Muscle Embryology

Question 1

where are muscles derived from?

Answer 1

mesoderm

Question 2

what is gastrulation?

Answer 2

process of cell division and migration resulting in the formation of the three germ layers - ectoderm, mesoderm, endoderm

Question 2

what is the notochord

Answer 2

a signalling centre that contains mesoderm cells which are thickened which signals to mesoderm and overlying ectoderm to tell it to become nervous system

Question 3

where is he paraxial mesoderm?

Answer 3

adjacent to notochord, closest to where vertebrae will form

Question 4

what does the intermediate mesoderm form?

Answer 4

genitourinary system

Question 5

what is the lateral plate mesoderm?

Answer 5

splits by a cavity (intraembryonic coelom) into two layers
1. somatic or parietal layer
2. splanchnic or visceral layer

Question 6

where is there no mesoderm?

Answer 6

oropharyngeal membrane and the cloacal membrane as these areas will break down

Question 7

what does the oropharyngeal membrane break down to form?

Answer 7

the mouth

Question 8

what does the cloacal membrane break down to form?

Answer 8

the anus

Question 9

when does mesoderm differentiation occur?

Answer 9

days 17-21

Question 10

what are the 3 regions of mesoderm?

Answer 10

paraxial
intermediate
lateral

Question 11

what is the paraxial mesoderm?

Answer 11

forms from cells moving bilateraly and cranialy from the primitive streak
lies adjacent to notochord and neural tube
forms the somites in the embryo

Question 12

where do skeletal muscles originate from?

Answer 12

paraxial mesoderm

Question 13

what is the neural tube?

Answer 13

goes on to form brain and spinal chord

Question 14

where do smooth muscles (gut and derivatives) originate from?

Answer 14

visceral layer, lateral plate mesoderm around gut tube

Question 15

where do smooth muscles (pupil, mammary and sweat glands) originate from?

Answer 15

ectoderm

Question 16

where does cardiac muscle originate from?

Answer 16

visceral layer, lateral plate mesoderm around heart tube

Question 17

what are the segments called when the paraxial mesoderm operates?

Answer 17

somites

Question 18

where do somites form?

Answer 18

alongside the developing neural tube in a craniocaudal sequence over time from d20

Question 19

at what rate do somites appear?

Answer 19

3 pairs per day until the and of week 5

Question 20

how is somitogenesis controlled?

Answer 20

notochord influences somite formation

Question 21

how is somitogeneis regulated?

Answer 21

-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

Question 22

what does FGF8 do?

Answer 22

washes up the somites. only have the effect of making a somite if the mesoderm is at the right time and expressing notch

Question 23

when do cells express notch?

Answer 23

when they are at the right time, it then allows them to react to the wave

Question 24

how many somites are present by the end of the 5th week?

Answer 24

42-44 pairs, these will form the axial skeleton

Question 25

what is epithelialisation?

Answer 25

segmented blocks of paraxial mesoderm are transformed into spheres, epithelial cells around a lumen

Question 26

what do cells in the ventral and medial area form during mesenchymal transition?

Answer 26

sclerotome, form the vertebrae and ribs

Question 27

what do cells in the dorsal half form during mesenchymal transition?

Answer 27

dermomyotome

Question 28

what does the dermomyotome split to form?

Answer 28

dermatome - dermis of back
myotome - muscles

Question 28

what are myocytes?

Answer 28

mature muscle cells. made from my oblasts which are muscle cell precursors

Question 29

what are primary myotubes?

Answer 29

when my oblasts align into chains and fuse, cell membranes disappear- multinucleate myotubes

Question 30

what is myogenin?

Answer 30

regulates myocyte fusion during development

Question 31

what are MYOD and MYF5?

Answer 31

-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

Question 32

what does the neural tube do?

Answer 32

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

Question 33

where produces WNT and BMP?

Answer 33

the lateral plate mesoderm and the neural tube

Question 34

what factors does the notochord produce?

Answer 34

sonic hedgehog and noggin which induce sclerotome (don’t want muscle formation here s we want to make bone) formation