Muscle & muscle function 2 Flashcards
What is determined by the capillary to muscle fiber ratio?
Exercise endurance capacity
During sustained (constant) contractions >60% capacity: X supply ATP
anaerobic processes
Muscle contains myoglobin: hemeprotein.
What does it do?
Characteristics?
How do oxygen dissociation properties differ from haemoglobin?
Intra-fibrillar storage of oxygen
Reddish colour of meat
(higher affinity for myoglobin)
Facilitates oxygen transfer to mitochondria at low PO2
Which of these 2 muscles has the highest myoglobin concentration?
A) m triceps barchii (upper arm)
B) m. soleus (lower leg)
C) similar levels
B) m. soleus (lower leg)
M soleus = ‘red muscle’, because it contains a lot of T1 fibers.
Slow-twitch muscle fibers are which type?
T1
T1 muscle fibers: name some characteristics
- Slow Ca2+ release (slow excitation-contraction coupling)
- Low myosin ATPase activity (which is required for breakdown of ATP and putting the myosin in the ‘cocking’ position
- Low glycolytic capacity
- High levels of myoglobin (red)
- Large and numerous mitochondria
- High oxidative capacity
- E.g., m. soleus: 88% T1 fibers: muscles are always mixed from different types
- T1 fibers: muscles for posture/standing, because we use them all the time
Fast-twitch muscle fibers are which type?
T2
T2 muscle fibers: name some characteristics
- High capability for electrochemical transmission of action potentials
- Rapid Ca2+ release (fast excitation-contraction coupling)
- High myosin ATPase activity
- High rate of cross-bridge turnover
- Low levels of myoglobin (white)
- High glycolytic capacity
- Low oxidative capacity (low mito frequency)
- Triceps: 70%
- M. gastrocnemius: 50%
What are T2 subtypes?
Type IIa
Moderately fast contracting (fast twitch)
Medium force production
Type IIb (not found in humans)
Very fast contracting (fast twitch)
Very high force production
Type IIx (previously IIb)
Fast contracting (fast twitch)
High force production
How can you histochemically distinguish which fiber type you see?
Type of fibers differ, besides from composition, in the myosin heavy chain protein.
Fiber distribution in different types of athletes: Cause or consequence?
Very controversial subject. Shift within T2 subtypes = sure, but from T1 to T2 and vice versa is unsure. Genetics is thought to play a major role.
What happens during ageing with fiber types?
- During ageing, there is a shift in % of T1 fibers: higher %. Probably not caused by shift T2 ->T1, but selective atrophy of type 2x. T2 fibers decreasing.
