Locomotion and Movement - Exercises

1. Draw the diagram of a sarcomere of skeletal muscle showing different regions. Answer: (Note: In a textual MDX format, we describe the components). A sarcomere is the functional unit of contraction between two successive 'Z' lines. It consists of:

• 'A' Band (Anisotropic band): The dark band containing thick myosin filaments.
• 'I' Band (Isotropic band): The light band containing thin actin filaments.
• 'H' Zone: The central part of the thick filament not overlapped by thin filaments.
• 'Z' Line: The elastic fibre that bisects each 'I' band.
• 'M' Line: The thin fibrous membrane that holds thick filaments together in the middle of the 'A' band.

2. Define sliding filament theory of muscle contraction. Answer: The sliding filament theory states that the contraction of a muscle fibre takes place by the sliding of the thin (actin) filaments over the thick (myosin) filaments.

3. Describe the important steps in muscle contraction. Answer:

1. Signal: CNS sends a signal via a motor neuron to the neuromuscular junction.
2. Release of Neurotransmitter: Acetylcholine is released, generating an action potential in the sarcolemma.
3. Calcium Release: The action potential spreads and causes the release of Ca++ ions from the sarcoplasmic reticulum into the sarcoplasm.
4. Binding: Ca++ binds to troponin on actin filaments, removing the masking of active sites for myosin.
5. Cross-bridge Formation: Myosin heads bind to exposed active sites using energy from ATP hydrolysis.
6. Sliding: Actin filaments are pulled towards the centre of the 'A' band, shortening the sarcomere.
7. Relaxation: Ca++ is pumped back, active sites are masked again, and the muscle returns to its relaxed state.

4. Write true or false. If false change the statement so that it is true. (a) Actin is present in thin filament. (True) (b) H-zone of striated muscle fibre represents both thick and thin filaments. (False - H-zone represents only the central part of the thick filament not overlapped by thin filaments) (c) Human skeleton has 206 bones. (True) (d) There are 11 pairs of ribs in man. (False - There are 12 pairs of ribs) (e) Sternum is present on the ventral side of the body. (True)

5. Write the difference between: (a) Actin and Myosin: Actin is a thin filament protein found in the 'I' band; Myosin is a thick filament protein found in the 'A' band. (b) Red and White muscles: Red muscles have high myoglobin and mitochondria (aerobic); White muscles have low myoglobin and few mitochondria (anaerobic). (c) Pectoral and Pelvic girdle: Pectoral girdle articulates forelimbs (shoulder); Pelvic girdle articulates hind limbs (hip).

6. Match Column I with Column II:

• (a) Smooth muscle - (iv) Involuntary
• (b) Tropomyosin - (ii) Thin filament
• (c) Red muscle - (i) Myoglobin
• (d) Skull - (iii) Sutures

7. What are the different types of movements exhibited by the cells of human body? Answer: Amoeboid (e.g., macrophages), Ciliary (e.g., in trachea), and Muscular (e.g., limbs, jaws).

8. How do you distinguish between a skeletal muscle and a cardiac muscle? Answer: Skeletal muscles are voluntary, striated, and unbranched. Cardiac muscles are involuntary, striated, and branched with special communication junctions.

9. Name the type of joint between the following: (a) atlas/axis: Pivot joint (b) carpal/metacarpal of thumb: Saddle joint (c) between phalanges: Hinge joint (d) femur/acetabulum: Ball and socket joint (e) between cranial bones: Fibrous joint (f) between pubic bones in the pelvic girdle: Cartilaginous joint (Pubic symphysis)

10. Fill in the blank spaces: (a) All mammals (except a few) have 7 cervical vertebra. (b) The number of phalanges in each limb of human is 14. (c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely tropomyosin and troponin. (d) In a muscle fibre Ca++ is stored in sarcoplasmic reticulum. (e) 11th and 12th pairs of ribs are called floating ribs. (f) The human cranium is made of 8 bones.