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SP MCAT Biology > Musculoskeletal System > Flashcards

Musculoskeletal System Flashcards

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1
Q

What main functions are served by muscle?

A
  • movement
  • support
  • thermoregulation
  • circulation
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2
Q

Explain the role of the muscular system in thermoregulation

A
  • In cold conditions, skeletal muscles are involved in shivering, in which they contract and convert energy to heat. Smooth muscle also facilitates vasoconstriction and piloerection (goosebumps), both of which reduce heat loss.
  • In warm conditions, smooth muscle facilitates vasodilation, which promotes the dissipation of body heat to the external environment
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3
Q

Explain the role of skeletal muscle in circulation

A
  • Skeletal muscles in the legs contract to compress nearby veins, assisting venous blood as it returns to the heart.
  • Specifically, blood returning from the lower regions of the body must counteract gravity. Since venous pressure is relatively low, the function of skeletal muscle is vital
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4
Q

Explain the role of smooth muscle in circulation

A
  • Smooth muscle lines arteries, arterioles, and veins. In response to a variety of factors, this muscle can contract (promoting vasoconstriction) or relax (promoting vasodilation).
  • Nervous system signaling and temperature changes, among other factors, are involved in promoting these responses
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5
Q

What are the 3 major types of muscle?

A
  • cardiac
  • skeletal
  • smooth
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6
Q

What features characterize smooth muscle?

A
  • mononucleated: single cell contains only one nucleus
  • cells are rounded and irregular in appearance
  • contain both actin and myosin but fibers are not well organized so no striation
  • controlled by the autonomic NS (involuntary)
  • can contract directly in response to stretch or other stimuli without NS input, known as myogenic activity
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7
Q

What features characterize skeletal muscle?

A
  • multinucleated: single cell contains more than one nucleus
  • innervated by somatic NS (voluntary control)
  • actin and myosin arranged in repeating units called sarcomeres, which are striated in appearance
  • contain both red fibers and white fibers
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8
Q

Myoglobin

A
  • oxygen carrier that uses iron in a heme group to bind oxygen
  • red in color
  • found in skeletal muscle
  • picks up oxygen that hemoglobin releases in the tissues, meaning that is has a higher O2 affinity than hemoglobin
  • only contains one monomer instead of 4 like Hb, meaning that is cannot undergo cooperative binding like Hb
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9
Q

Red Fibers

A
  • known as slow-twitch fibers
  • present in skeletal muscle
  • have high myoglobin content
  • primarily derive their energy aerobically
  • contain many mitochondria to carry out oxidative phosphorylation
  • found in muscles that contract slowly but can sustain activity
  • during strenuous exercise they eventually switch to anaerobic metabolism and produce lactic acid
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10
Q

White Fibers

A
  • known as fast-twitch fibers
  • contain less myoglobin and therefore less iron so appear white in color
  • found in muscles that contract rapidly but fatigue quickly
  • have fewer mitochondria so must rely on glycolysis and fermentation to make ATP
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11
Q

What features characterize cardiac muscle?

A
  • has characteristics of both smooth and skeletal muscle
  • primarily uninucleated, but some cells may contain 2 nuclei
  • innervated by autonomic NS (involuntary control)
  • appears striated
  • cells are connected by intercalated discs which contain many gap junctions (connections btw cytoplasm of adjacent cells, allowing for direct ion flow btw cells)
  • can define and maintain their own rhythm through myogenic activity
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12
Q

What muscle types require Ca2+ for contraction?

A

all of them – skeletal, smooth, and cardiac

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13
Q

What muscle types exhibit myogenic activity?

A

both smooth and cardiac muscle – their cells respond to nervous input but do not require external signals to undergo contraction

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14
Q

How does the role of calcium in skeletal and cardiac muscle contraction differ from its function in smooth muscle?

A
  • Skeletal and cardiac muscle require calcium to bind to troponin, exposing the myosin binding site.
  • Smooth muscle contains no troponin, but still relies on calcium for a signaling cascade that promotes contraction
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15
Q

A certain tissue sample displays three nuclei in a single cell. This sample is likely which type of muscle?

A

-The sample is probably skeletal muscle.

skeletal muscle is the only one of the three types that is generally multinucleated

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16
Q

A certain tissue sample displays numerous mitochondria and large amounts of microfilament-based structures. This sample is likely which type of muscle?

