Skeletal muscle integration (wk5)

Question 1

Identify the review sequence of events enabling muscle contractions:

Answer 1

Neuron synapse
Myelin sheath
T-Tubules
Acetylcholine
Plasma membrane
Sarcoplasmic reticulum
Calcium 2+ ions (Cas2+)
Myosin
Actin
ATP
ADP
Mitochondria

Question 2

Describe the review sequence components
-Neuron synapse, myelin sheath and T-Tubules

Answer 2

A – Neuron synapse -> Electrical impulses carried along neurons are responsible for all voluntary movement in skeletal muscle
B – Myelin sheath -> Many layers of myelin are wrapped around each neuron as insulation. This speeds up the transfer of electrical signals
C – T-Tubules -> These invaginations of the muscle cell membrane propagate signals throughout the entire muscle cell

Question 3

Describe the review sequence components
-Acetylcholine, plasma membrane, sarcoplasmic reticulum

Answer 3

D – Acetylcholine (Ach) -> This NT allows motor neurons to signal muscle cells. Botulism causes paralysis by blocking Ach release
E – Plasma membrane -> This membrane covers muscle cells. Each cell contains many myofibrils, which are a unit of muscle contraction
F – Sarcoplasmic reticulum -> This membrane uses calcium channels and pumps to control the level of calcium ions inside the muscle cell

Question 4

Describe the review sequence components
-Calcium 2+ ions, myosin and actin

Answer 4

G – Calcium 2+ ion (Cas2+) -> Calcium ions are important signals molecules. They bind to troponin in muscle cells, which is required for contraction
H – Myosin (thick filament) -> Myosin heads pull actin along myosin with the energy gained from breaking down ATP (only occurs when Cas2+ is present)
I – Actin (thin filament) -> Before actin can interact with myosin, a Ca2+ mediated troponin-tropomyosin shift mist uncover actin binding sites

Question 5

Describe the review sequence components
-ATP, ADP and mitochondria

Answer 5

J – ATP -> ATP fuels the movement of actin along myosin, and helps pump Ca2+ back into the sarcoplasmic reticulum
K – ADP -> When ATP is used to facilitate a reaction, it is broken down into ADP and recycled back into ATP in the mitochondria
L – Mitochondria -> Mitochondria generate the energy needed for almost all bodily functions in the form of the molecule ATP

Question 6

Discuss mechanisms inducing divergent muscle adaptations between strength and endurance athletes
-Motor unit level

Answer 6

• Endurance training -> Drop
• Strength training -> Increase. They are faster and so there is more generation of the muscles to produce a force, creating a larger central motor unit. Discharging motor units faster with strength training.
• Increase in strength in the 1st month due to EMG changes, but over time the EMG activity drops. Also, the max contraction and the muscle mass increases as well. EMG charge was the same with trained and untrained individuals, meaning that the nervous system is not relied upon but the muscle itself. They measured the propagation of the action potential and firing rate. They saw that due to the larger muscle mass, they have greater depolarisation upon the muscle fibre membrane.
• Late adaptation – fatigue of muscles Post training, delays, meaning that the contraction can be held for longer and faster. Endurance athletes can hold loads for a long rate and have a lower discharge rate which delays fatigue.

Question 7

Discuss mechanisms inducing divergent muscle adaptations between strength and endurance athletes
-Excitation-contraction coupling

Answer 7

Excitation-contraction coupling:
* Neuromuscular junction -> Increase in contractions which increases speed of the neuromuscular junction
* Strength/ endurance -> low forces – both groups have an increase in electrical conduction velocity. More presence in type 1 fibres
* Strength/ endurance -> Increased load = increased presence in type 1 fibres with an increased presence in type 2 fibres in the strength group
* Rate of twitch development – how fast the twitch is produced

Question 8

Discuss mechanisms inducing divergent muscle adaptations between strength and endurance athletes
-Muscle fibre level (MFCV, endurance athletes and max rate of twitch development)

Answer 8

• Muscle fibre conduction-velocity (MFCV). This is the velocity at which muscle fibres transmit action potentials prior to muscle contraction. Primarily, action potentials generated in end-plates are propagated towards the muscle fibre terminal.
• Endurance athletes will have a drop in conduction velocity of their muscles but will be able to hold the contraction for longer with training. They will use their central and muscle mechanisms to do this with the help of sodium and potassium.
• Max rate of twitch development is higher in strength trained athletes than endurance athletes. This is because they are trained in having quick and powerful movements. Endurance athletes have a much slower and longer/relaxed phase in the max rate of twitch development – they are fatigue resistant as well.

Question 9

Discuss mechanisms inducing divergent muscle adaptations between strength and endurance athletes
-Muscle fibre level (Whole muscle changes, sedentary lifestyle and fibre type changes)

Answer 9

• Whole muscle changes -> strength athletes have the largest muscle mass but not too much heavier as it means that they become slower
• Sedentary -> Collection of different fibre types. Endurance athletes -> Mitochondria around the type 1 fibres and have irrigation due to the larger blood flow. Power athletes -> Greater size of type 2x fibres. Strength -> Mix of type 1 and type 2a. Type 2 has largest hypertrophy potential.
• Fibre type changes -> Trained person will last longer in terms of contraction compared to an untrained person, even though they will have the same amount of force output. Power athletes -> lots of force produced in a very short time. Strength -> overcome power athlete in terms of contraction time.

Question 10

Discuss mechanisms inducing divergent muscle adaptations between strength and endurance athletes
-Molecular level (detail and endurance phenotype)

Answer 10

• Lose muscle mass as an adult -> see if exercise improves hypertrophy -> TORC-1 would be measured

1. Endurance phenotype characterized by;
   * Increased mitochondrial mass -> generate more endurance capacity
   * Increased oxidative enzymes
   * Decreased glycolytic enzymes
   * Increased slow contractile and regulatory proteins
   * Decrease in fast-fibre area
   * AVMK -> Can generate more mitochondria

Question 11

Discuss mechanisms inducing divergent muscle adaptations between strength and endurance athletes
-Molecular level (high resistance training)

Answer 11

2. High resistance training;
   * Increase in wet mass
   * Increase in fibre cross-sectional area
   * Increase in protein content
   * Increase in RNA content -> increase muscle hypertrophy from RNA (m TOR)