BODY MUSCELS SYSTEM 1 واحدی هوشنگ دکترامیر

توانبخشی و فیزیکی طب متخصص

2قسمت

Muscle Tissue Properties• Skeletal muscle tissue has 4 properties related to its

ability to produce force & movement about joints• Irritability• Contractility• Extensibility• Elasticity

Muscle Tissue Properties• Irritability - property of muscle being sensitive or

responsive to chemical, electrical, or mechanical stimuli• Contractility - ability of muscle to contract & develop

tension or internal force against resistance when stimulated

Muscle Tissue Properties• Extensibility - ability of muscle to be stretched back to its

original length following contraction• Elasticity - ability of muscle to return to its original length

following stretching

Muscle Terminology• Intrinsic - pertaining usually to muscles

within or belonging solely to body part upon which they act• Ex. small intrinsic muscles found entirely

within the hand

Muscle Terminology• Extrinsic - pertaining usually to muscles that arise

or originate outside of (proximal to) body part upon which they act• Ex. forearm muscles that attach proximally on distal

humerus and insert on fingers

Muscle Terminology• Action - specific movement of joint resulting from a

concentric contraction of a muscle which crosses joint• Ex. biceps brachii has the action of flexion at elbow

• Actions are usually caused by a group of muscles working together

Muscle Terminology• Innervation - segment of nervous system defined as being

responsible for providing a stimulus to muscle fibers within a specific muscle or portion of a muscle• A muscle may be innervated by more than one nerve & a particular

nerve may innervate more than one muscle or portion of a muscle

Muscle Terminology• Amplitude - range of muscle fiber length between maximal

& minimal lengthening• Gaster (belly or body)

• central, fleshy portion of the muscle that generally increases in diameter as the muscle contracts

• the contractile portion of muscle

Muscle Terminology• Origin - proximal attachment, generally considered the

least movable part or the part that attaches closest to the midline or center of the body

• Insertion - distal attachment, generally considered the most movable part or the part that attaches farthest from the midline or center of the body

Muscle Terminology• When a particular muscle contracts

• it tends to pull both ends toward the gaster• if neither of the bones to which a muscle is attached are stabilized

then both bones move toward each other upon contraction• more commonly one bone is more stabilized by a variety of factors

and the less stabilized bone usually moves toward the more stabilized bone upon contraction

Types of muscle contraction

Muscle Contraction(under tension)

Isometric Isotonic

EccentricConcentric

Types of muscle contraction• Isotonic contractions involve muscle developing tension to

either cause or control joint movement• dynamic contractions• the varying degrees of tension in muscles are causing joint angles

to change• Isotonic contractions are either concentric or eccentric on

basis of whether shortening or lengthening occurs

Types of muscle contraction• Movement may occur at any given joint without any

muscle contraction whatsoever• referred to as passive • solely due to external forces such as those applied by another

person, object, or resistance or the force of gravity in the presence of muscle relaxation

Types of muscle contraction• Concentric contractions involve muscle developing

tension as it shortens• Eccentric contractions involve the muscle lengthening

under tension• Contraction is contradictory regarding eccentric muscle activity,

since the muscle is really lengthening while maintaining considerable tension

• Eccentric muscle action is perhaps more correct

Types of muscle contraction• Concentric contraction

• muscle develops tension as it shortens• occurs when muscle develops enough force to

overcome applied resistance• causes movement against gravity or resistance• described as being a positive contraction

Types of muscle contraction• Concentric contraction

• force developed by the muscle is greater than that of the resistance• results in joint angle changing in the direction of the applied muscle

force• causes body part to move against gravity or external forces

Types of muscle contraction• Eccentric contraction (muscle action)

• controls movement with gravity or resistance• described as a negative contraction• force developed by the muscle is less than that of the resistance• results in the joint angle changing in the direction of the resistance

or external force• causes body part to move with gravity or external forces

(resistance)

Types of muscle contraction• Eccentric contraction (muscle action)

• muscle lengthens under tension• occurs when muscle gradually lessens in

tension to control the descent of resistance• weight or resistance overcomes muscle

contraction but not to the point that muscle cannot control descending movement

Types of muscle contraction• Isokinetics - a type of dynamic exercise using concentric

and/or eccentric muscle contractions• the speed (or velocity) of movement is constant• muscular contraction (ideally maximum contraction) occurs

throughout movement• not another type of contraction, as some have described• Ex. Biodex, Cybex, Lido

Muscle fibers a long cylindrical cell with hundreds of nuclei

10-100 mm in diameter

1-30 cm in length contractile component: myofabril non-contractile component: endomyosium

types slow twitch fiber (type I)

red in color because of abundant blood supply

slower to the peak when contracted

fatigue resistant fast twitch fiber (type IIA)

pale in color because of less blood supply

rapidly to the peak when contracted

easy fatigue intermediate fiber (type IIB)

