Chapter 3 - Muscle

Question 1

fusiform muscle

Answer 1

fibers running parallel to each other and the central tendon

Question 2

pennate muscle

Answer 2

approach central tendon obliquely

• more muscle fibers
• may be unipennate, bipennate, multipennate

Question 3

muscle fiber

Answer 3

structural unit of muscle

• individual cell with multiple nuclei
• cell is surrounded by connective tissue(endomysium)

Question 4

epimysium

Answer 4

surrounds muscle belly(bunches of fascicles)

- tightly woven collagen bundles highly resistive to stretch

Question 5

perimysium

Answer 5

beneath the epimysium

• surrounds fascicles = bunch of muscle fibers together
• provides conduit for vessels and nerves

Question 6

endomysium

Answer 6

surrounds individual muscle fibers

• partly connected to perimysium
• connections to muscle fibers allow for transmission of force to tendon

Question 7

physiologic cross-sectional area

Answer 7

amount of contractile protein available to generate force

• maximal force production is proportional to the sum of the cross-sectional area of all the fibers
• increase area = increase max force

Question 8

pennation angle

Answer 8

angle of orientation between fiber and tendon

• if greater than zero, then less from the muscle is transmitted to tendon
• can produce greater max force than fusiform muscles of similar size(fit more fibers)

Question 9

elasticity

Answer 9

temporarily stores part of the energy used to create the stretch
- helps prevent injury during maximal elongation

Question 10

viscosity

Answer 10

rate-dependent resistance encountered between surfaces of adjacent fluid-like tissues

Question 11

muscle ideal resting length

Answer 11

length that allows the greatest number of crossbridges and therefore the greatest potential force
- as the sarcomere is lengthened or shortened from resting length, number of potential crossbridges decreases which yields less force production with max muscle activation

Question 12

total length-tension curve

Answer 12

combines the active and passive length-tension curves

• allows for a large range of muscle force over a wide range of muscle length
• at shortened lengths, active force dominates
• passive tension begins to contribute as muscle is stretched beyond resting length
• passive tension dominates at end range of stretch

Question 13

isometric state

Answer 13

there is no movement

• internal torque = external torque
• static state

Question 14

max effort concentric activation

Answer 14

muscle force is inversely proportional to the velocity of muscle shortening

Question 15

max effort eccentric activation

Answer 15

muscle force is directly proportional to the velocity of muscle lengthening

Question 16

motor unit

Answer 16

the alpha motor neuron and all muscle fibers innervated by it

• must first recruit the motor neuron then select rate of sequential activation
• smaller motor neurons are recruited first, then bigger

Question 17

small motoneurons(SO)

Answer 17

twitch responses long in duration and low in amplitude

• slow to respond to a stimuli
• oxidative
• show relatively little fatigue

Question 18

large motoneurons(FF or FG)

Answer 18

twitch responses brief in duration and high in amplitude

• fast and fatigued
• fast and glycolytic

Question 19

intermediate sized motoneurons(FOG)

Answer 19

between slow and fast

• fast and fatigue resistant(FR)
• combined oxidative and glycolytic

Question 20

rate coding

Answer 20

rate of excitation

• muscle fiber twitch last longer than an action potential
• subsequent action potentials can occur prior to the muscle twitch relaxing
• muscle twitches summate and generate more peak force
• motor units activated at high rates are capable of generating greater overall force than the same number of motor units activated at lower rates

Question 21

fused tetanus

Answer 21

the greatest force level that is possible for a muscle fiber

Question 22

muscle fatigue

Answer 22

force will decrease even though the rate of activation remains the same

• nervous system compensates for fatigue by increasing rate of activation or recruiting more motoneurons
• rest periods allow muscle to return to normal performance
• type and intensity of contraction influences rest period needed
  - Rapidly fatigued = secs to minutes
  - slowly fatigued = hours

Question 23

central fatigue

Answer 23

affected by psychological factors such as sense of effort, physiological factors influencing descending pathways
- verbal encouragement may help temporarily

Question 24

peripheral fatigue

Answer 24

neurophysiological factors at level of motoneuron

- gradual reduction in acetylcholine release

Question 25

DOMS

Answer 25

delayed onset muscle soreness - more severe after repeated eccentric exercise - peaks 24-72 hours after exercise - caused by disruption of sarcomeres and damage to cytoskeleton within and around muscle fiber

Question 26

changes in muscle with strength training

Answer 26

neuromuscular system adapts - plasticity - muscle hypertrophy and increased strength(actin and myosin laid down) - eccentric activations produce greater force and more effective in promoting muscle hypertrophy

Question 27

muscle hypertrophy

Answer 27

results from increased protein synthesis within muscle fibers which leads to increased cross-sectional area of the whole muscle - primary cause of increased muscle mass - limited evidence of an increase in number of muscle fibers - greatest in fast twitch(type 2) fibers

Question 28

nervous system adaptation with strength gains

Answer 28

increased area of activity with cortex - increased motor neuron excitability - greater discharge frequency of motor units - decreased neural inhibition - increased muscle strength with imagery training - increased strength in contra-lateral, non-exercised side - strength gains due to more than just hypertrophy

Question 29

isometric exercise

Answer 29

a muscle contraction against a load which is immovable - muscle length remains constant - no joint movement - static or nonmoving contraction - zero speed, body segment does not move

Question 30

isotonic exercise

Answer 30

muscle contracts against a mechanical system which provides a constant load as the body segment moves against this constant load - the load remains the same, but the tension of the muscle changes - dynamic or moving contraction - constant resistance - can be varying speed

Question 31

isokinetic exercise

Answer 31

dynamic contraction - varying resistance - force exerted varies according to physiological and leverage factors(joint angle) - constant speed = speed is controlled so that the body segment moves at the same speed throughout the ROM