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The Muscular System:

The Muscular System

Slide 2:

There are 3 types of muscles

A. Function of Skeletal Muscles:

A. Function of Skeletal Muscles Produce movement Muscle pulls tendons to move the skeleton Maintain posture and body position Continuous muscle contraction Guard entrances and exits Encircle openings to digestive and urinary tracts. Control swallowing, defecation and urination Maintain body temperature Energy from contraction is converted to heat

Slide 4:

B. Anatomy of Skeletal Muscles - Gross Anatomy Surrounds muscle Divides muscle into compartments, each contain a bundle of muscle fibers called fascicle Bundle of muscle fibers Surrounds each muscle fiber, and tie adjacent fibers together All three layers attach muscle to bone

B. Anatomy of a Skeletal Muscle – Blood Vessels and Nerves:

B. Anatomy of a Skeletal Muscle – Blood Vessels and Nerves Muscle contractions require energy Blood vessels deliver oxygen and nutrients to produce energy(ATP) Muscle contractions are under stimulation from the CNS(central nervous system)

Microanatomy – Sarcolemma and T-Tubules:

Microanatomy – Sarcolemma and T-Tubules Very large cells 100’s of nuclei Cell membrane pores open to T-tubules Network of narrow tubules filled with extracellular fluid form passageways through muscle fiber


Myofibrils Cylinder as long as entire muscle fiber Each fiber contains 100s to 1000s Responsible for contraction When myofibrils contract the whole cell contracts Consist of proteins Actin – thin filaments Myosin – thick filaments

Sarcoplasmic Reticulum:

Sarcoplasmic Reticulum Specialized form of SER Tubular network around each myofibril In contact with T-Tubule


Sarcomere Smallest functional unit of muscle fiber Each myofibril contains 10,000 sarcomeres end to end Interaction between thick and thin filaments cause contraction Banded appearance

Thick and Thin Filaments:

Thick and Thin Filaments Thin twisted actin molecules Each has an active site where they interact with myosin Resting – active site covered by tropomyosin which is held in place by troponin Thick Myosin Head attaches to actin during contraction Can only happen if troponin changes position, moving tropomyosin to expose active site

Sliding Filaments and Cross Bridges:

Sliding Filaments and Cross Bridges Sarcomere contraction – Sliding Filament Theory Thin filaments slide toward center of sarcomere Thick filaments are stationary Myosin head attaches to active site on actin (cross bridge) Pull actin towards center, then detaches


Questions How would severing the tendon attached to a muscle affect the ability of the muscle to move a body part? Why does skeletal muscle appear striated when viewed through a microscope? Where would you expect the greatest concentration of calcium ions in resting skeletal muscles to be?

Control of Muscle Fiber Contraction:

Control of Muscle Fiber Contraction Under control of the nervous system

Slide 14:

Electrical signal travels to the muscle. Electrical signal spreads over entire sarcolemma, down t-tubules to sarcoplasmic reticulum Sarcoplasmic reticulum releases massive amounts of calcium Increase in calcium – sarcomeres contract

The Contraction Cycle:

The Contraction Cycle Step 1 Ca+ binds to troponin, changing the tropomyosin position, in turn exposing active site on actin Step 2 Myosin head attaches to actin Step 3 Pulling of actin towards center of sarcomere Step 4 Detachment of cross bridge


How would a drug that interferes with cross-bridge formation affect muscle contraction? What would you expect to happen to a resting skeletal muscle if the sarcolemma suddenly became very permeable to calcium ions? Questions

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