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7/30/2019 39038402 Skeletal Muscle
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MUSCULAR SYSTEM
• Muscle cells/myocytes
function --> movement
• Classification
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
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Skeletal Muscle
• Muscle fibers
- extrafusal
- intrafusal (musclespindle)
• endomysium
• fasciculi
• perimysium
• epimysium
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Attachment of skeletal muscle
• Tendons
• aponeuroses
• fascia
• origin• insertion
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Shape and fiber architecture
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Naming of muscles
• The names given to individual muscles
usually descriptive, based on their:
- shape
- size- number of heads or bellies
- position
- depth- attachment
- action
•These terms are often used in combination
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Blood Supply
• From adjacent vessels: one or several
anastomosing vessels
• Artery enters on the deep surface
• Form neurovascular bundle with veins and
nerves
• Veins have valves
• Lymphatic vessels commence at epimysium
& perimysium
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Innervation of Skeletal Muscle
• By one or more nerves
• Muscle’s nerves contain:
- -motor axon
- -motor axon
- autonomic efferents
- Ia afferent from muscle fibers of neuromuscular spindle
- Ib afferents from Golgi tendon organ -
pain fibers
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Motor Units
- A functional unit formed by a motoneuron and all
the muscle fibers that it innervates
- Accounts for simultaneous contraction of a
number of fibers within a muscle
- Size: small in muscles for precision tasks
large in postural muscles
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Gradation of muscle contraction
Strategy:
- Increase the impulse frequency of motoneuron
- Increase the number of motor unit recruited
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Fiber type of adult skeletal
muscle • Classification of muscle fibers
- morphology: red, white
- histochemistry: myosin ATPase, myosin phenotipe
- physiology: fast & slow contracting,
fatigue resistant.- biochemistry: oxidative, glycolytic, etc.
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Muscle Histochemistry
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Functional implications of shape
and fiber architecture
Direction of action:
- The resultant force generated by a muscle is directed
along the line of tendon
- Muscle with twist geometry:
the fibers shorten and brought to the same plane
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Force and Range of Contraction
Force:
- Summation of actin-myosin cross-bridges
- depend on the cross sectional area
Range:
- Summation of subtraction of min-maxoverlapping between actin and myosin
- depend on the length of the fibers
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Study of muscle action
• Anatomical method
• Localized electrical stimulation
• Manual palpation
• EMG
•
EMG + other tools• Clinical method
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Actions of muscles
• Isometric vs isotonic contraction
• concentric vs eccentric
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Classification of muscle role
• Prime mover
• antagonist
• fixator
• synergist
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Biomechanics
• First Class Lever
• Second Class Lever
• Third Class Lever
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Effect of muscle force on joints
• Turning effect
- M = F x L
• Reaction at the joint
- normal component
(Fc)
- tangential component
(Fs)
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Kinesiology
- Study of human movement
- a branch of biomechanics
M l k l t l Bi h i d
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Musculoskeletal Biomechanics and
Kinesiology
Significance:
Occupational ergonomics
Medical rehabilitation --> Occupational therapy
Orthopedics
Rehabilitation engineering
Bioinstrumentation
T i l
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Terminology
Mechanics = the study of forces and their effects
Biomechanics = the application of mechanical laws toliving structures
Musculoskeletal biomechanics = biomech concerning
the interrelations of skeleton, muscles + joints.Kinematics = deals with the geometry of the motion
without taking into account the forces that produce the
motion.Kinetics = study of the relationships between the force
system acting on a body and the changes it produces in
body motion
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Terminology
•Osteokinematics = gross movements of bones at joints
- flexion/extension
- abduction/adduction- internal rotation/external rotation
--> describe movements occur around center of
rotation/joint axis --> as if joint axis is fixed
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Terminology
• Arthrokinematics = small amplitude motions of
bones at joint surface
- roll
- glide
- spin
--> specific movements of joint surfaces.
