Muscle Embryology Flashcards
where are muscles derived from?
mesoderm
what is gastrulation?
process of cell division and migration resulting in the formation of the three germ layers - ectoderm, mesoderm, endoderm
what is the notochord
a signalling centre that contains mesoderm cells which are thickened which signals to mesoderm and overlying ectoderm to tell it to become nervous system
where is he paraxial mesoderm?
adjacent to notochord, closest to where vertebrae will form
what does the intermediate mesoderm form?
genitourinary system
what is the lateral plate mesoderm?
splits by a cavity (intraembryonic coelom) into two layers
1. somatic or parietal layer
2. splanchnic or visceral layer
where is there no mesoderm?
oropharyngeal membrane and the cloacal membrane as these areas will break down
what does the oropharyngeal membrane break down to form?
the mouth
what does the cloacal membrane break down to form?
the anus
when does mesoderm differentiation occur?
days 17-21
what are the 3 regions of mesoderm?
paraxial
intermediate
lateral
what is the paraxial mesoderm?
forms from cells moving bilateraly and cranialy from the primitive streak
lies adjacent to notochord and neural tube
forms the somites in the embryo
where do skeletal muscles originate from?
paraxial mesoderm
what is the neural tube?
goes on to form brain and spinal chord
where do smooth muscles (gut and derivatives) originate from?
visceral layer, lateral plate mesoderm around gut tube
where do smooth muscles (pupil, mammary and sweat glands) originate from?
ectoderm
where does cardiac muscle originate from?
visceral layer, lateral plate mesoderm around heart tube
what are the segments called when the paraxial mesoderm operates?
somites
where do somites form?
alongside the developing neural tube in a craniocaudal sequence over time from d20
at what rate do somites appear?
3 pairs per day until the and of week 5
how is somitogenesis controlled?
notochord influences somite formation
how is somitogeneis regulated?
-gene products tell cells to switch between a permissive and non permissive state in a constantly timed fashion
-a wave of factors then sweeps along the length of the embryo and interacts with the cells that are permissive at the right time in the right area
what does FGF8 do?
washes up the somites. only have the effect of making a somite if the mesoderm is at the right time and expressing notch
when do cells express notch?
when they are at the right time, it then allows them to react to the wave
how many somites are present by the end of the 5th week?
42-44 pairs, these will form the axial skeleton
what is epithelialisation?
segmented blocks of paraxial mesoderm are transformed into spheres, epithelial cells around a lumen
what do cells in the ventral and medial area form during mesenchymal transition?
sclerotome, form the vertebrae and ribs
what do cells in the dorsal half form during mesenchymal transition?
dermomyotome
what does the dermomyotome split to form?
dermatome - dermis of back
myotome - muscles
what are myocytes?
mature muscle cells. made from my oblasts which are muscle cell precursors
what are primary myotubes?
when my oblasts align into chains and fuse, cell membranes disappear- multinucleate myotubes
what is myogenin?
regulates myocyte fusion during development
what are MYOD and MYF5?
-transcription factors
-activate muscle specific genes
-enable the differentiation of myogenic precursor cells in the dermomtoyome into myoblasts
-powerful and can convert non muscle cells to cells expressing all the muscle proteins
what does the neural tube do?
produces signals, WNT proteins (activating) and BMP (inhibitory) combine to activate MYOD in the dermomyotome which creates a group of muscle cell precursors which express MYF5
where produces WNT and BMP?
the lateral plate mesoderm and the neural tube
what factors does the notochord produce?
sonic hedgehog and noggin which induce sclerotome (don’t want muscle formation here s we want to make bone) formation
