS

• Muscles that move the upper extremities
• Pectoralis majorflexes upper arm
• Latissimus dorsiextends upper arm
• Deltoidabducts upper arm
• Biceps brachiiflexes forearm
• Triceps brachiiextends forearm

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SKELETAL MUSCLE GROUPS

• Muscles of the trunk (Figure 7-8)
• Abdominal muscles
• Rectus abdominis
• External oblique
• Internal oblique
• Transversus abdominis
• Respiratory muscles
• Intercostal muscles
• Diaphragm

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SKELETAL MUSCLE GROUPS

• Muscles that move the lower extremities
• Iliopsoasflexes thigh
• Gluteus maximusextends thigh
• Adductor musclesadduct thighs
• Hamstring musclesflex lower leg
• Semimembranosus
• Semitendinosus
• Biceps femoris
• Quadriceps femoris groupextend lower leg
• Rectus femoris
• Vastus muscles
• Tibialis anteriordorsiflexes foot
• Gastrocnemiusplantar flexes foot
• Peroneus groupflex foot

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MOVEMENTS PRODUCED BY SKELETAL MUSCLE
CONTRACTIONS (Figures 7-9 through 7-11)

• Flexionmovement that decreases the angle between
  two bones at their joint bending
• Extensionmovement that increases the angle
  between two bones at their joint straightening
• Abductionmovement of a part away from the
  midline of the body
• Adductionmovement of a part toward the midline
  of the body
• Rotationmovement around a longitudinal axis

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