The Musculoskeletal System

Question 1

Red fibers/slow-twitch fibers

Answer 1

Have high myoglobin content and primarily derive their energy aerobically. Contains myoglobin and many mitochondria to carry out oxidative phosphorylation. Contract slowly but can sustain activity

Question 2

White fibers/fast-twitch fibers

Answer 2

Contains much less myoglobin than red-twitch fibers. They contract rapidly, but fatigue quickly

Question 3

Smooth muscle

Answer 3

Responsible for involuntary action

Question 4

Tonus

Answer 4

A constant state of low-level contraction, as may be seen in blood vessels

Question 5

Myogenic activity

Answer 5

When smooth muscle can actually contract without nervous system input –> muscle cells instead contract directly in response to stretch or other stimuli

Question 6

Cardiac muscle

Answer 6

Has characteristics of both smooth and skeletal muscle types: is primarily uninucleated, but cells may contain 2 nuclei. Cardiac muscle appears striated

Question 7

Sarcomere

Answer 7

The basic contractile unit of skeletal muscle: made of thick and thin filaments.

Question 8

What are the thick and thin filaments in a sarcomere made up of

Answer 8

Thick: Organized bundles of myosin
Thin: Actin along with 2 other proteins: troponin and tropomyosin

Question 9

Titin

Answer 9

Acts as a spring and anchors the actin and myosin filaments together, preventing excessive stretching of the muscle

Question 10

The parts of the sarcomere: bands and lines

Answer 10

M-HAIZ

M-Middle of the myosin filaments
H - H is a thick letter (contains thick filaments only)
A - All of the thick filament, whether or not it is overlapping
I - I is a thin letter (thin filaments only)
Z - Z is the end of the alphabet, and the end of the sarcomere

Question 11

Myofibrils

Answer 11

Formed when sarcomeres are attached end to end: surrounded by the sarcoplasmic reticulum (SR).

Question 12

Sarcoplasmic reticulum (SR)

Answer 12

A modified endoplasmic reticulum that contains a high concentration of Ca2+ ions.

Question 13

Sarcoplasm

Answer 13

A modified cytoplasm located just outside the sarcoplasmic reticulum

Question 14

Sarcolemma

Answer 14

The cell membrane of a myocyte. Capable of propagating an action potential and can distribute the action potential to all sarcomeres in a muscle using a system of transverse tubules (T-tubules) that are oriented perpendicularly to the myofibrils

Question 15

Myocyte

Answer 15

A muscle cell: contains many myofibrils arranged in parallel and can also be called a muscle fiber. Nuclei are usually found at the periphery of the cell.

Question 16

Where does muscular contraction start

Answer 16

The neuromuscular junction, where the nervous system communicates with muscles via motor (efferent) neurons.

Question 17

Pathway of contraction

Answer 17

Neuromuscular junction –> signal travels down neuron to nerve terminal/motor end plate –> acetylcholine binds to receptors on sarcolemma –> depolarization –> triggers action potential –> spreads down sarcolemma to T-tubules in muscle tissues–> reaches sacroplasmic reticulum –> Ca2+ released –> Ca2+ binds to regulatory subunit in troponin, triggering change in confirmation in tropomyosin –> exposes myosin-binding sites on actin thin filament

Question 18

Describe the actin-myosin cross-bridge cycle

Answer 18

A) Myosin carrying hydrolyzed ATP (ADP and an inorganic phosphate, Pi) is able to bind with the the myosin-binding site.
B) Release of inorganic phosphate and ADP in rapid succession provides the energy for the powerstroke and results in sliding of the actin filament over the myosin filament
C) ATP binds to actin head, releasing it from actin
D) ATP is hydrolyzed to ADP and Pi, which recocks the myosin head so that it is in position to initiate another cross-bridge cycle.

Question 19

Sliding filament model

Answer 19

Repetitive binding and releasing of myosin heads on actin filaments allows the thin filament to slide along the thick filament, causing sequential shortening of the sarcomere.

Question 20

Affect of band length when sarcomere contracts

Answer 20

Both the H-zone and I-band shorten while the A-band is unchanged.

Question 21

A simple twitch

Answer 21

The response of a single muscle fiber to a brief stimulus at or above threshold. Consists of a latent period, contraction period, and relaxation period.

Question 22

Latent period

Answer 22

The time between reaching threshold and the onset of contraction

Question 23

Tetanus

Answer 23

When contractions become so frequent that the muscle is unable to relax

Question 24

Creatine phosphate and its purpose in muscles

Answer 24

Created by transferring a phosphate group from ATP to creatine during times of rest.
Reaction can be reversed during muscle use to quickly generate ATP from ADP.
creatine + ATP —> creatine phosphate + ADP.

Question 25

Oxygen debt

Answer 25

The difference between the amount of oxygen needed by the muscles and the actual amount present

Question 26

Axial skeleton

Answer 26

Consists of the skull, vertebral column, ribcage, and hyoid bone (small bone in anterior neck); provides basic central framework for the body

Question 27

Appendicular skeleton

Answer 27

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

Question 28

Long bones

Answer 28

Typical of appendicular skeleton.
Characterized by cylindrical shafts called diaphyses that swell at each end to form metaphyses, and that terminate in epiphyses.
Outermost portion of bone composed of compact bone, whereas internal core is made of spongy bone

Question 29

Epiphyseal (growth) plate

Answer 29

A cartilaginous structure and the site of longitudinal growth; at the internal edge of epiphysis

Question 30

Periosteum

Answer 30

Fibrous sheath that surround the long bone to protect it as well as serve as a site for muscle attachment.

Question 31

Tendons

Answer 31

Attach muscle to bone

Question 32

Ligaments

Answer 32

Hold bones together at joints

Question 33

Bone matrix

Answer 33

Gives compact bone its strength; includes collagen, glycoproteins, and other proteins. AND
calcium, phosphate, and hydroxide ions

Question 34

Hydroxyapatite

Answer 34

Contains calcium, phosphate, and hydroxide ions

Question 35

Osteoblasts

Answer 35

Build bone

Question 36

Osteoclasts

Answer 36

Polynucleated resident macrophages of bone, and resorb bone.

Question 37

Vitamin D

Answer 37

Activated by parathyroid hormone, promotes resorption of bone.

Question 38

Cartilage

Answer 38

Consists of a firm but elastic matrix called chondrin that is secreted by cells called chondrocytes

Question 39

Endochondral ossification

Answer 39

Process whereby most of the bones of the body are created by hardening cartilage into bone

Question 40

Intramembranous ossification

Answer 40

Undifferentiated embryonic connective tissue is transformed into, and replaced by, bone. Occurs in bones of skull

Question 41

Immovable joints

Answer 41

Consist of bones that are fused together to form sutures or similar fibrous joints

Question 42

Articular cartilage

Answer 42

Contributes to the joint by coating the articular surfaces of the bones so that impact is restricted to the lubricated joint cartilage, rather than the bones.

Question 43

Origin

Answer 43

The end of the muscle with a larger attachment to bone (usually the proximal connection)

Question 44

Insertion

Answer 44

The end of the muscle with the smaller attachment to bone (usually the distal connection)

Question 45

Antagonistic pairs

Answer 45

Often how our muscles work: one relaxes while the other contracts