A

This information is inconclusive – all three muscle types contain mitochondria and substantial amounts of actin, a motor protein composed of microfilaments; while skeletal muscle does tend to possess more mitochondria than the other types, we do not know enough to answer this question

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17
Q

A biopsy is taken from the lining of an artery wall. Which type(s) of muscle might be found in this process?

A

-Smooth muscle would likely be found

(Arteries, veins, arterioles, and larger venules contain smooth muscle in addition to endothelium and connective tissue. Note that capillary walls contain only a single layer of endothelial cells)

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18
Q

A tissue sample is taken from the diaphragm. Which type(s) of muscle could this sample contain?

A

-The sample would likely contain skeletal muscle.

(diaphragm is the main muscle involved in respiration. It is composed of skeletal muscle, but can be controlled either voluntarily or involuntarily)

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19
Q

Muscle cells are likely to have large amounts of which eukaryotic organelle?

A

muscle cells are likely to contain high numbers of mitochondria. These organelles provide the ATP needed for contraction.

(Some types of muscle fiber, generally those specialized for aerobic respiration, are higher in mitochondria than others. For example, slow-twitch or red muscle fibers contain extremely high numbers of the structures)

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20
Q

Sarcomere

A
  • basic contractile unit of skeletal muscle
  • made of thick and thin filaments
  • each one is divided into different lines, zones and bands: Z-lines, M-line, I-band, H-zone, A-band
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21
Q

Thick Filaments

A

organized bundles of myosin

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22
Q

Thin Filaments

A

made of actin along with two other proteins: troponin and tropomyosin which help to regulate the interaction between the actin and myosin filaments

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23
Q

Titin

A

protein that acts a spring and anchors the actin and myosin filaments together, preventing excessive stretching of the muscle

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24
Q

Z-Lines

A
  • Z is at the end of the alphabet and the end of the sarcomere*
  • define the boundaries of the sarcomere
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25
Q

M-Line

A
  • Middle of the Myosin filaments*

- runs down the center of the sarcomere through the middle of the myosin filaments

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26
Q

I-Band

A
  • I is a thin letter – thin filaments only*

- the region containing exclusively thin filaments

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27
Q

H-Zone

A
  • H is a thick letter – thick filaments only*

- region containing exclusively thick filaments

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28
Q

A-Band

A
  • All of the thick filament, whether or not it is overlapping*
  • contains thick filaments in their entirety, including any overlap with thin filaments
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29
Q

What happens to the zones/bands/lines during contraction?

A
  • the H-zone, I-band, distance between Z-lines and distance between M-lines all become smaller
  • size of A-band remains constant b/c it is the entire length of the myosin filament which does not change in length, it just slides
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30
Q

Myofibrils

A
  • sarcomeres that are attached end to end
  • surrounded by a covering known as the sarcoplasmic reticulum (modified endoplasmic reticulum that contains a high concentration of Ca2+ ions)
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31
Q

Muscle Fiber

A
  • also known as a myocyte or muscle cell

- contains many myofibrils within it, arranged in parallel

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32
Q

Muscle

A

made up of parallel muscle fibers

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33
Q

Motor Unit

A

each nerve terminal controls a group of myocytes; together the nerve terminal and its myocytes constitute this unit

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34
Q

Sarcoplasm

A

modified cytoplasm located outside the sarcoplasmic reticulum

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35
Q

Sarcolemma

A
  • cell membrane of a myocyte
  • capable of propagating an action potential and can distribute the AP to all sarcomeres using a system of transverse tubules (T-tubules)
36
Q

List the steps involved in initiation of a muscle contraction (8)

A
  1. contraction starts at NMJ (where NS communicates with muscles via motor/efferent neurons)
  2. signal travels down neuron until it reaches the nerve terminal (synaptic bouton) where ACh is released into the synapse
  3. binding of Ach to receptors on the sarcolemma, causing depolarization
  4. depolarization triggers an AP which spreads down the sarcolemma to T-tubules
  5. T-tubules travel into muscle tissues to the SR
  6. AP at SR leads to release of Ca2+
  7. Ca2+ binds to troponin, triggering a change in the conformation of tropomyosin, to which troponin is bound
  8. conformational change exposes the myosin-binding sites on the actin thin filament
37
Q

What occurs during shortening of the sarcomere in muscle contraction?

