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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.

• Cells are muscle fibers

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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.

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Names and Actions of Skeletal Muscles

• Skeletal muscles are named based on characteristics.– Size. Gluteus maximus– Shape. Deltoid– Direction of muscle fibers. Rectus

abdominus– Number of attachments. Biceps brachii– Action. Extensor digitorum

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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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Skeletal Muscle Fiber Contraction

• Sarcolemma (plasma membrane)• Sarcoplasm• Myofibrils• T Tubule• Sarcoplasmic reticulum

– Contain Ca2+

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light and dark bands (striations)

sarcomeres

• thin filaments – actin

• thick filaments - myosin

Z line, A band, I band, H zone

Sliding Filament Theory – actin and myosin

filaments moving. Myosin does work. ATP

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Muscle Innervation

• Muscle fibers are 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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Muscle Innervation

• Released Calcium gets to troponin• Troponin causes a shift in tropomyosin• Myosin head attaches (ATP=ADP + P)• Stroke (ADP + P released)

– 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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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.

(recruitment)

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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.

forceful exercise can cause muscle size to increase or hypertrophy.

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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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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.