Embryology - Development of the Spinal Cord, PNS, SS, MS Flashcards
Describe neurulation
formation of the neural tube - sides of the neural plate elevate to from neural grove which then fuse.
what will the neural tube become?
brain and spinal cord
what forms neural crest cells?
neuroectoderm as the neural tube is closing - migrate into underlying mesoderm.
What do cranial neural crest cells form?
- bones, cartilage, fascia, ligaments and tendons of face and neck
- sensory ganglia, autonomic ganglia
- (shared) meninges, schwann cells, melanocytes
What do spinal neural crest cells form?
- dorsal root ganglia, autonomic ganglia
- fibrous skeleton of the heart
- (shared) meninges, schwann cells, melanocytes
What becomes the spinal cord?
neural tube caudal to 4th pair of somites
What are the three different regions that form in the neural tube and give rise to the different areas of the spinal cord.
ventricular - contains neuroepithelium that gives rise to neurons and glia
mantle - have alar and basal plate which become horns
marginal - outermost, will contain axons
What forms ventral motor horns and dorsal sensory horns?
neuroblasts
What forms astrocytes and oligodendrocytes?
gliablasts
Where does the spinal cord extend to at birth?
LV4-LV5
In adults where does the spinal cord end?
LV1-LV2
At what point does the vertebral cord extend the whole length of the vertebral column?
during the 3rd month of gestation
What is the active movement of axon toward an end organ or target?
neuronal pathfinding - follows signals released from somatic mesoderm
When do dorsal and ventral rami form?
when the somite splits into epimere (dorsal) and hypomere (ventral)
What three things does a somite split into?
myotome - skeletal muscle
dermatome - area of skin innervated by one spinal nerve
schleratome - axial skeleton
What results when vertebral arches of spinal cord fail to fuse?
spina bifida occulta
What results when the vertebral arches of the spinal cord fail to fuse, involving the meninges and/or neural tissue?
spina bifida cystics
- spina bifida with meningocele
- spina bifida with meningomyelocele
What results when the neural plate fails to elevate and fuse?
spina bifida with myeloschisis
What is the process where the caudal have of schlerotome fuses with cranial half of neighbor to form the vertebral body?
resegmentation
how do intervertebral disks form?
annulus fibrosis is formed from mesenchymal cells
nucelus pulposus formed from the notochord
what does rearrangement of sclerotomes result in?
- myotomes spanning the intervertebral discs
- spinal nerves exit between contiguous vertebrae
- intersegmental arteries pass midway over vertebral bodies
What do ribs form from?
originate from costal processes of the 12 thoracic vertebra
What does the sternum originate from?
form from ventral somatic ventral mesoderm of a pair of vertical bands called the sternal bars. ribs grow to and attach
What are two congenital causes of scoliosis?
asymmetric fusion of vertebra
half of vertebra doesnt form
What syndrome is caused by lack of resegmentation leading to fused cervical vertebrae?
Klippel-Feil Syndrome
Describe the difference between pectus excavatum and pectus carinatum?
both are cased by excessive rib growth
- excavatum: sunk in
- carinatum: protrudes out
Describe myogenesis.
mesoderm cells differentiate into myoblasts primordial muscle cells) which elongate and fuse together to form myotubes. Becomes a muscle fiber with the formation of contractile filaments in the cytoplasm of myotube.
What syndrome is characterized by absent/underdeveloped pectoralis muscles and syndactyly of the fingers possibly due to loss of blood supply to chest wall during development?
Poland syndrom
What is the ectodermal thickening at the apex of the limb bud called?
apical ectodermal ridge (AER)
When does limb bud formation occur?
upper = day 26/27 lower = day 27/28
During week 5 the ends of the limb buds begin to flatten and separate from limb bud. What is this structure called?
handplates or footplates
How are digital rays formed?
through ones of apoptosis (upper 6th, lower 7th)
How are joints formed?
joint cavity is formed by cell death and surrounding cells differentiate into joint capsule.
What limbs rotate the most causing a twisting of the dermatome?
lower limbs
Why do sensory nerves ‘spiral’ around limb while motor fibers are distributed through and dont follow dermatome innervation?
sensory nerves are ‘pulled’ into limb as it develops while motor nerves grow into limb with myotomes.
What portion of myotome becomes flexor muscles? extensor?
anterior = flexor posterior = extensor
What is it called when the limb is absent due to suppression of limb bud development?
Amelia
What is it called when only part of a limb is absent due to arrest of limb bud?
Meromelia
- phocomelia is type involving absence of long bones
shortness of digits?
brachydactyly
fusion of two or more digits from insufficient apoptosis between digital rays?
syndactyly
extra fingers and toes?
polydactyly
absence of digit?
ectrodactyly
What is cleft hand or foot?
absence of 3rd metacarpal as well as fusion of thumb to second digit, and fusion of 4th to 5th
how is clubfoot caused?
caused by abnormal position of the foot leading to deformed development, often by the presence of too little amniotic fluid
Why are amniotic membrane strips in the amniotic fluid a problem?
causes amniotic bands - encircle portions of the fetus cutting off blood supply and amputating limbs or digits
