Muscular System (Our Muscle)
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Transcript of Muscular System (Our Muscle)
MUSCULAR SYSTEM
OBJECTIVE:
•Identify the basic behavioral properties of the musculotendinous unit
•Structure of skeletal muscle
•Change in muscle length with tension development
•Factors affecting muscular force generation
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BEHAVIORAL PROPERTIES OF THE MUSCULOTENDINOUS UNIT
Four behavioral properties of muscle tissue: Extensibility Elasticity Irritability The ability to develop tension
These properties are common to all muscle, including the cardiac, smooth, & skeletal muscle of human beings.
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Extensibility & Elasticity
The properties of extensibility & elasticity are common to many biological tissues.
Extensibility – the ability to be stretched or to increase in length.
Elasticity – the ability to return to normal length after a stretch.
Muscle’s elasticity returns it to normal resting length following a stretch & provides for the smooth transmission of tension from
muscle to bone.
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Two major components of the elastic behavior of muscle:
Parallel elastic component (PEC) Passive elastic property of muscle derived from
the muscle membranes.
Series elastic component (SEC) Passive elastic property of muscle derived from
the tendons. Act as a spring to store elastic energy (EE) when a
tensed muscle is stretched.
Contractile component Muscle property enabling tension development by stimulated muscle fibers.
Membranes & tendons are respectively parallel to & in series (or in line) with the muscle fibers.
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Parallel Elastic Component
Contractile Component
Series Elastic
Component
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The elasticity of human skeletal muscle is believed to be due primarily to the SEC.
When a tensed muscle is stretched, the SEC causes an elastic recoil effect
The stretch promotes subsequent forceful shortening of the muscle
This pattern of eccentric contraction followed immediately by concentric contraction is known as the stretch-shortening cycle.
This phenomenon contributes to effective development of concentric muscular
force in many sport activities.
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The stretch-shortening cycle also promotes storage & use of elastic energy (EE) during running, particularly with the alternating
eccentric & concentric tension present in the gastrocnemius.
Both SEC & PEC have a viscous property that enable muscle to stretch & recoil in a time-
dependent fashion. When static stretch of a muscle group is maintained
over time, the muscle progressively lengthens, increasing joint range of motion
After a group has been stretched, it does not recoil to resting length immediately, but shortens gradually over
time
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ExtensibilityElasticityIrritabilityThe ability to develop tension
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Irritability & the Ability to Develop Tension
Irritability- The ability to respond to a stimulus.
Stimuli affecting muscles are either: Electrochemical – action potential from the
attaching nerve. Mechanical – an external blow to a portion of a
muscle.
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• The ability to develop tension is the one behavioral characteristic unique to muscle tissue.
• Development of tension = contraction (eccentric or concentric)
Muscle stimulus
Develop tension
STRUCTURAL ORGANIZATION OF SKELETAL MUSCLE
Approximately 434 muscles in the human body (40-45% of the body weight of most adult).
About 75 muscle pairs are responsible for body movements & posture, with the remainder involved in activities such as eye control &
swallowing.
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Bone
Perimysium
Endomysium(between individualmuscle fibers)
Muscle fiber (single muscle cell)
Fascicle(wrapped by perimysium)
Epimysium
Tendon
Epimysium
Muscle fiberin middle ofa fascicle
Blood vessel
Perimysium
Endomysium
Fascicle(a)
(b)
Structure of Skeletal Muscle (muscle fiber)
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Epimysium The outermost layer that surround the entire
muscle.Perimysium Connective tissue surround individual bundles
of muscle fibers (inward from the epimysium).Fascicle Individual bundle of muscle fibers.Endomysium Connective tissue surrounded for each muscle
fiber within the fasciculus.
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Sarcolemma◦ The cell membrane surrounding the muscle fiber
cell.
Myofibrils ◦ Numerous threadlike structure that contain the
contractile proteins (protein filaments) Myosin – thick filaments composed of the
protein. Actin – thin filaments composed primarily of
the protein.
Sarcoplasmic reticulum◦ The storage sites for calcium, which plays an
important role in muscular contraction.
Sarcomeres◦ Myofibrils further subdivided into individual
segments.
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Small part of one myofibril enlarged to show the myofilamentsresponsible for the banding pattern. Each sarcomere extends fromone Z disc to the next (basic structural unit of muscle fiber).
Enlargement of one sarcomere (sectioned lengthwise). Notice the myosin heads on the thick filaments.
