Muscles

Question 1

What are the three types of muscles in vertebrates?

Answer 1

1. cardiac
2. smooth
3. skeletal

Question 2

Smooth muscle

Answer 2

-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

Question 3

Cardiac muscle

Answer 3

-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

Question 4

Skeletal muscle

Answer 4

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

Question 5

What composes connective tissue?

Answer 5

Ligaments and tendons

Question 6

Ligaments

Answer 6

Hold bones together at a joint

Question 7

Tendons

Answer 7

Attach the muscles to the bones

Question 8

Structure of skeletal muscle

Answer 8

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

Question 9

Sarcomeres

Answer 9

-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

Question 10

How are the bundles of myosin filaments held in?

Answer 10

By titin

Question 11

Titin

Answer 11

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

Question 12

Contraction of Sarcomeres

Answer 12

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)

Question 13

What is a thin filament?

Answer 13

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

Question 14

Troponin has 3 binding sites for what?

Answer 14

actin, tropomyosin, and Ca2+

Question 15

What is a thick filament?

Answer 15

many myosin molecules arranged in parallel

Question 16

Structure of myosin

Answer 16

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

Question 17

Contractile Cycle (actin/myosin)

Answer 17

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

Question 18

Contractile Cycle (troponin, tropomyosin, Ca2+)

Answer 18

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

Question 19

How are contractions in skeletal muscle initated?

Answer 19

by action potentials from motor neurons

Question 20

What are T tubules?

Answer 20

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

Question 21

What is the sarcoplasmic reticulum?

Answer 21

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

Question 22

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

Answer 22

high concentration of Ca2+ in SR, low in cytoplasm

Question 23

Muscle Contraction Full Cycle

Answer 23

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

Question 24

What causes temporal summation?

Answer 24

faster twitching of INDIVIDUAL fibers

Question 25

What causes spatial summation?

Answer 25

an increase in the NUMBER OF UNITS in the contraction

Question 26

What is tetanus?

Answer 26

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

Question 27

Oxidative muscle fibers

Answer 27

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

Question 28

Glycolytic fibers

Answer 28

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

Question 29

Strength exercises increase _____________

Answer 29

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

Question 30

Aerobic exercises enhances ______________

Answer 30

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

Question 31

Slow oxidative fibers

Answer 31

-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

Question 32

Fast oxidative fibers

Answer 32

-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

Question 33

Fast glycolytic fibers

Answer 33

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

Question 34

What effect does CURARE have on muscles?

Answer 34

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

Question 35

Botulism

Answer 35

-food poisoning from ingesting neurotoxin produced by bacterium Clostridium botulinum

Question 36

Effect of botulism

Answer 36

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

Question 37

Botox

Answer 37

-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