thin filaments (myofibrils) extending from sarcomere ends (Z lines) toward center (M line) mysosin: thick filaments (myofibrils) extending from sarcomere center (M line) toward ends (A band = length of myosin) cross-bridge formation: myosin filaments overlap with actin filaments mysosin arms attach to actin, forming cross-bridges movement and breakage: movements of myosin arms ratchet along actin, contracting sarcomere myosin breaks attachment, reattaches to actin, and repeats ratcheting contraction of sarcomere ATP: ATP phosphorylation of myosin heads provides energy for ratcheting power stroke of muscle contraction Ca2+ ions: released from sarcoplasmic reticulum in response to neural depolarization attach to troponin
Option B - Physiology of Exercise Part I Muscles/Bones & Movement
Muscle Tissue•Muscle tissue consists of cells that have the ability to CONTRACT and exert a PULLING FORCE.
Types of Muscle – Skeletal/Striated• LARGE…contain…blood vessels, nerves, and connective tissue.• Voluntary movement.• Fibers contain striations.• Have many nuclei• Sarcoplasmic reticulum – ER in muscle cells. Stores and pumps CALCIUM.• Sarcolemma – cell membrane of muscle plus collagen
The EM View of the Skeletal MuscleYou must be able to draw this:
Structure of a Skeletal Muscle• Muscle tissue is made up of 2 types of proteins – Actin – molecules that form LONG, THIN chains. (Light Band) – Myosin – molecules that bundle together to form THICK fibers. (Dark Band)• Actin and Myosin are arranged in structures called SARCOMERES• In a muscle, sarcomeres group to form a threadlike structure: MYOFIBRIL• Mitochondria between myofibril
Muscle Contractions – Building of Muscle• Many myofibrils bundle together with cell organelles to form a MUSCLE CELL• Muscles cells grouped together to form a FASCICLE.• Groups of Fascicles = whole muscle• Membrane around muscle = sarcolemma_________________________________Actin and myosin sarcomere myofibril muscle cellFascicle muscle
Stages in Muscle Contraction• A sarcomere is the functional unit of muscle contraction.• When muscle cells contract the light and dark bands get closer. – Why? – myosin and actin filaments interact to shorten the length of a sarcomere.• Two proteins on actin: tropomyosin and troponin regulate the binding of actin and myosin.
Stages in Muscle ContractionRelaxed Skeletal Muscle: protein – tropomyosin blocks binding sites on actin.Regulatory Proteins (Troponin & Tropomyosin) In Skeletal Muscle FibersWhen a motor neuron stimulates a muscle fiber:• “Stimulus” – Ca+ ions released from sarcoplasmic reticulum.• Ca+ ions bind to protein - troponin --- causes tropomyosin to move to expose binding sites on actin• This allows the myosin heads to bind…..CONTRACTION:• Myosin filaments have “heads” which form CROSS BRIDGES when attached to binding sites on actin.
Stages: Mechanism of Muscle Contraction• ATP attaches to myosin head and causes them to break the cross bridges by detaching them from the binding site.• ATP is hydrolyzed. Causes he myosin head to change its “angle” The heads are “bent” and store the energy released.• The heads attach to binding sites on actin that are further from the center of the sarcomere.• The heads push the actin inward toward the center of the sarcomere: POWER STROKE!
Stages: Mechanism of Muscle ContractionThe synchronized shortening of sarcomeres along the whole muscle fiber causes the fiber….the whole muscle to contract.When thousands of actin and myosin filaments interact… the entire muscle shortens.THIS IS THE SLIDING FILAMENT THEORY Muscle contraction
Structure of Human Bones• Made of living cells, collagen, and inorganic compounds.• Bone Cells are arranged: • Periosteum – outer layer of connective tissue • Contain blood vessels • Compact Bone – thick layer. Dense. • Haversian Canals – in compact bone. Contain blood vessels and nerves. • Spongy Bone – less dense. Found ar the end of most long bones. Helps to add strength without mass. • Bone Marrow – inside bone cavities. Yellow( fat cells) and Red (makes blood cells)• Ossification – Bone formation