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MUSCLE TISSUE

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MUSCLE TISSUE Dr. Michael P. Gillespie * * FIGURE 3-18. A motor unit consists of the (alpha) motor neuron and the muscle fibers it innervates. – PowerPoint PPT presentation

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Title: MUSCLE TISSUE


1
MUSCLE TISSUE
  • Dr. Michael P. Gillespie

2
POSTURE / MOVEMENT
  • Stable posture results from a balance of
    competing forces.
  • Movement occurs when competing forces are
    unbalanced.
  • Force generated by muscles is the primary means
    for controlling the balance between posture and
    movement.

3
MUSCLE AS A SKELETAL STABILIZER
  • Muscle generates force to stabilize the skeletal
    system.
  • Muscle tissue is coupled to the external
    environment and internal control mechanisms
    provided by the nervous system allow it to
    respond to changes in the external environment.
  • Whole muscles consist of many individual muscle
    fibers.
  • Muscle adapts to the immediate (acute) and
    repeated long-term (chronic) external forces that
    can destabilize the body.
  • Fine control surgery
  • Large forces dead-lift

4
Types of Muscle Tissue
  • Skeletal muscle tissue
  • Cardiac muscle tissue
  • Autorhythmicity - pacemaker
  • Smooth muscle tissue

5
Functions of Muscle Tissue
  • Producing body movements
  • Stabilizing body positions
  • Storing and moving substances within the body
  • Sphincters sustained contractions of ringlike
    bands prevent outflow of the contents of a hollow
    organ
  • Cardiac muscle pumps nutrients and wastes through
  • Smooth muscle moves food, bile, gametes, and
    urine
  • Skeletal muscle contractions promote flow of
    lymph and return blood to the heart
  • Generating heat - thermogenesis

6
Properties of Muscle Tissue
  • Electrical excitability
  • Produces electrical signals action potentials
  • Contractility
  • Isometric contraction tension without muscle
    shortening
  • Isotonic contraction constant tension with
    muscle shortening

7
Properties of Muscle Tissue
  • Extensibility ability of a muscle to stretch
    without being damaged
  • Elasticity
  • Ability of a muscle to return to its original
    length

8
Connective Tissue Components
  • Fascia a sheet of fibrous CT that supports or
    surrounds muscles and other organs
  • Superficial fascia (subcutaneous layer)
    separates muscle from skin
  • Deep fascia holds muscles with similar
    functions together
  • Epimysium outermost layer encircles whole
    muscles
  • Perimysium
  • Surrounds groups of 10 100 individual muscle
    fibers separating them into bundles called
    fascicles

9
Connective Tissue Components
  • Endomysium
  • Separates individual muscle fibers within the
    fascicle
  • Tendon
  • All 3 CT layers may extend beyond the muscle to
    form a cord of dense regular CT that attaches
    muscle to the periosteum of bone
  • Aponeurosis
  • A broad, flat layer of CT

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11
BASIC COMPONENTS OF MUSCLE
12
MUSCLE SIZE
  • Whole muscles are made up of many individual
    muscle fibers.
  • These fibers range in thickness from 10 to 100 µm
    and in length from 1 to 50 cm.
  • Each muscle fiber is an individual muscle cell
    with many nuclei.
  • The individual muscle fibers contract, which will
    ultimately result in contraction of the entire
    muscle.

13
Nerve and Blood Supply
  • Skeletal muscles are well supplied with nerves
    and blood vessels
  • Neuromuscular junction the structural point of
    contact and the functional site of communication
    between a nerve and the muscle fiber
  • Capillaries are abundant each muscle fiber
    comes into contact with 1 or more

14
TWO TYPES OF PROTEINS IN MUSCLE
  • Contractile proteins
  • Actin and myosin
  • Shorten the muscle fiber and generate active
    force
  • Referred to as active proteins
  • Noncontractile proteins
  • Titan and desmin
  • Titan provides tensile strength
  • Desmin stabilizes adjacent sarcomeres
  • Make up the cytoskeleton within and between
    muscle fibers
  • Referred to as structural proteins

15
Sarcolemma, T Tubules, and Sarcoplasm
  • Sarcolemma the plasma membrane of a muscle cell
  • T (transverse) tubules Propogate action
    potentials extend to the outside of the muscle
    fiber
  • Sarcoplasm cytoplasm of the muscle fiber
  • Contains myoglobin protein that binds with
    oxygen

16
Myofibrils and Sarcoplasmic Reticulum
  • Myofibril the contractile elements of skeletal
    muscle
  • Sarcoplasmic reticulum (SR) encircles each
    myofibril stores CA2 (its release triggers
    muscle contractions)

