Class Topics

1. Muscle physiology Connective Tissue Coverings All or none principle Neuromuscular junction Innervation Myofibril Contraction “The beginning of wisdom is to call things by their right names.” Chinese proverb To learn about the physiology of muscles. Title: Anat & Phys 11/28/06 Class Topics Objectives: Friday, December 20, 201910:13 PM

2. Class Assignments What By When • Lab - Reaction Time 11/28/06 • Read 197-212 12/4/06 • Due this class period • Due next class period • Due in the future

3. Connective Tissue Coverings • Fascia - broad band of collagen-based connective tissue • Tendons - connective tissue connecting muscle to bone • connects in the periosteum for strength • Aponeurosis - fascia of one muscle attaching to that of another muscle

4. Connective Tissue Coverings • Epimysium - surrounding each muscle closely • Perimysium - divides the muscle into fascicles • around each bundle of muscle fibers • Endomysium - surrounding each muscle fiber

5. From: http://www.shef.ac.uk/~toa/js/histolo/cell_sha/maintext.htm From: http://www.bmb.psu.edu/courses/bisci004a /muscle/musc-img/fasicle.jpg

6. Skeletal Muscle • striated • all or none response • if a muscle fiber is exposed to a stimulus (electrical or nervous) it will contract to its full extent • How can we have smooth movements?

8. Neuromuscular Junction • Each muscle fiber is connected to a nerve fiber - motor neuron • Where they join is called the neuromuscular junction • one nerve cell may have several junctions with one muscle cell and even several muscle cells • nerve cells send messages to muscle cells by releasing neurotransmitters • chemicals that have receptors in muscle cells that stimulate contraction - acetylcholine Wisconsin Online - Animation

11. From: http://www.people.virginia.edu/~dp5m/phys_304/figures/synapse_2.jpg

12. Innervation • 1:10 • Eye muscles • 1:1000 • Leg muscles

13. Muscle fibers • each fiber represents 1 muscle cell • some organelles • Nuclei, sarcoplasmic reticulum, sarcolemma, ribosomes, mitochondria • mostly myofibrils • filaments that contain myosin and actin proteins and the location of contraction • Myosin - thick filament • Actin - thin filament

14. Contraction Terminology • A band - myosin filaments - dark area of myofibril • I band - actin filaments - light area of myofibril • Z line - Where actin filaments connect together (middle of I band) • H zone - non overlap area • Sarcomere - area from Z line to Z line

16. From: http://www.biology.eku.edu/RITCHISO/301notes3.htm

18. ContractionOverview • Filaments on myosin and actin merge causing muscle fibers to converge • Myosin - 2 protein strands with globular proteins (heads) sticking out that can react with active sites of actin to form cross bridges • Actin/troponin/tropomyosin • Actin – contains active site used to bond with myosin • Tropomyosin – resting position for myosin heads • Together with troponin • Troponin – bond to calcium ions • Changes shape to expose actin active sites • Together with tropomyosin

19. Contraction step by step • Stimulation - acetylcholine released from motor neuron • Muscle fiber stimulation by acetylcholine & calcium ions are released from the sarcoplasmic reticulum • Calcium ions bind to troponin molecule • Troponin molecules change shape causing tropomyosin to rotate and expose active sites on the actin molecule

20. Contraction step by step • Cross bridges form between actin (active sites) and myosin filaments (globular proteins) • Actin filaments slide along myosin filaments (ATP used) due to a swivel action of myosin globular protein • Muscle fiber shortens as contraction occurs Wisconsin Online - animation Texas A&M University - animation