M line Bisect each sarcomere (middle)
A band Contain thick, rough myosin filament, each of which is surrounded by thin, smooth actin filaments
I band Contain only thin actin filaments
Z lines (disc)
Attachment of thin actin filaments
H zones Center of A bands, contain only thick myosin filaments
Figure 9.5
Myofibril
Myofibrils
Triad:
Tubules ofthe SR
Sarcolemma
Sarcolemma
Mitochondria
I band I bandA band
H zone Z discZ disc
Part of a skeletalmuscle fiber (cell)
• T tubule• Terminal
cisternaeof the SR (2)
M line
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Motor Units
Composed of a single motor neuron & all fibers innervated by it.
Typically, there is only 1 end plate per fiber.
A single mammalian motor unit may contain from less than 100 to nearly 2000 fibers, depending on the type of movements the
muscle executes. Movements that are precisely controlled (eyes, fingers)
produced by motor units with small numbers of fibers Gross, forceful movements (gastrocnemius) result of the
activity of large motor units
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Figure 9.13a
Spinal cord
Motor neuroncell body
Muscle
Nerve
Motorunit 1
Motorunit 2
Musclefibers
Motorneuronaxon
Axon terminals atneuromuscular junctions
Axons of motor neurons extend from the spinal cord to the muscle. There each axon divides into a number of axon terminals that form neuromuscular junctions with muscle fibers scattered throughout the muscle.
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Motor end plate
Fiber Types
Slow twitch fiber (ST)◦ A fiber that reaches peak tension relatively
slowly.
Fast twitch fiber (FT)◦ A fiber that reaches peak tension relatively
quickly.◦ Fast-twitch Oxidative Glycolytic◦ Fast-twitch Glycolytic
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SKELETAL MUSCLE FIBER CHARACTERISTICS
CHARACTERISTIC TYPE 1 SLOW-TWITCH
OXIDATIVE (SO)
TYPE IIA FAST-TWITCH OXIDATIVE GLYCOLYTIC
(FOG)
TYPE IIB FAST-TWITCH GLYCOLYTIC
(FG)
Contraction speed Slow Fast Fast
Fatigue rate Slow Intermediate fast
Diameter Small Intermediate Large
ATPase concentration Low High High
Mitochondrial concentration High High Low
Glycolytic enzyme concentration
Low Intermediate High
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Time
FT
ST
Twitch tensio
n
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Fiber Architecture
Two categories of muscle fiber arrangement
◦ Parallel fiber arrangement Pattern of fibers within a
muscle in which the fibers are roughly parallel to the longitudinal axis of the muscle.
E.g. sartorius, rectus abdominis, biceps brachii.
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Pennate fiber arrangement Pattern of fibers within a
muscle with short fibers attaching to one or more tendons (lie at an angle).
E.g. tibialis posterior, rectus femoris, deltoids
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SKELETAL MUSCLE FUNCTION
When an activated muscle develops tension, the amount of tension present is constant throughout the length of the muscle, & at the sites of the musculotendinous attachments to bone.
The tensile force (stretching force) developed by the muscle pulls on the attached bones & create torque at the joints crossed by the muscle.
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Torque (Tm ) produced by a muscle at the joint center of rotation is the product of muscle force ( Fm ) & muscle moment arm ( d⊥ ).
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The torque exerted by the biceps brachii (Fb) must counteract the torques created by the force developed in the triceps brachii (Ft), the weight of the forearm & hand (wtf), & the weight of the shot held in the hand (wts).
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Recruitment of motor units
The CNS exerts an elaborate system of control that enables:◦ Matching of the speed & magnitude of
muscle contraction to the requirements of the movement so that: Smooth, delicate, & precise movements can
be executed.
Slow twitch (ST) motor units generally have low thresholds & are relatively easy to activate.Fast twitch (FT) motor units are supplied by nerves more difficult to activate.
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Change in Muscle Length with Tension Development
When muscular tension produces a torque larger than the resistive torque at a joint, the muscle shortens, causing a change in the angle at the joint.
Type of contraction;◦ Concentric◦ Eccentric ◦ Isometric
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Concentric Eccentric Isometric
Contraction involving shortening of muscleResulting joint movement is in the same
direction as the net torque generated by the muscle.
A single muscle fiber is capable of shortening to approximately one-half of its normal resting length.
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Concentric Eccentric Isometric
When opposing joint torque exceeds that produced by tension in a muscle, the muscle lengthens.
When a muscle lengthens as it is being stimulated to develop tension.
The direction of joint motion is opposite that of the net muscle torque.
The eccentric tension acts as a braking mechanism to control movement speed.
E.g. without the presence of eccentric tension in muscles, the forearms, hand, & weight would drop uncontrolled because of the force of gravity.
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Concentric Eccentric Isometric
Muscular tension is developed but no change in muscle length.
Opposing torque at the joint crossed by the muscle is equal to the torque produced by the muscle (with zero net torque present),◦ Muscle length remains unchanged & no
movement occurs at the joint.