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18
Atrophy and Hypertrophy
  • Muscular atrophy wasting away of muscles
  • Disuse
  • Denervation
  • Muscular hypertrophy an excessive increase in
    the diameter of muscle fibers

19
Filaments and the Sarcomere
  • Filaments structures within the myofibril
  • Thin
  • Thick
  • Sarcomere basic functional unit of a myofibril
  • Z discs separate one sarcomere from the next

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21
MYOFIBRIL ELECTRON MICROGRAPH
22
Filaments and the Sarcomere
  • A band predominantly thick filaments
  • Zone of overlap at the ends of the A bands
  • H zone contains thick, but no thin filaments
  • I band thin filaments
  • M-line middle of the sarcomere

23
Muscle Proteins
  • Contractile proteins generate force
  • Myosin
  • Actin
  • Regulatory proteins switch contraction on and
    off
  • Structural proteins

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25
Sliding Filament Mechanism
  • Muscle contraction occurs because myosin heads
    attach to the thin filaments at both ends of the
    sarcomere and pull them toward the M line.
  • The length of the filaments does not change
    However, the sarcomeres shorten, thereby
    shortening the entire muscle.

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27
RELAXED CONTRACTED MYOFIBRILS
28
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29
POWER STROKE OF CROSSBRIDGE CYCLING
30
Role of Ca2 in Contraction
  • An increase in calcium ion concentration in the
    cytosol initiates muscle contraction and a
    decrease in calcium ions stops it.

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32
MAJOR SEQUENCE OF EVENTS UNDERLYING MUSCLE FIBER
ACTIVATION
  • 1. Action potential is initiated and propagated
    down a motor axon.
  • 2. Acetylcholine is released from axon terminals
    at neuromuscular junction.
  • 3. Acetylcholine is bound to receptor sites on
    the motor endplate.
  • 4. Sodium and potassium ions enter and
    depolarize the muscle membrane.
  • 5. Muscle action potential is propagated over
    membrane surface.
  • 6. Transverse tubules are depolarized, leading
    to release of calcium ions surrounding the
    myofibrils.
  • 7. Calcium ions bind to troponin, which leads to
    the release of inhibition of actin and myosin
    binding. The crossbridge between actin and
    myosin heads is created.
  • 8. Actin combines with myosin adenosine
    triphosphate (ATP), an energy-providing molecule.
  • 9. Energy is released to produce movement of
    myosin heads.
  • 10. Myosin and actin slide relative to each
    other.
  • 11. Actin and myosin bond (crossbridge) is
    broken and reestablished if calcium concentration
    remains sufficiently high.

33
Rigor Mortis
  • After death the cellular membranes become leaky.
  • Calcium ions are released and cause muscular
    contraction.
  • The muscles are in a state of rigidity called
    rigor mortis.
  • It begins 3-4 hours after death and lasts about
    24 hours, until proteolytic enzymes break down
    (digest) the cross-bridges.

34
Neuromuscular Junction (NMJ)
  • Muscle action potentials arise at the NMJ.
  • The NMJ is the site at which the motor neuron
    contacts the skeletal muscle fiber.
  • A synapse is the region where communication
    occurs.

35
Neuromuscular Juntcion (NMJ)
  • The neuron cell communicates with the second by
    releasing a chemical called a neurotransmitter.
  • Synaptic vesicles containing the neurotransmitter
    acetylcholine (ach) are released at the NMJ.
  • The motor end plate is the muscular part of the
    NMJ. It contains acetylcholine receptors.
  • The enzyme acetlycholineesterase (AChE) breaks
    down ACh.

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37
Production of ATP
  • 1. From creatine phosphate.
  • When muscle fibers are relaxed they produce more
    ATP than they need. This excess is used to
    synthesize creatine phosphate (an energy rich
    compound).

38
Production of ATP
  • 2. Anaerobic cellular respiration.
  • Glucose undergoes glycolysis, yielding ATP and 2
    molecules of pyruvic acid.
  • Does not require oxygen.

39
Production of ATP
  • 3. Aerobic cellular respiration.
  • The pyruvic acid enters the mitochondria where it
    is broken down to form more ATP.
  • Slower than anaerobic respiration, but yields
    more ATP.
  • Utilizes oxygen.
  • 2 sources of oxygen.
  • Diffuses from bloodstream.
  • Oxygen released from myoglobin.

