Muscle Structure and Function - II Flashcards
What is isotonic?
Muscle tension remains unchanged where muscle length decreases
What is isokinetic?
Muscle length decreases with constant velocity
What are the three key
biochemical characteristics important to muscle fibre function?
1) Oxidative capacity (quantity of mitochondria, capillaries and myoglobin)
2) Type of myosin isoform expressed (3 types that differ in activity (rate of ATP breakdown)
3) Amount of contractile protein within fibre (amount of actin and myosin)
- (Type of motor neuron innervation)
On average, what % of type I fibres in arm and leg muscles?
45-55%
-Trend in distribution consistent across muscle groups (within individuals).
EXAMPLE: What % of type I and II fibres may a distance runner have?
Type I - 70 to 80%
Type II - 20-30%
What is speed of contraction regulated by?
myosin ATPase activity
What is the Maximal power output equation?
Maximal power output = force × shortening velocity.
* High force, fast fibres produce high power output.
What does muscle contraction speed depend on?
Rate of cross bridge cycling (depends on the myosin ATPase isoform)
What is Immunohistochemical staining?
- Selective antibody binds to unique myosin proteins
- Fibre types differentiated by colour difference
What is gel electrophoresis?
- Identify myosin isoforms specific to different fibre types
Why is the speed of shortening greater in fast fibres?
- SR releases Ca2+ at a faster rate.
- Higher ATPase activity.
What are the 4 main factors in force regulation of muscle?
- Number and types of motor units recruited (more + fast MU = greater force)
- Muscle length (‘ideal’ length for force generation, increased C-B formation)
- Firing rate of motor neurons (frequency of stimulation)
- Contractile history of muscle (rested vs muscle exposed to fatigue, warmup exercise results in postexercise potentiation)
Can the muscle fibres belonging to a single motor unit vary?
No - all muscle fibres that belong to
a single motor unit are of the
same fibre type
Muscle force is increased by recruiting more motor units. What factor influences muscle function?
Number of fibres per Motor Unit will determine how that muscle functions.
E.g., Small eye muscles. Large
amount of units @ ~ 10 fibres / motor unit.
Large weight bearing medial
gastrocnemius ~ 600 motor units
@ ~2000 fibres / motor unit
Motor neuron structure relates to function. Motor neurons supplying larger faster motor units have..?
- Larger cell bodies
- Larger diameter axons
- Greater number of axonal branches
- Sparse afferent innervation (less spindle excitatory input)
- More complex and extensive motor end plate of neuromuscular junction