11 - IBBiology Class of 2010



11.2 Principles of locomotion

11.2.1 State the roles of bones, ligaments, muscles, tendons and nerves in human movement. Human movement is made by the skeleton acting as simple lever machines. The physics of a lever system can be directly compared to that of a limb.

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|[pic] |

| |In general, terms the muscles and bones of the spine (red) are force magnifiers. The force is used to|

| |stabilize the skeleton and provide a stable platform for the movement of the limbs. Such levers |

| |produce very little range of movement but a great deal of force. |

| |The muscles and bones of the limbs are generally arranged into 3rd class levers and in such a way to |

| |become distance magnifiers. The reason for this is to provide range of movement for the limb rather |

| |than strength. |

| |The image illustrates the concept of 'range of movement' discussed above. |

| |These simple ideas of machines can be applied to the skeletal system and human movement. |

11.2.2 Label a diagram of the human elbow joint, including cartilage, synovial fluid, joint capsule, named bones and antagonistic muscles (biceps and triceps).

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Joint structure and antagonistic muscle pairs.

A. Humerus (upper arm) bone.

B. Synovial membrane that encloses the joint capsule and produces synovial fluid.

C. Synovial fluid (reduces friction and absorbs pressure).

D. Ulna (radius) the levers in the flexion and extension of the arm.

E. Cartilage (red) living tissue that reduces the friction at joints.

F. Ligaments that connect bone to bone and produce stability at the joint.

11.2.3 Outline the functions of the structures in the human elbow joint

Antagonistic Muscle Pairs:

▪ To produce movement at a joint muscles work in pairs.

▪ Muscles can only actively contract and shorten. They cannot actively lengthen.

▪ One muscle bends the limb at the joint, the flexor, (which in the elbow is the biceps).

▪ One muscle straightens the limb at the joint (extensor) which in the elbow is the triceps.

1. Humerus. This forms the shoulder joint and contains the origin for each of the two biceps tendons

2. Biceps (flexor) muscle provides force for an arm flexion (bending). As the main muscle, it is known as the agonist.

3. Biceps insertion on the radius of the forearm

4. Elbow joint. This is the fulcrum or pivot for arm movement

5. Ulna one of two levers of the forearm

6. Triceps muscle is the extensor whose contraction straightens the arm.

7. The elbow joint is also the pivot (fulcrum) for this movement.

It should be noted that the description of movement is complex. A true Triceps extension takes place against gravity.

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Exercise: Bend your arm in a flexion. Point your elbow upwards vertically. Raise your hand vertically above your head. This is a true concentric contraction of the Triceps

Pick up a heavy object in concentric Biceps flexion. Now lower and straighten your arm. You should feel your Biceps contracted but Triceps relaxed.

11.2.4 Compare the movements of the hip joint and the knee joint.

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| | |The knee joint is an example of a hinge joint. |

| | |The pivot is the knee joint. |

| | |The lever is the tibia and fibula of the lower leg. |

| | |A knee extension is powered by the quadriceps |

| | |muscles. |

| | |A knee flexion is powered by the hamstring muscles. |

| | |Movement is one plane only. |

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| |Rotation is in all planes and axis of movement. |

| |The lever is the femur and the fulcrum is the hip joint. |

| |The effort is provided by the muscles of quadriceps, hamstring and gluteus. |

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| |The shoulder is also a ball and socket joint. |

| |The humerus is the lever. |

| |The shoulder (scapula and clavicle) form the pivot joint. |

| |Force is provided by the deltoids, trapezius and pectorals. |

| |Movement is in all planes. |

11.2.5 Describe the structure of striated muscle fibers, including the myofibrils with light and dark bands, mitochondria, the sarcoplasmic reticulum, nuclei and the sarcolemma.

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1. Tendon connecting muscle to bone.

2. The muscle is surrounded by a membrane which forms the tendons at its ends.

3. Muscle bundle which contains a number of muscle cells

4. Fibers bound together. These are the strands we see in meat. The plasma membrane of a muscle cell is called the sarcolemma and the membrane reticulum is called the sarcoplasmic reticulum.

