The part of a skeletal muscle cell that is able to contract is called

Correct Answer: C

Rationale: Sarcomeres, within myofibrils, contract by sliding actin and myosin, shortening the myofibril and thus the cell. Sarcoplasm houses organelles, sarcolemma conducts signals, and sarcoplasmic reticulum stores calcium not contractile. Sarcomeres' role as the contractile engine distinguishes them, essential for muscle movement mechanics.

Correct Answer: A

Rationale: A muscle's origin (fixed point) and insertion (movable point) dictate its action e.g., biceps brachii originates on the scapula and inserts on the radius, flexing the elbow. Force of contraction depends on fiber type and size, not just attachments. Muscle name may reflect location (e.g., temporalis) but isn't determined solely by it action or shape also factor in. Load capacity relates to cross-sectional area, not just origin/insertion. Action's dependence on attachment points' leverage and pull direction makes 'a' the correct answer.

Correct Answer: B

Rationale: The linea alba is a long, midline tendon of collagen fibers where rectus abdominis muscles meet, running from xiphoid to pubis, aiding abdominal wall integrity. It's not a muscle , nor does it connect hip to knee (c that's the iliotibial tract). Tendinous inscriptions are transverse bands within rectus abdominis, not the linea alba. Its tendinous, central role in uniting abdominal muscles makes 'b' the correct definition.

Correct Answer: D

Rationale: A fossa is a depression or indentation in a bone, such as the mandibular fossa of the temporal bone where the mandible articulates, serving as a surface for muscle attachment or joint articulation. An air-filled cavity describes sinuses (e.g., frontal sinus), not all fossae. A hollow passage suggests a canal or foramen (e.g., carotid canal), not a fossa's shallow nature. Fused cartilage refers to structures like synchondroses, unrelated to fossae. The term 'fossa' (Latin for ditch) denotes a sunken area, making 'd' the precise anatomical definition.

Correct Answer: C

Rationale: Lordosis is an abnormal increase in the lumbar curvature, an exaggerated inward arch (swayback), often from posture, obesity, or pregnancy, altering spinal mechanics. Scoliosis is lateral curvature. Kyphosis affects the thoracic spine outward. Extension is a normal movement, not a condition. Lordosis's focus on lumbar hypercurvature, visible in sagittal views, makes 'c' the correct answer in orthopedic terminology.