Muscle -WK2 ( Ch 3)

Question 1

Describe the structural organization of skeletal muscle.

Answer 1

-muscles are made up of individual muscle fibers ( 10-100 micrometers x 1-50 cm)

• each muscle fiber is a muscle cell with multiple nuceli
• contractile proteins include action and myosin; non-contractile elements include connective tissue and titin, and desmin
• each muscle is covered in connective tissue called epimysium, fascicles of muscle fibers are covered in perimysium, and individual muscle fibers are covered in endomysium. Myofibrils within muscle fibers contain contractile proteins.

Question 2

What is the difference between series and parallel elastic components, and what is their significance within muscle tissue ?

Answer 2

• generates a spring like resistance within the muscle
• series: tissues attached in series to contractile proteins ( tendon, titin)
• parallel: tissues attached in parallel to contractile proteins

Question 3

Explain the sliding filament hypothesis.

Answer 3

• In the sliding filament hypothesis actin hinges on myosin and brings the sarcomeres z-disks together.

Question 4

How does a motor unit work ?

Answer 4

• motor unit= alpha motor neuron and muscle it activates
• excitation of alpha-motor unit can come from cortical descending neurons, spinal interneurons, afferent sensory neurons

Question 5

Explain each muscle fiber type including their characteristics, their different names, and examples of muscles for each.

Answer 5

Type I (S)- slow twitch, slow oxidative, tonic ( continuous tension), red ( postural muscles)
Type IIa (FR)- Intermediate, fast fatigue resistant
Type IIb or IIx ( FF)- fast twitch, fast- glycolytic, phasic, white ( fewer mitochondria )

Question 6

How does recruitment differ from rate coding ?

Answer 6

recruitment: activation of motor units

rate coding: modulation of sequential action-potentials after recruitment

Question 7

Explain Henneman’s Size Principle.

Answer 7

smaller and slower motor units are recruited first, faster-bigger recruited last.

Question 8

Why are EMG readings disturbed during motion ?

Answer 8

due to the electrical activation of motor units
isometric contractions provide most accurate EMG

Question 9

How do physiological cross sectional area and pennation angle affect muscle force production ?

Answer 9

• cross- sectional area= amount of active proteins available to generate active force; determined by dividing muscle volume by length
• “maximal force potential is proportional to the sum of the cross-sectional are of all it’s fibers”
• pennation angle refers to the angle at whcih a msucle pulls on its tendon
• a penn. angle of 0 degrees= 100% force production; 30 degrees= 86% force production

Question 10

Explain the difference between isometric, concentric, and eccentric muscle activation.

Answer 10

Isometric: no movement during contraction
Concentric: muscle shortening
Eccentric: muscle lengethening

Question 11

How does recruitment of motor units differ between concentric and eccentric activation ?

Answer 11

• eccentric, large force generated X cross bridge, less motor units to produce same amount of force as a concentric contraction.

Question 12

Explain the difference between isotonic, plyometric, and isokinetic

Answer 12

isotonic: equal tension, doing eccentric and concentric movements
plyometrics: muscle tendon complex stretched before a forceful contraction
isokinetic: same speed throughout ROM; more a description of joint motion

Question 13

What does reciprocal inhibition mean ?

Answer 13

relaxation of antagonist during contraction of agonist

Question 14

Explain the passive, active, and total-length tension curves.

Answer 14

Passive: passive tissues are slack until stretched to critical length at which point the tissues become taut
Active: tension developed by active tissues; cross-bridge formation
Total length: combination of active force and passive tension

Question 15

How do cross-bridges in the sarcomere affect active tension ?

Answer 15

the resting length of a muscle fiber or sarcomere is the length that allows the greatest number of cross bridges to be formed

the resting length is where the muscle can produce the most force

Question 16

Compare active and passive insufficiency.

Answer 16

Passive: muscle stretched at origin and insertion limiting antagonist
Active: decreased force production at the end of ROM

Question 17

How does tenodesis differ from passive insufficiency ?

Answer 17

tendodesis= passive tension of muscles over two joints may produce passive movements of those joints

Ex. finger flexing during wrist extension

Question 18

What is the significance of a muscle’s resting length ?

Answer 18

the resting length of a muscle fiber or sarcomere is the length that allows the greatest number of cross bridges to be formed

therefore the most potential for force production

Question 19

Describe the difference in concentric and eccentric activation as it relates to the force velocity relationship.

Answer 19

Con-: muscle contracts at higher velocity with no load; if load increases then velocity decreases; increased velocity, less cross bridge linkage

Ecc-: increased load to faster eccentric contraction

Question 20

How does hypertrophy of muscle occur during strength training ? How long does this usually take ?

Answer 20

increased protein synthesis that leads to an increased cross sectional area of the muscle worked

sarcomeres added in parallel

6wks, best in Type II fibers

Question 21

How does muscle fatigue relate to… force production, recruitment of motor units, muscle fiber type, type of muscle activation

Answer 21

force production: decreased force production
recruitment of motor units: increased
muscle fiber type: Type I; fatigue by low intensity, longer rest
Type II; fatigued by high intensity, shorter rest
type of muscle activation: concentric: more fatigue
eccentric: less fatigue

Question 22

Explain DOMS as if you were explaining it to a patient.

Answer 22

microscopic intra-muscular tears.

Question 23

What happens to muscle with reduced use and or immobilized in a shortened position ?

Answer 23

• atrophy and weakness
• reduced sarcomeres, thickening of peri- and endomysium, more connective tissue. stiffness

Question 24

What can we do as therapists to mitigate the effects of disuse from immobilization ?

Answer 24

-encourage and advocate for movement and strength training

• early remobilzation

Question 25

What is senile sarcopenia ? What changes occur in tissue because of it ?

Answer 25

loss of muscle mass as a result of ageing

decreased number of fibers; decreased fiber size esp. type II; loss of alpha motor neurons

no alteration to plasticity of neuromuscular system.