Energy Supply and Demand Flashcards
What are the THREE major energy sinks of a muscle cell?
- Na+/K+ ATPase of sarcolemmal membrane
- Ca2+ ATPase of sarcoplasmic reticular membrane (SERCA)
- Myosin ATPase of cross-bridges
What is the First Law of Thermodynamics?
Energy can be transferred or transformed, but it cannot be created or destroyed.
What is the Second Law of Thermodynamics?
Every energy transfer or transformation makes the universe more disordered.
What is Entropy?
A quantitative measure of disorder that is proportional to the amount of randomness (symbol, S).
What are the THREE sources of work in a cell?
- Elastic
- Electric
- Chemi-osmotic
What THREE processes contribute to energy production?
- Alactic anaerobic processes
- Lactic processes
- Oxidative Phosphorylation
What are the TWO alactic energy producing processes/reactions?
- Creatine phosphokinase reaction
2. Adenylate kinase reaction
What are the TWO lactic energy producing processes?
- Glycolysis
2. Glycogenolysis
The concentration of ATP stays constant until what percentage of CrP has been converted to Cr and P?
90%
How many ATP are produced per splitting of ONE CrP molecule?
1 ATP per CrP
If insufficient ATP is present to re-phosphorylate AMP, what two toxic products are formed and what activity do they inhibit?
Inosine monophosphate (IMP) and NH4+ They inhibit muscle contraction (by inhibiting myosin ATPase)
What are alactic anaerobic processes of energy generation useful for?
Short intense bursts of exercise
How many ATP are produced through glycolysis of 1 Glucose molecule?
nett 2 ATP
How many ATP are produced per event of glycogen-derived glycolysis (glycogenolysis)?
nett 3 ATP
How many ATP are produced through oxidative phosphorylation of 1 Glucose molecule?
nett 30-32 ATP (depending on which shuttle is used for transport from cytosol to mitochondria).
Cr is re-phosphorylated in the mitochondria to CrP by ATP produced by oxidative phosphorylation so that it can act as a ‘shuttle’ for Pi (TRUE or FALSE)
TRUE
What is the name of the enzyme used to re-phosphorylate Cr to CrP and is ubiquitous?
Creatine phosphokinase
What is the definition of fatigue?
A failure to maintain the required, or expected, power output, leading to reduced muscle performance
Name THREE of the causes of muscular fatigue
- A failure of the ‘will’
- Depression of the action potential in the motor nerve
- Synaptic fatigue
- Accumulation of K+ in the transverse-tubules
- Diminished release of Ca2+ from sarcoplasmic reticulum
- Accumulation of inhibitory end-products of metabolic reactions
- Diminution of the Free Energy of ATP hydrolysis
What are the consequences of central fatigue?
Decreased activation from CNS
Decreased number of motor units recruited
What are the consequences of peripheral fatigue?
Smaller Ca2+ transient
Reduced Ca2+ sensitivity of the myofilaments
Slower cross-bridge cycling
What are THREE of the ways in which fatigue can be studied?
- Trained athlete
- Exercising volunteers (sedentary vs. active)
- Experimental animals
- Isolated whole muscle preparations
- Isolated single muscle fibre preparations
- Contractile proteins in a test-tube
What are the THREE muscle fibre types and what are their basic properties?
Type I (slow twitch, no fatigue) Type IIa (fast twitch, fatigue resistant) Type IIb (fast twitch, fatigable)
What are the THREE factors which influence the time taken to reach fatigue?
- Required force
- Maximal force
- Intrinsic fatiguability of the muscle
Name THREE possible causes of fatigue at the cellular level
- T-tubule depolarisation (due to accumulation of K+)
- Decreased signals to open SR Ca2+ channels
- Decreased Ca2+ release from SR
- Decreased Ca2+ binding to Troponin-C
- Decreased cross-bridge attachment
- Decreased force/power generation by cross-bridges
What are the TWO proposed causes of peripheral fatigue?
- Accumulation of metabolites
2. Depletion of muscle energy supplies (e.g. glycogen)
What occurs with increased frequency of stimulation of muscle cells?
- Twitch - generates force and has time to decreased back to resting state (0 force).
- Summation - there is not quite enough time for the force to decrease back to resting so there is a slight increase in force generated for each stimulation.
- Unfused tetanus - force reaches a steady state with slight fluctuations in force.
- Fused tetanus - a constant force is produced with no fluctuation.
What is the name given to the response of decreased force production when there is little/no change in Ca2+ concentration?
Decreased myofilament calcium sensitivity
What type of metabolism dominates in fast-twitch fibres?
Anaerobic metabolism (short bursts of fast/powerful contractions).
What type of muscle fibres are rich in capillaries and mitochondria?
Slow twitch fibres (for aerobic metabolism)
What THREE metabolic end-products can cause fatigue?
- NH4+
- Pi
- pHi
When there is an increase in the concentration of inorganic phosphate (Pi) what effect does this have on the force of contraction of muscles?
Decreases the force of contraction
What are the THREE main sites of action of Pi to cause fatigue?
- ‘Direct’ - actomyosin cross-bridges
- SR Ca2+ release and Ca2+ force dependence
- Reduction in Free Energy from ATP hydrolysis (∆G ATP)
Does an increase in pHi increase or decrease the force of contraction?
Increases force of contraction
What is ∆G ATP?
The ‘free energy’ of ATP hydrolysis (-ve value because it is releasing energy)
What are the FOUR targets in the body for training to reduce fatigue?
- Heart - cardiac output
- Circulation - plasma volume and skin blood flow
- Blood vessels - capillaries
- Myocytes - enzyme adaptation and fuel source