40
Muscle Fatigue
  • Muscle fatigue is the inability of a muscle to
    contract forcefully after prolonged activity.
  • Central fatigue a person may develop feelings
    of tiredness before actual muscle fatigue.

41
Oxygen Debt or Recovery Oxygen Uptake
  • Added oxygen, over and above resting oxygen
    consumption, taken in after exercise.
  • Used to restore metabolic conditions.
  • 1. To convert lactic acid back into glycogen
    stores in the liver.
  • 2. To resynthesize creatine phosphate and ATP in
    muscle fibers.
  • 3. To replace the oxygen removed from hemoglobin.

42
Motor Units
  • A motor unit consists of the somatic motor neuron
    and all the skeletal muscle fibers it stimulates.
  • A single motor neuron makes contact with an
    average of 150 muscle fibers.
  • All muscle fibers in one motor unit contract in
    unison.

43
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44
MOTOR UNIT
45
Twitch Contraction
  • A twitch contraction is the brief contraction of
    all the muscle fibers in a motor unit in response
    to a single action potential.
  • A myogram is a record of a muscle contraction and
    illustrates the phases of contraction.

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47
Refractory Period
  • A period of lost excitability during which a
    muscle fiber cannot respond to stimulation.

48
Motor Unit Recruitment
  • The process in which the number of active motor
    units increases.
  • The weakest motor units are recruited first, with
    progressively stronger units being added if the
    task requires more force.

49
Muscle Tone
  • Even at rest a muscle exhibits a small amount of
    muscle tone tension or tautness.
  • Flaccid when motor units serving a muscle are
    damaged or cut.
  • Spastic when motor units are over-stimulated.

50
Isotonic and Isometric Contractions
  • Concentric isotonic activation (contraction) a
    muscle shortens and pulls on another structure.
  • Eccentric isotonic activation the length of a
    muscle increases during contraction.
  • Isometric activation muscle tension is created
    However, the muscle doesnt shorten or lengthen.

51
Types of Skeletal Muscle Fibers
  • Slow oxidative (SO) fibers.
  • Smallest of the fibers.
  • Least powerful.
  • Appear dark red much myoglobin and many
    capillaries.
  • Resistant to fatigue.

52
Types of Skeletal Muscle Fibers
  • Fast oxidative-Glycolytic (FOG) fibers.
  • Intermediate in diameter.
  • Appear dark red much myoglobin and many
    capillaries.
  • High level of intracellular glycogen.
  • Resistant to fatigue.

53
Types of Skeletal Muscle Fibers
  • Fast Glycolitic (FG) fibers.
  • Largest in diameter.
  • Contain the most myofibrils, therefore more
    powerful contractions.
  • Appear white low myoglobin and few capillaries.
  • Large amounts of glycogen anaerobic
    respiration.
  • Fatigue quickly.

54
TWITCH CLASSIFICATIONS
  • Slow twitch - Muscle fibers innervated by small
    motor neurons have twitch responses that are
    relatively long in duration and small in
    amplitude.
  • Classified as S (slow) due to slower contractile
    characteristics.
  • Associated fibers are classified as SO fibers due
    to their slow and oxidative histochemical
    profile.
  • Fast twitch muscle fibers associated with
    larger motor neurons have twitch responses that
    are relatively brief in duration and higher in
    amplitude.
  • Classified as FF (fast and easily fatigable).
  • Associated fibers are classified as FG due to
    their fast twitch, glycolytic profile.
  • Intermediate
  • Classified as FR (fast fatigue-resistant).
  • Associated fibers are classified as FOG due to
    utilization of both oxidative and glycoltyic
    energy sources.

55
MOTOR UNIT TYPES
56
Distribution and Recruitment of Different Types
of Fibers
  • Most skeletal muscles are a mixture of all three
    types.
  • The continually active postural muscles have a
    high concentration of SO fibers.

57
Distribution and Recruitment of Different Types
of Fibers
  • Muscles of the shoulders and arms are used
    briefly and for quick actions, therefore they
    have many FG fibers.
  • Muscle of the legs support the body and
    participate in quick activities, therefore they
    have many SO and FOG fibers.

58
MUSCLE MORPHOLOGY
  • Muscle morphology describes the basic shape of
    the muscle.
  • The shape will influence the ultimate function of
    the muscle.
  • The two most common forms are fusiform and
    pennate.

