Musculoskletal system Flashcards
week 3
How is muscle fibre tension created?
resting sarcomere length (length-tension relationship)
frequency of stimulation (intracellular calcium)
Intensity of stimulation (motor unit recruitment)
What does muscle tension depend on?
resting sarcomere length (length-tension relationship)
frequency of stimulation (intracellular calcium)
Intensity of stimulation (motor unit recruitment)
What is the length-tension relationship?
Resting sarcomere length relates to how much tension can be produced when muscle fiber contracts.
Due to overlap of thick and thin filaments
What happens if there is a long resting sarcomere length?
too much overlap = decreased ability to shorten
If there is a large number of fibres in the motor units it is….
postural
If there is a small number of fibres in the motor units it is….
fine motor control
what is a muscle twitch?
Contraction of single motor unit evoked by single AP
what are the three phases of a muscle twitch?
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.
Out of the extraocular muscle, gastrocnemius and soleus, which muscle has the longest and shortest tension ( max tension vs time)
long = soleus
short = extraocular muscle
Treppe
Initial twitches smaller than later twitches, despite SAME stimulus.
What are the two underlying physiological mechanisms of treppe?
Elevated resting sarcoplasmic Ca after initial contraction
Heat generated in contractions allows more efficient contractions.
What are the two ways for nervous stimulation to enhance muscle contraction
Increased frequency of single motor unit
Increased intensity of stimulation to whole muscle = recruits multiple motor units
What is the motor unit principle?
More motor units recruited by increasing stimulus strength
how recruitment of multiple motor units increases tension
Neurons have different threshold potentials (threshold for activation is relative to axon size)
Increase intensity –> more nerve fibres fire –> more recruited
What is the size principle?
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
What is the difference between treppe and wave summation?
- the muscle fully relaxes in treppe (no summation)
- successive twitches are produced before the first relaxes
isometric
same length, tension increases
isotonic
same tension, length changes
concentric vs eccentic
concentric = contracting muscle shortening)
eccentric = extending = muscle lengthing
Describe Slow Oxidative fibres
slow contraction and myosin ATPase activity
aerobic
high myoglobin content
first to be recruited (motor unit)
red, small diameter and many mitochondria
what fibres best suit:
a- endurance running
b- sprinting
c- hitting a baseball
a- slow oxidative
b- fast oxidative
c- fast glycolytic
describe fast oxidative fibres
fast contraction and myosin ATPase activity
aerobic and some anaerobic glycolysis
second recruitment
intermediate fatigue
red/pink
many mitochondria
intermediate diamtere
describe fast glycolytic fibres.
fast contraction and myosin ATPase
anaerobic
low myoglobin count, third recruitment and fast fatigue
white, large diamter and few mitochondria
Where is ATP stored?
Already hydrolysed to prime myosin head
ATP in sarcomplasm
two pathways for new ATP
New (how)
Through glycolysis (anaerobic = 2, aerobic)
Creatine phosphate (1CP: 1ATP)
peripheral vs central fatigue
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
Cachexia
Generalized wasting due to chronic disease
Sarcopenia
Atrophy due to aging
Satellite cells
Skeletal muscle stem cells at periphery of muscle fibers
Ensure constant number of nuclei per volume in muscle fibers
steps in injury repair
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
Describe why heat generated in contractions allows more efficient contractions
because myosin ATPase works at an optimal rate, the ‘warm-up’ produces heat and allowimg to become
active vs passive tension?
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)
Skeletal vs smooth muscle stretching.
Skeletal: decrease in active tension and increase in passive
