18. Types of striated muscles, energy source of muscle functioning, oxygen debt

Question 1

Muscle tissue is constructed from different fibres:

Answer 1

1. fast twitch fibre, capable of powerful contraction and can cover energy needs by means of anaerobic glycolysis: These are „white”, or phasic muscles.
2. slow twitch fibres, capable of more sustained work, and gaining energy only from glucose oxidation. Other names are „red”, or tonic muscle fibres.
3. intermediate types as well. Fibre types are usually intermixed in most of the muscles: the relative percentage of these distinct fibre types determine the type to which a muscle belongs.

Question 2

Muscle types

Answer 2

Question 3

1. ATPase type:
2. SR pump:
3. Junction/fibra:
4. T-system:
5. Muscle AP/neural AP:
6. Contraction time:
7. Metabolism:
8. Fatigue:
9. Fibre length:

Answer 3

1. ATPase type: The basic difference is found in the speed of the ATPase activity
2. SR pump: The activity of the ATPase must be quickly followed by the removal of calcium: this process can also determine the speed of the calcium signal and that of the muscle twitch.
3. Junction/fibra: myoneural junction in phasic fibres provides a 1:1 fibre:nerve connection ratio. A motor nerve fibre splits in many branches 25:1 fibre:nerve ratio is normal.
4. T-system: the development of a T-tubule system can obviously increase contractile speed.
5. Muscle AP/neural AP: Red muscles do not require frequent AP discharges to contract: rare AP signals are also able to cause almost continous contraction.
6. Contraction time: The fastest phasic fibres (e.g. in ocular muscles) are able to contract totally within a few milliseconds.
7. Metabolism: By definition, it is the type of metabolism what separates muscle fibre types.
8. Fatigue: Since red muscle is capable to produce energy continously by oxidative processes, and since lack of oxygen does not normally occur, red muscles practically are not exhaustible.
9. Fibre length: The longer the fibres are in a muscle, the more efficient becomes the mechanical movement.

Question 4

Energy sources of muscle functioning

Answer 4

• ATP
• Creatin-phosphate
• Anaerobic glycolysis
• Oxidative phosphorilation

The process is slow, The ATP resynthesis is slow, but the contraction is also slow, therefore the consumption of ATP is not more than, the production;

Question 5

Energy sources of muscle functioning

• ATP

Answer 5

• Both contraction + relaxation need ATP! ATP concentration of Myocyte :5 mmol/l
• Covers the O2 need for 2-3 sec only

Question 6

Energy sources of muscle functioning

• Creatin-phosphate

Answer 6

• Provides energy reserve for short term, intensive contraction
• Concentration of Myocyte CRP :20 mmol/l
• Energy-supply for 20-30 sec !

Question 7

Energy sources of muscle functioning

• Anaerobic glycolysis

Answer 7

• Energy source in case of outstanding load o Energy source can be:
  
  • glycogen(for fast movement;glycogenolysis)
  • glucose(energy source of prolonged, long term contraction!!).
• If more ATP is used than produced, it leads to oxygen debt
• Accumulated Lactic Acid inhibits contraction at sarcomer level

Question 8

Energy sources of muscle functioning

• Oxidative phosphorilation

Answer 8

• Energy source of very-long term muscle activity (Red-muscles)
• Pyruvate is transformed to AcCoA

Question 9

Oxygen debt

Answer 9

• Muscles, that cover most of their energy needs by anaerobic glycolysis during their active functioning resynthesize previously depleted energy stores after work: in this phase resynthesis is going under aerobic conditions. Muscles show increased oxygen consumption in this period.
• Stores used up by anaerobic mechanisms are resynthesized during rest: muscle can replenish glycogen, creatine-phosphate, etc., by oxygen consumption.