Essentials of Human Anatomy & Physiology

Seventh Edition

Elaine N. Marieb

Chapter 6

The Muscular System

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Slides 6.1 – 6.58

The Muscular System

Lecture Slides in PowerPoint by Jerry L. Cook

The Muscular SystemThe Muscular System

Muscles are responsible for all types ofbody movement

Three basic muscle types are found in

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Three basic muscle types are found inthe body

Skeletal muscle

Cardiac muscle

Smooth muscle

Characteristics of MusclesCharacteristics of Muscles

Muscle cells are elongated(muscle cell = muscle fiber)

Contraction of muscles is due to themovement of myofilaments – the muscle cellequivalent of the microfilaments of cytoskeletons

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equivalent of the microfilaments of cytoskeletons

All muscles share some terminology

Prefix myo refers to muscle

Prefix mys refers to muscle

Prefix sarco refers to flesh

Skeletal Muscle CharacteristicsSkeletal Muscle Characteristics

Most are attached by tendons to bones

Cells are multinucleate & cigar-shaped

Striated – have visible banding

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Striated – have visible banding

Voluntary – subject to conscious control

Cells are surrounded and bundled byconnective tissue

Connective Tissue Wrappings ofConnective Tissue Wrappings ofSkeletal MuscleSkeletal Muscle

Endomysium –connective tissuearound singlemuscle fiber

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muscle fiber

Perimysium –around a fascicle(bundle) of fibers

Figure 6.1

Connective Tissue Wrappings ofConnective Tissue Wrappings ofSkeletal MuscleSkeletal Muscle

Epimysium – covers theentire skeletal muscle

Figure 6.1

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Fascia – on the outsideof the epimysium

Skeletal Muscle AttachmentsSkeletal Muscle Attachments

Epimysium blends into a connectivetissue attachment

Tendon – cord-like structure

Aponeuroses – sheet-like structure

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Aponeuroses – sheet-like structure

Sites of muscle attachment

Bones

Cartilages

Connective tissue coverings

Smooth Muscle CharacteristicsSmooth Muscle Characteristics

Has no striations

Spindle-shaped cells

Single nucleus

Involuntary – no

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Involuntary – noconscious control

Found mainly in thewalls of hollow organs– visceral

Arranged in two sheetsor layers Figure 6.2a

Cardiac Muscle CharacteristicsCardiac Muscle Characteristics

Has striations

Usually has asingle nucleus

Joined to another

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Joined to anothermuscle cell at anintercalated disc

Involuntary

Found only in theheart Figure 6.2b

Function of MusclesFunction of Muscles

Produce movement

Maintain posture

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Stabilize joints

Generate heat

Microscopic Anatomy of SkeletalMicroscopic Anatomy of SkeletalMuscleMuscle

Cells are multinucleate

Nuclei are just beneath the sarcolemma– plasma membrane

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– plasma membrane

Figure 6.3a

Microscopic Anatomy of SkeletalMicroscopic Anatomy of SkeletalMuscleMuscle Sarcolemma – specialized plasma

membrane

Sarcoplasmic reticulum – specializedsmooth endoplasmic reticulum

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smooth endoplasmic reticulum

Figure 6.3a

Microscopic Anatomy of SkeletalMicroscopic Anatomy of SkeletalMuscleMuscle

Myofibril

Bundles of myofilaments

Myofibrils are aligned to give distinct bands

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Myofibrils are aligned to give distinct bands

I band =light band

A band =dark band

Figure 6.3b

Microscopic Anatomy of SkeletalMicroscopic Anatomy of SkeletalMuscleMuscle

Sarcomere

Contractile unit of a muscle fiber

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Figure 6.3b

Microscopic Anatomy of SkeletalMicroscopic Anatomy of SkeletalMuscleMuscle Organization of the sarcomere

Thick filaments = myosin filaments

Composed of the protein myosin

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Has ATPase enzymes

Figure 6.3c

Microscopic Anatomy of SkeletalMicroscopic Anatomy of SkeletalMuscleMuscle

Organization of the sarcomere

Thin filaments = actin filaments

Composed of the protein actin andregulatory proteins

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regulatory proteins

Figure 6.3c

Microscopic Anatomy of SkeletalMicroscopic Anatomy of SkeletalMuscleMuscle

Myosin filaments have heads(extensions, or cross bridges)

Myosin and

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Myosin andactin overlapsomewhat

Figure 6.3d

Microscopic Anatomy of SkeletalMicroscopic Anatomy of SkeletalMuscleMuscle

At rest, there is a bare zone that lacksactin filaments – the H zone

Sarcoplasmic

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Sarcoplasmicreticulum(SR) – forstorage ofcalcium

