MCAT Biology Review

Chapter 11: The Musculoskeletal System

Practice Questions

1.     

1.    Questions 1, 2, and 3 are based on the following diagram:

2.   

3.    During muscle contraction, which of the following regions decrease(s) in length?

1.    1 only

2.    1 and 2 only

3.    3 and 4 only

4.    2, 3, and 4 only

4.    Region 1 refers to:

1.    the thick filaments only.

2.    the thin filaments only.

3.    the A-band.

4.    the I-band.

5.    Which region represents one sarcomere?

1.    1

2.    2

3.    3

4.    4

2.    With which of the following molecules does Ca2+ bind after its release from the sarcoplasmic reticulum to regulate muscle contraction?

1.    Myosin

2.    Actin

3.    Troponin

4.    Tropomyosin

3.    Which of the following cells is correctly coupled with its definition?

1.    Osteoblasts—bone cells involved in the secretion of bone matrix

2.    Osteoclasts—immature bone cells

3.    Osteocytes—polynucleated cells actively involved in bone resorption

4.    Chondrocytes—undifferentiated bone marrow cells

4.    An X-ray of the right femur in a child shows that it is shorter than the opposite femur, and below the average length for a child of this age. Which region of the bone is most likely to have an abnormality?

1.    Diaphysis

2.    Metaphysis

3.    Epiphysis

4.    Periosteum

5.    Which of the following INCORRECTLY pairs a type of muscle fiber with a characteristic of that fiber?

1.    Red fibers—rich in mitochondria

2.    Red fibers—high levels of myoglobin

3.    White fibers—fast-twitching

4.    White fibers—predominantly uses aerobic respiration

6.    When the knee moves back and forth during walking, what prevents the surfaces of the leg bones from rubbing against each other?

1.    Articular cartilage

2.    Epiphyses

3.    Synovial fluid

4.    Smooth muscle

7.    Which type(s) of muscle is/are always multinucleated?

1.    Cardiac muscle

2.    Skeletal muscle

3.    Smooth muscle

1.    I only

2.    II only

3.    III only

4.    I and II only

8.    Which type(s) of muscle has/have myogenic activity?

1.    Cardiac muscle

2.    Skeletal muscle

3.    Smooth muscle

1.    I only

2.    II only

3.    III only

4.    I and III only

9.    Red bone marrow is involved in erythrocyte formation. In contrast, yellow bone marrow:

1.    is involved in leukocyte formation.

2.    is responsible for drainage of lymph.

3.    causes the formation of spicules.

4.    contains predominantly adipose tissue.

10.Which of the following statements regarding the periosteum is INCORRECT?

1.    The periosteum serves as a site of attachment of bone to muscle.

2.    Cells of the periosteum may differentiate into osteoblasts.

3.    The periosteum is a fibrous sheath that surrounds long bones.

4.    The periosteum secretes fluid into the joint cavity.

11.Which of the following bones is NOT a part of the appendicular skeleton?

1.    The triquetrum, one of the carpal bones

2.    The calcaneus, which forms the heel

3.    The ischium, one of the fused pelvic bones

4.    The sternum, or breastbone

12.To facilitate the process of birth, an infant’s head is somewhat flexible. This flexibility is given in part by the two fontanelles, which are soft spots of connective tissue in the infant’s skull. With time, the fontanelles will close through a process known as:

1.    endochondral ossification.

2.    intramembranous ossification.

3.    bone resorption.

4.    longitudinal growth.

13.A young woman presents to the emergency room with a broken hip. She denies any recent history of trauma to the joint. Blood tests reveal a calcium concentration of  (normal: 8.4–10.2). Which tissue is likely responsible for these findings?

1.    Thyroid

2.    Cartilage

3.    Parathyroid

4.    Smooth muscle

PRACTICE QUESTIONS

Answers and Explanations

1.    DWe are given a diagram of a sarcomere and asked to determine which regions shorten during muscle contraction. All bands and zones of the sarcomere shorten during contraction except the A-band, which is the full length of the thick filaments. In this diagram, that is region 1. Thus, the remaining regions all shorten, making choice (D) the correct answer. Region 2 represents the I-band, region 3 represents the H-zone, and region 4 is the length of the sarcomere between Z-lines.

