Chapter 11: The Musculoskeletal System

Question 1

The Muscular System

Answer 1

START

Question 2

There are three main types of muscle:

Answer 2

1. skeletal muscle
2. smooth muscle
3. cardiac muscle

Question 3

Skeletal muscle is involved in

Answer 3

support and movement, propulsion of blood in the venous system, and thermoregulation. It appears striated, is under voluntary (somatic) control, is polynucleated, and can be divided into red (slow-twitch) fibers that carry out oxidative phosphorylation and white (fast-twitch) fibers that rely on anaerobic metabolism.

Question 4

Smooth muscle is in the

Answer 4

respiratory, reproductive, cardiovascular, and digestive systems. It appears nonstriated, is under involuntary (autonomic) control, and is uninucleated. It can display myogenic activity, or contraction without neural input.

Question 5

Cardiac muscle comprises the

Answer 5

contractile tissue of the heart. It appears striated, is under involuntary (autonomic) control, and is uninucleated (some-times binucleated). It can also display myogenic activity. Cells are connected with intercalated discs that contain gap junctions.

Question 6

The sarcomere is the

Answer 6

basic contractile unit of striated muscle.

• Sarcomeres are made of thick (myosin) and thin (actin) filaments.
• Troponin and tropomyosin are found on the thin filament and regulate actin–myosin interactions.

Question 7

Sarcomeres are made of thick

Answer 7

(myosin) and thin (actin) filaments.

Question 8

__ and __ are found on the thin filament and regulate actin–myosin interactions.

Answer 8

Troponin

tropomyosin

Question 9

Troponin and tropomyosin are found on the

Answer 9

thin filament and regulate actin–myosin interactions.

Question 10

The sarcomere can be divided into different

Answer 10

lines, zones, and bands.

• The boundaries of each sarcomere are defined by Z-lines.
• The M-line is located in the middle of the sarcomere.
• The I-band contains only thin filaments.
• The H-zone consists of only thick filaments.
• The A-band contains the thick filaments in their entirety. It is the only part of the sarcomere that maintains a constant size during contraction.

Question 11

The boundaries of each sarcomere are defined by

Answer 11

Z-lines

Question 12

The M-line is located in the

Answer 12

middle of the sarcomere.

Question 13

The I-band contains only

Answer 13

thin filaments.

Question 14

The H-zone consists of only

Answer 14

thick filaments.

Question 15

The A-band contains the

Answer 15

thick filaments in their entirety. It is the only part of the sarcomere that maintains a constant size during contraction.

Question 16

Sarcomeres attach end-to-end to become

Answer 16

myofibrils, and each myocyte (mus-cle cell or muscle fiber) contains many myofibrils.

• Myofibrils are surrounded by the sarcoplasmic reticulum, a calcium-containing modified endoplasmic reticulum, and the cell membrane of a myocyte is known as the sarcolemma.
• A system of T-tubules is connected to the sarcolemma and oriented perpen-dicularly to the myofibrils, allowing the action potential to reach all parts of the muscle.

Question 17

Myofibrils are surrounded by the

Answer 17

sarcoplasmic reticulum, a calcium-containing modified endoplasmic reticulum, and the cell membrane of a myocyte is known as the sarcolemma.

Question 18

A system of T-tubules is connected to the

Answer 18

sarcolemma and oriented perpen-dicularly to the myofibrils, allowing the action potential to reach all parts of the muscle.

Question 19

Muscle contraction begins at the

Answer 19

Muscle contraction begins at the neuromuscular junction, where the motor neuron releases acetylcholine that binds to receptors on the sarcolemma, caus-ing depolarization.

• This depolarization spreads down the sarcolemma to the T-tubules, trigger-ing the release of calcium ions.
• Calcium binds to troponin, causing a shift in tropomyosin and exposure of the myosin-binding sites on the actin thin filament.
• Shortening of the sarcomere occurs as myosin heads bind to the exposed sites on actin, forming cross bridges and pulling the actin filament along the thick filament, which results in contraction. This is known as the sliding filament model.
• The muscle relaxes when acetylcholine is degraded by acetylcholinesterase, terminating the signal and allowing calcium to be brought back into the SR. ATP binds to the myosin head, allowing it to release from actin.

Question 20

Muscle cells exhibit an

Answer 20

all-or-nothing response called a simple twitch.

• Addition of multiple simple twitches before the muscle has an opportunity to fully relax is called frequency summation.
• Simple twitches that occur so frequently as to not let the muscle relax at all can lead to tetanus, a more prolonged and stronger contraction.

Question 21

Muscle cells have additional energy reserves to reduce

Answer 21

oxygen debt (the dif-ference between the amount of oxygen needed and the amount present) and forestall fatigue.

• Creatine phosphate can transfer a phosphate group to ADP, forming ATP.
• Myoglobin is a heme-containing protein that is a muscular oxygen reserve

Question 22

Creatine phosphate can transfer a

Answer 22

phosphate group to ADP, forming ATP.

Question 23

Myoglobin is a

Answer 23

heme-containing protein that is a muscular oxygen reserve.

Question 24

The Skeletal System

Answer 24

START

Question 25

Internal skeletons (like those in humans) are called

Answer 25

endoskeletons; external skeletons (like those in arthropods) are called exoskeletons.

Question 26

The human skeletal system can be divided into

Answer 26

The human skeletal system can be divided into axial and appendicular skeletons.