Figure 6.3d

Properties of Skeletal MuscleProperties of Skeletal MuscleActivityActivity

Irritability – ability to receive andrespond to a stimulus

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respond to a stimulus

Contractility – ability to shorten when anadequate stimulus is received

Nerve Stimulus to MusclesNerve Stimulus to Muscles

Skeletalmuscles mustbe stimulatedby a nerve tocontract

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contract

Motor unit

One neuron

Muscle cellsstimulated bythat neuron

Figure 6.4a

Nerve Stimulus to MusclesNerve Stimulus to Muscles

Neuromuscularjunctions –

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junctions –association siteof nerve andmuscle

Figure 6.5b

Nerve Stimulus to MusclesNerve Stimulus to Muscles

Synaptic cleft –gap betweennerve andmuscle

Nerve and

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Nerve andmuscle do notmake contact

Area betweennerve and muscleis filled withinterstitial fluid Figure 6.5b

Transmission of Nerve Impulse toTransmission of Nerve Impulse toMuscleMuscle

Neurotransmitter – chemical released bynerve upon arrival of nerve impulse

The neurotransmitter for skeletal muscle isacetylcholine (ACh)

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acetylcholine (ACh)

Neurotransmitter attaches to receptors onthe sarcolemma

Sarcolemma becomes temporarilypermeable to sodium (Na+) that rushes intothe cell giving it a positive charge

Transmission of Nerve Impulse toTransmission of Nerve Impulse toMuscleMuscle

Sodium rushing into the cell generates anaction potential

Once started, muscle contraction cannot bestopped

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stopped

To return to resting state

Potassium ions (K+) diffuse out of the cell

Sodium-potassium pump pumps sodium andpotassium back to their original positions

The Sliding Filament Theory ofThe Sliding Filament Theory ofMuscle ContractionMuscle Contraction

Activation by nervecauses myosinheads (crossbridges) to attach to

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bridges) to attach tobinding sites on thethin filament

Myosin heads thenbind to the next siteof the thin filamentwhen ATP is present

Figure 6.7

The Sliding Filament Theory ofThe Sliding Filament Theory ofMuscle ContractionMuscle Contraction

This continued actioncauses a sliding of themyosin along the actin

The result is that the

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The result is that themuscle is shortened(contracted)

Calcium ions are requiredfor the attachment ofmyosin cross bridges toactin Figure 6.7

The Sliding Filament TheoryThe Sliding Filament Theory

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Figure 6.8

Contraction of a Skeletal MuscleContraction of a Skeletal Muscle

Muscle fiber contraction is “all or none”

Within a skeletal muscle, not all fibers maybe stimulated during the same interval

Different combinations of muscle fiber

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Different combinations of muscle fibercontractions may give differing responses

Graded responses – different degrees ofskeletal muscle shortening

Changing frequency of stimulation

Changing number of muscle cells stimulated

Types of Graded ResponsesTypes of Graded Responses

Twitch

Single, brief jerky contraction

Not a normal muscle function

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Figure 6.9a, b

Types of Graded ResponsesTypes of Graded Responses

Tetanus (summing of contractions)

One contraction is immediately followed byanother

The muscle does

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The muscle doesnot completelyreturn to aresting state

The effectsare added

Figure 6.9a, b

Types of Graded ResponsesTypes of Graded Responses

Unfused (incomplete) tetanus

Some relaxation occurs betweencontractions

The results are summed

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The results are summed

Figure 6.9a, b

Figure 6.9c,d

Types of Graded ResponsesTypes of Graded Responses

Fused (complete) tetanus

No evidence of relaxation before thefollowing contractions

The result is a sustained muscle contraction

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The result is a sustained muscle contraction

Figure 6.9a, b

Figure 6.9c,d

Muscle Response to Strong StimuliMuscle Response to Strong Stimuli

Muscle force depends upon the numberof fibers stimulated

More fibers contracting results in

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More fibers contracting results ingreater muscle tension

Muscles can continue to contract unlessthey run out of energy

Energy for Muscle ContractionEnergy for Muscle Contraction

Initially, muscles used stored ATP forenergy

Bonds of ATP are broken to release energy

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Bonds of ATP are broken to release energy

Only 4-6 seconds worth of ATP is stored bymuscles

After this initial time, other pathwaysmust be utilized to produce ATP

Energy for Muscle ContractionEnergy for Muscle Contraction

Direct phosphorylation

Only muscle cells containcreatine phosphate (CP)

CP is a high-energymolecule

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molecule

After ATP is depleted, ADP isleft

CP transfers energy to ADP,to regenerate ATP

CP supplies are exhausted inabout 20 seconds

Figure 6.10a

Energy for Muscle ContractionEnergy for Muscle Contraction

Aerobic Respiration

Series of metabolicpathways that occur inthe mitochondria

Glucose is broken down

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Glucose is broken downto carbon dioxide andwater, releasing energy

