Smooth muscles relax when: a) myosin kinase phosphorylates the myosin head b) myosin phosphatase removes a phosphate group from myosin c) Ca2 + binds to calmodulin d) Ca2 + flows out of the sarcoplasmic reticulum

1. During muscle contraction, hydrolysis of ATP results in A) a change in the conformation of actin B) a change in the conformation of myosin C) association of myosin head to actin D) dissociation of myosin from actin E) no effect on muscle contraction

14) after a muscle fiber has contracted, the calcium a) is secreted by the Golgi apparatus  b) is chemically bound to the myofilaments  c) renters the sarcoplasmic reticulum  d) is destroyed

33) which of the following is released into the synaptic cleft and is responsible for depolarizing the sarcolemma? a) tropomyosin b) acetylcholine  c) troponin  d) cal

You know from experience that skeletal muscle tires quite quickly, especially if there is not enough oxygen. Interestingly, shellfish such as clams can maintain a month-long contraction in the muscle that keeps the shell closed. No oxygen gets in this situation. These muscles have a different version of myosin called paramyosin. Knowing what you know about the cellular mechanism of muscle contraction, propose a hypothesis to explain how paramyosin might work.

Identify the structure highlighted in green: Sarcolemma Myofibril Sarcoplasm

What happens to contraction of a muscle cell if some of the Ca2+ that was released during a contraction is still in the cytoplasm (sarcoplasm) when the next stimulus arrives?   - The muscle contracts with the same tension generated as during the first contraction, because the number of cross-bridges formed is always the same during a contraction. - The muscle contracts with greater tension generated because more troponin molecules bound means greater myosin-binding sites (active sites) are revealed on the actin, leading to a larger number of cross-bridges formed. - The muscle contracts with greater tension generated because there will be more Ca2+ in the sarcoplasm after the second stimulation, which will bind to more troponin molecules. - The muscle contracts with the same tension generated as during the first contraction, because muscles contract in an all-or-none fashion.

A sarcomere contracts when a) Thin filaments (actin) slide b) Thick filaments (myosin) slide c) Thin filaments (actin) contract d) Thick filaments (myosin ) contract

Can you match the sacromere anatomy with the proper answer from the list below the table graph? Sarcomere Anatomy Description/Reaction Thin Filaments ? Thick Filaments  ? A Band  ? I Band ? M Line ? H Zone ? Z Disc ? A) G-Actin, F-Actin, Troponin, Tropomyosin B) Myosin C) Bisected by the M Line, this area shows only the thick filaments without any thin filamentous overlap D) The point of origin for myosin filaments found in the center of the sarcomere E) An area in the center of the sarcomere marked by the entire length of the thick filaments F) A space between sarcomeres with the z-disc in the center; this region shows Actin's anchorage points and extension without myosin overlap G) Anchoring point for the thin filaments

If you were to watch muscle tissue contract: Under a light microscope, would you see the muscle fibers get narrower, or the striations get thinner? Explain. At the EM level, focusing on one sarcomere, you would be able to see a region of thick filaments overlapping two regions of thin filaments. Use the structure of the thick filaments to explain how ONE region of thick filaments is able to pull in microfilament in two opposite directions (both toward the center of the sarcomere).