WEEK THIRTEEN - MUSCLE METABOLISM AND TYPES

Question 1

Describe the different mechanisms of ATP production for skeletal muscle during exercise of different intensities

Answer 1

ATP production for immediate energy
- oxygen briefly supplied by myoglobin within muscle fibres [rapidly depleted]
- muscles meet most ATP glands by borrowing phosphate groups from other molecules and transferring to ADP until respiratory/cardiovascular systems catch up with O2 demand
- TWO enzymes control phosphate transfers

1. myokinase
   [transfers phosphate from one ADP to another converting to ATP]
2. creatine kinase

Direct phosphorylation = Creatine phosphate + ADP → ATP + creatinine

[obtains phosphate from phosphate storage molecule - creatine phosphate]
- fast acting system that maintains ATP level while other ATP mechanisms are activated

ATP production for short term energy
glycolysis
-No O2 needed [anaerobic]
-Glucose comes from EITHER bloodstream [insulin needed to allow glucose entry into bloodstream from liver] OR glycogen stored in muscle cells
-Waste product = lactic acid - send into bloodstream/kidneys to excrete
-Lasts ~ 45 seconds
- generate 2 ATP for every 1 glucose molecule

ATP production for long term energy
Aerobic respiration produces ~ 36 ATP per glucose

• After ~ 40 sec the respiratory and cardiovascular systems ‘catch up’ and deliver oxygen to muscles
• Efficient means of meeting the ATP demands of prolonged exercise
• Little H+ accumulates under these steady state conditions which are below the anaerobic/ lactate threshold
• Depletion of glycogen and blood glucose + loss of fluid and electrolytes through sweating = limits endurance/performance

Question 2

Discuss factors that affect muscular strength

Answer 2

1. muscle size [hypertrophy]
   - A muscle can exert tension of 3-4kg per cm2 of cross sectional area
   - Pennate STRONGER&raquo_space;parallel STRONGER&raquo_space; circular
2. size of motor units [individual motor neuron and all of the muscle fibers that it innervates ]
   - Larger the motor unit = stronger the contraction
   - Slow twitch = generally SMALLER in fibre diameter = less force - however very resistant to fatigue [increased mitochondria and capillary density]
   - Fast glycolytic fibres are generally BIGGER in diameter + have more myofibrils in them = generates more force [not fatigue resistant]
3. motor unit summation
   - Faster firing rates of motor unit =summation of AP = greater tension produced by muscle
   - Length - tension relationship - a muscle resting at optimal length = better prepared to contract more forcefully > than a muscle that is excessively contracted/stretched
   - Force-velocity relationship - increased velocity of contraction equals decreased levels of strength

Question 3

Describe the structural and physiological differences between cardiac muscle, smooth muscle and skeletal muscle.

Answer 3

Smooth + skeletal muscle found all over body

Smooth muscle fibres = fusiform [tapered ends]
[internal organs/viscera]

Skeletal muscle fibres = significantly longer and bigger in diameter than smooth/cardiac fibres

skeletal
cell length - 100 μm - 12cm
cell diameter - 50-100 μm
CT : endomysium, perimysium, epimysium

cardiac
cell length - 50-100 μm
cell diameter - 10-20 μm
CT: endomysium

smooth
muscle length - 30-200 μm
cell diameter - 5-10 μm
CT: endomysium