Skeletal muscle metabolism

Question 1

Key features to metabolic demands of skeletal muscle

Answer 1

1. Adaptability: can switch between metabolic pathways based on activity demands
2. Rapid ATP production: skeletal muscle can quickly produce ATP to meet immediate energy needs when switch to intense activities from rest
3. Fatigue: metabolic by-products can lead to muscle fatigue during intense activities

Question 2

3 main energy pools for skeletal muscle

Answer 2

1. ATP-creatine phosphate (immediate)
2. Glycolytic (fast and short term)
3. Oxidative (slow and long term)

Question 3

ATP-Creatine phosphate

Answer 3

• ATP binds with creatine to form creatine phosphate and ADP in relaxed muscles
• Reverse reaction: Creatine kinase takes P from creatine phosphate and binds it to ADP to make ATP in active muscles
• Provides energy for short, high-intensity bursts (less than 10secs)
• Rapid regeneration of ATP from creatine phosphate

Question 4

Creatinine

Answer 4

a by-product of creatine and used as an indicator for kidney function

Question 5

Glycolytic pathway of skeletal muscle

Answer 5

Anaerobic pathway
- Lactate produced. Can cause muscle fatigue and metabolic acidosis

• Provide energy for moderate to high-intensity activities (up to 2 mins)

Question 6

Oxidative pathway for skeletal muscle energy (uses glucose or FFA

Answer 6

Aerobic pathway
- Relies on TCA and the ETC
- requires oxygen
- muscles use myoglobin (oxygen-binding protein)

• Predominantly used in prolonged, low-intensity activities

Question 7

Fiber types and metaoblism

Answer 7

1. Type I (slow twitch; oxidative)
2. Type IIA (fast-twitch; oxidative)
3. Type IIB (fast twitch; glycolytic)

Question 8

Type I fiber

Answer 8

• slow twitch
• aerobic, high endurance, red (due to heme group in myoglobin)
• High mitochondrial content, high fat content, low glycogen content

Question 9

Type IIA fiber

Answer 9

• fast-twitch
• oxidative
• mix of aerobic and anaerobic, moderate endurance
• Intermediate mitochondria, fat, and glycogen content

Question 10

Type IIB fiber

Answer 10

• Fast twitch
• glycolytic
• predominantly anaerobic, low endurance, white
• Low mitochondrial and fat content, high glycogen content

Question 11

Fast vs. slow twitch

Answer 11

Refers to speed of contraction, related to Vmax

Question 12

Fatigability of different types of motor units

Answer 12

Each motor unit will only have 1 muscle type

• Fast-twitch fiber- generates more force, but for less time
• Slow-twitch fiber- generates less force, but for more time

Question 13

What is causing this fatigue in muscle fibers?

Answer 13

Lactic acid, pH, and other unknown factors

Question 14

Fiber type varies from muscle to muscle

Answer 14

• Muscle type variance: Each muscle throughout the body will have different percentages of each muscle type
• Different breeds will also show different muscle fiber types
  Ex. Horse for endurance: will have more slow twitch muscle fibers

Question 15

Skeletal muscle: adaptation

Answer 15

1. sarcomeres increasing as animal grows
2. skeletal muscle adapts for what activity it is conducting

Question 16

Sarcomere growth of skeletal muscle

Answer 16

1. hypertrophy
2. hyperplasia

Question 17

Hypertrophy in skeletal muscle

Answer 17

increases actin/myosin in parallel to increase force (not adding more muscle fibers, but instead adding sarcomeres in parallel)

Question 18

Hyperplasia in skeletal muscle

Answer 18

rare, requires satellite cells with intact endomysium for successful repair after injury

Question 19

Skeletal muscle adaptations based on type of activity

Answer 19

• Learning/coordination: increases rate and accuracy of motor skills
• Endurance (submaximal, sustained efforts): increased oxidative capacity in all involved motor units with limited cellular hypertrophy
• Strength (brief, maximal efforts): hypertrophy and enhanced glycolytic capacity of motor units employed