Musculoskeletal System Development Flashcards
when does neuralation occur?
around day 19
what is the notochord?
signals surface ectoderm to differentate into the neural ectoderm (neural plate)
what happens at day 20?
the neural groove forms as lateral edges move
what happens at day 22-23
the neural groove fuses in cervical region
progresses cranial to caudal
what are the neuropores and when do they fuse?
ends of neural tube
day 25 - cranial closes
day 27 - caudal closes
what does the neural tube for?
brain and spinal cord
neural fold?
becomes the neural tube
neural crest?
pinched off as the neural tube forms
forms dorsal root ganglion
what gives rise to central nervous system?
neural tube cells
what gives rise to peripheral nervous system?
neural crest cells
the neural crest cells give rise to?
- sensory ganglia of cranial and spinal nerves
- autonomics (all peripheral S and PS ganglia, -sympathetic chain ganglia, prevertebral -sympathetic ganglia, PS ganglia)
- schwann cells
- meninges
what are the three layers of the neural tube?
ventricular, mantle, marginal zone
lumen > superficial**
ventricular zone
most inner layer
is the neuroepithelium
in adult - simple layer of ependymal cells
what gives rise to ependymal cells in adult
ventricular zone cells
what is the mantle zone?
composed of neuroblast cell bodies
-forms the basal and alar plate
alar plate?
forms the dorsal horn
**sensory
basal plate?
forms the ventral horn
**motor
what is the marginal layer?
outer layer
is the nerve processes
will become white layer when myelinated
motor cell body?
ventral motor root
basal plate**
sensory cell body?
dorsal motor root
alar plate**
how do spinal nerves develop?
cranial to caudal
gliablast?
form astrocytes and oligodendrocytes
spinal cord at 3 months?
extends the entire length
spinal cord at birth?
ends at LV4-LV5
spinal cord in adult?
ends at LV1-LV2
what guides process of nerve formation?
mainly mesoderm (somites)
when do dorsal and ventral rami form?
when somite splits into dorsal and ventral portions
myotome
skeletal muscle innervated by one spinal nerve
dermatome
area of skin innervated by one spinal nerve
each somite has what?
spinal nerve
will guide its formation
31 somites and spinal nerves
epimere
dorsal somite
hypomere
ventral somite
where does spina bifida most often occur?
lumbosacral region
what is spina bifida?
neural tube defect
spinal bifida occulta
15-20% of population
vertebral arches fail to fuse
does not typically involve meninges or nervous system
**often see a patch of hair
spina bifida cystics
spina bifida that involves meninges or neural tisue
meningocele
spina bifida that involves meninges
meningomyelocele
spina bifida involves meninges and spinal cord
meninges in spina bifida?
arachnoid and dura - therefore you have CSF in cavity
spina bifida with myeloschisis
most severe form
neural plate fails to elevate and fold
cord remains open and is represented as a flattened mass of nervous tissue
what tissue forms vertebral column?
somites
what do somites form?
dermatome
myotome
sclerotome
what does intermediate mesoderm form?
uro-genital structures
what are the three segments of mesoderm
paraxial, intermediate, lateral plate mesoderm
what are the somites derived from?
paraxial mesoderm
sclerotome
will give rise to axial skeleton
- vertebral column
- ribs
- portions of skull
what happens when sclerotomes shift?
during week 4
-shift to surround spinal cord and notochord
what happens during resegmentation
the sclerotome splits
caudal and cranial portions fuse of adjacent sclerotomes to form vertebrae
what is CV1 formed from?
caudal half of first cervical sclerotome and cranial half of second cervical sclerotome
what forms the nucleus pulposus?
notochord
what forms the annulus fibrosis?
mesenchymal cells between cranial and caudal portions of original sclerotome
what is significant after resegmentation?
myotomes span two vertebral levels
- how deep back muscles have fine control over vetebrae
spina bifida
neural tube defect
secondary is a defect of fusion of vertebral column
congenital scoliosis
due to hemivertebrae
after resegmentation
-only right or left ossification occurs
klippel feil syndrome
genetic syndrome causing the fusion of cervical vertebrae
**bc resegmentation doesn’t take place
what happens if resegmentation does not occur
fusion of vertebrae
costal process?
on all of the vertebrae
signaled to grow on thoracic - ribs
what forms the sternum
not from the somite**
from lateral plate mesoderm
-form sternal bars that fuse
pectus excavatum
anterior thoracic sunken in
pectus carinatum
anterior thoracic protrudes
what are congenital anomalies from incorrect sternum and rob formation?
pectus excavatum and pectus carinatum
**mostly cosmetic but can cause respiratory and cardiac problems
where does all skeletal muscle develop from?
paraxial mesoderm > somite > myotome
**myotome divides to dorsal and ventral myotomes
dorsal myotome?
epimere
innervated by dorsal rami
ventral myotome?
hypomere
innervated by ventral rami
what does epimere give rise to?
intrinsic muscles of back
what does hypmoere give rise to?
anterior/lateral neck, trunk, limb muscles
modification of myotome?
tangenital splitting
-abdominal obliques and intercostal
longitudinally splitting
-trap and sternocleidomastoid
what forms the skeletal muscles cells?
myoblasts form from mesoderm cells
formation of skeletal muscle cells?
mesoderm > myoblast > fuse together > myotubes > contractile filaments form > muscle fiber
myotube
fused, multinucleate myoblasts**
why is skeletal muscle multi-nucleate?
because myoblasts fuse
what gives rise to epidermis of limb?
surface ectoderm
where does the appendicular skeleton form from?
lateral plate mesoderm
what does limb muscle develop from?
myotome of somite
when does upper limb form?
day 26-27
when does lower limb form?
day 27-28
what is a limb bud?
evagination from ventrolateral body wall
apical ectodermal ridge (AER)
at apex of limb bud (ectodermal thickening)
function of AER?
induces continued proliferation of distal limb bud mesenchyme
**but not differentiation
what cells differentiate during limb development?
proximal mesenchyme cells
when do hand/foot plates form?
around week 5
-limb bud with flattened distal portion
digital rays
4 zones of apoptosis in separate hand and foot plates result in 5 digital rays
when do digital rays form?
upper limb - 6 week
lower limb - 7 week
brachydactyly
short digits
syndactyly
fusion of two or more digits
polydactyly
extra fingers/toes
ectrodactyly
absence of digit
amelia
absence of limb due to suppression of limb bud formation during week 4
meromelia
absence of part of limb
-arrest of limb bud development during 5-7 weeks
**due to thalidomide (for morning sickness)
cleft hand or foot?
lobster claw deformity
absence of third metacarpal (tarsal) and 3rd digit
fusion of thumb and second digit, fusion of fourth and fifth digits
axis of limbs?
proximal-distal - easy
anterior-posterior -
- anterior - thumb
- posterior - little finger
dorsal-ventral
- dorsal - back of hand/foot
- ventral - palm of hand/ plantar of foot
what is the thumb?
anterior
what is the plantar surface of foot?
ventral
when does cartilage formation occur?
week 5
when does primary ossification occur?
starts in week 7
-present in all long bones by 12th week
when do secondary ossification occur?
mostly after birth
-important for growth
how do joints form?
where mesenchyme is less dense
interzone?
where the joint cavity will form
what forms joint cavity?
cell death
club foot
caused by fetal constraints
-oligohydroaminos
what does lateral plate mesoderm form in limb
mostly connective tissue
when does limb muscle development occur?
week 5
from myotome
- after cartilage models form
- hypomere portion
will go to extensor (dorsal) and flexor (ventral) compartments
what forms the muscles of limb?
hypomere myotome
