Skeletal muscle Flashcards
(46 cards)
What is the sarcolemma?
The cell membrane of muscle fibres
Starting from superficial, what are the 8 layers of skeletal muscle?
Epimysium
Perimysium
Muscle fascicles
Endomysium
Sarcolemma
Muscle fibres
Myofibrils
Myofilaments
What are the different types of muscle fibres?
Type 1
Type 2A
Type 2B
Describe the respiration of Type 1 muscle fibres.
Aerobic - slow oxidative respiration
Describe the respiration of Type 2A muscle fibres.
Aerobic + anaerobic - fast oxidative respiration
Describe the respiration of Type 2B muscle fibres.
Anaerobic respiration
Describe the:
-mitochondria
-myoglobin content
-colour
of Type 1 muscle fibres.
Lots of mitochondria and myoglobin
Red in colour
Describe the:
-mitochondria
-myoglobin content
-colour
of Type 2A muscle fibres.
Lots of mitochondria and myoglobin
Red in colour
Describe the:
-mitochondria
-myoglobin content
-colour
of Type 2B muscle fibres.
Low levels of mitochondria and myoglobin
Pale in colour
Describe the:
-contraction speed
-fatigue resistance
of Type 1 muscle fibres.
Slow contraction
Fatigue resistant
Describe the:
-contraction speed
-fatigue resistance
of Type 2A muscle fibres.
Intermediate contraction
Moderate fatigue resistance
Describe the:
-contraction speed
-fatigue resistance
of Type 2B muscle fibres.
Fast, powerful contraction
Rapidly fatigable
What is meant by a motor unit?
The motor neuron and the muscle fibres it innervates
Describe the chain of events that occurs in the neuromuscular junction to bring about contraction of muscle fibres.
- An action potential arrives and depolarises the pre-synaptic membrane of the motor neuron.
- Depolarisation triggers the opening of voltage-gated calcium channels, allowing Ca2+ influx into the cell.
- Ca2+ triggers the fusion of vesicles containing ACh with the membrane and release ACh into the synaptic cleft via exocytosis.
- ACh binds to nicotinic ACh receptors on the post-synaptic membrane (motor end plate).
- Nicotinic receptors are ligand-gated ion channels. Binding of ACh causes Na+ to enter, and K+ to leave the cell, depolarising the motor end plate and creating an end-plate potential.
- If the end-plate potential is strong enough, it triggers an action potential which spreads across the muscle fibre.
- ACh is broken down by acetylcholinesterase into acetate and choline.
What is the pathophysiology of Myasthenia Gravis?
Autoantibodies against nicotinic ACh receptors on the post-synaptic membrane
What is meant by synaptic rundown?
When a neuron fires repeatedly, it releases less and less ACh due to depletion of the vesicles
What is meant by the safety factor?
The difference between the end-plate potential and the threshold required to trigger an action potential in the muscle fibre.
The EPP is typically larger than necessary to generate an AP, ensuring the muscle fibre contracts even with some variability in neurotransmitter release.
What are the 2 main things which affect the safety factor?
Amount of ACh released
Number of functioning ACh receptors
Which drug can be used to treat Myasthenia Gravis?
Why is this a different drug than is used to treat dementia?
Pyridostigmine - it does not readily cross the blood-brain barrier
How does the botulinum toxin prevent normal functioning of the NMJ?
Degrades SNARE protein complex
What are T-tubules?
Invaginations of the sarcolemma
What is the functional unit of muscle contraction?
Sarcomere
What are thin filaments composed of?
Actin
Troponin
Tropomyosin
What are thick filaments composed of?
Myosin
