Muscle Tissue Chapter 10 Lecture Notes

1
Muscle TissueChapter 10 Lecture Notes

• to accompany
• Anatomy and Physiology From Science to Life
• textbook by
• Gail Jenkins, Christopher Kemnitz, Gerard Tortora

2
Chapter Overview

• 10.1 Three Types of Muscle Tissue
• 10.2 Function and Properties of Muscle Tissue
• 10.3 Skeletal Muscle Support Tissues
• 10.4 Skeletal Muscle Fibers
• 10.5 Neuromuscular Junction
• 10.6 Sliding Filament Mechanism
• 10.7 Muscle Fiber Tension
• 10.8 ATP Production
• 10.9 Skeletal Muscle Fiber Types
• 10.10 Cardiac and Smooth Muscle

3
Introduction

• Primary function to turn chemical energy into
  mechanical energy
• Alternating contraction and relaxation
• creates motion
• stabilizes body position
• regulates organ volume
• generates heat
• propels fluids and food
• 40-50 of total body weight

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Concept 10.1Three Types of Muscle Tissue
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Properties of Muscle Tissue

• Three types
• Skeletal
• Cardiac
• Smooth
• Characteristics and Variances
• Striations
• Control
• Primarily Voluntary or Involuntary
• Nervous or Endocrine or both
• Location and number of nuclei
• Tissue Location

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Variance of Muscle Tissues
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Table 4.3 pt 1
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Table 4.3 pt 2
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Table 4.3 pt 3
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Concept 10.2 Function and Properties of Muscle
Tissue
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Functions and Properties

• Functions
• producing body movement
• stabilizing body positions
• storing and moving substances through body
• producing heat
• Properties
• electrical excitability
• contractility
• extensibility
• elasticity

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Concept 10.3 Skeletal Muscle Support Tissues
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Connective Tissue Components

• Layers of skeletal muscle connective tissue
• epimysium
• outermost layer
• wraps entire muscle
• dense irregular connective tissue
• perimysium
• middle layer
• wraps fascicle
• 10-100 or more muscle fibers
• dense irregular connective tissue
• endomysium
• wraps individual muscle fibers
• areolar connective tissue

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Connective Tissue Components

• Tendon
• cord of dense regular connective tissue
• three layers of connective tissue wrapping that
  extend beyond muscle fibers
• parallel bundles of connective tissue
• attaches to periosteum of bone
• Aponeurosis
• broad flat tendon
• Tendon sheath
• enclosed by tubes of fibrous connective tissue
• similar in structure to bursae with film of
  synovial fluid

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Figure 10.2
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Nerve Supply

• Motor neurons
• stimulate skeletal muscle
• axon (signal sending portion of neuron)
• extends from brain or spinal cord to muscle
• axon collaterals (branches)
• attach to different muscle fibers
• neuromuscular junction
• junction between axon and muscle fiber

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Blood Supply

• Each fiber is in close contact with one or more
  capillaries
• bring oxygen and nutrients
• remove heat and wastes products

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Concept 10.4 Skeletal Muscle Fibers
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Fiber Characteristics

• Diameter 10 100 microns
• Length 10 cm average
• can be up to 30 cm
• Mature muscle cells are nonmitotic
• a few myoblasts persist as satellite cells
• retain capacity to fuse with one another or
  damages muscle fibers to repair damage
• Muscle growth occurs by hypertrophy
• enlargement of existing muscle cells

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Figure 10.4
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Sarolemma, Transverse Tubules, and Sarcoplasm

• Sarcolemma
• plasma membrane
• Transverse Tubules (T tubules)
• tunnel like extensions of sarcolemma extend
  toward center of each muscle fiber
• open to outside of fiber and filled with
  interstitial fluid
• Sarcoplasm
• cytoplasm of muscle fiber

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Myofibrils Sarcoplasmic Reticulum

• myofibrils
• contractile elements of skeletal muscle
• 2 microns in diameter
• extend entire length of muscle fibers
• sarcoplasmic reticulum
• similar to endoplasmic reticulum
• wraps around each myofibril
• dilated end sacs called terminal cisterns
• stores calcium ions which when released triggers
  contraction of myofibrils

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Filaments

• thin filaments
• actin
• 2 per myofibril
• 8 micron diameter
• thick filaments
• myosin
• 1 per myofibril
• 16 micron diameter
• arrangement
• overlap depending on extent of contraction
• pattern of overlap found in structure of sarcomere

