Slide 0 Copyright © 2005, Elsevier, Inc. All Rights Reserved. Chapter 7 The Muscular System

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Chapter 7Chapter 7

The Muscular System

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Chapter 7Lesson 7.1Chapter 7Lesson 7.1

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IntroductionIntroduction

• Muscular tissue enables the body and its parts to move Movement is caused by ability of muscle cells

(called fibers) to shorten or contract Muscle cells shorten by converting chemical

energy (obtained from food) into mechanical energy, which causes movement

Three types of muscle tissue exist in the body

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Muscle TissueMuscle Tissue

• Types of muscle tissue Skeletal muscle—also called striated or

voluntary muscle Is 40% to 50% of body weight; attached to bones Microscope reveals crosswise stripes or striations Contractions can be voluntarily controlled

(Cont’d…)

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Muscle TissueMuscle Tissue

• Types of muscle tissue (cont’d)

Cardiac muscle—composes bulk of heart Cardiac muscle cells branch frequently Characterized by unique dark bands called

intercalated disks Interconnected nature of cardiac muscle cells

allows heart to contract efficiently as a unit

(Cont’d…)

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Muscle TissueMuscle Tissue

(…Cont’d)

Types of muscle tissue (cont’d) Nonstriated muscle or involuntary muscle—also

called smooth or visceral muscle Lacks cross stripes or striation when seen under a

microscope; appears smooth Found in walls of hollow visceral structures such

as digestive tract, blood vessels, and ureters Contractions not under voluntary control;

movement caused by contractions is involuntary Function—all muscle cells specialize in

contraction (shortening)

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Muscle TissueMuscle Tissue(…Cont’d)

Muscle tissue

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Structure of Skeletal MuscleStructure of Skeletal Muscle

• Structure Skeletal muscle: an organ composed mainly of

skeletal muscle cells and connective tissue Extend from one bone across a joint to another

bone

(Cont’d…)

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Structure of Skeletal MuscleStructure of Skeletal Muscle

(…Cont’d)

• Structure

Parts of a skeletal muscle: Origin—attachment to the bone that remains

relatively fixed when movement at the joint occurs

Insertion—point of attachment to the bone that moves when a muscle contracts

Body—main part of the muscle

(Cont’d…)

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Structure of Skeletal MuscleStructure of Skeletal Muscle

(…Cont’d)

Muscles attach to the bone by tendons—strong cords of fibrous connective tissue

Some tendons: enclosed in synovial-lined tubes and lubricated by synovial fluid

Bursae—small synovial-lined sacs containing a small amount of synovial fluid

(Cont’d…)

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Structure of Skeletal MuscleStructure of Skeletal Muscle(…Cont’d)

Attachments of a skeletal muscle

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Structure of Skeletal MuscleStructure of Skeletal Muscle

(…Cont’d)

• Microscopic structure Muscle tissue consists of specialized contractile

cells called fibers Each fiber contains two kinds of very fine,

threadlike structures: Thick myofilaments =Myosin Thin myofilaments =Actin

(Cont’d…)

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Structure of Skeletal MuscleStructure of Skeletal Muscle

(…Cont’d)

Sarcomere: basic functional (contractile) unit Separated from each other by dark bands

called Z lines Sliding filament model explains mechanism of

contractiono Thick and thin myofilaments slide past each other as

a muscle contracts

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Functions of Skeletal MuscleFunctions of Skeletal Muscle

• Movement Muscles produce movement As muscle contracts, it pulls the insertion bone

closer to the origin bone Movement occurs at the joint between the origin

and the insertion

(Cont’d…)

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Functions of Skeletal MuscleFunctions of Skeletal Muscle

(Cont’d…)

• Movement Groups of muscles usually contract to produce a

single movemento Prime mover—contraction is mainly responsible for

producing a movemento Synergist—contractions help the prime mover

produce a movemento Antagonist—actions oppose the action of a prime

mover in a movement

(Cont’d…)

