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Chapter 11

Muscular System

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Outline• Types and Functions of Muscles

– Smooth– Cardiac– Skeletal

• Muscle Innervation• Whole Muscle Contraction

– Oxygen Deficit– Athletics and Muscle Contraction

Slow and Fast Twitch Fibers• Muscle Disorders

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Types and Functions of Muscles

• Smooth muscle is located in the walls of hollow internal organs and contracts involuntarily.

• Cardiac muscle forms the heart wall and contracts involuntarily.

• Skeletal muscle runs the entire length of the muscle and contracts voluntarily.

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Types of Muscle

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Functions of Skeletal Muscles

• Body support.• Bone movement.• Maintenance of body temperature.• Assist movement in cardiovascular and

lymphatic vessels.• Protect internal organs.• Stabilize joints.

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Skeletal Muscles of the Body

• A whole muscle contains bundles of skeletal muscle fibers, fascicles.

• Muscles are covered with fascia that becomes tendons.

• Muscles originate on the stationary bone, and insert on the bone that moves.

• Cooperating muscle pairs have prime movers and synergists.

• Antagonistic pairs work opposite one another to move in opposite directions.

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Skeletal Muscles

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Names and Actions of Skeletal Muscles

• Skeletal muscles are named based on characteristics.– Size.– Shape.– Direction of muscle

fibers.– Number of

attachments.– Action.

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Skeletal Muscle Fiber Contraction

• Overview of Muscular Contraction.– Nerve impulses originate in the brain,

travel down motor neurons, and stimulate muscle fibers at neuromuscular junctions.

When muscle fibers are stimulated to contract, myofilaments slide past one another, causing sarcomeres to shorten.

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Muscle Innervation• Muscle fibers are innervated.

– Stimulated to contract by motor nerve fibers.

Signaled when nerve impulses bring about release of neurotransmitter molecules at a neuromuscular junction.

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Neurotransmitter Junction

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Muscle Innervation

• Myosin filament heads break down ATP and attach to an actin filament, forming cross-bridges that pull the actin filament to the center of the sarcomere.– Contraction continues until nerve

impulses cease.

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Whole Muscle Contraction

• Muscle Twitch - Single muscle contraction.– Divided into three stages.

Stimulation.Contraction.Relaxation.

• If a muscle is given a rapid series of threshold stimuli, muscle contraction summates in a sustained contraction, tetanus.

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Physiology of Skeletal Muscle Contraction

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Whole Muscle Contraction

• A motor neuron, together with all of the muscle fibers that it innervates, is a motor unit.– As the intensity of nervous stimulation

increases, more motor units are activated.

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Energy for Muscle Contraction

• ATP produced previous to strenuous exercise lasts a few seconds, and then muscles acquire new ATP in three ways.– Phosphate breakdown. (anaerobic)– Fermentation. (anaerobic)– Cellular respiration. (aerobic)

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Oxygen Deficit

• When a muscle uses the anaerobic means of supplying energy, it incurs an oxygen deficit.– Repaying an oxygen deficit requires

replenishing creatine phosphate supplies and disposing of lactic acid.

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Athletics and Muscle Contraction

• Muscles that are not used, or are used in only weak contractions can atrophy.– Can cause muscle fibers to progressively

shorten, leaving body parts contracted in contorted positions.

Hypertrophy occurs if the muscle contracts to at least 75% of its maximum tension.

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Athletics and Muscle Contraction

• Slow-twitch fibers produce most of their energy aerobically and tire only when their fuel supply is gone.

• Fast-twitch fibers tend to be anaerobic and seem to be designed for strength as their motor units contain many fibers.– Can develop greater, and more rapid,

maximum tension than slow-twitch fibers.

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Slow-and-Fast Twitch Muscle Fibers

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Muscle Disorders

• Spasms are sudden, involuntary muscular contractions most often accompanied by pain.– Multiple spasms of skeletal muscles are

called a seizure or convulsion.• A strain is an overstretching of a muscle near

a joint, while a sprain is a twisting of a joint leading to swelling and injury.

• Myalgia refers to inflammation of muscle tissue.

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Muscular Disorders

• Muscular dystrophy is a broad term applied to a group of disorders characterized by progressive muscle degeneration and weakening.

• Myasthenia gravis is an autoimmune disease characterized by weakness that especially affects the muscles of the eyelids, face, neck, and extremities.

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Homeostasis

• Cardiac muscle contraction accounts for the heartbeat, delivering blood to the tissues.

• Smooth muscle contraction accounts for peristalsis and urination.

• Skeletal muscle contraction returns blood to the heart and moves bones, allowing for body movement.

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Review

• Types and Functions of Muscles– Smooth– Cardiac– Skeletal

• Muscle Innervation• Whole Muscle Contraction

– Oxygen Deficit– Athletics and Muscle Contraction

Slow and Fast Twitch Fibers• Muscle Disorders

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