Flashcards in Histology of nerve and muscle Deck (12):
Describe the basic structure of skeletal muscle
Myofibres arranged in fascicles
From Golgi tendon organs
Skeletal muscle histology
Can be studied by muscle biopsy
Requires the use of frozen sections and good orientation
What is enzyme histochemistry, what does it reveal in skeletal muscle
Enzyme histochemistry reveals different fibre types
skeletal muscle fibre types
Slow twitch (red fibres) – type 1, oxidative, fatigue resistant (marathon)
Fast twitch – fatigue rapidly but generate a large peak of muscle tension (sprint)
2A – glycolytic and oxidative (intermediate)
2B – glycolytic (white)
What is a motor neuron?
Motor neuron (lower) and the fibres it innervates
-Neuron and its fibres of same type
-Fibre type dependent on neuron
-Size of motor unit varies between muscles
How are motor units altered in denervating diseases?
Loss of innervation causes fibre atrophy
Collateral sprouting from adjacent motor units allows reinnervation
Larger motor units result – this can be detected electrophysiologically
Conversion of fibres results in fibre type grouping
What occurs in re-innervation?
When muscle fibres have been denervated (they lose their motor neuron)
The fibres can be re-innervated if a different motor neuron innervates them (must be the same type)
Describe the organisation of myofibrils
-repeating assemblies of thick and thin filaments
What occurs during sliding filament theory?
1. Myosin heads bind actin
2. Hydrolysis of ATP provides energy for a conformational change of the myosin head, pulling the actin
3. Sarcomeric shortening due to sliding of the filaments
Troponin/tropomyosin – mediate Ca2+ regulation
Maintaining architecture of the filament – e.g. nebulin, titin
Sliding filament theory requires ATP - where does this energy come from?
High energy requirement from ATP
Creatine phosphate a short term energy store
CP replenished by creatine kinase (CK)
CK is released on muscle fibre damage
Measurement of serum CK clinically useful
What is Dystrophin?
A large protein encoded by a 2.4 million bp gene on Xp21
Confers stability to the muscle cell membrane
Deletion resulting in disruption of the reading frame results in Duchenne
In Becker’s, and in-frame deletion results in a truncated product