{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

3-21 motor systems - M O TOR SYSTE MS L.1 How do muscles...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
MOTOR SYSTEMS LIFE 47 47.1 How do muscles contract? Skeletal muscle is responsible for all voluntary movements, such as running or playing a piano. It also generates the unconscious movements of breathing. Cardiac muscle is responsible for the beating action of the heart. Smooth muscle creates the movement in many hollow internal organs , such as the gut , bladder, and blood vessels, and it is under the control of the autonomic (involuntary) nervous system. 47.1.1 Sliding filaments cause skeletal muscle to contract - Skeletal muscle cells, called muscle fibers , are large and have many nuclei -A specific muscle such as your biceps (which bends your arm) is composed of hundreds or thousands of muscle fibers bundled together by connective tissue -Muscle contraction is due to the interaction between the contractile proteins actin and myosin . Actin filaments ( thin filaments ), and myosin filaments ( thick filaments ) lie parallel to each other. When muscle contraction is triggered, the actin and myosin filaments slide past each other in a telescoping fashion -The myofibril consists of repeating units called sarcomeres . Each sarcomere is made of overlapping filaments of actin and myosin , which create a distinct banding pattern. The bundles of myosin filaments are held in a centered position within the sarcomere by a protein called titin . Titin is the largest protein in the body; it runs the full length of the sarcomere from Z line to Z line. Each titin molecule runs right through a myosin bundle. Between the ends of the myosin bundles and the Z lines, titin molecules are very stretchable, like bungee cords. In a relaxed skeletal muscle , resistance to stretch is mostly due to the elasticity of the titin molecules . -Each sarcomere is bounded by Z lines , which anchor the thin actin filaments. Centered in the sarcomere is the A band , which contains all the myosin filaments. The H zone and the I band , which appear light, are regions where actin and myosin filaments do not overlap in the relaxed muscle. The dark stripe within the H zone is called the M band ; it contains proteins that help hold the myosin filaments in their regular arrangement - sliding filament theory : as the muscle contracts, the sarcomeres shorten, and the band pattern changes. The H zone and the I band become much narrower, and the Z lines move toward the A band as if the actin filaments were sliding into the region occupied by the myosin filaments 47.1.2 Actin-myosin interactions cause filaments to slide
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
-A myosin molecule consists of 2 long polypeptide chains coiled together, each ending in a large globular head. A myosin filament is made up of many myosin molecules arranged in parallel, with their heads projecting laterally from one or the other end of the filament -An actin filament consists of two chains of actin monomers twisted together like two strands of pearls in a helix. Twisting around the actin chains is another protein , tropomyosin , and attached to the tropomyosin at intervals are molecules of troponin .
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern