Week 3 Physiology Flashcards
Sarcomere
- Functional unit of striated muscle, unit of muscle contraction
- Made up of striations, nucleus, skeletal muscle
Sarcomere molecular components
- M line
- Actin (thin) filament
- Myosin (thick) filament
- I band
- H band
M line
Represents the middle of the sarcomere, does not move
Actin (thin) filament
- Attached to the Z line and will move towards the M line with each contraction
- Made up of actin
- Has myosin binding sites where myosin heads can attach
Regulatory proteins: - Tropomyosin - long, thin protein that weaves around the actin filament, it covers the binding sites when the muscle is at rest - prevents actin from binding with myosin
- Troponin - blue molecule with three binding sites, separate ones for tropomyosin, actin, calcium ions
Myosin (thick) filament
- Attached to the M line
- Made up of myosin
- Has a series of myosin heads that project at the end of the filament and myosin tails
- Have myosin-actin binding sites
I band
Region that contains the actin filament
H band
Region with myosin present, including where myosin overlaps actin
Sliding filament theory
- Calcium channels on the sarcoplasmic reticulum (SR) open, calcium ions flow into the sarcoplasm
- Calcium ions bind to troponin, shifting tropomyosin away from the myosin binding sites on actin
- Myosin (thick filament) heads bind to actin (thin filament) forming cross bridges
- Myosin heads flex and perform power stroke, generating force and contracting a single sarcomere
- Myosin heads detach from actin and reset, ATP is utilised
- Cross bridge cycling continues (simultaneous contractions of sarcomeres shorten the entire muscle)
Sources of energy in the form of ATP
ATP is stored in muscle cells and provides energy via three metabolic processes:
* Creatine-phosphate
* Anaerobic glycolysis
* Aerobic respiration
Creatine-phosphate
- Easy and immediate source of ATP
- Doesn’t last very long (approximately 15 seconds)
- Used when producing energy quickly
- Relaxed muscle - ATP donates the phosphate to produce creatine phosphate
- Muscle contraction - ADP takes a phosphate from creatine to produce ATP
(Graph)
Anaerobic glycolysis
- Anaerobic = no oxygen present
- Glycolysis = breakdown of glucose
- Uses glucose as energy source
- Longer duration (approximately a few minutes)
- Glucose sources - muscle glycogen, from blood
(Graph)
Aerobic respiration
- Aerobic = oxygen present
- Respiration = breathing
- Uses oxygen to breakdown glucose, amino acids, and fatty acids to produce ATP
- Can last as long as there is access to nutrients and oxygen (several minutes to hours)
- Nutrients - Glucose, amino acids, fatty acids
- Byproducts - heat, 30-32 ATP, carbon dioxide, water
(Graph)
Muscle contraction
- Each muscle comprises of a number of muscle fibres
- Not all muscle fibres within a whole muscle are activated at the same time during a contraction (some fibres will contract whilst others relax)
- Motor neurons control force contractions and the necessary changes
- Motor neurons send signals down the axon, branch along the muscle and each terminal supplies a muscle fibre
How to vary the force production in each muscle fibre
- Frequency of stimulation
- Sarcomere length prior to contraction
Twitch contaction
- The force of contraction in a single muscle fibre
- Once a muscle is stimulated it cannot stop without going through its contraction and relaxation period
- Graph measures changing force of contraction with different phases of a muscle contraction
Twitch contraction phases
- Latent period
- Contraction period
- Relaxation period
(Graph)
Latent period
Time that acetylcholine (Ach) is crossing the synaptic cleft, has stimulated our sarcolemma and calcium is starting to be released into the sarcoplasm, no change in contraction force yet
Contraction period
Where we can physically see the increase in muscle tension as we get more calcium ions binding our troponin causing sarcomeres to contract, the more calcium binding the longer the contraction period lasts
Relaxation period
Decrease in muscle tension as calcium detaches from the troponin, calcium is reabsorbed back into the sarcoplasmic reticulum
Muscle fibre types
- Type I: slow oxidative fibres
- Type IIa: fast oxidative-glycolytic fibres
- Type IIb: fast glycolytic fibres
Type I: slow oxidative fibres
- Slow twitch
- Uses aerobic respiration to produce ATP
- High amounts of mitochondria
- High concentration of myoglobin
- Example - long distance running
Type IIa: fast oxidative-glycolytic fibres
- Fast twitch
- Uses aerobic respiration and anaerobic glycolysis to produce ATP
- High amounts of mitochondria
- Low concentration of myoglobin
- Example - 400m sprint
Type IIb: fast glycolytic fibres
- Fast twitch
- Uses creatine phosphate to produce ATP
- Low amounts of mitochondria
- Low concentration of myoglobin
- Example - 100m sprint
