Muscle Physiology Flashcards
how much of your bodyweight does skeletal muscle make up?
30% - females
40% - males
what does skeletal muscle impact?
affects metabolic rate, blood glucose, lipid profiles, CVD risk
what can change muscle characteristics?
-use
-age
-disease
-affects metabolic regulation of glucose
-lipids
-mobility
-work
where does the strength come from in muscles?
from bundling
what are fascicles?
bundles of cells surrounded by connective tissue
what makes up a motor unit?
single motor neurone and all the muscle fibres it innervates
what are motor units?
-functional units of Motor control
-the final common pathway for information leaving the CNS
-a muscle can contain hundreds
-a motor unit can contain hundreds of fibres
how does the number of motor units in a muscle differ?
relates to its function
what are the 3 types of motor units present in humans?
FF, FFR and S
what are the classification properties of skeletal muscle?
-mechanical
-histological
-motor neurone properties
-colour
-use
what is mechanical classification?
twitch responses ; speed, force, rate of fatigue
what is histological classification?
metabolic profile ; oxidative, glycolytic, aerobic, anaerobic
Myosin ATPase activity
what are the motor neurone property classifications?
cell body size, axon diameter, synaptic inputs, axon branching
what is the most common simple classification?
speed of contraction and fatigue rate
what are the 3 main types of skeletal muscle?
slow (S or type 1)
fast fatigue resistant (FFR,2a)
fast fatiguing (FF,2b,2x etc)
what does larger twitch lead to?
faster rise
faster fatigue
what does smaller twitch lead to?
slower rise
slower fatigue
what is fatigue?
inability to maintain power output, reversible by rest
what does fatigue lead to?
-reduces force and power
-force, shortening velocity and relaxation rate all decline
-fatigue reduces power
-recover time depends on the nature of the fatigue
-distinc from injury
what is peripheral fatigue?
-within muscle fibres
-failure of excitation contraction coupling, T tubule action potential, SR activation, Ca+ release
-failure of force generated at cross bridges
-failure of ATP generation by depletion of energy stores
what is central fatigue?
-within the nervous system
-loss of excitability of motor cortex
-relfex inputs from metabolic receptors in muscle
-can also include failure of transmission in peripheral nerve and NMJ
what are the sensory inputs of central fatigue?
-central actions of group III and IV muscle afferents
-ergoreceptors and mechanoreceptors and nociceptors
what happens when ATP runs out?
muscle goes into rigor not failure
what causes fatigue?
not due to reductions in ATP
during fatigue ADP, Pi and H+ all increase which changes impair calcium fluxes and impair force delivery at cross bridges
what is produced when ATP breaks down?
ADP + Pi + H+
what happens at the actin myosin cross bridges?
at any ATPase site, accumulation of any produce RHS inhibits function
H+ was once thought to be important
Pi effect is greater than the ADP effect
what are the calcium fluxes?
excitation conraction coupling
ADP, Pi and H+ inhibits Ca2+ release and reuptake into SR. This affects force and speed of shortening and relaxation. H+ also cometes with Ca2+ for troponin binding
what is long duration exercise?
low power, uses type 1 (S units), aerobic, carbohydrate and lipid metabolism
what is moderate duration exercise?
higher power, uses type 1 and 2 (S+FFR), mostly aerobic, fuel mix uses more carbs
what is short duration exercise?
higher power still. All units active (S+FFR+FF), aerobic and anaerobic metabolism. Mostly carbs + includes some inefficient glycolysis
what does training for strength involve?
-multiple repetitions off the same exercise
-small numbers of repetitions of high force contractions
-loads close to max but 10-30 contractions
-can increase muscle mass
what does training for endurance involve?
-uses large numbers of repetitions of Low force contractions
-how many contractions in a 10km run
-can reduce muscle mass
what happens during strength training?
type FF and For muscle fibres hypertrophy
eventually increase in muscle mass and body mass
what happens during endurance training?
there is no demand for increased strength
type S fibres may Hypertrophy but 2 FF fibres shrink
FFF response is variable
reduce body weight by combination a loss of fat mass and loss of FF muscle
what are the stages of strength training?
first 4-6 weeks neural as activation of motor units improves
hypertrophic phase as large motor units grow
connective tissues also strengthen. different growth factors, different rate
how does the number of branches differ?
big axons branch allot
small axons branch less maybe only 15-100
what are small motor units more appropriate for?
precise movement
what do steroids do?
don’t make the connective tissue grow, only makes muscles bigger on the same tendon
what are symptoms of steroid use?
tendon and ligament damage
-oedema
-skin changes and thinking
-irritability and mood changes
-enlarged breasts in men
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what effect does endurance training have on the muscle fibres?
increased mitochondrial biogenesis
increased capillary density
a muscle activity lasting a few seconds (between 2 and 7 seconds) is generated by:
creatine phosphate
