Download Skeletal Muscles and Functions

Skeletal Muscles and Functions
Huei-Ming Chai, PT, Ph.D.
School of Physical Therapy
National Taiwan University
Classification of Muscles
• striated muscles
– skeletal muscles: voluntary contraction
– cardiac muscles
• non-striated (smooth) muscles
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Skeletal Muscle Statistics
• the most abundant tissue in the body,
accounting for 40-45% BW
• > 430 skeletal muscles
• Most movements are completed by < 80 pairs
of skeletal muscles
Skeletal Muscle and Function
 Structure of skeletal muscle
• Muscle contraction
• Muscle coordination
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Properties of Skeletal Muscle
• Muscle fiber
– extensibility
– elasticity
– contractility
• tendon or aponeurosis
– viscoelasticity
– non-contractility
Organization of Skeletal Muscle
epimysium
muscle
muscle fasciculus
perimysium
endomysium
muscle fiber
muscle fibril
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Muscle Fiber
• a long cylindrical cell with hundreds of nuclei
– 10-100 m in diameter
– 1-30 cm in length
•
Contractile component: myofabril
• Non-contractile component: endomyosium
Organization of Muscle Fiber
endomysium
muscle fiber
muscle fibril
sarcomere
cross section
actin filament
myosin filament
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Contractile Component
-- Sarcomere
actin
myosin
A band
I band
H band
crossbridge
Z line
Types of Muscle Fibers
• slow twitch fiber (Type I)
– red in color
– slow to peak when contracted
– fatigue resistant
• fast twitch fiber (Type IIA)
– white in color
– fast to peak when contracted
– easy fatigue
• intermediate (Type IIB)
Smith, p.88
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Fiber Architecture
• parallel fiber arrangement： parallel to the
longitudinal axis of the muscle
–
–
–
–
longitudinal： sartorius
quadrate or quadralateral： rhomboid
triangular or fan-shaped： pectoralis major
fusiform or spindle-shaped： biceps brachii
• pennate fiber arrangement： at an angle to
the longitudinal axis of the muscle,
– unipenniform： extnesor digitorum longous
– bipenniform： flexor hallucis longus
– multipenniform： middle deltoid
Effect of Pennation
• pennation angle   effective force
transmitted to the tendon 
• tension in the muscle fibers   pennation
angle 
• pennate arrangement:
to allow packing of
more fibers
given the same space.
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Skeletal Muscle and Function
• Structure of skeletal muscle
 Muscle contraction
• Muscle coordination
Functions of Skeletal Muscle
• To move the body limb by creating motion
• To provide strength by generating active force
• To protect joints by absorbing shock
• specific functions of connective tissues within
muscle
– To provide gross structure to muscle
– To generate passive tension against stretch
– To transmit force to the bone and across the joint
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Sliding Filament Mechanism
• AF Huxley & HE Huxley, 1964
• active shortening of sacromere, resulting from
the relative movement of actin and myosin
filaments with retaining its original length
• force of contraction is developed by the
crossbridges of myosin
Movement of Cross Bridges
Lengths of myosin and actin
keep the same
shortening
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Types Based on Changes in Length
resting
concentric
(shortening)
isometric
(static)
eccentric
(lengthening)
Abdominal Muscle Contraction
• concentric contraction
– to create trunk flexion (resisting gravity)
• eccentric contraction
– to control trunk extension (checking gravity)
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Triceps Brachii Action
• downward motion
– elbow flexion
– elbow extensors (antagonist) eccentric contraction
• upward motion
– elbow extension
– elbow extensors (agonist)
concentric contraction
Abdominal Muscle Actions
concentric
eccentric
direction of motion
muscle length
concentric
gravity-resisted
shortening
eccentric
gravity-assisted
lengthening
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Elbow Flexion at 90 of Shoulder ABD
elbow flexor, eccentric
elbow extensor, concentric
elbow flexor, concentric
elbow extensor, eccentric
Quadriceps Actions
closed
kinematic
chain
open
kinematic
chain
motion? gravity? muscle contraction? muscle length?
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What if ….
shoulder extensor
concentric contraction
to create force
Shoulder Extension
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Types Based on
Tension Development
• isotonic contraction
• isometric contraction
• isokinetic contraction
Isotonic Contraction
• iso = equal； tonus = tension
• defined by muscle physiologists as a kind of muscle
contraction that develops constant tension throughout
the whole muscle excursion as isotonic contraction
– seldom seen in the living body
– clinically refer to a muscle contraction that causes a joint to
move through some range of motion
• Even though the resistance remains the same, the
tension generated by the muscle is not equal tension
because
– moment arm to the joint axis changing throughout the motion
– resistance with respect to the gravity changing throughout the
motion
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Slight Squatting
• quadriceps action
• calf action
• shoulder flexor
• elbow flexor
Isokinetic Contraction
• iso = equal； kinetos = move
• first introduced by Hislop and Perrine in 1967
• definition: one kind of muscle contraction that
occurs when the rate of movement is constant
• not occur in the living body without using
special machine (isokinetic dynamometer)
• equal motion speed with
accommodating resistance
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Isokinetic Testing
Isokinetic Testing System
• Cybex: torque
• Kin-Com: force
Cybex:
dynamometer
amplitude
ext.
flex.
Kin-Com:
load cell
angle
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Isokinetic Contraction
dynamometer
joint moment
Isokinetic
M

