The Muscular System

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The Muscular System

• Chapter 8

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Read Page 168

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8.1 Introduction

• Muscle an organ composed of specialized cells
  that uses chemical energy stored in nutrients to
  contract
• Functions
• movement
• muscle tone
• propel body fluids and food
• generate heartbeat
• distribute heat
• Types
• skeletal
• smooth
• cardiac

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8.2 Structure of a Skeletal Muscle

• Fascia
• layer of fibrous connective tissue
• separates muscles holds in position
• projects beyond muscle to form tendon
• attaches to periosteum of bone
• Aponeuroses
• broad fibrous sheet
• attaches to bone or coverings of other muscles

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8.2 Structure of a Skeletal Muscle

• Epimysium
• layer of connective tissue most closely
  surrounding muscle
• Perimysium
• connective tissue extending inward from epimysium
  to separate the muscle tissue into smaller
  compartments
• Fasicles
• compartments containing bundles of skeletal
  muscle fibers

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8.2 Structure of a Skeletal Muscle

• Skeletal Muscle Fiber
• single cell
• contracts in response to stimulation
• Contains
• Sarcolemma cell membrane
• Sarcoplasm cytoplasm
• nuclei
• mitochondria
• myofibrils parallel threads

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8.2 Structure of a Skeletal Muscle

• Myofibrils
• Contain two types of protein filaments causes
  striations in muscle fiber
• Myosin thick
• Actin - thin

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I bands light, thin actin filaments, connect to
Z line A bands dark, thick myosin overlaps thin
actin H zone thick filaments only M line
proteins holding thick filaments in
place Sarcomere area from Z line to Z line

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Sarcoplasmic reticulum membranous channels
surrounding myofibril, run parallel T tubules
channels extending inward, passes all the way
through Cisternae enlarged portion of
sarcoplasmic reticulum These areas activate
muscle contration
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Life Connection

• Muscle strain
• tearing of muscle fibers and connective tissues
• Mild
• few fibers torn
• fascia intact
• minimal loss of function
• Severe
• everything torn
• function may be completely lost

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Review

• Describe how connective tissue is a part of a
  skeletal muscle.
• Describe the general structure of a skeletal
  muscle fiber.
• Explain why skeletal muscles appear striated.
• Explain the relationship between the sarcoplasmic
  reticulum and transverse tubules.

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8.2 Structure of a Skeletal Muscle

• Neuromuscular
• Junction
• connection of
• motor neuron
• and muscle fiber

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8.2 Structure of a Skeletal Muscle

• Motor End Plate
• specialized part of muscle fiber
• abundant mitochondria and nuclei
• sarcolemma folded
• Neurotransmitters
• chemical excreted by axon
• stimulates muscle contraction
• Muscle fiber has single motor
• end plate but axons are
• densely branched
• Motor Unit
• motor neuron and fibers it controls

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Review

• Which two structures approach each other at a
  neuromuscular junction?
• Describe a motor end plate.
• What is the function of a neurotransmitter?
• What is a motor unit?

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8.3 Skeletal Muscle Contraction
Myosin molecule two twisted protein strands
with cross bridges Myosin filament many
molecules put together Actin molecule contains
binding site for cross bridges Actin filament
many molecules twisted into double helix
containing troponin and tropomyosin
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Sliding Filament Theory
1 2 Calcium ion concentration rises, binding
sites on actin filaments open, cross bridges
attach
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Sliding Filament Theory
3 4 Upon binding to actin, cross bridges
spring from the cocked position and pull on actin
filament

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Sliding Filament Theory

5. ATP binds to cross bridge causing it to
release from the actin filament. 6. ATP
breakdown provides energy to cock the unattached
myosin cross bridge. Cycle continues as long as
ATP and calcium are present.
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8.3 Skeletal Muscle Contraction

• Neurotransmitter Acetylcholine
• Nerve impulse causes release into synaptic cleft
• Binds to receptors in muscle fibers
• Stimulates muscle impulse
• Impulse travels through T-tubules
• Reaches sarcoplasmic reticulum
• Calcium ions diffuse into sarcoplasm
• Troponin and Tropomyosin expose binding sites on
  actin
• Actin and myosin filaments link
• Muscle fiber contracts

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When a skeletal muscle contracts the individual
sarcomeres shorten as thick and thin filaments
slide past one another.

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8.3 Skeletal Muscle Relaxation

• Nerve impulses stop
• Acetylcholine broken down by acetylcholinesterase
• Calcium transported back into sarcoplasmic
  reticulum
• Links between actin and myosin break
• Troponin and Tropomyosin block binding sites on
  action
• Muscle fiber relaxes

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Real World

• Bacteria Clostridium botulinum
• Prevents release of acetylcholine
• Muscle fibers arent stimulated paralyzed
• bad if youre trying to breathe
• Botox injections used to smooth wrinkles by
  preventing local muscles from contracting

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8.3 Energy Sources

• ATP only lasts short time have to make more
  from ADP and Phosphate
• Creatine Phosphate molecule with high energy
  phosphate bonds
• more abundant than ATP in muscle fibers
• stores excess energy from mitochondria
• when ATP low this excess energy is transferred to
  ADP molecules to make more ATP
• Cellular respiration of glucose used when other
  sources depleted

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8.3 Oxygen Supply

• Needed to breakdown glucose in mitochondria
• Blood carries oxygen from lungs to body cells
• During rest or moderate activity respiratory and
  cardiovascular systems have no trouble supplying
  oxygen.
• Aerobic respiration-glucose broken into CO2 and O2