11.2.6 Sliding Filament theory (theory muscle contraction)

There are many parallel protein structures inside called myofibrils. Myofibrils are combinations of two filaments of protein called actin and myosin. The filaments of actin and myosin overlap to give a distinct banding pattern when seen with an electron microscope. This model shows the arrangement of the actin and myosin filaments in a myofibril. Note how the thick myosin filaments overlap with the thinner actin filaments

|[pic] |The muscle fiber or cell is multinucleated It contains many parallel |

| |protein structures called myofibrils. Myofibrils are made of 2 |

| |protein filaments: actin and myosin. |

|[pic] |The filaments of actin and myosin overlap to give a distinct banding |

| |pattern under the electron microscope. This model shows the |

| |arrangement of the actin and myosin filaments in a myofibril. Note |

| |how the thick myosin filaments overlap with the thinner actin |

| |filaments. |

| |Myofibril cross section: |

| |a) Actin only |

| |b) Myosin only |

| |c) Myosin attachment region adds stability |

| |d) Actin and myosin overlap in cross sections |

|[pic] |[pic] |

| |Note: the large number of mitochondria, Diagonal myofibrils |

| |Sarcoplasmic reticulum (see 11.2.6) |

11.2.6 Draw and label a diagram to show the structure of a sarcomere, including Z lines, actin filaments, myosin filaments with heads, and the resultant light and dark bands.

No other terms for parts of the sarcomere are expected. A sarcomere is a repeating unit of the muscle myofibrils defined by the distance between two Z lines

11.2.7 Explain how skeletal muscle contracts, including the release of calcium ions from the sarcoplasmic reticulum, the formation of cross-bridges, the sliding of actin and myosin filaments, and the use of ATP to break cross-bridges and re-set myosin heads. Details of the roles of troponin and tropomyosin are not expected.

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|1. An action potential arrives at the end of a motor neuron, at the neuromuscular junction. |

|2. This causes the release of the neurotransmitter acetylcholine. |

|3 This initiates an action potential in the muscle cell membrane |

|4. This action potential is carried quickly throughout the large muscle cell by structures called T-tubules. |

|5. The action potential causes the sarcoplasmic reticulum to release stored calcium into the myofibrils. |

|6. Myosin filaments have cross bridge extensions. |

|7. Cross bridges include an ATPase, which can release energy from ATP. |

|8. The cross bridges can link across to the parallel actin filaments. |

|9. Actin polymer is associated with tropomyosin which occupies the binding sites where myosin binds |

|10. When relaxed the tropomyosin sits on the outside of the actin blocking the binding sites. |

|11. Myosin cannot cross bridges with actin until the tropomyosin moves into the groove. |

|12. The calcium binds to troponin on the thin filament, which changes shape, moving tropomyosin into the groove. |

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Cross Bridge Cycle:

The energy for the cycle is produced by the ATPase section of the crossbridge structure. This energy temporarily changes the shape of the crossbridge which is now attached to the actin polymer. The two slide relative to each other giving an overall shortening

1. The cross bridge swings out from the thick filament and attaches to the thin filament.

2. The cross bridge changes shape and rotates through 45°, causing the filaments to slide. The energy from ATP splitting is used for this “power stroke” step, and the products (ADP + Pi) are released.

3. A new ATP molecule binds to myosin and the cross bridge detaches from the thin filament.

4. The cross bridge changes back to its original shape, while detached (so as not to push

11.2.8 Analyze electron micrographs to find the state of contraction of muscle fibers.

Aim 7: Data logging could be carried out using a grip sensor to study muscle fatigue and muscle strength.

Muscle fibers can be fully relaxed, slightly contracted, moderately contracted and fully contracted.

If electron micrographs of a relaxed and contracted myofibril are compared it can be seen that each sarcomere gets shorter (Z-Z) when the muscle contracts, so the whole muscle gets shorter. However, the dark band, which represents the thick filament, does not change in length. This shows that the filaments do not contract themselves, but instead they slide past each other.

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