2.    CRegion 1 contains both thick and thin filaments overlapping one over the other. This region refers to the A-band and is measured from one end of the thick filaments to the other. This is also the only portion of the sarcomere that does not change length during muscle contraction.

3.    DThe sarcomere is the contractile unit in striated muscle cells. One sarcomere is represented by the area between the two vertical lines, referred to as the Z-lines. In addition, the Z-lines anchor the thin filaments. In the diagram, a sarcomere is therefore defined by region 4.

4.    CCalcium is released from the sarcoplasmic reticulum into the sarcoplasm. It binds the troponin molecules on the thin filaments, causing the strands of tropomyosin to shift, thereby exposing the myosin-binding sites on the filaments.

5.    ALet’s quickly define each one of the four cells discussed in the answer choices. Osteoblasts are bone cells involved in the secretion of bone matrix, as choice (A) states. Osteoclasts are large, polynucleated cells involved in bone resorption. Osteocytes are mature bone cells that eventually become surrounded by their matrix; their primary role is bone maintenance. Finally, chondrocytes are cells that secrete chondrin, an elastic matrix that makes up cartilage.

6.    CThis question is essentially asking where longitudinal growth occurs in bones. The most likely site of abnormalities in this child’s femur is the epiphyseal plate, a disk of cartilaginous cells at the internal border of the epiphysis, because the epiphyseal plate is the site of longitudinal growth. Damage to the epiphysis (with or without metaphysis involvement) can imply damage to the epiphyseal plate.

7.    DRed fibers are slow-twitching fibers that have high levels of myoglobin and many mitochondria. They derive their energy from aerobic respiration and are capable of sustained vigorous activity. This eliminates choices (A) and (B). White fibers, on the other hand, are fast-twitching fibers and contain lower levels of myoglobin and fewer mitochondria. Because of their composition, they derive more of their energy anaerobically and fatigue more easily. This eliminates choice (C) and makes choice (D) the correct answer.

8.    AThe articular surfaces of the bones are covered with a layer of smooth articular cartilage. The epiphysis is a portion of the bone itself, eliminating choice (B). Synovial fluid lubricates the movement in the joint space, but does not stop the bones from contacting one another; this is the job of articular cartilage, eliminating choice (C). There is no appreciable function for smooth muscle in the joint space, eliminating choice (D).

9.    BThe only type of muscle that is always multinucleated is skeletal muscle, making choice (B) the correct answer. Cardiac muscle may contain one or two centrally located nuclei, so statement I is incorrect. Smooth muscle, on the other hand, always has only one centrally located nucleus.

10.DMyogenic activity refers to the ability of a muscle to contract without nervous stimulation in response to other stimuli like stretching. Smooth and cardiac muscle both possess myogenic activity.

11.DYellow marrow is largely inactive and is infiltrated by adipose tissue, making choice (D) the correct answer.

12.DThe periosteum, a fibrous sheath that surrounds long bones, is the site of attachment to muscle tissue. Some periosteum cells are capable of differentiating into bone-forming cells called osteoblasts. This eliminates choices (A)(B), and (C). It is the synovium that secretes fluid into the joint cavity (joint space), not the periosteum, making choice (D) the correct answer.

13.DThe axial skeleton consists of the skull, vertebral column, rib cage, and hyoid bone. The sternum is a point of attachment of the rib cage and is thus a part of the axial, not appendicular, skeleton. The limb bones, pectoral girdle, and pelvis are all part of the appendicular skeleton.

14.BBones form in one of two ways: endochondral ossification and intramembranous ossification. Endochondral ossification is the replacement of a cartilaginous skeleton with bone and occurs mostly in long bones, eliminating choice (A). Intramembranous ossification is the formation of bone from undifferentiated connective tissue cells (mesenchyme) and occurs mostly in the skull, making choice (B) the correct answer. Bone resorption is the breakdown of bone, not its formation, eliminating choice (C). Longitudinal growth occurs in long bones and is responsible for increasing height over time, but does not play a role in fontanelle ossification, eliminating choice (D).

15.CAn unprovoked fracture of the hip is not a normal finding in a young woman. Given that she has a high calcium level, it is likely that she has an increased level of bone resorption that is causing her bones to be more fragile. Parathyroid hormone causes calcium release from bones. If this woman had an overactive parathyroid gland—or even cancer in this gland—then it is likely that calcium could still be resorbed from her bones even though her blood calcium levels are already high.