Energy Supply and Demand

Question 1

What are the THREE major energy sinks of a muscle cell?

Answer 1

1. Na+/K+ ATPase of sarcolemmal membrane
2. Ca2+ ATPase of sarcoplasmic reticular membrane (SERCA)
3. Myosin ATPase of cross-bridges

Question 2

What is the First Law of Thermodynamics?

Answer 2

Energy can be transferred or transformed, but it cannot be created or destroyed.

Question 3

What is the Second Law of Thermodynamics?

Answer 3

Every energy transfer or transformation makes the universe more disordered.

Question 4

What is Entropy?

Answer 4

A quantitative measure of disorder that is proportional to the amount of randomness (symbol, S).

Question 5

What are the THREE sources of work in a cell?

Answer 5

1. Elastic
2. Electric
3. Chemi-osmotic

Question 6

What THREE processes contribute to energy production?

Answer 6

1. Alactic anaerobic processes
2. Lactic processes
3. Oxidative Phosphorylation

Question 7

What are the TWO alactic energy producing processes/reactions?

Answer 7

1. Creatine phosphokinase reaction

2. Adenylate kinase reaction

Question 8

What are the TWO lactic energy producing processes?

Answer 8

1. Glycolysis

2. Glycogenolysis

Question 9

The concentration of ATP stays constant until what percentage of CrP has been converted to Cr and P?

Answer 9

90%

Question 10

How many ATP are produced per splitting of ONE CrP molecule?

Answer 10

1 ATP per CrP

Question 11

If insufficient ATP is present to re-phosphorylate AMP, what two toxic products are formed and what activity do they inhibit?

Answer 11

Inosine monophosphate (IMP) and NH4+
They inhibit muscle contraction (by inhibiting myosin ATPase)

Question 12

What are alactic anaerobic processes of energy generation useful for?

Answer 12

Short intense bursts of exercise

Question 13

How many ATP are produced through glycolysis of 1 Glucose molecule?

Answer 13

nett 2 ATP

Question 14

How many ATP are produced per event of glycogen-derived glycolysis (glycogenolysis)?

Answer 14

nett 3 ATP

Question 15

How many ATP are produced through oxidative phosphorylation of 1 Glucose molecule?

Answer 15

nett 30-32 ATP (depending on which shuttle is used for transport from cytosol to mitochondria).

Question 16

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)

Answer 16

TRUE

Question 17

What is the name of the enzyme used to re-phosphorylate Cr to CrP and is ubiquitous?

Answer 17

Creatine phosphokinase

Question 18

What is the definition of fatigue?

Answer 18

A failure to maintain the required, or expected, power output, leading to reduced muscle performance

Question 19

Name THREE of the causes of muscular fatigue

Answer 19

1. A failure of the ‘will’
2. Depression of the action potential in the motor nerve
3. Synaptic fatigue
4. Accumulation of K+ in the transverse-tubules
5. Diminished release of Ca2+ from sarcoplasmic reticulum
6. Accumulation of inhibitory end-products of metabolic reactions
7. Diminution of the Free Energy of ATP hydrolysis

Question 20

What are the consequences of central fatigue?

Answer 20

Decreased activation from CNS

Decreased number of motor units recruited

Question 21

What are the consequences of peripheral fatigue?

Answer 21

Smaller Ca2+ transient
Reduced Ca2+ sensitivity of the myofilaments
Slower cross-bridge cycling

Question 22

What are THREE of the ways in which fatigue can be studied?

Answer 22

1. Trained athlete
2. Exercising volunteers (sedentary vs. active)
3. Experimental animals
4. Isolated whole muscle preparations
5. Isolated single muscle fibre preparations
6. Contractile proteins in a test-tube

Question 23

What are the THREE muscle fibre types and what are their basic properties?

Answer 23

Type I (slow twitch, no fatigue)
Type IIa (fast twitch, fatigue resistant) 
Type IIb (fast twitch, fatigable)

Question 24

What are the THREE factors which influence the time taken to reach fatigue?

Answer 24

1. Required force
2. Maximal force
3. Intrinsic fatiguability of the muscle

Question 25

Name THREE possible causes of fatigue at the cellular level

Answer 25

1. T-tubule depolarisation (due to accumulation of K+) 2. Decreased signals to open SR Ca2+ channels 3. Decreased Ca2+ release from SR 4. Decreased Ca2+ binding to Troponin-C 5. Decreased cross-bridge attachment 6. Decreased force/power generation by cross-bridges

Question 26

What are the TWO proposed causes of peripheral fatigue?

Answer 26

1. Accumulation of metabolites | 2. Depletion of muscle energy supplies (e.g. glycogen)

Question 27

What occurs with increased frequency of stimulation of muscle cells?

Answer 27

1. Twitch - generates force and has time to decreased back to resting state (0 force). 2. 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. 3. Unfused tetanus - force reaches a steady state with slight fluctuations in force. 4. Fused tetanus - a constant force is produced with no fluctuation.

Question 28

What is the name given to the response of decreased force production when there is little/no change in Ca2+ concentration?

Answer 28

Decreased myofilament calcium sensitivity

Question 29

What type of metabolism dominates in fast-twitch fibres?

Answer 29

Anaerobic metabolism (short bursts of fast/powerful contractions).

Question 30

What type of muscle fibres are rich in capillaries and mitochondria?

Answer 30

Slow twitch fibres (for aerobic metabolism)

Question 31

What THREE metabolic end-products can cause fatigue?

Answer 31

1. NH4+ 2. Pi 3. pHi

Question 32

When there is an increase in the concentration of inorganic phosphate (Pi) what effect does this have on the force of contraction of muscles?

Answer 32

Decreases the force of contraction

Question 33

What are the THREE main sites of action of Pi to cause fatigue?

Answer 33

1. 'Direct' - actomyosin cross-bridges 2. SR Ca2+ release and Ca2+ force dependence 3. Reduction in Free Energy from ATP hydrolysis (∆G ATP)

Question 34

Does an increase in pHi increase or decrease the force of contraction?

Answer 34

Increases force of contraction

Question 35

What is ∆G ATP?

Answer 35

The 'free energy' of ATP hydrolysis (-ve value because it is releasing energy)

Question 36

What are the FOUR targets in the body for training to reduce fatigue?

Answer 36

1. Heart - cardiac output 2. Circulation - plasma volume and skin blood flow 3. Blood vessels - capillaries 4. Myocytes - enzyme adaptation and fuel source