IB Biology HL II Clegg: 361-369 Musculosketal System IB Biology HL II Clegg: 361-369

11.2.1 Describe the roles of nerves, muscles and bones in producing movement or locomotion

Nerve Stimulus to Muscles Skeletal muscles must be stimulated by a nerve to contract Motor unit One neuron Muscle cells stimulated by that neuron

Discuss why joints are necessary. What components are in joints? Identify the areas of your body that contain joints. Use your list from above to categorize joints.

Joints joint: holds bones together and make movement possible ligament: flexible, tough band of fibrous connective tissue that attaches one bone to another at a joint Copyright © 2005 Mosby, Inc. All rights reserved.

meniscus: crescent-shaped cartilage found in the knee cavities tendon: band of fibrous connective tissue that attaches muscle to bone bursa: small, fluid-filled sac that allows easy movement of one part of a joint over another Copyright © 2005 Mosby, Inc. All rights reserved.

Joint Types Joints allow movement of limbs and appendages Movements that occur because of multiple joints are compound movements

synovia: fluid secreted by the synovial membrane; found in joint Knee Joint Copyright © 2005 Mosby, Inc. All rights reserved.

11.2.2 label a diagram of the human elbow joint, including cartilage, synovial fluid, joint capsule, bones, muscles

11.2.3 Outline the functions of the above-named structures of the human elbow joint

Function of Muscles Cells are multinucleate 11.2.6 Explain how skeletal muscle contracts by the sliding of filaments Function of Muscles Produce movement, Maintain posture, Stabilize joints, Generate heat Microscopic Anatomy of Skeletal Muscle Cells are multinucleate

Muscles Provides movement, posture, joint stability, and heat production The body consists of more than 600 muscles. skeletal muscles (striated): attached to bones by tendons and make body movement possible. Skeletal muscles produce action by pulling and by working in pairs. Also known as voluntary muscles because we have control over these muscles. Copyright © 2005 Mosby, Inc. All rights reserved.

Microscopic Anatomy of Skeletal Muscle Myofibril Bundles of myofilaments Myofibrils are aligned to give distinct bands Sarcomere Contractile unit of a muscle fiber

Microscopic Anatomy of Skeletal Muscle Organization of the sarcomere Thick filaments = myosin filaments Composed of the protein myosin Thin filaments = actin filaments Composed of the protein actin

Microscopic Anatomy of Skeletal Muscle Myosin and Actin overlap somewhat Once started, muscle contraction cannot be stopped

The Sliding Filament Theory of Muscle Contraction Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament Myosin heads then bind to the next site of the thin filament This continued action causes a sliding of the myosin along the actin The result is that the muscle is shortened (contracted

The Sliding Filament Theory

Contraction of a Skeletal Muscle Muscle fiber contraction is “all or none” Within a skeletal muscle, not all fibers may be stimulated during the same interval Different combinations of muscle fiber contractions may give differing responses

Energy for Muscle Contraction Initially, muscles used stored ATP for energy Bonds of ATP are broken to release energy Only 4-6 seconds worth of ATP is stored by muscles After this initial time, other pathways must be utilized to produce ATP

Energy for Muscle Contraction Direct phosphorylation Muscle cells contain creatine phosphate (CP) CP is a high-energy molecule After ATP is depleted, ADP is left CP transfers energy to ADP, to regenerate ATP CP supplies are exhausted in about 20 seconds

Energy for Muscle Contraction Aerobic Respiration Series of metabolic pathways that occur in the mitochondria Glucose is broken down to carbon dioxide and water, releasing energy This is a slower reaction that requires continuous oxygen Figure 6.10c

Energy for Muscle Contraction Anaerobic glycolysis Reaction that breaks down glucose without oxygen Glucose is broken down to pyruvic acid to produce some ATP Pyruvic acid is converted to lactic acid

Energy for Muscle Contraction Anaerobic glycolysis (continued) This reaction is not as efficient, but is fast Huge amounts of glucose are needed Lactic acid produces muscle fatigue

Muscle Fatigue and Oxygen Debt When a muscle is fatigued, it is unable to contract The common reason for muscle fatigue is oxygen debt Oxygen must be “repaid” to tissue to remove oxygen debt Oxygen is required to get rid of accumulated lactic acid Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

11.2.6 Explain how skeletal muscle contracts by the sliding of filaments

11.2.5 Draw the structure of skeletal muscle fibers as seen in electron micrographs