MSK Embryology Flashcards
What does the neural tube become
brain and spinal cord (CNS)
when do the neuro pores of the neural tube close in development
cranial neuropore day 25 and caudal day 27
Where do Neural Crest Cells arise from
neuroectoderm as the neural tube is closing
What do the cranial neural crest cells become
bones, catilage, fascia, ligaments and tendons of face, neck
also sensory ganglia and autonomic ganglia
What do the spinal neural crest cells become
DRG and autonomic ganglia, heart(fibrous skeleton)
what do both cranial and spinal nerual crest cells become
meninges, schwann cells and melanocytes
How many regions form from neural tube and how does this happen?
3 different regions because of neuron migration from neuroepithelium
What are the 3 regions of neural tube
Ventricular
Mantle
Marginal
Describe the differences in and embryo and adult in regards to the ventricular zone
embryo- thick pseudo stratified epithelium called neuroepithelium and gives rise to nerons and most glia of spinal cord
adult- single layer of ependymal cells
Describe the Mantle zone
superficial to neuroepithelium
composed of neuroblasts(primitive neurons)
alar and basal plactes separated by sulcus limitans
What will the alar plate form and what will the basal plate form (of Mantle zone)
alar- sensory dorsal horn
basal- motor ventral horn
Describe Marginal zone
outermost layer of spinal cord, composed of nerve processes, axons and dendrites
What makes up a spinal n
a ventral nerve root and an dorsal nerve root
Where are DRG derived from
spinal neural crest
Where are neuroblasts derived from and what are they
derived from neuroepithelium and form the ventral motor horn neurons and dorsal sensory horn neurons
Where are gliablasts derived and what do they form
derived from neuroepithelium
and form astrocytes and oligodendrocytes
Describe the position of spinal cord to vertebrae at 3 months of development, at birth and in and adult
3rd month- spinal cord extends entire length of vertebral column
birth- spinal cord ends LV4-LV5
adult- spinal cord ends LV1-LV2
What is neuronal pathfinding
active movement of the actual axon to the target organ based on signals release from somatic mesoderm
When do the dorsal and ventral rami form
when somite splits
What is the epimere and the hypomere
splits of the somite. epimere is the dorsal ramus and hypomere is the ventral ramus
When does motor and sensory innervation get established in development
when spinal nerve innervates somite. have a myotome and dermatome
What is the difference between myotome and dermatome
myotome is all the skel m innervated by one spinal n while dermatome is all the skin innervated by one spinal n
What is the most common form of spin Bifida
spina bifida occulta when the vertebral arches of spinal cord fail to fuse typically not involving meninges or nervouse tissue
Types of spin Bifida cystics
meningocele- involves meninges
meningomyelocyte- involves meninges and spinal cord
What is Spina bifid a myeloschisis
most severe. neural plate fails to elevate and fold- cord reamins open and represented as a flattened mass of nervous tissue
What are the different fates of somites
Sclerotome- axial skeleton
dermatome- dermis
myotome- skel m
What happens at week 4 in vertebral column development
sclerotome shifts to surround spinal cord and notochord
What is the process called when verrtebral bodies form
resegmentation
Describe general resegmentation
caudal portion of each sclerotome condenses and then is split. caudal part fuses with cranial part below
What sclerotome is CV1 made from
caudal half of first sclerotome and cranial half of CV2 sclerotome
What makes up the intervertebral discs
annulus fibrosis and nucleus pulposus
What components make the annulus fibrosis
from mesenchymal cells which remain between the cranial and caudal portions of original sclerotome
Where do ribs originate from
paraxial mesoderm, sclerotome
Where does the sternum originate from
lateral plate mesoderm and somatic layer
What forms the sternal bars
ventral somatic mesoderm forms pairs of vertevral bands
What is congenital scoliosis
asymmetric fusion of vertebrae
half of vertebrae does not form
Klippel-feil syndrome
fused cervical vertebrae, lack resegmentation during development
