44.4 Skeletal Muscle Function
- Skeletal muscle has a variety of functions – locomotion, stretching, chewing, breathing, maintaining balance.
- Muscle fibres are classified based on their rates of shortening and the way they produce ATP for contraction.
Skeletal Muscle Fibres are adapted for Different Types of Movement
- Fast fibres contain myosin with high ATPase activity and is 4x faster at cross-bridge cycling than slow fibres, but the
maximal force produced is the same.
- Slow fibres contain myosin with low ATPase activity.
- Oxidative fibres are fibres with numerous mitochondria and have a high capacity for oxidative phosphorylation, so
they rely on many small blood vessels to deliver oxygen.
- They can also contain myoglobin, an oxygen-binding protein which provides an intracellular reservoir of oxygen,
which gives these fibres a dark red colour.
o Oxidative fibres are often called red muscle fibres.
- Glycolytic fibres have few mitochondria but possess a high concentration of glycolytic enzymes and large stores of
glycogen. They use very little oxygen, myoglobin and is surrounded by few blood vessels, earning them the name
‘white muscle fibres’.
- There are 3 types of skeletal muscle:
1. Slow-oxidative fibres (red muscle)
- Low ATPase activity but can make large amounts of ATP due to lots of mitochondria.
- Used for prolonged, endurance activity.
o Ex. Flight, long-distance swimming, maintenance of posture
2. Fast-oxidative fibres
- High ATPase activity and can make lots of ATP.
- For prolonged, long-term activity like the slow-oxidative fibres – the difference is this fibre is for rapid activities.
o Ex. Rapid trilling sounds of throat muscles of birds, clicking sounds of rattlesnake’s tail.
3. Fast-glycolytic fibres
- High myosin ATPase activity, but no ATP production since source is glycolysis.
- Used for rapid, intense actions because they fatigue rapidly.
o Ex. Sprinting, cat pouncing on prey.
- Depending on the actions you’re performing, motor nerve inputs can be adjusted to stimulate different ratios of fibre
CH 43: NEUROSCIENCE- SENSORY SYSTEMS
- A sense is a system that consists of sensory cells that respond to a specific type of chemical or