Neuromuscular Transmission Flashcards
what is the embryonic origin of neural crest cell
ectoderm
how does the myotube form
myogenic precursors come from neural crest cells
these line up to form myoblasts
myoblasts fuse to form myotube
where does the innervation to the myotube come from
the neural tube
what change is seen in the ACh receptor structure from embryo to adult?
In embryo before nerve contacts muscle receptors are made up of 2 alphas, beta gamma delta
however in adult we have 2 alpha beta epsilon delta - change that occurs at innervation
what is the role of agrin
agrin causes the aggregation of acetylcholine receptors during synaptogenesis. this occurs once the nerve makes contact with the muscle fibre
agrin activates MuSK to cluster AChRs via the cytoplasmic linker protein, rapsyn.
define a motor unit
motor unit is muscle fibres under control of a single motor nerve
outline initiation of muscle contraction
action potential in the cell membrane
goes down t tubule to the dihydropyridine receptor
this directly links to sarcoplasmic reticulum ryanodine receptor
this releases calcium and bathes myofibrils which cause contraction and pulls filaments together
what effect does the motor neurone have on muscle
the motor neurone has a trophic effect on muscle, controlling gene expression
describe slow and fast twitch muscle fibres
most muscles are a mixture od slow (red) and fast-twitch (white) fibres determined by expression of the contractile proteins, troponin I, determined by motor neurone activity
typically slow - express alpa-actinin-2 and troponin I slow (TnIs)
Typically fast - express alpha-actinin-2 and alpha-actinin-3 and troponin I fast (TnIf)
denervation results in a loss of slow and fast phenotypes
what does nicotine insecticed poisoning do to AChR?
desensitisation of AChR and depolarising neuromuscular block
