PowerPoint to accompany

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Human Anatomy and Physiology
Chapter 9 Muscular System
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Chapter 9Muscular System
Three Types of Muscle Tissues -All designed to
contract

• Cardiac Muscle
• wall of heart
• not under conscious control
• striated

• Skeletal Muscle
• usually attached to bones
• under conscious control
• striated

• Smooth Muscle
• walls of most viscera, blood vessels, skin
• not under conscious control
• not striated

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Structure of a Skeletal Muscle

• Skeletal Muscle
• organ of the muscular system
• skeletal muscle tissue
• nervous tissue
• blood
• connective tissues
• fascia- tissue surrounds each muscle
• tendon- attach muscle to bone
• aponeuroses- attach muscle to muscle

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Structure of a Skeletal Muscle

• muscle is surrounded by epimysium
• muscle is divided into fasicles by perimysium
• Fasicle is divided into muscle fibers (cells) by
  endomysium

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Skeletal Muscle Fiber

• sarcolemma surrounds muscle fiber (muscle cell)
  and contains many nuclei, mitochondria, and
  myofibrils
• sarcoplasmic reticulum contains calcium ions
• muscle fiber is made of many myofibrils
• are made of actin (thin) and myosin (thick)
• are divided into sections called sarcomeres

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Myofilaments

• Thin Filaments
• composed of actin (protein)
• associated with troponin and tropomyosin

• Thick Filaments
• composed of myosin (protein)
• cross-bridges

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Sarcomere

• Sarcomeres are the active unit of the cell
• I band
• A band
• H zone
• Z line
• M line

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Neuromuscular Junction

• site where axon (end of nerve) and muscle fiber
  communicate
• motor neuron
• motor end plate
• synaptic cleft
• synaptic vesicles
• neurotransmitters

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Motor Unit

• group of muscle fibers attached to a single
  motor neuron
• all muscle fibers controlled by motor neuron
• muscle fibers act as group

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Stimulus for Contraction

• acetylcholine (ACh) neurotransmitter
• nerve impulse causes release of acetylcholine
  from synaptic vesicles
• binds to acetylcholine receptors on motor end
  plate
• generates a muscle impulse
• muscle impulse eventually reaches sarcoplasmic
  reticulum

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Excitation Contraction Coupling

1. muscle impulses cause sarcoplasmic reticulum to
   release calcium ions into cytosol
2. calcium binds to troponin-tropomyosin complex to
   change its shape
3. position of t-t complex is altered
4. binding sites on actin exposed
5. myosin binds to actin

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Cross-bridge Cycling
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1. myosin cross-bridge pulls actin

1. ADP and phosphate released from myosin

1. new ATP binds to myosin

1. linkage between actin and myosin cross-bridge
   break

1. ATP splits

12. stimulus stopped, calcium pumped out, t-t
complex recovers binding sites or process keeps
cycling (back to step 5 further down the actin
filament)

1. myosin cross-bridge goes back to original position

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Sliding Filament Theory

• When sarcomeres shorten, thick and thin
  filaments slide past one another
• H zones and I bands get narrower
• Z lines move closer together

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Relaxation

• motor neuron impulse stops
• acetylcholinesterase released breaks down
  acetylcholine
• calcium moves back into sarcoplasmic reticulum
• t-t complex covers binding site
• myosin and actin binding prevented

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Energy Sources for Contraction
1) Cellular respiration ATP Production 2)
Creatine Phosphate

• creatine phosphate stores energy that quickly
  converts ADP to ATP

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Oxygen Supply and Cellular Respiration

• Aerobic Phase
• use oxygen
• citric acid cycle
• electron transport chain
• produces most ATP (36)
• myoglobin stores extra oxygen

• Anaerobic Phase
• no oxygen
• glycolysis
• produces little ATP (2)

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Anaerobic threshold
Anaerobic threshold- point at which there is not
enough O2 and cell transitions to anaerobic
respiration

• oxygen not available
• glycolysis continues
• pyruvic acid is converted to lactic acid
• liver converts lactic acid to glucose

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Muscle Fatigue

• inability to contract
• commonly caused from
• lack of oxygen/lungs at capacity or
• decreased blood flow
• anaerobic respiration
• decrease in available ATP
• accumulation of lactic acid
• ion imbalances
• cramp sustained, involuntary contraction

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Heat Production

• by-product of cellular respiration
• muscle cells are major source of body heat
• blood transports heat throughout body

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Muscular Responses

• Threshold Stimulus
• minimal strength required to cause contraction

• Recording a Muscle Contraction
• twitch- single contraction
• latent period
• period of contraction
• period of relaxation
• refractory period
• all-or-none response

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Summation

• process by which individual twitches combine
• produces sustained contractions
• can lead to tetanic contractions sustained
  contraction that lacks relaxation

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Recruitment of Motor Units

• recruitment - increase in the number of motor
  units activated (causes stronger contraction)

• whole muscle composed of many motor units

• as intensity of stimulation increases,
  recruitment of motor units continues until all
  motor units are activated

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Sustained Contractions

• smaller motor units recruited first
• larger motor units recruited later
• produces smooth movements
• muscle tone continuous state of partial
  contraction

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Types of Contractions

• isotonic muscle contracts and changes length

• isometric muscle contracts but does not change
  length

• concentric shortening contraction

• eccentric lengthening contraction

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Fast and Slow Twitch Muscle Fibers

• Fast-twitch fatigue-resistant fibers (type IIb)
• intermediate fibers
• oxidative
• intermediate amount of myoglobin
• pink to red in color

• Slow-twitch fibers (type I)
• always oxidative
• resistant to fatigue
• red fibers
• most myoglobin
• good blood supply
• posture muscles

• Fast-twitch glycolytic fibers (type II)
• white fibers (less myoglobin)
• poorer blood supply
• susceptible to fatigue

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Smooth Muscle Fibers

• Compared to skeletal muscle fibers
• shorter
• single nucleus
• elongated with tapering ends
• no striations
• myofilaments randomly organized
• lack transverse tubules
• sarcoplasmic reticula not well developed

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Types of Smooth Muscle

• Multiunit Smooth Muscle
• fibers function separately
• irises of eye
• walls of blood vessels

• Visceral Smooth Muscle
• single-unit smooth muscle
• sheets of muscle fibers
• exhibit rhythmicity/ peristalsis
• walls of most hollow organs

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Smooth Muscle Contraction

• Resembles skeletal muscle contraction
• interaction between actin and myosin
• both use calcium and ATP
• both depend on impulses

• Different from skeletal muscle contraction
• smooth muscle lacks troponin
• two neurotransmitters affect smooth muscle
• acetlycholine and norepinephrine
• hormones affect smooth muscle
• stretching can trigger smooth muscle contraction
• smooth muscle slower to contract and relax
• smooth muscle more resistant to fatigue

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Cardiac Muscle

• only in the heart
• muscle fibers joined together by intercalated
  discs
• fibers branch
• network of fibers contracts as a unit
• self-exciting and rhythmic
• longer refractory period than skeletal muscle

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Skeletal Muscle Actions

• origin immovable end
• insertion movable end

• prime mover (agonist) primarily responsible
  for movement
• synergists assist prime mover
• antagonist resist prime movers action and
  cause movement in the opposite direction

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Life-Span Changes

• myoglobin, ATP, and creatine phosphate decline
• by age 80, half of muscle mass has atrophied
• adipose cells and connective tissues replace
  muscle tissue
• exercise helps to maintain muscle mass and
  function

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