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

2. 11.2.1 Describe the roles of nerves, muscles and bones in producing movement or locomotion

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

4. 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.

5. 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
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6. 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
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7. Joint Types Joints allow movement of limbs and appendages
Movements that occur because of multiple joints are compound movements

8. synovia: fluid secreted by the synovial membrane; found in joint
Knee Joint
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9. label a diagram of the human elbow joint, including cartilage, synovial fluid, joint capsule, bones, muscles

12. 11.2.3 Outline the functions of the above-named structures of the human elbow joint

13. Function of Muscles Cells are multinucleate
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

14. 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.
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15. Microscopic Anatomy of Skeletal Muscle Myofibril
Bundles of myofilaments
Myofibrils are aligned to give distinct bands
Sarcomere
Contractile unit of a muscle fiber

16. 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

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

18. 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

19. The Sliding Filament Theory

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

28. 11.2.6 Explain how skeletal muscle contracts by the sliding of filaments

29. 11.2.5 Draw the structure of skeletal muscle fibers as seen in electron micrographs