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BSCI 1511 > Muscles > Flashcards

Muscles Flashcards

1
Q

What are the three types of muscles in vertebrates?

A
  1. cardiac
  2. smooth
  3. skeletal
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2
Q

Smooth muscle

A

-simplest
-mononucleated
-spindle-shaped
-smooth sheets
-NO striated > actin and myosin NOT arranged regularly
-moves food through digestive tract, controls blood flow, empties urinary bladder

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3
Q

Cardiac muscle

A

-branched into a meshwork
-striated
-in electrical contact w/ each other by gap junctions
-heart will beat bc of special pacemaker muscle cells that have self-generated heartbeat

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4
Q

Skeletal muscle

A

-voluntary movements (under conscious control)
-striated muscle
-aka muscle fibers, many nuclei
-moves body by contraction by antagonistic muscle pairs (one contracting, one relaxing)

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5
Q

What composes connective tissue?

A

Ligaments and tendons

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6
Q

Ligaments

A

Hold bones together at a joint

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7
Q

Tendons

A

Attach the muscles to the bones

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8
Q

Structure of skeletal muscle

A

Each muscle fiber is packed w/ bundles of myofibrils made up of thin actin units surrounding thick myosin units

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9
Q

Sarcomeres

A

-make up myofibrils
-surrounded by Z lines that anchor the thin actin filaments
-Center: A band (houses all myosin filaments)
-M band: contains proteins that support the myosin filaments
-H zone and I band are areas where actin and myosin do not overlap in relaxed muscle and appear less dense

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10
Q

How are the bundles of myosin filaments held in?

A

By titin

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11
Q

Titin

A

Runs the full length of the sarcomere from Z line to Z line, each titin molecule runs through the myosin bundle

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12
Q

Contraction of Sarcomeres

A
  1. muscle contracts
  2. sarcomere shortens
  3. H zone and I band become much narrower
  4. Z lines move toward the A band
  5. actin filaments slide into region previously occupied only by myosin filaments (sliding filament theory)
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13
Q

What is a thin filament?

A

two chains of actin molecules twisted together w/ troponin and tropomyosin

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14
Q

Troponin has 3 binding sites for what?

A

actin, tropomyosin, and Ca2+

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15
Q

What is a thick filament?

A

many myosin molecules arranged in parallel

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16
Q

Structure of myosin

A

two long polypeptide chains coiled together ending in a large globular head, the heads have sites that bind to actin forming bridges between actin and myosin, myosin heads have ATPase activity

17
Q

Contractile Cycle (actin/myosin)

A
  1. myosin head is bound to ATP and is in its low energy conformation
  2. myosin hydrolyses ATP to ADP + Pi (high energy)
  3. myosin head binds actin forming cross-bridges
  4. myosin releases ADP + Pi and returns to low energy and slides the actin filament
  5. Binding a new ATP releases the myosin from actin
  6. Cycle restarts
18
Q

Contractile Cycle (troponin, tropomyosin, Ca2+)

A
  1. Muscle at rest: tropomyosin and troponin block myosin binding sites on the actin filament
  2. If troponin binds Ca2+, troponin and tropomyosin go through a conformational change and unmask the myosin binding sites
  3. W/ binding sites exposed, actin-myosin bonds are made and filaments are pulled past each other
19
Q

How are contractions in skeletal muscle initated?

A

by action potentials from motor neurons

20
Q

What are T tubules?

A

a system of tubules that branch through the cytoplasm of a muscle cell that is continuous w/ the plasma membrane

21
Q

What is the sarcoplasmic reticulum?

A

a network of intracellular membranes (modified ER) only in muscle cells that stores Ca2+

22
Q

What are the levels of Ca2+ in the SR at rest?

A

high concentration of Ca2+ in SR, low in cytoplasm

23
Q

Muscle Contraction Full Cycle

A
  1. ACh from synaptic terminal diffuses across synaptic cleft and binds to receptor proteins on muscle fiber’s PM which triggers an action potential
  2. Action potential is propagated along PM and down T tubules
  3. Action potential triggers Ca2+ release from SR
  4. Ca2+ bind to troponin and troponin changes shape, removing blocking action of tropomyosin. Myosin-binding sites exposed
  5. Myosin cross-bridges attach to actin and detach, pulling actin filaments toward center of sarcomere (powered by ATP)
  6. Cytosolic Ca2+ is removed by active transport into SR after action potential ends
  7. Tropomyosin blockage of myosin-binding sites is restored, contraction ends, and muscle fiber relaxes
24
Q

What causes temporal summation?

A

faster twitching of INDIVIDUAL fibers

25
Q

What causes spatial summation?

A

an increase in the NUMBER OF UNITS in the contraction

26
Q

What is tetanus?

A

At high stimulation levels (like in spatial summation), the Ca2+ pumps in SR can no longer remove Ca2+ btwn action potentials and maximum tension is generated

27
Q

Oxidative muscle fibers

A

-many mitochondria
-a lot of myoglobin
-provide steady, prolonged ATP production
-long-term aerobic work

28
Q

Glycolytic fibers

A

-fewer mitochondria
-very little myoglobin
-high ATPase activity but cannot replenish ATP fast enough to sustain long-time contraction
-sudden, maximum strength

29
Q

Strength exercises increase _____________

A

the number of new actin and myosin filaments (bigger muscles)

30
Q

Aerobic exercises enhances ______________

A

the oxidative capacity of muscles by increasing the density of capillaries in the muscles, myoglobin content, and number of mitochondria in fast twitch fibers

31
Q

Slow oxidative fibers

A

-large amts of myoglobin
-many mitochondria
-many blood capillaries
-high capacity for generating ATP but split at slow rate
-resistant to fatigue
-long distance running

32
Q

Fast oxidative fibers

A

-large amts of myoglobin
-many mitochondria
-many blood capillaries
-high capacity for generating ATP but split at very rapid rate
-not as resistant to fatigue as slow ox
-middle distance running and swimming

33
Q

Fast glycolytic fibers

A

-low myoglobin content
-few mitochondria
-few blood capillaries
-large amt of glycogen
-splits ATP very quickly
-fatigues easily
-sprinting

34
Q

What effect does CURARE have on muscles?

A

paralyzes muscles by blocking ACh from reaching receptors
-death occurs bc the muscles that move the diaphragm become paralyzed and breathing stops (asphyxiation)

35
Q

Botulism

A

-food poisoning from ingesting neurotoxin produced by bacterium Clostridium botulinum

36
Q

Effect of botulism

A

causes paralysis; toxins attach themselves to proteins necessary for ACh release at neuromuscular junctions (blocks ACh release)

37
Q

Botox

A

-low doses
-after a few hours to a couple of days after injection, contractions are reduced or eliminated altogether
-effects are not permanent
-injected directly into a certain muscle or muscle group to limit the spread

BSCI 1511 (25 decks)

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