short neck. genetic maybe
Pectus excavatum
anterior thoracic wall caves inward due to malformation of sternum and ribs
Pectus carinatum
anterior thoracic wall protrudes outward due to malformation of sternum and ribs
Where does skel mm arise from
paraxial mesoderm (somites)
Where does smooth m arise from
splanchnic lateral plate mesoderm
where does cardiac m arise from
specialized region of the splanchnic lateral plate mesoderm
Describe skel m formation
mytome splits into dorsal and ventral portions epimere(dorsal) gives rise to intrinsic back mm ventral part (hypomere) forms anterior and lateral neck musculature, trunk mm and limbs
What mm utilize tangential splitting of myotomes
abdominal obliques and intercostal musculature
what mm derive from myotomes splitting longitudinally
trapezius and sternocleidomastoid
what lineage do myoblasts arise from
mesoderm cells
what forms the muscle fiber
when myoblasts elongate and fuse to form myotubes and then contractile elements appear in cytoplasm of myotube
Poland Syndrome
absent of underdeveloped pectorals, usually unilateral
seen with syndactyly of the fingers
cause unknown
What lineage do the skeletal and cT parts of limbs come from
lateral plate mesoderm
When do limb buds form and where
Upper day 26 or 27 form opposite lower cervical and upper thoracic segments
Lower day 27 or 28 from opposite lumbar and upper sacral segments
What is the apical ectodermal ridge
ectodermal thickening at the apex of the limb buds
What is the role of the AER
induces continued proliferation of distal limb bud mesenchyme
Proximal mesenchymal cells on a limb bud differentiate into what?
chondroblasts (cartilage cells)
What happens to the limb buds at week 5
distal ends flatten to paddle like hand and footplates, separated by circular constriction
When do the digital rays forma nd how?
4 zones of apoptosis separate hnad and footplates. week 6 for upper limb
week 7 for lower limb
Describe the proximal distal limb axis
shoulder- fingertips
describe the anterior-posterior limb axis
thumb(anterior)- little finger(posterior)
describe the dorsal ventral limb axis
back of hand (dorsal) to palm (ventral)
what substrate determines the anterior posterior limb axis
RETINOIC ACID
what bones begin ossification after birth
carpals, tarsals, patella
When do secondary ossification centers form
mostly after birth
What forms from areas where mesnchyme is less dense (inter zones)
joints
Initially when myoblasts enter limb bud at week 5 are the one muscle mass or flexor/extensor
1 muscle mass. later splits into ventral and dorsal compartments
When the upper and lower limbs originally form what direction are they in
laterally and caudally with thumb and great toe pointing laterally
What happens to limb position at week 6
limbs rotate about 90 degrees and bend to a more ventral position with flexor surface now directed medially
What happens to limb position in week 7
both limbs rotate but in opposite directions
upper limb laterally and lower medially (180 degrees total)
why do dermatomes spiral around the limbs
because of limb rotation
How do motor n get into limb buds
grow into limb after its formed with myotomal mesoderm. upper spinal nerves more proximally and lower spinal nerves distally
induces differentiation of myotome mesoderm into myoblasts
Amelia
absence of limb due to suppression of limb bud during development WEEK 4
Meromelia
absence of part of a limb
arrest of limb bud development during weeks 5-7 of development
Phacomelia
type of meromeilia involving absence of long bones
brachydactyly
shortness of digits
syndactyly
fusion of 2+ digits
most common hand/foot anomaly
insufficient apoptosis
polydactyly
extra fingers or toes
Ectrodactyly
absence of digit
Cleft hand or foot
absence of thir metacarpal or metatarsal and 3rd digit
fusion of thumb and second digit, fusion of 4th and 5th digit
Congenital clubfoot
abnormal position because foot is inverted, adducted in plantar flexion.
caused by oligohydramnios
amniotic bands
parts of amnion membrane free flowing and entrap portions of fetus cutting of circulation
Congenital hip dislocation
underdevelopment of acetabulum and head of femur, laxity of joint capsule.occurs before birth
common in breech deliveries
