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Development of Musculoskeletal System
Development of MusculoskeletalSystemPosted on September 26, 2010 by terrichan Read up Foundation 1 Embryology & 1st aid basic sciences.
OLIS
http://elearning.imu.edu.my/file.php/4236/StudyGuide/Musculo/week1/xms1_7.html
Skeletal system develops from:
Paraxial mesoderm
forms somites
a segmented series of blocks on each side of neural tube
somites form:
vertebral column
muscles of axial skeleton
body wall
head
Lateral plate mesoderm (somatic layer)
forms:
pelvic
pectoral girdle
long bones (of limbs)
1st pair of somites appear on the 20th day
at cervical region
formation of the somites
cranial-caudally
3 somites per day
By the 5th week, have 44 pairs
Occipital 4
1st pair disappear at 4th week
Cervical 8
Thoracic 12
Lumbar 5
Sacral 7
Coccygeal 8 to 10
Last 7 pairs disappear at 4th week
Ventromedial: sclerotome
mesoderm of sclerotome
surrounds neural tube & notochord
forms vertebral column
Dorsolateral: dermo-myotome
dermatome
forms skin
myotome
forms muscle
Sclerotomic blocks
separated by intersegmental arteries
caudal part of each segment proliferate
caudal half of one sclerotome binds to cranial half of next one (see image below)
therefore body of vertebrae is of intersegmental origin (segmented)
Messenchymal cells between cranial and caudal half of sclerotome
form intervertebral disc
annulus fibrosus (purple)
The remains of notochord
forms nucleuss pulposus
Developmental abnormalities
Neural tube defect diagnostic:
maternal alpha-fetoprotein
prevention
folic acid supplementation
Neural crest cells
forms mesoderm of head
which forms bones of face & skull
Occipital somites
forms cranial vault & base of skull
Types of ossification (skull)Membranous (messenchyme > bone)
Neurocranium (inner part of skull)
forms cranial cavity
houses the brain
membranous part of neurocranium
fontanelles
flat ones of cranial vault sutures
enables babys skull to enlarge to accommodate growing brain
failure of formation
brain exposed to amnion causing degeneration
anencephaly
with herniation of brain
cranial meningocele
Viscerocranium (outer part of skull)
facial skeleton
from 1st & 2nd pharyngeal arches
Chondrocranium
base of skull
Cells of somites migrate to form precursors of:
limb bud
body wall musculature
but retains nerves from segment of origin (?).
By the end of 4th week,
limb buds out pocket
from ventral body wall
start from a mesoderm core
derived from somatic layer of lateral plate mesoderm
upper limb buds appear 1st
lower limb buds appear 2 days later
mesenchyme in bud condenses
6th week 1st cartilage model
7th week 1st limb muscles at base of limb bud
pattern of muscle depends on connective tissue into which myoblasts migrate
head region
C/T from neural crest cells
axial, body wall, limbs
C/T from somatic mesoderm
thickened ectoderm at distal border of limb bud (at the tip)
Apical ectodermal ridge (AER)
induces the pattern of the limb
differentiation of
limb bone
cartilage
muscle
if defected
fingers/toes may not form properly
At the 7th week,
limbs rotate in the opposite direction
upper limb: 90% lateral
extensor muscles
lateral & posterior surface
thumb
lateral side (anatomical position)
lower limb: 90% medial
extensor muscles
anterior surface
great toe
medial side (anatomical position)
Bone growth with age
Muscle development
Prospective muscle cells Epimere
extensors of vertebral column
innervated by: dorsal rami of spinal nerve
Hypomere
limb and body muscle wall
innervated by: ventral rami of spinal nerve
thoracic hypomere
splits into 3 layers
external intercostal
internal intercostal
innermost intercostal
abdominal hypomere
splits into 3 layers
external oblique
internal oblique
transversus abdominis
Anomalies
Dwarfism
9 members of fibroblast growth factors & fibroblast growth factor receptors (FGFR)
regulate cellular events in proliferation and differentiation
FGFR-3
expressed in cartilage growth plates in long bones
mutation in p-arm of chromosome 4
autosomal dominant hereditary
amino acid substitution
proliferation on chondrocytes in epiphyseal plate is disturbed
achondroplasia
most common causes of dwarfism
large head, small face, limbs shorted than trunk, bowed
Amelia
complete absense of limbs
Meromelia
partial absense of limbs
Phocomelia
long bones absense
rudimentary hands & feet
Causes:
hereditary
drug induced
mothers on thalidomide
teratogen damage
mostly 3rd 8th week
Polydactyly
extra digits
Ectrodactyly
absence of digits
Syndactyly
abnormal fusion
caused by: anti-convulsant phenytoin
Lobster claw deformity
cleft hand & foot
Congenital hip dislocation
due to underdevelopment of acetabulum & head of femur
mostly female