Muscle Physiology III Flashcards
Motor Units component
Single alpha motor neuron (spinal cord -> muscle) + all muscle fibres innervated by that neuron
Which muscle units are recruited first
Small oxidative (Type I)
Which muscle fibres are recruited last
Large glycolytic (Type 2B)
Why are small oxidative units recruited first
Lower threshold
Motor Endplate two domains
Crests and Fold Depths
What is at muscle endplate crest
ACh receptors and AChR-clustering proteins rapsyn + utrophin that align AChRs
What is at depths of muscle endplate folds
Voltage Gated Na+ channels
At nerve terminals what happens when nerve AP depolarises it
Opens Voltage gated Ca2+ channels -> Ca2+ initiates exocytosis of vessels containing ACh
Vesicle Release Process
Vesicles filled with ACh
Vesicles form vesicle cluster
Vesicle clusters dock at active zone
Vesicles are primed
Ca2+ initiates vesicle release into synaptic junction
Vesicle recycling methods
Reuse, recycle, destruction via endocytosis
What happens when ACh binds to motor endplate
ACh-gated Na+ channel opens = depolarises motor endplate = voltage gated Na+ channel opens = depolarises muscle fibre -> propagation
What are alpha toxins
Block ACh receptors at neuromuscular junction (can be fatal if strong, or used as anaesthetic if weak)
How is ACh recycled
AChE (acetylcholinesterase) hydrolyses ACh into choline and acetate
Choline then reabsorbed by presynaptic terminal and reformed into ACh
What happens if you block AChE (eg. Military nerve gas)
Can’t recycle ACh therefore too much ACh = muscle over-excitation
Myasthenia Gravis muscles commonly effected
Face (and can spread lower = fatal if breathing)
