Muscle Contraction

1. Muscle Contraction • Tendon- Cord-like structure; attaches muscle to bones with cartilage. • Epimysium-Connective tissue membrane that covers the entire skeletal muscle. • Perimysium-Connective tissue membrane that is around a fascicle (bundle) of fibers. • Endomysium-Around single muscle fiber. • Fascicle- A bundle of fibers. • Myofiber- A muscle cell. • Myofibril-A long, filamentous organelle found within cells; has a banded appearance. Marisa Haynes February 4, 2010 Human Physiology 347-001 Mrs. Caldeira 3rd Quarter http://academic.kellogg.edu/herbrandsonc/bio201_McKinley/f10-1a_structural_organ_c.jpg

2. Myofiber & Myofibril • Myofiber- A muscle cell. • Myofibril-A long, filamentous organelle found within muscle cells; has a banded appearance. • Myofilaments- Filaments composing the myofibrils. Of course two types: actin and myosin. • Actin- A contractile protein of muscle. • Myosin- One of the principal contractile proteins found in the muscle. • Z line-A dark, disc-like membrane within the I-band. • I band- Actin = light band. (thin filament) • A band- Myosin= dark band. (thick filament) • Sarcomere-Is the distance between 2 z-lines. It is a contractile unit of a muscle fiber. • Sarcolemma-Cell membrane of the muscle cell. http://legacy.owensboro.kctcs.edu/gcaplan/anat/images/Image286.gif

3. The Neuromuscular Junction • Motor unit- A motor neuron and all the muscle cells it supplies. • Synaptic cleft- The fluid-filled space at a synapse between neurons. • Acetylcholine-A chemical transmitter substance released by certain nerve endings. • Motor neuron- Part of each motor unit, located in the spinal cord. • Axon terminal- Branches of which forms junctions with the sarcolemma of a different muscle cell. • Vesicle-A sac or bladder-like structure. • Motor end plate- The flattened end of a motor neuron that transmits impulses to a muscle. • Acetylcholine receptor- Protein membrane that responds to the binding of acetylcholine. • http://faculty.etsu.edu/forsman/Histology%20of%20musclefor%20web_files/image015.jpg • http://www.cartage.org.lb/en/themes/sciences/lifescience/generalbiology/physiology/NervousSystem/NerveMessage/synapse.gif

4. The Steps of Muscle Contraction A motor neuron is activated, and an action potential moves down the motor neuron axon towards the motor unit. The axon branches provide a number of muscle fibers called a motor unit, and the action potential is sent to a motor end plate on each muscle fiber. At the axon terminals at the motor end plate, the action potential causes the discharge of the neurotransmitter acetylcholine into the synaptic clefts on the surface of the muscle fiber at the motor end plate. http://4.bp.blogspot.com/_FlhB437Wa_U/SCfnR1wHuyI/AAAAAAAAAiU/euIG6mdzh8Y/s400/Image331.gif

5. The Steps of Muscle Contraction Acetylcholine causes the electrical lying potential under the motor end plate to change, and this then begins an action potential which passes in both directions along the sarcolemma, the surface of the muscle fiber. The action potential enters the opening of each transverse tubule on the muscle fiber surface, the action potential spreads inside the muscle fiber. At each point where a transverse tubule touches part of the sarcoplasmic reticulum, it causes the sarcoplasmic reticulum to discharge Ca++ ions. http://4.bp.blogspot.com/_FlhB437Wa_U/SCfnR1wHuyI/AAAAAAAAAiU/euIG6mdzh8Y/s400/Image331.gif

6. The Steps of Muscle Contraction The calcium ions result in movement of troponin and tropomyosin on their thin filaments (actin), and this enables the myosin molecule heads to “grab & swivel” their way along the thi/actin filament. This is the driving force of muscle contraction. Myosin ATPase activated and ATP resolved. Which supplies the energy necessary for muscle contraction. Acetylcholine at the neuromuscular junction is broken down by the enzyme acetylcholinesterase, and this cancels the stream of action potentials along the muscle fiber surface. 5. ATP split favors myosin   cross-bridges attach-detach   from actins... pulls filament   toward M-line.6. Ca is removed by Ca-pump        (uptake by SR)7. Tropomyosin blocks actin   sites and muscle relaxes. 1.Acetylcholine is released at   neuromuscular junction2. AP is propagated along   membrane & down T-tubule3. Ca released from SR via a    voltage gated Ca channel4. Ca binds to Troponin-C -     conformation changes in TnI    & TnT favor tropomyosin    opening actin myosin binding    sites. http://www.bio.miami.edu/~cmallery/150/neuro/c49x36contraction-cycle.htm

7. The Steps of Muscle Contraction The sarcoplasmic reticulum refrains to release calcium ions, and immediately starts to separate all the calcium ions that have been released. In the vacancy of calcium ions, a change in the form of troponin and tropomyosin then blocks the action of the myosin molecule heads, and contraction ceases. Muscles goes back to the relaxed position. 5. ATP split favors myosin   cross-bridges attach-detach   from actins... pulls filament   toward M-line.6. Ca is removed by Ca-pump        (uptake by SR)7. Tropomyosin blocks actin   sites and muscle relaxes. 1.Acetylcholine is released at   neuromuscular junction2. AP is propagated along   membrane & down T-tubule3. Ca released from SR via a    voltage gated Ca channel4. Ca binds to Troponin-C -     conformation changes in TnI    & TnT favor tropomyosin    opening actin myosin binding    sites. http://www.bio.miami.edu/~cmallery/150/neuro/c49x36contraction-cycle.htm