L12: Skeletal Muscle Plasticity Flashcards
What are the 3 Key Physiological Differences between Fibre Types
- Type of Myosin expressed
- Oxidative vs glycolytic energy production
- Type of SERCA pump expressed
What makes the types of myosin different?
Speed of:
– ATP utilisation (determines if fatigue prone or fatigue resistant)
– cross-bridge cycling
– speed of contraction
Describe oxidative energy production
High oxidative activity (mitochondria) can generate ATP continuously using O2 and substrates from blood but only relatively slowly [e.g. standing or marathon]
Describe glycolytic energy production
High glycolytic activity can generate ATP quickly from muscle glycogen but glycogen stores limited
What makes the types of SERCA pump different?
- faster or slower clearance of Ca2+ from sarcoplasm into SR .: faster or slower drop in tension/relaxation curve
describe 5 properties of type 1 muscle fibres
Type I: Slow Oxidative Fibres
- long steady increase to peak and long steady decrease (slower SERCA isoform)
- fatigue resistance
- lots of mitochondria = lots of ATP
- fatigue ⇒ ATP not strictly used up, but metabolic products build up an impair muscle function
- more pink colour because rich blood supply
Describe 4 properties of type IIB muscle fibres
Type IIB: Glycolytic Fibres
- Fast form of myosin ATPase
- Fast form of SERCA
- fast tension producer, fast relaxation
- Few mitochondria, low levels of oxidative enzymes, fewer capillaries
- ATP from ready pools of energy that can be accessed quickly, but used up quickly as well → fatiguable
Describe 3 properties of type IIA muscle fibres
- Fast form of myosin ATPase
- Mix of oxidative and glycolytic enzymes
- Intermediate speed/fatigue
Describe the physiological effects of strength training (2)
- More actin & myosin → increased fiber diameter (hypertrophy)
- More cross-bridges → more force
Describe the physiological effects of endurance training (4)
- more mitochondria,
- more capillaries,
- more myoglobin
- increased muscle stores of lipids and increased ability to use lipids directly from blood
What is a motor unit?
= a motor neuron and all the muscle fibres it innervates, size varies from 6 - 2000 fibres
what determines max FORCE of a motor unit?
size
what does recruitment refer to?
The number of fibres activated. Regulated by how many neurons are active at one time
T or F, muscles get recruited from biggest to smallest. Why?
F - - small units recruited first, so more tonically active.
= fine graded control of small forces
- Bigger units automatically recruited as required force increases
What is tetanus and how do we get there?
continuous muscle contraction, rather than a muscle twitch. lots of APs -> SERCA cannot clear Ca2+ between twitches = no chance for any relaxation => max force is transmitted to tendon, continuously
