39038402 Skeletal Muscle

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MUSCULAR SYSTEM

• Muscle cells/myocytes

function --> movement

• Classification

- Skeletal muscle

- Cardiac muscle

- Smooth muscle

Skeletal Muscle

• Muscle fibers

- extrafusal

- intrafusal (musclespindle)

• endomysium

• fasciculi

• perimysium

• epimysium

Attachment of skeletal muscle

• Tendons

• aponeuroses

• fascia

• origin• insertion

Shape and fiber architecture

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

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

Innervation of Skeletal Muscle

• By one or more nerves

• Muscle’s nerves contain:

- -motor axon

- autonomic efferents

- Ia afferent from muscle fibers of neuromuscular spindle

- Ib afferents from Golgi tendon organ -

pain fibers

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

Gradation of muscle contraction

Strategy:

- Increase the impulse frequency of motoneuron

- Increase the number of motor unit recruited

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.

Muscle Histochemistry

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

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

Study of muscle action

• Anatomical method

• Localized electrical stimulation

• Manual palpation

• EMG

EMG + other tools• Clinical method

Actions of muscles

• Isometric vs isotonic contraction

• concentric vs eccentric

Classification of muscle role

• Prime mover

• antagonist

• fixator

• synergist

Biomechanics

• First Class Lever

• Second Class Lever

• Third Class Lever

Effect of muscle force on joints

• Turning effect

- M = F x L

• Reaction at the joint

- normal component

- tangential component

Kinesiology

- Study of human movement

- a branch of biomechanics

M l k l t l Bi h i d

Musculoskeletal Biomechanics and

Kinesiology

Significance:

Occupational ergonomics

Medical rehabilitation --> Occupational therapy

Orthopedics

Rehabilitation engineering

Bioinstrumentation

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

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

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

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

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

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

• Force = mechanicaldisturbances or load

• Moments = the tendency of

the force (F) to turn the

bones about the joint.

M = F * L

L = moment arm

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.

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

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

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.

Levers

• First Class Lever

• Second Class Lever

• Third Class Lever

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

Second-class lever

- the resistance/load is between the axis and the force

- example: opening the mouth against resistance

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.

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.

Mechanical Model of a Muscle

•Contractile component: Muscle fibers

• Series of elastic component: Tendon

• Parallel elastic component: Muscle membrane &

connective tissues

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.

Mechanical Properties of Skeletal Muscle

• Length-tension relationship

• In a muscle force generation capacity increaseswhen the muscle is slightly stretch because of the

effect of both active and passive component

• Muscle force decreases as the velocity of

contraction increases only true for concentric

contraction

• 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

Factors affecting Muscle Strength

• Body temperature

• Muscle hypertrophy

• Muscle atrophy

39038402 Skeletal Muscle

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