Muscle Physiology

Question 1

how much of your bodyweight does skeletal muscle make up?

Answer 1

30% - females
40% - males

Question 2

what does skeletal muscle impact?

Answer 2

affects metabolic rate, blood glucose, lipid profiles, CVD risk

Question 3

what can change muscle characteristics?

Answer 3

-use
-age
-disease
-affects metabolic regulation of glucose
-lipids
-mobility
-work

Question 4

where does the strength come from in muscles?

Answer 4

from bundling

Question 5

what are fascicles?

Answer 5

bundles of cells surrounded by connective tissue

Question 6

what makes up a motor unit?

Answer 6

single motor neurone and all the muscle fibres it innervates

Question 7

what are motor units?

Answer 7

-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

Question 8

how does the number of motor units in a muscle differ?

Answer 8

relates to its function

Question 9

what are the 3 types of motor units present in humans?

Answer 9

FF, FFR and S

Question 10

what are the classification properties of skeletal muscle?

Answer 10

-mechanical
-histological
-motor neurone properties
-colour
-use

Question 11

what is mechanical classification?

Answer 11

twitch responses ; speed, force, rate of fatigue

Question 12

what is histological classification?

Answer 12

metabolic profile ; oxidative, glycolytic, aerobic, anaerobic
Myosin ATPase activity

Question 13

what are the motor neurone property classifications?

Answer 13

cell body size, axon diameter, synaptic inputs, axon branching

Question 14

what is the most common simple classification?

Answer 14

speed of contraction and fatigue rate

Question 15

what are the 3 main types of skeletal muscle?

Answer 15

slow (S or type 1)
fast fatigue resistant (FFR,2a)
fast fatiguing (FF,2b,2x etc)

Question 16

what does larger twitch lead to?

Answer 16

faster rise
faster fatigue

Question 17

what does smaller twitch lead to?

Answer 17

slower rise
slower fatigue

Question 18

what is fatigue?

Answer 18

inability to maintain power output, reversible by rest

Question 19

what does fatigue lead to?

Answer 19

-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

Question 20

what is peripheral fatigue?

Answer 20

-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

Question 21

what is central fatigue?

Answer 21

-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

Question 22

what are the sensory inputs of central fatigue?

Answer 22

-central actions of group III and IV muscle afferents
-ergoreceptors and mechanoreceptors and nociceptors

Question 23

what happens when ATP runs out?

Answer 23

muscle goes into rigor not failure

Question 23

what causes fatigue?

Answer 23

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

Question 24

what is produced when ATP breaks down?

Answer 24

ADP + Pi + H+

Question 25

what happens at the actin myosin cross bridges?

Answer 25

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

Question 26

what are the calcium fluxes?

Answer 26

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

Question 27

what is long duration exercise?

Answer 27

low power, uses type 1 (S units), aerobic, carbohydrate and lipid metabolism

Question 28

what is moderate duration exercise?

Answer 28

higher power, uses type 1 and 2 (S+FFR), mostly aerobic, fuel mix uses more carbs

Question 29

what is short duration exercise?

Answer 29

higher power still. All units active (S+FFR+FF), aerobic and anaerobic metabolism. Mostly carbs + includes some inefficient glycolysis

Question 30

what does training for strength involve?

Answer 30

-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

Question 31

what does training for endurance involve?

Answer 31

-uses large numbers of repetitions of Low force contractions
-how many contractions in a 10km run
-can reduce muscle mass

Question 32

what happens during strength training?

Answer 32

type FF and For muscle fibres hypertrophy
eventually increase in muscle mass and body mass

Question 32

what happens during endurance training?

Answer 32

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

Question 33

what are the stages of strength training?

Answer 33

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

Question 34

how does the number of branches differ?

Answer 34

big axons branch allot
small axons branch less maybe only 15-100

Question 35

what are small motor units more appropriate for?

Answer 35

precise movement

Question 36

what do steroids do?

Answer 36

don’t make the connective tissue grow, only makes muscles bigger on the same tendon

Question 37

what are symptoms of steroid use?

Answer 37

tendon and ligament damage
-oedema
-skin changes and thinking
-irritability and mood changes
-enlarged breasts in men
-

Question 38

what effect does endurance training have on the muscle fibres?

Answer 38

increased mitochondrial biogenesis
increased capillary density

Question 39

a muscle activity lasting a few seconds (between 2 and 7 seconds) is generated by:

Answer 39

creatine phosphate