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Functions of Skeletal MuscleFunctions of Skeletal Muscle(…Cont’d)

• Posture Tonic contraction: specialized muscle

contraction that enables us to maintain body position Only a few of a muscle’s fibers shorten at one

time Tonic contractions produce no movement

Tonic contractions maintain muscle tone called posture

(Cont’d…)

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Functions of Skeletal MuscleFunctions of Skeletal Muscle

(…Cont’d)

• Heat production Survival depends on the ability to maintain

constant body temperature Fever—an elevated body temperature; often a

sign of illness Hypothermia—a reduced body temperature

Contraction of muscle fibers produces most of the heat required to maintain normal body temperature

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FatigueFatigue

• Reduced strength of muscle contraction• Caused by repeated muscle stimulation• Repeated muscular contraction depletes

cellular ATP store and outstrips the ability of the blood supply to replenish oxygen and nutrients

(Cont’d…)

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FatigueFatigue

(…Cont’d)

• Contraction in the absence of adequate oxygen produces lactic acid, which contributes to muscle soreness

• Oxygen debt—the continued metabolic effort required to burn excess lactic acid that may accumulate during prolonged periods of exercise

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Role of Other Body Systems in MovementRole of Other Body Systems in Movement

• Muscle functioning depends on the functioning of many other parts of the body

• Respiratory, circulatory, nervous, muscular, and skeletal systems play essential roles in producing normal movements

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Motor UnitMotor Unit• Stimulation of a muscle by a nerve impulse is

required to produce movement• Motor neuron: specialized nerve that

transmits an impulse to a muscle, causing contraction

• Neuromuscular junction: specialized point of contact between a nerve ending and the muscle fiber it innervates

• Motor unit: the combination of a motor neuron with the muscle cell(s) it innervates

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Muscle StimulusMuscle Stimulus

• A muscle will contract only if an applied stimulus reaches a certain level of intensity Threshold stimulus: minimal level of stimulation

required to cause a muscle fiber to contract

• Once stimulated by a threshold stimulus, a muscle fiber will contract completely, a response called all or none

(Cont’d…)

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Muscle StimulusMuscle Stimulus

(…Cont’d)

• Different muscle fibers in a muscle are controlled by different motor units having different threshold-stimulus levels Although individual muscle fibers always

respond all or none to a threshold stimulus, the muscle as a whole does not

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Types of Skeletal Muscle ContractionTypes of Skeletal Muscle Contraction

• Twitch and tetanic contractions Twitch contractions—a quick, jerky response

to stimulus Single contraction of muscle fibers caused by

a single threshold stimulus Tetanic contractions—sustained, steady

muscular contractions Caused by a series of stimuli bombarding a

muscle in rapid succession

(Cont’d…)

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Types of Skeletal Muscle ContractionTypes of Skeletal Muscle Contraction

(…Cont’d)

• Isotonic contractions Contraction of a muscle that produces

movement at a joint The muscle changes length, causing the

insertion end of the muscle to move relative to the point of origin

Most types of body movements such as walking and running are isotonic contractions

(Cont’d…)

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Types of Skeletal Muscle ContractionTypes of Skeletal Muscle Contraction

(…Cont’d)

• Isometric contractions Muscle contractions that do not produce

movement The muscle as a whole does not shorten

No movement occurs during isometric contractions, but tension within the muscle increases

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Types of Skeletal Muscle ContractionTypes of Skeletal Muscle Contraction(…Cont’d)

Types of Muscle Contraction

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Effects of Exercise on Skeletal MusclesEffects of Exercise on Skeletal Muscles

• Regular, properly practiced exercise improves muscle tone and posture,

• Results in more efficient heart and lung functioning

• Reduces fatigue

(Cont’d…)

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Effects of Exercise on Skeletal Muscles Effects of Exercise on Skeletal Muscles

• Effects of Exercise on Skeletal Muscles Prolonged inactivity causes disuse atrophy Regular exercise increases muscle size, called

hypertrophy

(Cont’d…)

