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Muscle formation, pharyngeal arch primary muscle group, deveopling spinal…
Muscle formation
basics
skeletal muscle
paraxial mesoderm (day 17)
segementation
somitomeres
association with neural plate segementation at cranial region
neuromeres
mesenchyme in head
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caudual side of occipital region
Somites (total :42-44) (growth direction-cranial to caudal
cervical x8
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thoracic x12
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occipital x4
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lumbar x5
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sacral x5
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cocccygeal x8-x10
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smooth muscle
ectoderm
pupillary muscle- from optic cup
mammary/sweat gland (myoepithelial cells)
lateral plate mesoderm
visceral layer
circulatory smooth muscle
somatic layer
gut smooth muscle
cardiac muscle
visceral mesoderm (surrounding heart tube)
tendons
origin:sclerotome adjacent to myotomes
transcription factor:SCLERAXIS
development
trunk musclature (mytome)
example of myotome division
dorsal:epaxail division
dorsal muscles
intrinsic back muscle
extensor muscles of neck
vertebral column muscles
ventral: hypaxial division
limbic muscles
body wall muscle
prevetebral muscles
intercostal muscles
pelvic muscles
perineal muscles
further development
stayed in mytome
segementally muscles (ex: intercostal muscle)
leave myotome
non segemented muscle (primary)
limb musclature
general development
origin: ventrolateral somites
hypaxial muscle group
ventral muscle block
Flexor muscle
dorsal muscle block
extensormuscle
intermuscular septa (border)
extend
periosteum of bone
location
Upper limbs
lower 5 cervical segements
upper thoracic segements
lateral rotation
dorsal: extensor muscles
ventral: flexor muscles
lower limbs
lower 4 lumbar segement
upper sacral segement
medial rotation
dorsal: flexor muscle
ventral: extensor muscle
molecular regulation
determine position on body axis
general regulator: HOX gene
Process (factor regulator: HOX gene)
anterior-posterior (ex:determine location of thumb)
primary: zone of polaring activity (ZPA)
secrete Sonic Hedgehog (SHH)
specify anteroposterior axis (high SHH at posterior side)
normally stay at posterior side (contain lots of SHH)
dorsoventral
dorsal: WnT7a
produce LMX1
maintain SHH expression in ZPA
ventral: BMPs+engrailed-1
BMPs:produce EN1 to inhibit LMX1
ENGRAILED-1: repress RADICAL fringe to form AER
proximal-distal (first proximal than distal)
establishment of AER (primary action)
AER:SER-2
FGF-4+FGF-8 maintain undifferentiated zone+SHH in posterior side
ventral border: ENGRAlLED-2
dorsal border: radical fringe
head+neck
pharyngeal arches
myoblast migrate to pharyngel arch
somitomere 6
pharyngeal arch 2 (CN VII)
fascial expression muscle
ex: orbicularis oris / levator labii superioris
posterior belly of diagastric
stylohyoid
stapedieus
somitomere 4
pharyngeal arch 1(CN V)
muscle of mastication
medial pterygoid
massenter
temporalis
lateral pterygoid
mylohyoid
anterior belly of digastric
tensor tympani
tensor veli palatini
somitomere 7
pharyngeal arch 3 (CNIX)
stylopharyngeus
somite 1+2
pharyngeal arch 4 (CN X)
pharyngeal muscles (except stylopharyngeus)
cricothyroid
muscles of soft palate (except tensor veli palatini)
pharyngeal arch 6 (CN X)
muscles of larynx (except cricothyroid)
esophageal muscle
occipital (postotic) myotome (1st-4nd myotome)
tongue muscle (-glossus) (CN XII)
upper+anterior neck musculature
preotic myotome (3 pairs)
mesnchymal cells near prechordal plate
extrinsic muscles of the eye (CN III,IV,VI)
ex:superior rectus, inferior oblique muscle
cells
myoblast
master regulatory transcription factor: MyoD
inhibitor:myostatin
origin: mesenchymal cells in myotome
pharyngeal arch primary muscle group
facial expression muscle (CN VII)
primarily arch 2
pharynx + larynx muscle (CN IX,X)
muscle of masstification (CN V)
primarily arch 1
deveopling spinal cord
ventral primary ramus
dorsal primary ramus
(note :diffferentiated zone determined by HOX genes) (upstream:FGF+SHH+WNTa)
middle: zeugopod (HOXA11)
distal : autopod (HOXA13)
proximal: stylopod (retinoids +MEIS1)
morphogens
directly influence target cells
exert different effect via different concentration
from somitomere 1,2,3,5
from myotome hypaxial division
note: bone development also develop from proximal to distal
note:SHH also joins midline structure formation in bones
note:cell death of certain parts of AER generate digits