Normal movement is necessary to ensure long-term
joint integrity
Joint surfaces move with respect to one another by
simultaneously rolling, gliding and spinning
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Arthrokinematics
•If the moving joint surface rolls on its partnerswithout simultaneously gliding, the surfaces would
separeted (gap or subluxate) in some place and
impinge in others
• Relation shape between bony shapes at joint surface
and the surfaces’ movements --> rules of concavity
and convexity
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Rules of Concavity and Convexity
•Each joint involves two bony surfaces, one convexthe other concave
- When the concave surface is fixed and the convex
surface moves on it--> the convex surface rolls and glides in opposite
directions
- When the convex surface is fixed and the concavesurface moves on it
--> the concave surface rolls and glides in the same
direction
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Principles of applied mechanics
• Vector quantity =quantity with magnitude
+ direction
•Vector addition: addition/ subtraction
- tip of 1st vector
coincide with tail of 2nd
vector - tip of 1st vector joint
to tail of 2nd vector to
create a resultant
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Principles of applied mechanics
• Force = mechanicaldisturbances or load
• Moments = the tendency of
the force (F) to turn the
bones about the joint.
M = F * L
L = moment arm
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Principles of applied mechanics
-
1st law: A body tends to remain in its inertial
state of rest or motion unless and until acted upon by
an external disturbing force.
- 2nd law: Acceleration of a body is directionally
proportional to the net force acting on the body and
inversely proportional to its mass.
- 3rd law:For every action, there is always an equaland opposite reaction.
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Mass & Center of Mass
Mass = a physical quantity of matter composing abody = a property of matter that causes it to have
weight in a gravitational field
F = ma W = mg
Center of Mass (COM)
= the point where the entire weight of the body is
concentrated= the point in a body about which all the parts
exactly balance each other
- Whole body mass - Segmental mass
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Mass and Center of Mass
STABILITY MOBILITY
mass large small
COG position low high
BOS size large small
COG Vertical
projection
To point near
BOS center
To point near
BOS boundary
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Levers
= rigid bar that pivots about a fixed point, called the
axis or fulcrum, when a force applied to it.
Force is applied by muscles at some point along the
lever to move the body part (resistance/load).
The relationship of fulcrum to force to resistance
distinguishes the different classes of levers.
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Levers
• First Class Lever
• Second Class Lever
• Third Class Lever
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First-class lever
- the axis (fulcrum) is located between the force and
the resistance/load
- the longer the lever arm is, the less force is required
to overcome the resistance.
- example: the forearm moving from a position of
flexion into extension at the elbow through contraction
of the triceps brachii muscles
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Second-class lever
- the resistance/load is between the axis and the force
- example: opening the mouth against resistance
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Third-class lever
- the force is between the axis and the resistance
- allow muscle to be inserted near the joint and therebyproduce increased speed of movement although at a
sacrifice a force.
- example: flexion of the elbow joint through
contraction of the biceps brachii muscle.
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Basic Behavior of Skeletal Muscle
Extensibility: the ability to be stretched or to increasein length
Elasticity: the ability to return to the original length
after a stretchIrritability: the ability to respond to a a stimulus
Ability to develop tension: the ability to decrease in
lengthIncrease in tension does not imply decrease in muscle
length.
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Mechanical Model of a Muscle
•Contractile component: Muscle fibers
• Series of elastic component: Tendon
• Parallel elastic component: Muscle membrane &
connective tissues
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Structural Organization of Skeletal Muscle
• muscle fiber
• motor unit
• fiber types
• fiber architecture
parallel fiber arrangement: parallel to the longitudinal axis
of the muscle, e.g. sartorius, masseter, biceps brachii, etc.
pennate fiber arrangement: at an angle to the longitudinalaxis of the muscle, e.g. rectus femoris, deltoid, etc.
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Mechanical Properties of Skeletal Muscle
• Length-tension relationship
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Mechanical Properties of Skeletal Muscle
• In a muscle force generation capacity increaseswhen the muscle is slightly stretch because of the
effect of both active and passive component
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Mechanical Properties of Skeletal Muscle
• Muscle force decreases as the velocity of
contraction increases only true for concentric
contraction
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Mechanical Properties of Skeletal Muscle
• Stretch-shortening cyclesWhen a muscle is
stretched just prior to contraction, the resulting
contraction is more forceful than in the absence of
the pre-stretch.
• possible contributors to forceful tension
development
elastic recoil effect of the series elastic component of
the actively stretched muscle
stretch reflex of the forced lengthening muscle
example: wind-up during baseball pitching
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Factors affecting Muscle Strength
• Body temperature
• Muscle hypertrophy
• Muscle atrophy
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