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Sarcomere

• visible as striations
• functional arrangement of filaments
• z discs
• separate sarcomeres
• A band
• extends entire length of thick filaments
• H zone
• narrow center of each A band
• I band
• lighter less dense area with thin filaments only
• M line
• middle of sarcomere

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Figure 10.6
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Contractile Muscle Proteins

• myosin (thick filament)
• achieves movement
• converts chemical energy to mechanical energy
• 300 per thick filament
• shaped like two golf clubs twisted together
• actin (thin filaments)
• twisted into a helix
• myosin binding sites

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Figure 10.7a
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Figure 10.7b
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Regulatory Muscle Proteins

• tropomyosin (regulatory protein)
• wrapped around actin covering myosin binding site
• troponin
• holds tropomyosin in place when not bound to
  calcium ions
• Structural Proteins
• titin
• third most plentiful protein
• after actin and myosin
• spans half of sarcomere
• from Z disc to M line
• anchors and stabilizes thick filament

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Figure 10.5
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Concept 10.5 Neuromuscular Junction
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Neuromuscular Junction (NMJ)

• region of synaptic contact between motor neuron
  and skeletal muscle fiber
• synapse
• region where communication between neuron and
  another cell
• gap between cells called synaptic cleft
• neuron ends in end bulb
• within end bulb are synaptic vesicles containing
  neurotransmitter acetylcholine (ACh)
• motor end plate
• region of sarcolemma adjacent to end bulb

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Figure 10.13
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Figure 10.3
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Action Potential Generation

• nerve impulse arrives at end bulb
• synaptic vesicles undergo exocytosis
• acetylcholine liberated into synaptic cleft
• ACh receptors activated opening sodium ion
  channel
• sodium influx triggers action potential along
  sarcolemma and down T tubules
• ACh in synaptic cleft broken down by
  acetylcholinesterase
• Each impulse triggers one muscle action potential

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Figure 10.8
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Concept 10.6 Sliding Filament Mechanism
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Sliding Filament Mechanism

• Each action potential releases calcium ions from
  the sarcoplasmic reticulum, binds myosin heads
  to actin, which pulls actin toward center of
  sarcomere

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Excitation-Contraction Coupling

• When calcium is released from the SR, it binds to
  troponin
• This bonding moves tropomyosin away from
  myosin-binding site on actin
• when the myosin-binding sites on actin are
  exposed, myosin heads bind to them

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Figure 10.9
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Contraction Cycle

• Four steps
• ATP splits
• reorients and energizes myosin head
• myosin attaches to actin
• forming crossbridges
• releases phosphate
• power stroke occurs
• myosin head rotates and releases ADP
• generates force pulling actin filament past thick
  filament toward M line
• myosin detaches from actin
• ATP binds to myosin and head detaches

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Figure 10.14
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Figure 10.10
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Figure 10.11
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Relaxation

• nerve impulse ceases
• ACh release stops and is broken down
• ion channels close
• calcium release from SR ceases
• calcium ions concentration lowered
• calcium ions returned to SR
• via calcium ion active transport pumps
• calsequestrin binds calcium ions
• troponin-tropomyosin slide back over myosin
  binding sites on myosin
• thin filaments return to relaxed position

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Relaxation
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Figure 10.12
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Concept 10.7 Muscle Fiber Tension
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Muscle Fiber Tension

• tension of single muscle fiber depends on rate at
  which nerve impulses arrive at NMJ
• frequency of stimulation
• number of impulses per second
• tension of whole muscle depends on number of
  fibers contracting in unison

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Motor Units

• one motor neuron plus all skeletal muscle fibers
  it stimulates
• one neuron stimulates 150 muscle fibers
• contract in unison
• muscles that control fine motor unit have many
  small motor units
• 2 or 3 fibers per motor unit
• muscles that control gross motor unit have fewer
  motor units and many muscle fibers
• 2000 to 3000 fibers per motor unit

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Twitch Contraction

• brief contraction of all muscle fibers in a motor
  unit in response to single nerve impulse
• can be produced in lab by direct electrical
  stimulation of motor neuron or its muscle fibers
• record of muscle contraction called myogram

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Twitch Contraction

• latent period
• occurs between application of the stimulus and
  beginning of contraction
• calcium released
• contraction period
• repetitive power strokes are occurring
• generating tension or force of contraction
• relaxation period
• calcium being transported back into SR
• power stroke ceases