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8.3 Oxygen Debt

• Anaerobic Respiration
• Glucose broken down into pyruvic acid
• Pyruvic acid then produces lactic acid
• Lactic acid gets into bloodstream and is taken to
  the liver
• Liver uses ATP to make glucose out of the lactic
  acid
• During exercise not enough oxygen for liver to
  make glucose
• Debt amount of oxygen needed for liver to make
  glucose amount muscles need to restore ATP and
  creatine phosphate to their original
  concentrations

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8.3 Oxygen Debt

• Repayment may take several hours
• Can change metabolism with training
• increase amount of glycolytic enzymes
• more capillaries and mitochondria form

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8.3 Muscle Fatigue

• Fatigue loss of ability to contract
• Can be caused by interruption of blood supply of
  lack of acetylcholine
• Usually caused by too much lactic acid
• lowers pH and fibers cant contract
• Cramp sustained involuntary contraction

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Real Life

• Rigor Mortis
• Calcium ions easily diffuse into membrane
• Decrease in ATP prevents relaxation
• Actin and Myosin stay linked until muscles start
  to decompose

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8.3 Heat Production

• ½ of bodys energy used for metabolic purposes
• ½ becomes heat
• All cells generate heat, but muscle is big part
  of body mass
• Blood takes heat generated in muscles to other
  parts of body to maintain temperature

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Review

• Which biochemicals provide the energy to
  regenerate ATP?
• What are the sources of oxygen for aerobic
  respiration?
• How are lactic acid, oxygen debt, and muscle
  fatigue related?
• What is the relationship between cellular
  respiration and heat production?

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8.4 Muscular Responses

• Threshold Stimulus
• minimal strength required to cause a contraction
• All-or-None Response
• fibers dont partly contract
• either it contracts all the way or not at all

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8.4 Recording Contractions

• Twitch
• single contraction
• Latent Period
• delay time
• between stimulus
• and response

Myogram
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Real World

• Normal people
• ½ fast twitch and ½ slow twitch
• Olympic sprinter
• 80 fast twitch
• muscles bigger
• stronger contractions
• Olympic marathoner
• 90 slow twitch
• resists fatigue
• abundant mitochondria (aerobic)

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Individual Twitches

Summation muscle not completely relaxed before
next stimulus arrives
Tetanic Contraction Tetanus sustained
contraction with no relaxation
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8.4 Muscular Responses

• Recruitment
• Increase in the number of motor units being
  activated
• low stimulus few motor neurons stimulated
• high stimulus many neurons stimulated
• Summation and Recruitment produce sustained
  contractions of increasing strength
• Muscle Tone
• response to nerve impulses that stimulate a few
  muscle fibers
• needed to keep us from collapsing like when we
  lose consciousness

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Review

• Define threshold stimulus.
• What is an all-or-none response?
• Distinguish between a twitch and a sustained
  contraction.
• How is muscle tone maintained?

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8.5 Smooth Muscle

• Not striated
• contains actin and myosin filaments, but they
  arent well organized
• sarcoplasmic reticulum not developed

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8.5 Smooth Muscle

• Two types
• Multiunit
• muscle fibers separate
• irises of eyes and walls of blood vessels
• contract only in response to stimulation by motor
  nerve impulses or hormones
• Visceral
• sheets of cells in close contact with each other
• walls of hollow organs (stomach, intestines,
  etc.)
• stimulate each other
• rhythmicity pattern of repeated contractions
• Peristalsis forces the content of the organs
  along their lengths

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8.5 Smooth Muscle Contraction

• Like skeletal
• include actin and myosin
• triggered by membrane impulses and increased
  calcium concentration
• use ATP
• Different from skeletal
• Neurotransmitters acetylcholine and
  norepinephrine stimulate contractions in some
  muscles and inhibit in others
• affected by hormones
• slower to contract and relax
• maintain forceful contractions longer
• fibers can change length without changing
  tautness
• stomach can fill up without losing pressure

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Review

• Describe two major types of smooth muscle.
• What special characteristics of visceral smooth
  muscle make peristalsis possible?
• How does smooth muscle contraction differ from
  that of skeletal muscle?

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8.6 Cardiac Muscle

• Only found in heart
• Composed of
• branching striated cells
• sarcoplasmic reticulum
• many mitochondria
• large transverse tubules
• cisternae not well developed
• intercalated discs
• crossbands connecting opposing ends of cardiac
  cells
• helps impulses pass quickly
• Cells contract as unit
• Self-exciting and rhythmic

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Review

• How is cardiac muscle similar to smooth muscle?
• How is cardiac muscle similar to skeletal muscle?
• What is the function of intercalated discs?
• What characteristic of cardiac muscle contracts
  the heart as a unit?

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Origin The immovable end of the
muscle Insertion The movable end of the
muscle When a muscle contracts the insertion is
pulled toward its origin

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8.7 Interaction of Skeletal Muscles

• Muscles usually function in groups
• Prime mover Agonist
• The muscle doing the main work
• Deltoid lifts arm horizontally
• Synergist
• Muscles that contract to assist the prime mover
• Makes prime movers actions more effective
• Hold shoulder steady
• Antagonist
• Resist prime movers action and cause movement in
  opposite direction
• Lowers the arm

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Review

• Distinguish between the origin and the insertion
  of a muscle.
• Define prime mover.
• What is the function of a synergist? An
  antagonist?

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FYI

• Human body contains over 600 muscles
• Face has 60
• 40 used to frown
• 20 to smile
• Smallest
• stapedius middle ear
• Largest
• gluteus maximus
• Longest
• sartorius

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