59
FUSIFORM PENNATE MUSCLE FIBERS
  • Fusiform
  • Fusiform muscles have fibers running parallel to
    one another and the central tendon (i.e. biceps
    brachii).
  • Pennate (Latin feather)
  • Pennate muscles possess fibers that approach
    their central tendon obliquely.
  • Pennate muscles have a greater number of muscle
    fibers and generate larger forces.
  • Most muscles in the body are considered pennate.
  • Subdivisions
  • Unipennate
  • Bipennate
  • Multipennate

60
MUSCLE SHAPES
61
FEATURES THAT AFFECT THE FORCE THROUGH A MUSCLE
ON THE TENDON
  • Physiological cross-sectional area
  • The amount of active proteins available to
    generate a contraction force
  • With full activation, the maximal force potential
    of a muscle is proportional to the sum of the
    cross-sectional area of all its fibers.
  • A thicker muscle generates greater force than a
    thinner muscle of similar morphology.
  • Pennation angle
  • Pennation angle refers to the angle of
    orientation between the muscle fibers and tendon.

62
PENNATION ANGLE DEGREE OF FORCE
  • If muscle fibers attach parallel to the tendon
    the angle is defined as 0 degrees (essentially
    all the force generated is transmitted across the
    joint).
  • If the pennation angle is greater than 0 degrees,
    then less of the force produced is transmitted
    through the tendon.
  • A muscle with a pennation angle of 0 degrees
    transmits 100 of its contractile force
    (theoretically).
  • A muscle with a pennation angle of 30 degrees
    transmits 86 of its contractile force.
  • Most human muscles have pennation angles that
    range from 0 to 30 degrees.

63
PENNATION ANGLE VECTOR OF FORCE
64
PENNATE VS. FUSIFORM
  • In general, pennate muscles produce greater
    maximal force than fusiform muscles of similar
    volume.
  • Orienting muscle fibers obliquely to the central
    tendon allows for more total muscle fibers into a
    given length of muscle. This increases the
    physiological cross-sectional area and therefore
    the force.

65
PASSIVE TENSION
  • There are noncontractile elements of the muscle
    and tendon.
  • These noncontractile elements are referred to as
    parallel and series elastic components of muscle.
  • Series elastic components are tissues that lie in
    series with active proteins.
  • Parallel elastic components are tissues that
    surround or lie in parallel with the active
    proteins. These are the extracellular connective
    tissues (epimysium, perimysium, and endomysium).
  • Stretching the whole muscle by extending the
    joint elongates both the parallel and series
    elastic components, generating a spring like
    resistance, or stiffness, within the muscle.
  • This resistance is referred to as passive tension.

66
PARALLEL SERIES ELASTIC COMPONENTS
67
PASSIVE TENSION CONTINUED
  • The passive elements within a muscle begin
    generating passive tension after a critical
    length at which all of the relaxed (i.e. slack)
    tissue has been brought to an initial level of
    tension.
  • Tension progressively increases after this until
    the muscle reaches very high levels of stiffness.
  • Eventually, the tissue ruptures or fails.
  • At very long lengths the muscle fibers begin to
    lose their active force-generating capability
    because there is less overlap among the active
    proteins that generate force. The additional
    passive tension becomes very important.

68
PURPOSE OF PASSIVE TENSION
  • Passive tension helps with movement and joint
    stabilization against the forces of gravity,
    physical contact, or other activated muscles.
  • Stretched muscle tissue stores potential energy
    which can be released to augment the overall
    force potential of a muscle.
  • The elasticity from the passive tension can serve
    as a damping mechanism that protects the
    structural components of the muscle and tendon.

69
PASSIVE LENGTH-TENSION CURVE
70
ACTIVE TENSION
  • Muscle tissue generates force actively in
    response to a stimulus from the nervous system.
  • The sarcomere is the fundamental active force
    generator within the muscle fiber.
  • The sliding filament hypothesis explains how the
    actin and myosin filaments can contract and exert
    their force.
  • Each myosin head attaches to an adjacent actin
    filament, forming a crossbridge.
  • The amount of force generated within each
    sarcomere depends on the number of simultaneously
    formed crossbridges. The greater the number of
    crossbridges, the greater the force generated
    within the sarcomere.

71
ACTIVE LENGTH-TENSION CURVE
  • The amount of active force depends upon the
    instantaneous length of the muscle fiber.
  • A change in fiber length- from either active
    contraction or passive elongation- alters the
    amount of overlap between actin and myosin.
  • The ideal resting length of a muscle fiber (or
    individual sarcomere) is the length that allows
    the greatest number of crossbridges and therefore
    the greatest potential force.
  • As the sarcomere lengthens of shortens from its
    resting length, the number of potential
    crossbridges decreases so that lesser amounts of
    active force are generated.