A
  • free globular heads of myosin molecules move toward and bind with exposed sites on actin, forming myosin-actin cross bridges
  • cross-bridges allow myosin to pull on actin, which draws the thin filaments toward the M-line, resulting in shortening of the sarcomere
38
Q

List the steps involved in the Actin-Myosin Cross-Bridge Cycle

A
  1. resting state: ATP on myosin head is hydrolyzed (ADP and Pi)
  2. Ca2+ binds to troponin which allows the binding of myosin to actin at the myosin-binding site
  3. release of Pi and ADP from myosin in rapid succession provides the energy for the power-stroke to occur, resulting in contraction of the sarcomere (sliding of actin filament over myosin filament)
  4. new ATP binds to myosin causing detachment of myosin head from actin; this ATP is hydrolyzed to ADP and Pi which recocks the myosin head so that it is in a position to initiate another cross-bridge cycle
39
Q

Sliding Filament Model

A

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

40
Q

What is responsible for the power-stroke?

A

the dissociation of ADP and Pi from myosin

41
Q

How does muscle relax after contraction?

A
  • Ach is degraded in the synapse by enzyme acetylcholinesterase, resulting in termination of the signal to the NMJ and repolarization of the sarcolemma
  • Ca2+ release ceases and SR takes up Ca2+ from the sarcoplasm
  • myosin binding sites on actin are covered by tropomyosin, which prevents muscle contraction
42
Q

How are muscle cells similar to neurons?

A

they both exhibit an all-or-nothing response; either they respond completely to a stimulus or not at all

43
Q

Simple-Twitch

A
  • response of a single muscle fiber to a brief stimulus at or above threshold
  • consists of a latent period, contraction period and relaxation period
44
Q

Latent Period

A
  • time between reaching threshold and the onset of a contraction
  • during this time the AP spreads along the muscle and allows for Ca2+ to be released from the SR
45
Q

Frequency Summation

A
  • occurs when a muscle fiber is exposed to frequent and prolonged stimulation, meaning it does not have sufficient time to relax
  • muscle contractions combine, become stronger and more prolonged
46
Q

Tetanus

A
  • occurs when muscle contractions become so frequent that the muscle is unable to relax at all
  • prolongation of this results in muscle fatigue
47
Q

What are the two oxygen reserves muscles use to reduce oxygen debt?

A
  • creatine phosphate

- myoglobin (heme containing protein)

48
Q

Creatine Phosphate

A
  • created by transferring a phosphate group from ATP to creatine during times of rest
  • this reaction can be be reversed during muscle use to generate ATP from ADP
  • creatine + ATP creatine phosphate + ADP
49
Q

What happens to the oxyhemoglobin dissociation curve when someone is exercising?

A

it undergoes a rightward shift in the presence of increased CO2 concentration (decreased pH) and increased temperature

50
Q

Oxygen Debt

A

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

51
Q

Curare, a plant-based toxin, blocks nicotinic acetylcholine receptors at the neuromuscular junction. What symptom might be seen in a person poisoned with curare?

A

-person would likely be paralyzed.

(For skeletal muscle contraction to be initiated, acetylcholine must bind to receptors at the NMJ. If these receptors are blocked, no contraction can occur)

52
Q

In skeletal muscle, how does the role of tropomyosin differ from that of troponin?

A
  • Tropomyosin directly attaches to actin. In the absence of calcium, it physically blocks the myosin binding site.
  • Troponin binds to tropomyosin. It binds to calcium (when the ion is present) and triggers a conformational change in the tropomyosin molecule.
53
Q

After death, the cells of the body no longer synthesize ATP. What effect does this have on the condition of skeletal muscle?

A

Skeletal muscle becomes permanently contracted in a condition known as rigor mortis

54
Q

What main functions are served by the skeletal system?

A
  • protection of internal organs
  • structure and support
  • calcium storage
  • immune cell and erythrocyte production
55
Q

Axial Skeleton

A

consists of the skull, vertebral column, ribcage, and hyoid bone (small bone in the anterior neck used for swallowing)

56
Q

Appendicular Skeleton

A

consists of the bones of the limbs (humerus, radius, ulna, carpals, metacarpals, phalanges, femur, tibia, fibula, tarsals, metatarsals), the pectoral girdle (scapula, clavicle), and pelvis

57
Q

How many bones does an adult human have?

A

206

58
Q

What are the two major types of bone?

A
  • compact (cortical bone)

- spongy (cancellous bone)

59
Q

What features characterize compact bone?

A
  • hard and dense
  • mainly composed of the minerals, salts, and collagen that form the bony matrix
  • makes up the outermost portion of bones
  • comprised of cylindrical subunits called osteons
60
Q

What features characterize spongy bone?

