week 3: 10.6 skeletal muscles produce increased tension by recruiting additional motor units

Question 1

why does regulating the number of stimulated muscle fibers control the tension of a skeletal muscle

Answer 1

the amount of tension produced by a muscle as a whole is the sum of the tensions generated by its individual muscle fibers as they are pulling together

Question 2

isotonic contractions

Answer 2

muscle length changes with constant force
-tension increases and the skeletal muscle length changes
-lifting object, running

Question 3

isometric contractions

Answer 3

length of the muscle does not change with a constant force
-muscle as a whole does not change length, tension produced never exeeds the load
e.g carrying bag, holding up head

Question 4

concentric contraction

Answer 4

muscle shortens

Question 5

eccentric contraction

Answer 5

muscle lengthens

Question 6

motor unit

Answer 6

motor neuron and all the muscle fibers it controls

Question 7

what does the size of a motor unit indicate

Answer 7

how fine or precise a movement can be

Question 8

smaller motor units, 4-6 muscle fibers

Answer 8

precise control
eyes and fingers

Question 9

large motor units

Answer 9

1000-2000 muscle fibers
precise control is not urgent
weight baring muscles of hips and thighs

Question 10

why does the direction of pull exerted on the tendon not change when the number of activated motor units change

Answer 10

muscle fibers of each motor unit are intermingled

Question 11

fasciculation

Answer 11

involuntary
synchronous contraction of a motor unit

Question 12

recrutiment

Answer 12

smooth but steady increase in muscular tension produced by increasing the number of active motor units

Question 13

when does peak tension occur

Answer 13

all motor units in the muscle contract in a state of complete tetanus

Question 14

during a sustained contraction, motor units

Answer 14

activated on a rotating basis so some of them are resting and recovering while other are actively contracting

Question 15

advantage of asynchronous motor unit summation

Answer 15

each motor unit can recover before it is stimulated again

Question 16

muscle tone

Answer 16

some motor units are always active even when the entire muscle is not contracting
contractions do not produce enough tension to cause movement however they do tense and firm the muscle

Question 17

why can skeletal muscles act as shock absorbers that cushion sudden impact

Answer 17

elastic nature of muscles and tendons

Question 18

isotonic concentric contraction

Answer 18

muscle tension exceeds load and muscle shortens

Question 19

isotonic eccentric contractions

Answer 19

peak tension developed is less than the load
muscle elongates due to the contraction of another muscle or the pull of gravity

Question 20

movement of muscle fibers during isometric contraction

Answer 20

muscle as a whole does not shorten but the individual muscle fibers shorten as connective tissues stretch

Question 21

why can you lift a light object more rapidly than a heavy object

Answer 21

load and speed of contraction are inversely related

Question 22

why does it take longer more movement to begin if a load is heavier

Answer 22

muscle tension increases gradually
muscle tension must exceed load before shortening can occur

Question 23

muscle relaxation- elastic forces

Answer 23

contraction ends, initial energy used in stretching tendons and distorting intracellular organelles is recovered as they recoil to their original dimensions
elasticity gradually helps return the muscle fibers in the muscle to their optimal resting length

Question 24

muscle relaxation- opposing muscle contraction

Answer 24

contraction of opposing muscles can return muscle to original resting length

Question 25

muscle relaxation-gravity

Answer 25

gravity may assist opposing muscle groups in quickly returning a muscle to its resting length after a contraction