72
CROSSBRIDGE
73
ACTIVE LENGTH-TENSION CURVE
74
LENGTH-FORCE (LENGTH-TENSION)
  • The ideal resting length of the muscle fiber
    allows for the optimum length-force relationship.
  • While the phrase length-force is more
    appropriate, the term length-tension is used
    instead due to its wide acceptance in the
    physiology literature.

75
TOTAL LENGTH-TENSION CURVE OF MUSCLE
  • The active length-tension curve, when combined
    with the passive length-tension curve, yields the
    total length-tension curve of muscle.
  • The combination of active force and passive
    tension allows for a large range of muscle forces
    over a wide range of muscle length.

76
TOTAL LENGTH-TENSION CURVE
77
ISOMETRIC MUSCLE FORCE
  • Isometric activation of a muscle produces force
    without significant change in its length.
  • This occurs when the joint over which an
    activated muscle crosses is constrained from
    movement.
  • Constraint can occur from a force produced by an
    antagonistic muscle or from an external source.
  • Isometrically produced forces provide stability
    to the joints and the body as a whole.

78
MAXIMAL ISOMETRIC FORCE AS AN INDICATOR OF A
MUSCLES PEAK STRENGTH
  • Maximal isometric force of a muscle is often used
    as a general indicator of a muscles peak
    strength and can indicate neuromuscular recovery
    after injury.
  • A muscles internal torque generation can be
    measured isometrically at several joint angles.
  • The magnitude of isometric torque differs
    considerably based on the angle of the joint at
    the time of activation, even with maximal effort.
  • The internal torque produced isometrically by a
    muscle group can be determined by asking an
    individual to produce a maximal effort
    contraction against a known external torque.
  • It is important that clinical measurements of
    isometric torque include the joint angle so that
    future comparisons are valid.

79
DYNANOMETER
  • A dynamometer is an instrument used to measure
    force, moment of force (torque), or power.
  • In the fields of rehabilitation, therapy,
    kinesiology, and ergonomics, force dynanometers
    are used to measure back, grip, arm, or leg
    strength in order to evaluate physical status,
    performance, or task demands.

80
HAND DYNANOMETER
81
RESISTING A FORCE
  • The nervous system stimulates a muscle to resist
    a force by concentric, eccentric, or isometric
    activation.
  • During concentric activation, the muscle shortens
    (contracts). The internal (muscle) torque
    exceeds the external (load) torque.
  • During eccentric activation, the external torque
    exceeds the internal torque. The muscle is
    driven by the nervous system to contract but it
    is elongated in response to a more dominating
    force (an external force or an antagonistic
    muscle).
  • During isometric activation, the length of the
    muscle remains nearly constant, as the internal
    and external torques are equally matched.

82
MODULATING FORCE THROUGH CONCENTRIC AND ECCENTRIC
ACTIVATION
  • During concentric and eccentric activations, a
    very specific relationship exists between a
    muscles maximum force output and its velocity of
    contraction (or elongation).
  • Concentric activation
  • A muscle contracts at a maximum velocity when the
    load is negligible.
  • As the load increases, the maximum contraction
    velocity of the muscle decreases.
  • Eventually, a very large load results in a
    contraction velocity of zero (i.e. isometric
    state).
  • Eccentric activation
  • A load that barely exceeds the isometric force
    level causes the muscle to lengthen slowly.
  • Speed of lengthening increases as a greater load
    is applied.
  • There is a maximal load level the muscle cannot
    resist, beyond which the muscle uncontrollably
    lengthens.

83
RELATIONSHIP BETWEEN LOAD AND MAXIMAL SHORTENING
VELOCITY
84
FORCE-VELOCITY CURVE
85
POWER WORK
  • Power, or the rate of work, can be expressed as a
    product of force and contraction velocity.
  • A constant power output of a muscle can be
    sustained by increasing the load (resistance)
    while proportionately decreasing the contraction
    velocity, or vise versa. switching gears on a
    bike
  • Positive work
  • A muscle undergoing a concentric contraction
    against a load is doing positive work on a load.
  • Negative work
  • A muscle undergoing eccentric activation against
    an overbearing load is doing negative work.
  • A muscle can act as either an active accelerator
    of movement against a load while the muscle is
    contracting (i.e. concentric activation) or as a
    brake or decelerator when a load is applied and
    the activated muscle is lengthening (i.e.
    eccentric activation).
  • The quadriceps muscles act concentrically when
    one ascends the stairs and lifts the weight of
    the body (positive work). The quadriceps perform
    eccentrically as they lower the body down the
    stairs in a controlled fashion (negative work).
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