This is a slower reactionthat requires continuousoxygen

Figure 6.10c

Energy for Muscle ContractionEnergy for Muscle Contraction

Anaerobic glycolysis

Reaction that breaksdown glucose withoutoxygen

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oxygen

Glucose is broken downto pyruvic acid toproduce some ATP

Pyruvic acid isconverted to lactic acid

Figure 6.10b

Energy for Muscle ContractionEnergy for Muscle Contraction

Anaerobic glycolysis(continued)

This reaction is not as

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This reaction is not asefficient, but is fast

Huge amounts ofglucose are needed

Lactic acid producesmuscle fatigue

Figure 6.10b

Muscle Fatigue and Oxygen DebtMuscle Fatigue and Oxygen Debt

When a muscle is fatigued, it is unable tocontract even when stimulated

The common reason for muscle fatigue isoxygen debt

Oxygen must be “repaid” to tissue to remove

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Oxygen must be “repaid” to tissue to removeoxygen debt

Oxygen is required to get rid of accumulatedlactic acid

Increasing acidity (from lactic acid) and lackof ATP causes the muscle to contract less

Types of Muscle ContractionsTypes of Muscle Contractions

Isotonic contractions – “same tone” ortension

Myofilaments are able to slide past eachother during contractions

The muscle shortens

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The muscle shortens

Isometric contractions – “samemeasurement” or length

Tension in the muscles increases

The muscle is unable to shorten

Muscle ToneMuscle Tone

Some fibers are contracted even in arelaxed muscle

Different fibers contract at different

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Different fibers contract at differenttimes to provide muscle tone

The process of stimulating variousfibers is under involuntary control

Effects of Exercise on MuscleEffects of Exercise on Muscle

Results of increased muscle use

Increase in muscle size

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Increase in muscle strength

Increase in muscle efficiency

Muscle becomes more fatigue resistant

Muscles and Body MovementsMuscles and Body Movements

Movement isattained due to

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attained due toa musclemoving anattached bone

Figure 6.12

Muscles and Body MovementsMuscles and Body Movements

Muscles areattached to at leasttwo points

Origin –

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Origin –attachment to animmoveable bone

Insertion –attachment to amovable bone

Figure 6.12

Types of Ordinary Body MovementsTypes of Ordinary Body Movements

Flexion – brings 2 bones closer together

Extension – increases distance between 2bones

Rotation

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Rotation

Abduction – moving a limb away from themidline of the body

Adduction – moving a limb toward the midline

Circumduction – combination of all of theabove except rotation

Body MovementsBody Movements

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Figure 6.13

Special MovementsSpecial Movements

Dorsiflexion – lifting the foot

Plantar flexion – depressing the foot

Inversion – turn foot inward

Eversion – turn foot outward

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Eversion – turn foot outward

Supination – hand facing upward

Pronation – hand facing downward

Opposition – touching thumb to other fingers

Types of MusclesTypes of Muscles

Prime mover – muscle with the majorresponsibility for a certain movement

Antagonist – muscle that opposes orreverses a prime mover

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reverses a prime mover

Synergist – muscle that aids a primemover in the same movement and helpsprevent rotation or unwanted movement

Fixator – stabilizes the origin of a primemover so all tension can be used tomove the insertion bone

Naming of Skeletal MusclesNaming of Skeletal Muscles

Direction of muscle fibers

Example: rectus (straight) or oblique (slanted)

Relative size of the muscle

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Relative size of the muscle

Examples: maximus (largest), minimus(smallest), longus (long)

Naming of Skeletal MusclesNaming of Skeletal Muscles

Location of the muscle

Example: many muscles are namedfor bones (e.g., temporalis, which is

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Example: many muscles are namedfor bones (e.g., temporalis, which isnear the temporal bone)

Number of origins

Example: biceps, triceps, quadriceps(two, three, or four origins or heads)

Naming of Skeletal MusclesNaming of Skeletal Muscles

Location of the muscle’s origin andinsertion

Example: sterno (on the sternum) cleido(clavicle) mastoid (on the mastoid process)

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Shape of the muscle

Example: deltoid (triangular)

Action of the muscle

Example: flexor and extensor (flexes orextends a bone)

Head and Neck MusclesHead and Neck Muscles

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Figure 6.14

Trunk MusclesTrunk Muscles

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Figure 6.15

Deep Trunk and Arm MusclesDeep Trunk and Arm Muscles

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Figure 6.16

Muscles of the Pelvis, Hip, and ThighMuscles of the Pelvis, Hip, and Thigh

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Figure 6.18c

Muscles of the Lower LegMuscles of the Lower Leg

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Figure 6.19

Superficial Muscles: AnteriorSuperficial Muscles: Anterior

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Figure 6.20

Superficial Muscles: PosteriorSuperficial Muscles: Posterior

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Figure 6.21