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