Skeletal muscle 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 fibers of the deltoid

Note ： Lieber RL(1992) divided skeletal muscle architecture into 3 general types

longitudinal architecture ： biceps brachii unipennate architecture ： vastus lateralis multipennate architecture ： gluteus medius

Angle of Pennation

Angle of Pennation – the angle of orientation between the muscle fibers and tendon

With an increase in the angle of pennation, less force from each individual fiber is transmitted along the long axis of the muscle’s tendon

Despite a less efficient transfer of force per muscle fiber, a greater degree of pennation allows for more muscle fibers to attach to the tendon as compared to a fusiform muscle

A multipennate muscle structure (gastrocnemius) has an even greater force generation potential due to more fibers fitting into a given length of muscle, attaching on its’ central tendon

effect of the angle of pennation

the greater the angle of pennation, the smaller the amount of effective force transmitted to the tendon

the angle of the pennation increases as tension progressively increases in the muscle fibers

The pennate arrangement will allow the packing of more fibers given the same space.

Types based on changes in length concentric contraction (shortening contraction) · isometric contraction (static contraction)

isos = equal ； metron = measure

definition ： muscle contraction with muscle length kept no change

The joint angle remains the same when an isometric strength is developed.

There is no motion existed during isometric contraction

  eccentric contraction (lengthening contraction)

definition ： muscle contraction with the length of the entire muscle lengthened

In daily activities, if the gravity is the only external force acting on the body, the antagonist muscle contracts eccentrically during gravity-assisted motions

Types of muscle contraction, based on development of tension

isotonic

iso = equal ； tonus = tension

Muscle physiologists defined a kind of muscle contraction that develops constant tension throughout the whole muscle excursion as isotonic contraction; however, it is seldom seen in the living body

Clinicians use isotonic contraction commonly and 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

1.    the moment arm to the joint axis is changing throughout the motion

2.    the resistance with respect to the gravity is changing throughout the motion

isometric

equal muscle length and same joint angle

zero motion speed with varying resistance

 

isokinetic

iso = equal ； kinetos = move

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)

first introduced by Hislop and Perrine in 1967

equal motion speed with accommodating resistance

·comparison of different types of muscle contraction

Tension Length Speed

isotonic varying varying varying

isometric varying equal zero

isokinetic

accomodating

resistance

(varying)

varying constant

mechanical model of muscle fiber

contractile component ： actin and myosin crossbridges structures

parallel elastic component ： muscle connective tissue e.g. epimyosium, perimyosium, or endomyosium

series elastic component ： connective tissues within the tendon

tension generated by active contraction

resting length of a sacromere ： the length that allows the greatest number of cross-bridge attachments and the greatest potential active force

active length-tension curve ： an inverted U-shape with its peak at the resting length

tension generated by passive stretch

developed when series and parallel elastic components are stretched

passive length-tension curve ： the tissue is slack before stretched and then the tension builds as an exponential function

total length tension curve of muscle

at shortened lengths ： active contraction dominates force generation

just beyond its resting length ： passive tension begins to contribute and active tension is compromised

at more elongated lengths ： passive tension accounts for most of the total force

　

Passive Length-Tension

• Connective tissues (CT) located within the muscle (epi, peri & endomysium) have some elastic properties and therefore can generate resistive force when elongated or stretched

• Passive Tension – The resistive force (stiffness) generated within a muscle’s CT and its tendon in response to an applied stretch to the muscle

• Passive tension of a muscle stabilizes skeletal structures against gravity and responds to loads imposed upon the body

• Stretched muscle tissue exhibits both elastic (allows a stretched muscle to return to its original length) and viscoelastic (increasing resistance to elongation as rate of stretch increases) properties.

Passive Length Tension Curve

Stress-Strain Curve

Active Length-Tension Myofibrils – contractile structures within the individual muscle fiber; hundreds to thousands of myofibrils are housed within each fiber

Myofibrils contain the contractile components (myofilaments) of the muscle fiber Actin & Myosin

The active force or “tension” generated within a myofibril is directly dependent on the number of simultaneous cross-bridges formed

The ideal resting length of a muscle fiber or sarcomere is the length that allows the greatest number of cross-bridge attachments, and therefore, the greatest potential active force

As the sarcomere is lengthened or shortened from its resting length, the number of potential cross-bridge attachments decreases, lessening the active force potential even at full muscle fiber activation

Actin

Myosin

Actin & Myosin cross-bridging

Myosin cross bridge attaches to the actin myofilament

1

2

3

4 Working stroke—the myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line

As new ATP attaches to the myosin head, the cross bridge detaches

As ATP is split into ADP and Pi, cocking of the myosin head occurs

Myosin head (high-energy configuration)

Thick filament

Myosin head (low-energy configuration)

