Skeletal and Muscular System: Bones, Joints, Muscles

The correct answer is D, the sartorius. It is a thin, strap-like muscle that runs across the front of the thigh from the hip bone to the inner side of the knee, and because it crosses two joints it is the longest muscle of the human body; it helps in bending the hip and the knee and in turning the thigh outwards, the movement of sitting cross-legged. A is wrong because the soleus is a broad calf muscle used in standing and walking. B is wrong because the gracilis, though also a long thigh muscle, is shorter than the sartorius. C is wrong because the trapezius is the large triangular muscle of the upper back and neck. Learn it with the other superlatives: gluteus maximus is the largest muscle, stapedius the smallest and masseter the strongest in force.

The correct answer is D, four. An adult set of thirty-two permanent teeth has eight incisors for cutting, four canines for tearing, eight premolars and twelve molars for grinding, so there is one canine on each side of each jaw. The dental formula of an adult is written as two incisors, one canine, two premolars and three molars in each half of each jaw. A is wrong because three is not a possible number for a feature that is symmetrical on both sides. B is wrong because eight is the number of incisors, and also of premolars. C is wrong because two would mean only one canine in each jaw. Note that a child has twenty milk teeth with no premolars, and that the enamel covering these teeth is the hardest substance in the body.

The correct answer is B, two hundred and six. The adult skeleton has eighty bones in the axial part, that is the skull with the ear ossicles and hyoid, the vertebral column, the ribs and the sternum, and one hundred and twenty-six in the appendicular part, that is the limbs with the pectoral and pelvic girdles, making two hundred and six in all. A is wrong because one hundred and eighty-six matches no division of the skeleton. C is wrong because two hundred and eighty is simply a distractor between the adult and the infant figures. D is wrong for a reason worth remembering: a newborn has about three hundred separate bony elements, and the number falls to two hundred and six as bones such as those of the sacrum, the coccyx and the skull fuse during growth.

The correct answer is A, the stapes. It is the innermost of the three ear ossicles of the middle ear and is shaped like a stirrup; it passes vibrations from the incus to the oval window of the inner ear and is the smallest bone of the body. B is wrong because the malleus, or hammer, is the outermost of the three ossicles, attached to the eardrum, and is larger than the stapes. C is wrong because the patella is the knee cap, a sesamoid bone of moderate size that protects the knee joint. D is wrong because the hyoid is the U-shaped bone of the neck that supports the tongue and is remarkable for a different reason, namely that it articulates with no other bone. The femur, at the other extreme, is the longest and strongest bone.

The correct answer is B, twenty-six. The adult column is counted as seven cervical vertebrae in the neck, twelve thoracic vertebrae bearing the ribs, five lumbar vertebrae in the lower back, one sacrum and one coccyx, giving twenty-six bones in all. A is wrong because twenty-four counts only the separate cervical, thoracic and lumbar vertebrae and leaves out the sacrum and the coccyx. C is wrong because thirty matches no stage of development. D is wrong for the reason that makes this question a trap: a child has thirty-three vertebrae, of which five fuse into the sacrum and four into the coccyx, so the adult number becomes twenty-six. Remember also that the first cervical vertebra is the atlas and the second the axis, and the pivot joint between them turns the head.

The correct answer is C, twelve pairs, that is twenty-four rib bones. All of them are attached behind to the thoracic vertebrae. In front, the first seven pairs join the sternum directly and are called true or vertebrosternal ribs; the next three pairs join the seventh rib through cartilage and are called false or vertebrochondral ribs; and the last two pairs have no attachment in front and are called floating or vertebral ribs. Together with the sternum they form the rib cage, which protects the heart and the lungs and moves in breathing. A and B are wrong because they drop the floating or the false pairs from the count. D is wrong because no human has fourteen pairs; the usual exam trap is to ask for bones rather than pairs, where the answer is twenty-four.

The correct answer is B, a ball and socket joint. The rounded head of the humerus sits in the socket of the shoulder blade and the head of the femur sits in the socket of the hip bone, which lets the limb move forwards, backwards, sideways and in rotation; these are synovial joints with a fluid-filled cavity. A is wrong because a hinge joint, as at the elbow, the knee and the finger joints, allows movement in only one plane, like a door. C is wrong because a pivot joint is the one between the atlas and the axis, which lets the head turn from side to side. D is wrong because gliding joints, as between the small bones of the wrist and the ankle, allow only slight sliding. Also recall that the saddle joint at the base of the thumb gives the human hand its grip.

The correct answer is B, muscle to bone. A tendon is a cord of white fibrous connective tissue, with very little elasticity, that transmits the pull of a contracting muscle to the bone it moves; the Achilles tendon at the heel is the best known example. A is wrong because bone is joined to bone by a ligament, which is elastic yellow fibrous tissue, and the common injury called a sprain is a torn ligament. C is wrong because muscles are not joined to one another in this way; they act in antagonistic pairs such as the biceps and the triceps. D is wrong because the meeting place of a nerve and a muscle is the neuromuscular junction, where a chemical messenger carries the signal across. Keeping the tendon and ligament definitions apart is enough to answer several questions.

The correct answer is A, actin and myosin. In the sliding filament theory of contraction, a nerve impulse causes calcium to be released from the sarcoplasmic reticulum; the calcium exposes binding sites on the thin actin filaments, the heads of the thick myosin filaments attach to them and swivel, using energy from ATP, and the actin is pulled towards the centre of the sarcomere, so the muscle shortens. B is wrong because collagen is the fibrous protein of tendons, bone and skin, and keratin that of hair and nails. C is wrong because albumin and globulin are plasma proteins of blood. D is wrong because insulin and glucagon are pancreatic hormones that control blood sugar, not muscle proteins. During hard exercise with little oxygen, lactic acid gathers in the muscle and causes cramp.

The correct answer is B, striated and involuntary. Cardiac muscle shows the cross stripes of skeletal muscle under the microscope, but it is not under the control of the will and it beats rhythmically on its own, driven by the pacemaker of the heart; its cells are branched and joined end to end by intercalated discs, which let the impulse spread quickly through the heart wall. A is wrong because voluntary control belongs to skeletal muscle attached to bones. C is wrong because no muscle in the body is both non-striated and voluntary. D is wrong because non-striated and involuntary describes smooth muscle, found in the walls of the stomach, intestine, blood vessels and urinary bladder. This three-way comparison of muscle types is one of the most frequently asked questions from the chapter.

The correct answer is C, vitamin D. Vitamin D, which the skin makes in sunlight and which is also present in milk, eggs and fish liver oil, is needed for the absorption of calcium and phosphorus from food. Without it the bones of a growing child do not harden properly, the legs bow and the wrists and ribs thicken, a condition called rickets; the same deficiency in an adult softens formed bone and is called osteomalacia. A is wrong because a lack of vitamin A causes night blindness and dryness of the eye. B is wrong because a lack of vitamin C causes scurvy, with bleeding gums and poor healing. D is wrong because vitamin K is needed for the clotting of blood. Osteoporosis, by contrast, is a loss of bone mass with age rather than a single vitamin deficiency.