Locomotion and Movement

Cartilaginous joint is present between ribs and sternum. It allows only limited movement. An angular joint allows movement in two directions - side to side and back and forth. Wrist and metacarpophalangeal joints are of this type. Gliding joint permits sliding movements of two bones over each other, e.g. joints between sternum and clavicles. Fibrous joints do not allow movement and are present between the bones of cranium.

Sternum is connected to ribs by hyaline cartilage (= giving a shiny glass like appearance and gives flexibility and support at the joints). Sternum is also called breast bone. It is a narrow, elongated and flattened structure, present just under the skin in the middle of front of the chest. It consists of three parts - manubrium, mesosternum and xiphoid process. Manubrium is the thickest, strongest part and articulates with the clavicle of pectoral girdle and first pair of ribs. Mesosternum provide articulation to second to sixth pairs of ribs and xiphoid process (also called metasternum) articulates with seventh pair of ribs in association with mesosternum.

Atlas is the first cervical vertebra. Coracoid is part of the pectoral girdle. Pterygoid is a small bone articulated with palatine. Arytenoids are cartilage present at the back of larynx.

The correct statement for muscle contraction is :

Option A: Length of H-zone decreases During muscle contraction, the sliding filament theory explains that the thin filaments (actin) slide over the thick filaments (myosin) toward the center of each sarcomere. This results in a decrease in the length of the H-zone, which is the region in the center of the sarcomere that is primarily composed of myosin and devoid of actin. To present the information more clearly: - Option A: Length of H-zone decreases - Correct.

- Option B: Length of A-band remains constant - This is also correct; however, it is not the choice that is being asked for confirmation. The A-band length, which corresponds to the length of the myosin filaments, indeed remains constant during contraction.

- Option C: Length of I-band increases - This is incorrect. The I-band, which contains thin filaments with no overlapping thick filaments, actually decreases during muscle contraction.

- Option D: Length of two Z-line increases - This is incorrect. The distance between two Z-lines, or the length of the sarcomere, decreases during muscle contraction as the Z-lines move closer together. The H-zone's change in length is a direct indicator of muscle contraction because it specifically refers to the action of the sliding filaments during the process.