Musculoskletal system

Question 1

How is muscle fibre tension created?

Answer 1

resting sarcomere length (length-tension relationship)

frequency of stimulation (intracellular calcium)

Intensity of stimulation (motor unit recruitment)

Question 2

What does muscle tension depend on?

Answer 2

resting sarcomere length (length-tension relationship)

frequency of stimulation (intracellular calcium)

Intensity of stimulation (motor unit recruitment)

Question 3

What is the length-tension relationship?

Answer 3

Resting sarcomere length relates to how much tension can be produced when muscle fiber contracts.

Due to overlap of thick and thin filaments

Question 4

What happens if there is a long resting sarcomere length?

Answer 4

too much overlap = decreased ability to shorten

Question 5

If there is a large number of fibres in the motor units it is….

Answer 5

postural

Question 6

If there is a small number of fibres in the motor units it is….

Answer 6

fine motor control

Question 7

what is a muscle twitch?

Answer 7

Contraction of single motor unit evoked by single AP

Question 8

what are the three phases of a muscle twitch?

Answer 8

Latent: following stimulation, excitation and coupling occurs

Contraction: cross bridges actively cycle = tension

Relaxation: Ca returned to SR, cross bridge detachment and active sites covered.

Question 9

Out of the extraocular muscle, gastrocnemius and soleus, which muscle has the longest and shortest tension ( max tension vs time)

Answer 9

long = soleus
short = extraocular muscle

Question 10

Treppe

Answer 10

Initial twitches smaller than later twitches, despite SAME stimulus.

Question 11

What are the two underlying physiological mechanisms of treppe?

Answer 11

Elevated resting sarcoplasmic Ca after initial contraction

Heat generated in contractions allows more efficient contractions.

Question 12

What are the two ways for nervous stimulation to enhance muscle contraction

Answer 12

Increased frequency of single motor unit

Increased intensity of stimulation to whole muscle = recruits multiple motor units

Question 13

What is the motor unit principle?

Answer 13

More motor units recruited by increasing stimulus strength

Question 14

how recruitment of multiple motor units increases tension

Answer 14

Neurons have different threshold potentials (threshold for activation is relative to axon size)

Increase intensity –> more nerve fibres fire –> more recruited

Question 15

What is the size principle?

Answer 15

Size principle

order of motor unit recruitment depends on axon diameter

Motor units with small muscle fibers are activated before those with intermediate and large fibers

Question 16

What is the difference between treppe and wave summation?

Answer 16

1. the muscle fully relaxes in treppe (no summation)
   2. successive twitches are produced before the first relaxes

Question 17

isometric

Answer 17

same length, tension increases

Question 18

isotonic

Answer 18

same tension, length changes

Question 19

concentric vs eccentic

Answer 19

concentric = contracting muscle shortening)

eccentric = extending = muscle lengthing

Question 20

Describe Slow Oxidative fibres

Answer 20

slow contraction and myosin ATPase activity
aerobic
high myoglobin content

first to be recruited (motor unit)

red, small diameter and many mitochondria

Question 21

what fibres best suit:
a- endurance running
b- sprinting
c- hitting a baseball

Answer 21

a- slow oxidative
b- fast oxidative
c- fast glycolytic

Question 22

describe fast oxidative fibres

Answer 22

fast contraction and myosin ATPase activity

aerobic and some anaerobic glycolysis

second recruitment

intermediate fatigue

red/pink
many mitochondria
intermediate diamtere

Question 23

describe fast glycolytic fibres.

Answer 23

fast contraction and myosin ATPase

anaerobic

low myoglobin count, third recruitment and fast fatigue

white, large diamter and few mitochondria

Question 24

Where is ATP stored?

Answer 24

Already hydrolysed to prime myosin head

ATP in sarcomplasm

Question 25

two pathways for new ATP

Answer 25

New (how)

Through glycolysis (anaerobic = 2, aerobic)

Creatine phosphate (1CP: 1ATP)

Question 26

peripheral vs central fatigue

Answer 26

Peripheral

Failure to contract even with stimulation (failure in PNS)

Can’t be overcome as due to unresponsive neurons

Central

Psychological fatigue (failure in CNS)

Can be overcome

Question 27

Cachexia

Answer 27

Generalized wasting due to chronic disease

Question 28

Sarcopenia

Answer 28

Atrophy due to aging

Question 29

Satellite cells

Answer 29

Skeletal muscle stem cells at periphery of muscle fibers

Ensure constant number of nuclei per volume in muscle fibers

Question 30

steps in injury repair

Answer 30

Proliferation and migration of satellite cells to necrotic area

Differentiation into myoblasts

Myoblasts fuse into myotubes

Myotubes extend until reach sarcolemma of damaged fiber

New and damaged fibers fuse

Question 31

Describe why heat generated in contractions allows more efficient contractions

Answer 31

because myosin ATPase works at an optimal rate, the ‘warm-up’ produces heat and allowimg to become

Question 32

active vs passive tension?

Answer 32

Active tension is generated by the muscle in response to stimulus, and is the result of actin/myosin crossbridge cycling.

Passive tension is generated by stretch, occurs irrespective of stimulus, and is due to the elastic resistance by noncontractile proteins in the muscle (mainly titin)

Question 33

Skeletal vs smooth muscle stretching.

Answer 33

Skeletal: decrease in active tension and increase in passive