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Frequency of Stimulation

• wave summation
• second stimulus occurs before muscle fiber has
  relaxed completely second contraction will be
  stronger than first
• unfused tetanus
• frequency of 20-30 stimuli per second
• sustained but wavering contraction
• fused tetanus
• frequency of 80-100 stimuli per second
• sustained contraction that lacks even partial
  relaxation

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Figure 10.15
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Motor Unit Recruitment

• number of contracting motor units increased
• alternating contraction of motor units
• delays muscle fatigue
• allows for smooth muscle movements
• allows for precision movements
• as one unit is turned off another is turned on
  maintaining tension but allowing restoration of
  relaxation

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Muscle Tone

• small amount of tautness or tension
• due to weak involuntary contractions of small
  number of motor units
• keeps skeletal muscles firm but doesnt result in
  a contraction
• Helps maintain posture, holding up head,
  maintaining body position
• Plays a role in the skeletal muscle pump

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Isotonic Contractions

• isotonic contraction
• change in length of muscle but no change in
  tension
• used for body movements and for moving objects
• concentric isotonic contraction
• muscle shortens and pulls on another structure
  such as tendon to produce movement and reduce
  angle
• great enough to overcome load
• picking up an object

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Figure 10.16a
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Figure 10.16b
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Isometric Contractions

• muscle does not shorten
• tension not enough to pull thin filaments inward
• when load equals or exceeds muscle tension
• example holding a book steady using outstretched
  arm

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Figure 10.16c
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Concept 10.8 ATP Production
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ATP Production

• ATP only molecule within muscle fibers that can
  directly transfer energy
• only enough present in muscles to power
  contraction for a few seconds
• if activity continues beyond that, more ATP must
  be produced
• Three methods of ATP Production
• Creatine Phosphate
• Anaerobic Cellular Respiration
• Aerobic Cellular Respiration

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Creatine Phosphate

• excess ATP produced during relaxation
• used to synthesize creatine phosphate
• one of ATPs high energy phosphate groups is
  transferred to creatine
• three to six times more plentiful than ATP in
  sarcoplasm of relaxed muscle fiber
• when contraction begins, phosphate transferred
  back to ADP
• provides enough energy for 15 seconds

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Figure 10.17a
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Anaerobic Cellular Respiration

• when muscle activity continues beyond 15 second
  mark
• glucose taken up by cells
• glycolysis begins
• if not enough oxygen is available
• anaerobic processes turn pyruvic acid into lactic
  acid
• liver can convert some lactic acid back to
  glucose
• can provide enough energy for 30-40 seconds of
  maximal muscle activity

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Figure 10.17b
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Aerobic Cellular Respiration

• series of oxygen requiring reactions that produce
  ATP in mitochondria
• if enough oxygen is present
• pyruvic acid from glycolysis enters mitochondria
• completely oxidized to 36 molecules of ATP,
  carbon dioxide, water, and heat
• Sources of oxygen
• diffused from blood
• released by myoglobin in sarcoplasm

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Figure 10.17c
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Aerobic Cellular Respiration

• provides enough ATP for prolonged activity as
  long as sufficient oxygen and nutrients are
  available
• nutrients include
• pyruvic acid
• fatty acid (from triglycerides)
• amino acids
• ATP produced by aerobic cellular respiration
• activities lasting more than 10 minutes, most ATP
• endurance events 100 of ATP

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Muscle Fatigue

• initial desire to stop, feeling of tiredness
  caused by CNS changes
• may be protective mechanism
• factors thought to contribute
• inadequate calcium ion release
• depletion of creatine phosphate
• insufficient oxygen
• depletion of glycogen and other nutrients
• build up of lactic acid and ADP
• failure of nerve impulses in motor neurons to
  release enough acetylcholine

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Oxygen Consumption

• After exercise and muscle contraction
• increases in breathing effort and blood flow
  enhance oxygen delivery to muscle tissue
• heavy breathing continues for a period of time
• and oxygen consumption remains above resting
  level
• recovery period can be a few minutes or a several
  hours depending on intensity of exercise
• oxygen pay back restores normal metabolic
  conditions
• convert lactic acid back to glycogen in liver
• resynthesize creatine phosphate and ATP
• replace oxygen removed from myoglobin

