The scapula (shoulder blade) is an example of which type of bone?

Correct Answer: D

Rationale: The scapula is a flat bone, characterized by its thin, broad shape. Flat bones provide protection and muscle attachment surfaces; the scapula protects the shoulder region and anchors upper limb muscles. Long bones are cylindrical, short bones are cube-like, and irregular bones have complex shapes, making 'Flat bone' the correct answer.

Correct Answer: A

Rationale: Electrical impulses (action potentials) from motor neurons travel to the muscle, depolarizing the sarcoplasmic reticulum via T-tubules, triggering calcium release. Acetylcholine initiates the nerve signal, but the direct trigger is the electrical impulse, making 'Electrical impulses from motor neurons' correct.

Correct Answer: B

Rationale: The 'all-or-none' principle states that a muscle fiber contracts fully or not at all when stimulated above a threshold. It doesn’t contract partially; the strength varies with the number of fibers recruited, not individual fiber response, making 'The idea that muscles can either contract fully or not at all' correct.

Correct Answer: B

Rationale: The human spine, or vertebral column, consists of 26 individual bones in children (33 before some fuse in adulthood), collectively called vertebrae. These include 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused into the sacrum), and 4 coccygeal (fused into the coccyx). Ribs protect the chest, skull bones form the head, and pelvic bones support the lower body, making 'vertebrae' the correct answer.

Correct Answer: C

Rationale: At joints, cartilage—specifically articular cartilage—covers bone ends, acting as a cushion to absorb shock and reduce friction during movement (e.g., knee cartilage). Ligaments stabilize joints by connecting bones, tendons attach muscles to bones, and muscles move bones, but cartilage directly protects and cushions, making it the correct answer.