The Muscular System: Lecture 17

Question 1

muscle twitch

Answer 1

smallest muscle contraction; occurs in laboratory not in whole muscles of body

Question 2

phases of twitch

Answer 2

latent period, contraction period, relaxation period

Question 3

myogram

Answer 3

diagram of muscle twitch

Question 4

latent period

Answer 4

time for action potential to propagate across sarcolemma

Question 5

contraction period

Answer 5

repeated crossbridge cycles generate tension

Question 6

relaxation period

Answer 6

calcium ion levels reduced in cytosol by SR pumps; tension diminishes

Question 7

refractory period

Answer 7

begins at onset of latent period and ends at beginning of contraction period
muscle is unable to respond to further stimuli

Question 8

refractory period in smooth and cardiac muscle

Answer 8

periods are as long as their contractions; must FULLY relax before contracting again

Question 9

tension in twitch

Answer 9

varies with several factors: timing and frequency of stimulation, length of fiber at rest, type of muscle fiber

Question 10

wave summation

Answer 10

increase in tension caused by repeated stimulation of muscle fiber by motor neuron
repeated stimulation results in progressively greater tension production
-pumps don’t have time to pump all released calcium ion back before restimulation, leading to cytosol increases with each new stimulation

Question 11

unfused tetanus

Answer 11

stimulated about 50 times per second; fiber partially relaxes between stimuli
tension pulsates (individual twitches remain visible) and increases to about 80% of maximum

Question 12

fused (complete) tetanus

Answer 12

stimulated about 80-100 times per second; fiber does not relax between stimuli
tension stays at nearly 100% of maximum

Question 13

type I fibers

Answer 13

slow twitch
low myosin ATPase activity
extended periods of contraction, sustained oxidative ATP
well developed blood supply

dark meat

Question 14

type II fibers

Answer 14

fast twitch
high myosin ATPase activity
powerful, quickly fatigues, sustained anaerobic ATP
smaller blood supply

light meat

Question 15

Class I

Answer 15

slow oxidative, extensive blood supply
small to intermediate diameter
standing, sitting

Question 16

Class IIa

Answer 16

fast oxidative glycolytic, less extensive blood supply
large diameter
walking, writing

Question 17

Class IIx

Answer 17

fast glycolytic, limited blood supply
intermediate diameter
heavy lifting, sprinting

fastest!

Question 18

motor units

Answer 18

single motor neurons with multiple axon branching
stimulate average 150 fibers
fibers within motor unit are of the same type
activation: recruitment, muscle tone, shivering

Question 19

recruitment

Answer 19

more motor units recruited as required

Question 20

muscle tone

Answer 20

alternating motor unit contractions to maintain muscle tone

Question 21

shivering

Answer 21

random motor unit contractions to generate heat; brief normal hypertonia

Question 22

isotonic concentric contraction

Answer 22

force generated by muscle greater than load, muscle shortens

Question 23

isotonic eccentric contraction

Answer 23

force generated by muscle is less than load, muscle lengthens

Question 24

isometric contraction

Answer 24

length of muscle does no change (static position)

Question 25

muscle shapes

Answer 25

parallel, convergent, pennate, circular (sphincter), spiral, fusiform

Question 26

muscle names

Answer 26

based on: shape/appearance, size, structural characteristics, location, body region, points of attachment, action (flexion or extension)

Question 27

skeletal muscle functions

Answer 27

locomotion, breathing, swallowing initiation, sound modulation, voluntary control over defecation and urination, shivering

Question 28

functional groups of muscles

Answer 28

take cooperation of several individual muscles working group to perform movement; agonists, antagonists, synergists, fixators

Question 29

agonists

Answer 29

prime movers; provide most force for given muscle action

Question 30

antagonists

Answer 30

usually on opposite sides of bones and joint where they meet; opposite action of agonist; allows for modulation and control of agonist movement

Question 31

synergists

Answer 31

aid agonists by supplying supplemental force, minimizing unwanted movement; help stabilize joints; provide for more efficient movement

Question 32

fixators

Answer 32

provide stabilizing force that anchors bone; provides movement efficiency and protection from injury due to unnecessary movements

Question 33

lever system

Answer 33

three components: load or resistance, applied force that moves load, and pivot point (fulcrum)

Question 34

first-class level

Answer 34

fulcrum sits between load and applied force; load moved in opposite direction than applied force

Question 35

second-class lever

Answer 35

fulcrum is at one end of level, applied force is near other end, load is somewhere in between; load moved in same direction as applied force

Question 36

third-class lever

Answer 36

fulcrum and applied force are close to one another at same end of lever; load in near other end, moved in same direction as applied force

Question 37

myoplasticity

Answer 37

changes in muscle structure as result of changes in function related to physical training; changes within muscle fibers, do not involve changes in number of muscle fibers

Question 38

satellite cells

Answer 38

cells that retain mitotic ability, can help repair injured skeletal muscle

Question 39

endurance training

Answer 39

large increase in frequency of motor unit activation and moderate increase in force production (more repetitions with lighter weight) primarily biochemical changes: -increased oxidative enzymes and mitochondria -increased fatigue resistance -more efficient use of fuels -increase in blood vessel network

Question 40

resistance or strength training

Answer 40

moderate increase in frequency of motor unit activation and large increase in force production (fewer repetitions with heavier weight) primarily anatomical changes -number of myofibrils and diameter of muscle fibers increase -decrease endurance

Question 41

hypertrophy

Answer 41

number of myofibrils and diameter of muscle fibers increase

Question 42

atrophy

Answer 42

decrease in number of myofibrils and size of fiber; decrease in oxidative enzymes caused by disuse of muscle