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Recovery Oxygen Uptake

• much of lactic acid is converted back to pyruvic
  acid and used for ATP production via aerobic
  cellular respiration
• elevated temperature after exercise increases
  rate of chemical reactions in body
• faster reactions use more ATP
• more oxygen is needed
• heart muscles and respiration muscles still
  working harder than normal consuming more ATP
• tissue repair processes occurring at increased
  pace

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Concept 10.9 Skeletal Muscle Fiber Types
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Functional Types of Fibers

• vary structurally in content of myoglobin
• low myoglobin fibers called white muscle fibers
• high myoglobin fibers called red muscle fibers
• vary in speed of contraction and which reactions
  are used to generate ATP
• slow oxidative fibers
• fast oxidative-glycolytic fibers
• fast glycolyic fibers

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Slow Oxidative (SO) Fibers

• smallest in diameter
• least powerful type
• appear dark red
• high myoglobin content
• high density of capillaries
• generate ATP mainly by aerobic cellular
  respiration
• slow use of ATP
• slow speed of contraction
• very resistant to fatigue
• adapted to maintaining posture and for aerobic,
  endurance-type activities

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Fast Oxidative-Glycolytic (FOG)

• intermediate diameter
• contain large amounts of myoglobin
• many capillaries
• generate considerable ATP by aerobic cellular
  respiration
• moderately high resistance to fatigue
• glycogen level is high
• also generate ATP by glycolysis
• fast use of ATP
• faster use of ATP than slow fibers
• used in walking and sprinting

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Fast Glycolytic (FG) Fibers

• largest in diameter
• contain most myofibrils
• can generate most powerful contractions
• white fibers
• low myoglobin and few blood capillaries
• large amounts of glycogen
• generate ATP mainly by glycolysis
• contract strong and quickly
• adapted for intense anaerobic movements of short
  duration like weight lifting or throwing a ball
• fatigue quickly

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Fast Glycolytic (FG) Fibers

• weight training
• increase in
• size of fibers
• up to 50 larger than sedentary person or
  endurance athlete
• due to increase of muscle proteins
• strength of fibers
• glycogen content in fibers
• overall size of muscle increase due to
  hypertrophy of FG fibers

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Distribution and Recruitment

• most muscles are mixture of all three types of
  fibers
• proportions vary somewhat depending on
• action of muscle
• persons training regimen
• genetic factors
• motor units all have same type of fibers
• different motor units recruited in specific
  orders depending on need
• SO for weak contraction
• FOG for more force
• FG for maximal force

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Table 10.1
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Concept 10.10 Cardiac Smooth Muscle
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Cardiac Muscle

• found only in heart wall
• fibers are shorter in length than skeletal
• less circular in transverse section
• exhibit branching
• usually one centrally located nucleus
• connected to one another via intercalated discs
• cell junctions called desmosomes
• gap junctions
• autorhythmic
• generating spontaneous action potentials

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Figure 10.18a
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Cardiac Muscle

• average contraction 75 per minute
• requires constant supply of oxygen and nutrients
• mitochondria larger and more numerous
• mostly aerobic cellular respiration
• can use lactic acid to make ATP

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Figure 10.18b
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Physiology of Smooth Muscle

• no T tubules
• delayed contraction and relaxation cycles
• can sustain long term tone
• innervated by autonomic nervous system
• relax in response to
• stretching
• hormones (epinephrine)
• changes in pH, oxygen, and carbon dioxide levels,
  temperature, and ion concentration

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Two Types of Smooth Muscle

• visceral (single unit) muscle tissue
• found in sheets that form walls of small arteries
  and veins and hollow organs
• autorhythmic
• connect by gap junction
• cells contract as single unit
• multiunit smooth muscle
• individual fibers
• each with own motor neuron terminals
• few gap junctions
• walls of large arteries, airways to lungs,
  arrector pili muscles of hair follicles, internal
  eye muscles

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Two types of Smooth Muscle
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Physiology of Smooth Muscle

• sliding filament mechanism generates tension
  transmitted to intermediate filaments
• intermediate filaments pull on dense bodies
  attached to sarcolemma
• causes lengthwise shortening of muscle fiber
• contraction results in corkscrew twists
• relaxes in opposite direction
• starts more slowly and lasts much longer
• can both shorten and stretch to greater extent
  than other muscle types
• regulatory protein
• calmodulin rather than troponin

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Smooth Muscle Contraction
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Table 10.2
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End Chapter 10