Skeletal Muscle: Structure and Types of Muscle Fibres Flashcards
What can muscle fibres be categorised into?
Slow twitch (Type I) and fast twitch (Type II)
Describe slow twitch muscle fibres.
- Generate ATP slower than fast twitch
- ATP generated aerobically (so relatively slow)
- Have large, numerous mitochondria
- High levels of myoglobin: red pigmentation
- Fatigue resistant
- Found in large muscles e.g. gluteals
Describe fast twitch muscle fibres.
- Generate ATP faster than slow twitch
- Capable of rapid level of calcium release and uptake by SR
- Contract at higher speed: regenerate short term energy transfer by anaerobic respiration
- Tension developed x2/3 faster than slow twitch
- Tire faster
- Found in smaller muscles e.g intrinsic muscles of the eye
What are the three types of muscle fibre?
- Slow oxidative
- Fast oxidative-glycolytic (Aerobic)
- Fast glycolytic (Anaerobic)
What muscle fibres are skeletal muscles composed of?
Skeletal muscle is composed as a mixture of the 3 muscle fire types and relative proportions depend of how muscle is used and what it is used for.
What are slow oxidative muscle fibres?
Aka slow twitch
- Red muscle fibres; commonly found in the back
- Large amounts of myoglobin and mitochondria
- ATP generation: aerobic respiration
- Small diameter and relatively weak: takes longest to reach tension
- Very resistant to fatigue: capable of providing sustained muscle contraction
What are fast oxidative-glycolytic muscle fibres?
Aka fast twitch Type A
- Red muscle fibres with high myoglobin and blood vessel count
- ATP generation: aerobic cellular respiration and anaerobic glycolysis (due to high intracellular glycogen levels)
- Intermediate at reaching tension
- Fairly resistant to fatigue
- Cannot sustain tension for as long as slow twitch
What are fast glycolytic muscle fibres?
Aka fast twitch Type B
- White muscle fibres with low myoglobin content
- ATP generation: glycolysis (lots of glycogen)
Contract forcefully and quickly i.e. most powerful contraction
- most myofibrils
- Fatigue very quickly
- Tension maintained for short period of time
Slow twitch v fast twitch: myosin ATPase
ST: has slow form of myosin ATPase
- ATP broken down at a slower rate so energy not available as quickly.
FT: has fast form of myosin ATPase
- ATP split more quickly so energy is available more quickly.
What is in-between the muscle origin and insertion?
The belly.
*Muscles can have numerous origins, insertions and bellies.
What is the hierarchical structure of skeletal muscle?
- Myofilaments (proteins responsible for contraction) grouped into myofibrils.
- Myofibrils grouped into bundles - muscle fibres.
- Muscle fibres (muscle cells) grouped together into muscle fascicles.
- Groups of muscle fascicles make up the muscle.
What is the connective tissue layers in and around skeletal muscle?
Endomysium - thin layer of connective tissue surrounding each muscle fibre.
Perimysium - thick layer of connective tissue grouping muscle fibres into fascicles.
Epimysium - thick layer of connective tissue surrounding the entire skeletal muscle.
What is the role of the perimysium?
It protects the fascicle from damage and contains capillaries and nerve fibres allowing nutrient transfer within the muscle.
What is the role of the epimysium?
Separates muscle from surrounding tissues and organs.
*May continue at end of belly as the the tendon and thus becomes continuous with the periosteum of the bone.
What is the plasma membrane of the muscle fibres called and what does it do?
Sarcolemma
- Invaginated in places forming transverse tubules (T-tubules)
- Many nuclei
- Receives electrical stimulation, conducting an action potential to internal structure via T-tubules
