Tendons and Ligaments

1. How do banding patterns change when a muscle contracts?
a. The H zones and I zones decrease in width when a muscle contracts. 2. What’s the difference between a muscle organ, a muscle fiber, myofibril, and myofilaments? a. Muscle organ – a bundle of muscle fibers

b. Muscle fiber – forms of muscles bundled together with proteins called myofibril that allow them to contract c. Myofibril – bundles of fine fibers that fill the sarcoplasm of a cell that are made up of bundles of myofilaments d. Myofilaments – very small thread-like structures found in myofibrils 3. Outline the molecular mechanism for skeletal muscle contraction. At what point is ATP used and why? a. Muscle fiber shortens causing thin filaments to propel toward the center of the sarcomere by movements of the myosin cross bridges i. This is where ATP splits and is used for muscle contraction and is used to pump the calcium out of the cells which is needed to release the contraction b. Contraction occurs when cytosolic calcium concentration is increased (triggered by action potential in the plasma membrane).

The calcium ions bing on the thin filaments which causes change in shape which then allows the cross bridges to bind to the thin filaments c. Branches of a motor neuron axon create neuromuscular junctions made up of muscle fibers that are innervated by a branch from one motor neuron. i. Acetylcholine released by action potential in a motor neuron binds to receptors on the motor end plate of the muscle membrane 1. This opens ion channels to allow sodium and potassium ions in; end-plate is depolarized 4. Explain why rigor mortis occurs.

a. Actin and myosin cross-bridge attachment work together to allow for muscle contraction. The muscle fibers get shorter and shorter until they are full contracted or until ATP is present. ATP reserves are quickly used up when the muscles contract, so the actin and myosin fibers will remain linked
until the muscles decompose.

Post-Lab Questions:
1. Label the arrows in the slide images below based on your observations from the experiment.
a. Chondrocytes
b. Collagen
c. Collagen Fibers
d. Skeletal muscle fibers
e. Nuclei
f. Collagen fibers
2. How does the extracellular matrix of connective tissues contribute to its function? a. ECM consists of protein fibers embedded in proteoglycan. It is secreted by cells that derived from fibroblasts, and gives strength, support, and protection to cartilage and bone (where matrix contains collagen fibers and mineral deposits) 3. Why are tendons and ligament tissues difficult to heal?

a. Tendons and ligaments have no blood supply and/or vessels to transport new nutrients and protein to rebuild or repair famage. 4. Sketch and label the hierarchy of tendons, starting with the reticular membrane through tropocollagen.

a. Tendon
i. Reticular membrane
ii. Fascicular membrane
b. Fascicle
i. Fibroblasts
c. Fibril
d. Sub-fibril
i. Staining sites
e. Micro-fibril
f. Tropocollagen
5. What difference do you see between the tendon – muscle insertion image and the tendon image?
a. Tendon-Muscle Insertion
i. Collagen lines are more scattered and uneven
ii. Tendon looks rough and undefined
b. Tendon
i. Collagen lines are straighter and more even
ii. Tendon looks smooth and defined
6. What differences do you see between the tendon and ligament sections? a. Tendon
i. Smooth
ii. Thin outside boarder
iii. Collagen fibers are thin and dark
b. Ligament
i. Well-defined lines
ii. Thicker outside boarder
iii. Collagen fibers are think and light