A
  • softer and less dense than compact bone
  • contains many blood vessels as well as gaps in its structure that are filled with both yellow and red bone marrow
  • composed of bony spicules (points) known as trabeculae
  • makes up the internal portion of bone
61
Q

Red Marrow

A

filled with hematopoietic stem cells which are responsible for generation of all cells in our blood

62
Q

Yellow Marrow

A

composed primarily of fat and is relatively inactive

63
Q

Epiphyseal Growth Plate

A
  • located at the internal edge of the epiphysis
  • cartilaginous structure that is the site of longitudinal growth
  • prior to adulthood it is filled with mitotic cells that contribute to growth
  • plates close during puberty and vertical growth is halted
64
Q

Periosteum

A
  • fibrous sheath that surrounds the long bone to protect it and serve as a site for muscle attachment
  • some of these cells can differentiate into bone-forming cells
65
Q

Tendons

A
  • strip of tough connective tissue
  • connects a muscle to a bone
  • composed of collagen
  • generally function to facilitate movement
66
Q

Ligament

A
  • strip of tough connective tissue
  • connects a bone to another bone
  • composed of collagen
  • generally function to stabilize joints
67
Q

Bone Matrix

A
  • what gives connective bone strength

- has both organic (collagen, glycoproteins, other peptides) and inorganic (calcium, phosphate, OH- ions) compounds

68
Q

Structure of the Bone Matrix

A
  • ordered into structural units called osteons or Haversian systems
  • each osteon contains concentric circles of bony matrix called lamellae surround a central channel
  • Haversian canals: longitudinal channels with an axis parallel to the bone
  • Volkmann’s canals: transverse channels with an axis perpendicular to the bone
  • lacunae: small spaces between lamellar rings that contain mature bone cells (osteocytes)
  • canaliculi: tiny channels that connect lacunae, allow for exchange of nutrients and wastes btw osteocytes and Haversian and Volkmann’s canals
69
Q

What two cells are largely responsible for building and maintaining bone?

A
  • osteoblasts

- osteoclasts

70
Q

Osteoblasts

A
  • build bone
  • promote the synthesis of bone, while removing Ca2+ in the process
  • decrease blood Ca2+ levels
71
Q

Osteoblasts

A
  • chew bone
  • break down bone and release its Ca2+ content into the plasma
  • leads to an increase in blood Ca2+ levels
72
Q

Parathyroid Hormone

A
  • peptide hormone released by the parathyroid glands
  • released in response to low blood Ca2+
  • promotes resorption of bone
  • increases concentrations of calcium and phosphate in the blood
  • stimulates osteoclasts
73
Q

Vitamin D

A
  • activated by parathyroid hormone

- promotes resorption of bone

74
Q

Calcitonin

A
  • peptide hormone released by the parafollicular cells of the thyroid
  • released in response to high blood Ca2+ levels
  • stimulates osteoblasts
75
Q

Cartilage

A
  • form of connective tissue that is less rigid than bone
  • avascular (without blood or lymphatic vessels) and is not innervated
  • includes elastin, protein fibers, proteoglycan and collagen
  • fetal skeletons are mostly made of this
76
Q

Chondrocytes

A

cells that secrete chondrin which is the elastic matrix of cartilage

77
Q

Endochondral Ossification

A
  • process used by the body to create bones by hardening cartilage into bone
  • responsible for formation of most of the long bones in the body
78
Q

Intramembranous Ossification

A
  • another way to form bones
  • undifferentiated embryonic connective tissue (mesenchymal tissue) is transformed into bone
  • occurs in the bones of the skull
79
Q

Immovable Joints

A
  • bones that are fused together to form sutures or similar fibrous joints
  • primarily found in the head
80
Q

Movable Joints

A
  • includes hinge joints, ball and socket joints
  • permit bones to shift relative to one another
  • strengthened by ligaments
  • consist of a synovial capsule which encloses the actual joint/articular cavity
81
Q

What name classifies movable joints that contain closed regions filled with lubricating fluid?

A

Synovial joints
-synovial joints allow for flexibility at the junctions between bones. The rigid bones are separated by synovial fluid. Ball-and-socket joints are an example of this type of structure.

82
Q

Flexor Muscle

A

decreases the angle across a joint (ex. bicep)

83
Q

Extensor Muscle

A

increases or straightens the angle produced by the flexor muscle (ex. tricep)

84
Q

Abductor

A

moves a part of the body away from the middle (ex. deltoid)

85
Q

Adductor

A

moves a part of the body toward the middle (ex. pecs)

SP MCAT Biology (21 decks)

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