Development/Developmental Disorders Flashcards
Gastrulation
- phase in development during which the single layered blastula is reorganized into three germ layers (trilaminar)
- begins with formation of Primitive Streak (13-14 days)
3 Germ Layers
Ectoderm (nervous tissue, skin)
Mesoderm (CT, musculoskeletal)
Endoderm (visceral linings)
Neurulation (creates 3 things)
- Starts at 18 days
- Begins with formation of a neural plate
- Accomplishes 3 things: 1. Creates neural tube 2. creates neural crest 3. creates epidermis
Neural Plate
- thickening of ectoderm caused when cuboidal epithelial cells become columnar (formation of neural plate is beginning of neurulation)
- invaginates into mesoderm and edges approximate to form neural tube
Neural Tube
- formed from neural plate, gives rise to CNS
- formed by day 20
Neural Crest (6 things)
- migrates away from dorsal surface of neural tube, gives rise to diverse set of cell types
- becomes DRG, ANS ganglia, adrenal medulla, pigmented cells of skin/retina, pia matter, post lobe pituitary
Epidermis
covers neural tube once created
Implantation of the blastula occurs on Day ___
6
Primitive Streak
- 13-14 days
- invagination of cells to form the 3 germ layers
- Beginning of gastrulation
Primary Vesicle Stage
- begins when neural tube is fully closed (28 days)
- formation of prosencephalon, mesencephalon, rhombencephalon
Rhombencephalon
hindbrain
Mesencephalon
midbrain
Prosencephalon
forebrain
Cervical flexure
when mesen folds onto rhomben
Secondary Vesicle Stage
- 6 weeks
- prosencephalon becomes telencephalon (cerebral hemisphere) and diencephalon (thalamus)
- mesencephalon stays the same
- rhombencephalon becomes metencephalon (cerebellum, pons) and myelencephalon (medulla oblongata)
3 months
- telencephalon grows lateral, posterior over diencephalon
- peak of neural cell proliferation
6 months
- start to see sulci
- glial cell proliferation at peak
mantle layer of neural tube
-becomes grey matter, where neurons form
Marginal layer of neural tube
-becomes white matter (myelinated axons)
Basal plate & Alar plate of neural tube
basal plate forms ventral horn
alar plate forms dorsal horn
Surface ectodern
becomes epidermis, lens of eye
Somites
-each somite is divided into sclerotome, dermatome, and myotome
Myotome (2 parts)
supplied by one spinal nerve
2 parts:
1. epaxial division (dorsal rami - extensors of neck and back)
2. hypaxial (ventral rami - neck, prevertebral, and limb ms)
Occipital Myotomes (postotic)
give rise to muscles of tounge supplied by hypoglossal nerve
Preotic Myotomes
- cranial to occipital myotomes
- extra-ocular muscles of eye ( CN 3, 4, 6)
Otic Somites
balance/equilibrium, hearing
Pharyngeal (branchial) arches
- form in utero (week 4) as a series of mesodermal outpouchings on sides of developing pharynx
- form visceral structures
Myeloschisis (3 types)
- developmental anomoly characterized by a cleft spinal cord
- neuroplate fails to form complete tube
- spina bifida, anencephaly, Arnold-Chiari syndrome
Spina Bifida (5 types)
- most common form myeloschisis
- occulta, meningocele, meningomyelocele, syringomyelocele, myelocele
Spina Bifida Occulta
- failure of neural arches of vertebrae to fuse dorsally
- still have complete NS, get dimple in back with hair
Meningocele
- subarachnoid space bulges through unfused neural arches (dura and arachnoid bulge out)
- cyst made of dura and arachnoid passes through hole in vertebrae, filled w fluid
- surgically repaired
- can also happen in cranial meninges (named for location on skull)
Meningomyelocele
- caudal spinal cord and nerve root bulge though arch
- surgically repaired (if not problems with posture, bladder)
Syringomyelocele
- dorsal 1/2 of cord bulges out in cyst
- not compatible with life
Myelocele
-enitre cord bulges out, exposed to environment (no cyst)
Arnold-Chiari Syndome
-congenital anomoly in which cerebellum and medulla protrude into SC through foramen magnum
Anencephaly
- congenital absence of cranial vault
- defect in development of rostral neural tube – cerebral hemispheres don’t develop
Meningocephalocele
- protrusion of part of cerebellum, covered by meninges and skin
- defect at foramen magnum
Meningohydroencephalocele
-protrusion of part of occipital lobe containing part of
posterior horn of lateral ventricle
-defect at posterior fontanelle