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Effects of Exercise on Skeletal MusclesEffects of Exercise on Skeletal Muscles

(…Cont’d)

Strength training: exercise involving contractions of muscles against heavy resistance Increases number of myofilaments in each muscle

fiber Total mass of the muscle increases Does not increase the number of muscle fibers

(Cont’d…)

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Effects of Exercise on Skeletal Muscles Effects of Exercise on Skeletal Muscles

(…Cont’d)

Endurance training: exercise that increases a muscle’s ability to sustain moderate exercise over long periods Sometimes called aerobic training Allows more efficient delivery of oxygen and

nutrients to a muscle via increased blood flow Increases the number of blood vessels in a muscle Does not usually result in muscle hypertrophy

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Chapter 7Lesson 7.2Chapter 7Lesson 7.2

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Skeletal Muscle GroupsSkeletal Muscle Groups

• Muscles of the head and neck Facial muscles

Orbicularis oculi, orbicularis oris, zygomaticus Muscles of mastication

Masseter, temporal Sternocleidomastoid—flexes head Trapezius—elevates shoulders and extends

head

(Cont’d…)

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Skeletal Muscle GroupsSkeletal Muscle Groups(…Cont’d)

Muscles of the head and neck

(Cont’d…)

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Skeletal Muscle GroupsSkeletal Muscle Groups

(…Cont’d)

• Muscles that move the upper extremities Pectoralis major—flexes upper arm Latissimus dorsi—extends upper arm Deltoid—abducts upper arm Biceps brachii—flexes forearm Triceps brachii—extends forearm

(Cont’d…)

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Skeletal Muscle GroupsSkeletal Muscle Groups

(…Cont’d)

• Muscles of the trunk Abdominal muscles

Rectus abdominis External oblique Internal oblique Transversus abdominis

Respiratory muscles Intercostal muscles Diaphragm

(Cont’d…)

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Skeletal Muscle GroupsSkeletal Muscle Groups(…Cont’d)

Muscles of the trunk(Cont’d…)

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Skeletal Muscle GroupsSkeletal Muscle Groups

(…Cont’d)

• Muscles that move the lower extremities Iliopsoas—flexes thigh Gluteus maximus—extends thigh Adductor muscles—adduct thighs Hamstring muscles—flex lower leg

Semimembranosus Semitendinosus Biceps femoris

(Cont’d…)

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Skeletal Muscle GroupsSkeletal Muscle Groups

(…Cont’d)

• Muscles that move the lower extremities Quadriceps femoris group—extend lower leg

Rectus femoris Vastus muscles

Tibialis anterior—dorsiflexes foot Gastrocnemius—plantar flexes foot Peroneus group—flex foot

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Types of Movements Produced by Skeletal Muscle ContractionsTypes of Movements Produced by Skeletal Muscle Contractions

• Flexion—decreases the angle between two bones at their joint: bending

• Extension—increases the angle between two bones at their joint: straightening

• Abduction—movement of a part away from the midline of the body

• Adduction—movement of a part toward the midline of the body

• Rotation—movement around a longitudinal axis

(Cont’d…)

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Types of Movements Produced by Skeletal Muscle ContractionsTypes of Movements Produced by Skeletal Muscle Contractions(…Cont’d)

Flexion and extension of the elbow(Cont’d…)

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Types of Movements Produced by Skeletal Muscle ContractionsTypes of Movements Produced by Skeletal Muscle Contractions

(…Cont’d)

• Supination and pronation—hand positions from rotation of the forearm Supination: palm turned to the anterior position Pronation: palm faces posteriorly

• Dorsiflexion and plantar flexion—foot movements Dorsiflexion: elevation of the dorsum or top of the

foot Plantar flexion: bottom of the foot is directed

downward

(Cont’d…)

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Types of Movements Produced by Skeletal Muscle ContractionsTypes of Movements Produced by Skeletal Muscle Contractions

(…Cont’d)

Examples of body movements