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Recruitment of motor unitsChange in muscle length with
tension developmentRoles assumed by muscles
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SKELETAL MUSCLE FUNCTION
Roles Assumed by Muscles
Agonist
Antagonist
Stabilizers
Neutralizer
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Agonist
Prime mover.When a muscle contracts & causes movement
of a body segment at a joint.E.g.
◦ During the elbow flexion phase of a forearm curl, the brachialis & the biceps brachii act as the primary agonist, with the brachioradialis, extensor carpi radialis longus, & pronator teres serving as assistant agonist.
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Antagonist
Muscle with actions opposite those of the agonist act.
Opposers by developing eccentric tension at the same time that the agonists are causing movement.
Agonists & antagonists are typically positioned on opposite sides of a joint.
E.g.◦ During elbow flexion when the brachialis &
the biceps brachii are primary agonists, the triceps could act as antagonists by developing resistive tension.
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Stabilizers
Stabilizing a portion of the body against a particular force.◦ The force may be internal, from tension in
other muscles, or external, such as the weight of an object being lifted.
E.g.◦ The rhomboids act as stabilizers by
developing tension to stabilize the scapulae against the pull of the tow rope during water skiing, or on tug-of-war event.
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Neutralizer
Neutralizers muscle prevent unwanted accessory actions that normally occur when agonists develop concentric tension.
E.g.◦ When the biceps brachii develops concentric
tension, it produces both flexion at the elbow & supination of the forearm. If only elbow flexion is desired, the pronator teres act as a neutralizer to counteract the supination of the forearm.
Performance of human movements typically involves the cooperative actions of many muscle groups acting sequentially & in concert.
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Factors Affecting Muscular Force Generation
The magnitude of the force generated by muscle is also related to:
Velocity of muscle shorteningLength of the muscle when it is stimulatedPeriod of time since the muscle received a
stimulus
Factors affecting:Force-Velocity relationshipLength-Tension RelationshipElectromechanical Delay (EMD)
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Force-Velocity Relationship for muscle tissue
When the resistance (force) is negligible, muscle contracts with maximal velocity. As the load progressively increases, concentric
contraction velocity slows to zero at isometric maximum. As the load increases further, the muscle lengthens
eccentrically.
FVR does NOT imply that it is impossible to move a heavy resistance at a fast speed.
The stronger a muscle, the greater the magnitude of maximum isometric tension
FVR also does NOT imply that it is impossible to move a light load at a slow speed.
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Maximally
activated
muscle
Length-Tension Relationship
The total tension present in a stretched muscle is the sum of the active tension provided by the muscle fibers & the passive tension provided by the tendons & muscle membranes.
Within the human body, force generation capability increases when the muscle is lightly stretched.Parallel-fibered muscles produce maximum tensions at
just over resting length.Pennate-fibered muscles generate maximum tension at
between 120% & 130% of resting length.This phenomenon is due to the contribution of the elastic
components of muscle (primarily the SEC), which add to the tension present in the muscle when the muscle is stretched.
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Total tension = active tension (muscle fibers) + passive tension (tendons &muscle membranes)
Electromechanical Delay (EMD)
When a muscle is stimulated, a brief period of time elapse before the muscle begins to develop tension.
ED- time between the arrival of neural stimulus and tension development by the muscle 41
EMD where the period of time is believed to be needed for the contractile component of the muscle to stretch the SEC.During this time, muscle laxity is eliminated.Once the SEC is sufficiently stretched, tension
development proceeds.
Researchers have found shorter EMDs produced by muscles with high percentages of FT fibers as compared to muscles with high percentages of ST fibers.
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Muscular Strength, Power & Endurance
Muscular StrengthThe maximum amount of force a muscle
can produce in a single effort
Muscular PowerThe product of muscular force and the
velocity of muscle shortening
Muscular EnduranceThe ability of a muscle to exert a sub-
maximal force repeatedly over time
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What is the effect of muscle temperature (warm up) ?
The speeds of nerve and muscle functions increase.
Normal body temperature
Elevated body temperature
With warm-up, there is a shift to the right in
the force-velocity curve, with higher
maximum isometric tension and higher
maximum velocity of shortening possible at
a given load.
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velo
city
force
Common Muscle Injuries
Delayed-Onset Muscle Soreness (DOMS)◦ occurs after some period of time following
unaccustomed exercise.◦ arises 24 – 72 hours after participation in a long
or strenuous bout of exercise.
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Strains - overstretching of muscle tissue
Contusions - compressive forces sustained during impacts
Cramps - electrolytes imbalance, deficiencies in calcium & magnesium, dehydration