EDU2HBS Human Body Systems 1 The Muscular System 1

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EDU2HBS Human Body Systems

The Muscular System 1The Muscular System 1

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EDU2HBS Human Body Systems

Muscles are responsible for all types of body movement

Three basic muscle types are found in the body

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EDU2HBS Human Body Systems

Characteristics of MusclesCharacteristics of Muscles

Muscle cells are elongated (all muscle cells are called muscle fibers)

All muscles share some terminology

Prefix myo refers to muscle

Prefix mys refers to muscle

Prefix sarco refers to flesh

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EDU2HBS Human Body Systems

Skeletal Muscle CharacteristicsSkeletal Muscle Characteristics

Cells are multinucleate

Striated – have visible banding

Cells are surrounded and bundled by connective tissue

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EDU2HBS Human Body Systems

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EDU2HBS Human Body Systems

Connective Tissue Wrappings ofConnective Tissue Wrappings ofSkeletal MuscleSkeletal Muscle

Endomysium – around single muscle fiber

Perimysium – around a fascicle (bundle) of fibers

Fascia – on the outside of the epimysium

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EDU2HBS Human Body Systems

Skeletal Muscle AttachmentsSkeletal Muscle Attachments Epimysium blends into a connective

tissue attachment Tendon – cord-like structure

Aponeuroses – sheet-like structure

Sites of muscle attachment

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EDU2HBS Human Body Systems

Smooth Muscle CharacteristicsSmooth Muscle Characteristics Has no striations

Spindle-shaped cells

Found mainly in the walls of hollow organs

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EDU2HBS Human Body Systems

Cardiac Muscle CharacteristicsCardiac Muscle Characteristics Has striations

Usually has a single nucleus

Joined to another muscle cell at an intercalated disc

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EDU2HBS Human Body Systems

Function of MusclesFunction of Muscles

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EDU2HBS Human Body Systems

Microscopic Anatomy of SkeletalMicroscopic Anatomy of SkeletalMuscleMuscle

Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum

Figure 6.3a

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EDU2HBS Human Body Systems

Microscopic Anatomy of Skeletal MuscleMicroscopic Anatomy of Skeletal Muscle

Myofibril

Bundles of myofilaments

Myofibrils are aligned to give distrinct bands

Figure 6.3b

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EDU2HBS Human Body Systems

Microscopic Anatomy of Skeletal MuscleMicroscopic Anatomy of Skeletal Muscle

Sarcomere

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EDU2HBS Human Body Systems

Microscopic Anatomy of Skeletal MuscleMicroscopic Anatomy of Skeletal Muscle

Organization of the sarcomere

Thick filaments = myosin filaments

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EDU2HBS Human Body Systems

Microscopic Anatomy of Skeletal MuscleMicroscopic Anatomy of Skeletal Muscle

Organization of the sarcomere

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EDU2HBS Human Body Systems

Microscopic Anatomy of Skeletal MuscleMicroscopic Anatomy of Skeletal Muscle

Myosin and actin overlap somewhat

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EDU2HBS Human Body Systems

Microscopic Anatomy of Skeletal MuscleMicroscopic Anatomy of Skeletal Muscle

Sarcoplasmic reticulum (SR) – for storage of calcium Figure 6.3d

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EDU2HBS Human Body Systems

Nerve Stimulus to MusclesNerve Stimulus to Muscles Skeletal

muscles must be stimulated by a nerve to contract

Motor unit

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EDU2HBS Human Body Systems

Motor unitsMotor unitsDefinition: A motor neuron and all the

muscle fibers it contacts

– Motor neuron activation causes contraction of all associated muscle fibers

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EDU2HBS Human Body Systems

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EDU2HBS Human Body Systems

Nerve Stimulus to MusclesNerve Stimulus to Muscles

Neuromuscular junctions

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EDU2HBS Human Body Systems

Nerve Stimulus to MusclesNerve Stimulus to MusclesSynaptic cleft –

Nerve and muscle do not make contact

Area between nerve and muscle is filled with interstitial fluid Figure 6.5b

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EDU2HBS Human Body Systems

Transmission of Nerve Impulse to Transmission of Nerve Impulse to MuscleMuscle Neurotransmitter – chemical released

by nerve upon arrival of nerve impulse

The neurotransmitter for skeletal muscle is acetylcholine

Neurotransmitter attaches to receptors on the sarcolemma

Sarcolemma becomes permeable to sodium (Na+)

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EDU2HBS Human Body Systems

Transmission of Nerve Impulse to Transmission of Nerve Impulse to MuscleMuscle

Sodium rushing into the cell generates an action potential

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EDU2HBS Human Body Systems

The Sliding Filament Theory of Muscle The Sliding Filament Theory of Muscle ContractionContraction Activation by nerve

causes myosin heads (crossbridges) to attach to binding sites on the thin filament

Myosin heads then bind to the next site of the thin filament

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EDU2HBS Human Body Systems

The Sliding Filament Theory of Muscle The Sliding Filament Theory of Muscle ContractionContraction

Slide 6.17b

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

This continued action causes a sliding of the myosin along the actin

Figure 6.7

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EDU2HBS Human Body Systems

The Sliding Filament TheoryThe Sliding Filament Theory

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EDU2HBS Human Body Systems

Contraction of a Skeletal MuscleContraction of a Skeletal Muscle Muscle fiber contraction is “all or none”

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

Different combinations of muscle fiber contractions may give differing responses

Graded responses – different degrees of skeletal muscle shortening

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EDU2HBS Human Body Systems

Muscle Response to Strong StimuliMuscle Response to Strong Stimuli

More fibers contracting results in greater muscle tension

Muscles can continue to contract unless they run out of energy