ADP and Pi (inorganic phosphate) released

Sequential Events of Contraction

Thin filament

Total Length Tension

Total Length Tension Curve Total Length Tension – the combination of passive and active tension of a muscle

The combination of the two tensions allows for a large range of muscle force over a wide range of muscle length

As the active force (tension) begins to decline with increasing muscle fiber length, the passive tension rises

Passive tension declines as a muscle fibers approaches its resting length; this is accompanied by an optimal cross-bridge arrangement, which increases active force potential within the fiber

Force-Velocity Relationship

force decreased as velocity increased during concentric contraction

· force increased as velocity decreased during eccentric contraction

· force = 0 during isometric contraction

Force-Velocity Relationship

•During concentric & eccentric activation, the rate of change of a muscle’s length is

significantly related to the muscle’s maximal force potential

•As the velocity of a contraction increases, the F generating capabilities of the

muscle decreases. This is demonstrated by the Force Velocity Curve.

Conversely, as the velocity of a contraction slows, F generating

capabilities increase•From this F-V curve, it is evident that the

greatest force production capability is with slow eccentric activities (i.e. eccentric component of a squat)

•Activities requiring high velocity concentric actions produce the lowest

force (i.e. throwing a wiffle ball)

Muscle activities during motion focal muscle agonist or prime mover

agon = contest

the principal muscle that produces a joint motion or maintains a static posture

can be concentric, isometric, or eccentric antagonist

anti = against; agon = contest

the muscle that contracts in the opposite direction of the agonist

passively elongates or shortens to allow motion acted by agonist

  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

Actions of multi-joint muscles

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.

active insufficiency • unable to reach the contraction force because of the limit of

muscle length

passive insufficiency • unable to reach full range of motion because of the limit of

muscle length • NOTE ： The totally insufficient grip strength produced with the

wrist fully flexed is due to the combination of active insufficiency of the long finger flexors and passive insufficiency of the long finger extensors

FASCICLE ARRANGEMENT TO

MUSCLE STRUCTURE

Arrangement of Fascicles

• (a): Circular pattern:• Fascicles arranged in

concentric rings• Muscles with this

arrangement surround external openings, which they close by contracting

• General term for these muscles is sphincters (squeezers)

• Examples:• Orbicularis muscles

surrounding the eyes (Orbicularis oculi) and the mouth (Orbicularis oris)

Arrangement of Fascicles

• (b): Convergent pattern: • Muscle has a broad origin,

and its fascicles converge toward a single tendon of insertion

• Such a muscle is triangular or fan shaped like the pectoralis major muscle of the anterior thorax

Arrangement of Fascicles

•(c()f :) Parallelpattern:

•The long axes of the fascicles run parallel to the

long axis of the muscle•Such muscles are either :

•straplike (c: parallel)•spindle (f: fusiform)

•shaped with an expanded belly (midsection)

•Examples:•Sartorius of thigh (c)•Biceps brachii muscle of the

arm (f)

Arrangement of Fascicles• (d)(e)(g): Pennate pattern:

• In a pennate (feather) pattern of arrangement the fascicles are short and attach obliquely to a central tendon that runs the length of the muscle

• Types:• Unipennate: d

• Fascicles insert into only one side of the tendon

• Example: extensor digitorum muscle of the leg

• Bipennate: g• Fascicles insert into the tendon from

opposite sides (muscle grains resemble a feather)

• Example: rectus femoris muscle of the thigh

• Multipennate: e• Arrangement looks like many

feathers situated side by side, with all their quills inserted into one large tendon

• Example: deltoid muscle, which forms the roundness of the shoulder

Organization of Skeletal Muscle Fibers• 4 patterns of fascicle organization:

• parallel• convergent• pennate• circular

Contraction – muscle gets shorter but body increases in diameter

• Fascicles are parallel to the long axis of the muscle (most muscles)• Firm attachment by a tendon extends from the free tip to a movable bone of the skeleton – flat bands with aponeuroses; spindle shaped with cordline tendons; have a central body, belly or gaster (‘stomach)

Fig 9.14

• Muscle fibers cover a broad area, but all fibers come together at a common attachment site and pull on a tendon, a tendinous sheet, or a raphe (band of collagen fibers)• Fibers on opposite sides of the tendon pull in different directions

Fig 9.14

Unipennate – all muscle cells are on the same side of the tendon

• Pennate muscles have 1 or more tendons that run through the body, fascicles form an oblique angle to the tendon• Have more fibers than a parallel - generates more tension than a parallel muscle of the same size

Fig 9.14

Bipennate Muscle – muscle fibers on both sides of the tendon

Fig 9.14

Multipennate – triangular deltoid muscle covers the superior surface of the shoulder joint

Fig 9.14

• Sphincter, fibers are concentric around an opening or recess• Contraction – opening diameter decreases; guard entrances and exits of internal passageways (digestive and urinary tracts)

Fig 9.14