• The axial skeleton consists of structures in the midline such as the skull, vertebral column, rib cage, and hyoid bone. • The appendicular skeleton consists of the bones of the limbs, the pectoral girdle, and the pelvis.

Question 27

The axial skeleton consists of

Answer 27

structures in the midline such as the skull, vertebral column, rib cage, and hyoid bone.

Question 28

The appendicular skeleton consists of the

Answer 28

bones of the limbs, the pectoral girdle, and the pelvis.

Question 29

Bone is derived from

Answer 29

embryonic mesoderm and includes both compact and spongy (cancellous) types.

• Compact bone provides strength and is dense.

• Spongy or cancellous bone has a lattice-like structure consisting of bony spicules known as trabeculae. The cavities are filled with bone marrow.
• Long bones contain shafts called diaphyses that flare to form metaphyses and terminate in epiphyses. The epiphysis contains an epiphyseal (growth) plate that causes linear growth of the bone.
• Bone is surrounded by a layer of connective tissue called periosteum.

• Bones are attached to muscles by tendons and to each other by ligaments.

Question 30

Compact bone provides

Answer 30

strength and is dense.

Question 31

Spongy or cancellous bone has a

Answer 31

lattice-like structure consisting of bony spicules known as trabeculae. The cavities are filled with bone marrow.

Question 32

Long bones contain shafts called

Answer 32

diaphyses that flare to form metaphyses and terminate in epiphyses. The epiphysis contains an epiphyseal (growth) plate that causes linear growth of the bone.

Question 33

Bone is surrounded by a layer of connective tissue called

Answer 33

periosteum

Question 34

Bones are attached to muscles by

Answer 34

by tendons and to each other by ligaments.

Question 35

Bone matrix has both

Answer 35

organic components, like collagen, glycoproteins, and other peptides; and inorganic components, like hydroxyapatite.

• Bone is organized into concentric rings called lamellae around a central Haversian or Volkmann’s canal. This structural unit is called an osteon or Haversian system.
• Between lamellar rings are lacunae, where osteocytes reside, which are con-nected with canaliculi to allow for nutrient and waste transfer.

Question 36

Bone is organized into

Answer 36

concentric rings called lamellae around a central Haversian or Volkmann’s canal. This structural unit is called an osteon or Haversian system.

Question 37

Between lamellar rings are

Answer 37

lacunae, where osteocytes reside, which are con-nected with canaliculi to allow for nutrient and waste transfer.

Question 38

Bone remodeling is carried out by

Answer 38

osteoblasts and osteoclasts. Osteoblasts build bone, while osteoclasts resorb bone. • Parathyroid hormone increases resorption of bone, increasing calcium and phosphate concentrations in the blood.

• Vitamin D also increases resorption of bone, leading to increased turnover and, subsequently, the production of stronger bone.
• Calcitonin increases bone formation, decreasing calcium concentrations in the blood.

Question 39

____increases resorption of bone, increasing calcium and phosphate concentrations in the blood.

Answer 39

Parathyroid hormone

Question 40

___ also increases resorption of bone, leading to increased turnover and, subsequently, the production of stronger bone.

Answer 40

Vitamin D

Question 41

___ increases bone formation, decreasing calcium concentrations in the blood.

Answer 41

Calcitonin

Question 42

Parathyroid hormone does what?

Answer 42

Parathyroid hormone increases resorption of bone, increasing calcium and phosphate concentrations in the blood.

Question 43

Vitamin D does what?

Answer 43

Vitamin D also increases resorption of bone, leading to increased turnover and, subsequently, the production of stronger bone.

Question 44

Calcitonin does what?

Answer 44

Calcitonin increases bone formation, decreasing calcium concentrations in the blood.

Question 45

Cartilage is a

Answer 45

Cartilage is a firm, elastic material secreted by chondrocytes. Its matrix is called chondrin.

• Cartilage is usually found in areas that require more flexibility or cushioning.
• Cartilage is avascular and is not innervated.

Question 46

Cartilage is usually found in

Answer 46

areas that require more flexibility or cushioning.

Question 47

Cartilage is ___ and is not ___.

Answer 47

avascular

innervated

Question 48

In fetal life, bone forms from cartilage through

Answer 48

endochondral ossification. Some bones, especially those of the skull, form directly from undifferentiated tissue (mesenchyme) in intramembranous ossification.

Question 49

Joints may be classified as

Answer 49

immovable or movable.

• Immovable joints are fused together to form sutures or similar fibrous joints.
• Movable joints are usually strengthened by ligaments and contain a synovial capsule.
• Synovial fluid, secreted by the synovium, aids in motion by lubricating the joint.
• Each bone in the joint is coated with articular cartilage to aid in movement and provide cushioning.

Question 50

Immovable joints are

Answer 50

Immovable joints are fused together to form sutures or similar fibrous joints.

Question 51

Movable joints are

Answer 51

Movable joints are usually strengthened by ligaments and contain a synovial capsule.

Question 52

Synovial fluid, secreted by the

Answer 52

Synovial fluid, secreted by the synovium, aids in motion by lubricating the joint.

Question 53

Each bone in the joint is coated with

Answer 53

articular cartilage to aid in movement and provide cushioning.

Question 54

Muscles that serve opposite functions come in ______; when one muscle contracts, the other lengthens.

Answer 54

antagonistic pairs