Isotonic

joint angle
F
mg
Comparison of Muscle Contraction
• isotonic contraction
– varying tension
– varying length
– varying speed
• Isometric contraction
– varying tension
– equal length
– zero speed
• isokinetic contraction
– accommodating resistance (various tension)
– varying length
– equal speed
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tension
Tension Developed by
A Single Muscle Fiber Contraction
active
tension
resting
length
length
Mechanical Model of
Musculotendinous Unit
• Keele, Neil, Joels, 1982
parallel elastic component
series
elastic
component
contractile component
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Length-Tension Curve
-- maximum isometric contraction
passive
tension
active
tension
length
resting
length
Force-Velocity Curve
Hill’s model
eccentric
concentric
isometric
force
tension
total tension
0
contraction velocity
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Skeletal Muscle and Function
• Structure of skeletal muscle
• Muscle contraction
 Muscle coordination
Muscle Activities During Motion
• focal muscle
– agonist (prime mover)
– antagonist
– synergist
• stabilizer
• neutralizer
• postural muscle
– anticipatory postural adjustment (APA)
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Agonist
• the principal muscle that produces a joint
motion or maintains a static posture
• can be concentric, isometric, or eccentric
Antagonist
• 拮抗肌
• the muscle that contracts in the opposite
direction of the agonist
• passively elongates or shortens to allow
motion acted by agonist
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Synergist
• Syn = together; ergon = work
• the muscle that contracts together with the
agonist
– stabilizer: to stabilize the proximal component of
the joint involved
– neutralizer: to rule out unwanted motions
Stabilizer
teres minor
• scapular muscles stabilize the scapula
deltoid can elevate the arm
teres minor can rotate the arm externally
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Neutralizer
upper trapezius
scapula
adduction
neutralize
lower trapezius
Cocontraction
co-contraction: agonist and antagonist
contract simultaneously
co-contraction  joint approximation
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Single- vs. Multi-Joint Muscle
• single-joint muscle: a muscle that cross one
joint only, e.g. the brachialis, the short head
of the biceps brachii
• two-joint muscle: a muscle that cross two
joints, e.g. the long-head of the biceps brachii,
the grastrocnemius, etc.
• multi-joint muscle: a muscle that cross more
than one joint e.g. the long finger flexors, the
long finger extensors, etc.
Action of Two-Joint Muscle
• active insufficiency
– unable to reach the contraction force because of
the limit of muscle length
– e.g. make a fist as wrist extended vs. that as wrist
flexed
• passive insufficiency
– unable to reach full range of motion because of
the limit of muscle length
– e.g. open the hand as wrist extended vs. that wrist
flexed
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Active Insufficiency
• unable to reach the contraction force because
of the limit of muscle length
• examples：
– Making a fist with the wrist extended is stronger
than that with the wrist flexed
– the strength of the elbow flexor decreases as the
shoulder joint is more flexed
Mechanism of Active Insufficiency
• the contractile tension of the agonist is
markedly weak when a multi-joint muscle is
attempt to contract at a shortened position
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Passive Insufficiency
• unable to reach full range of motion because
of the limit of muscle length
• examples：
– automatically open the hand as wrist flexed
– difficult to reach the toes with the knee extended
as compared to that with the knee flexed
• Even though the agonist may contract
strongly, motion may be limited because of
the lack of excursion of the antagonist
Practice of Two Joint Muscles
• biceps brachii
• hamstring
• gastrocnemius
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