Chapter 5 - Development Flashcards
Pre-embryonic stage
- conception to day 14
- fertilization in ovum
blastocyst
- pre-embryonic stage
- solid sphere of cells with cavity inside
- when cavity forms in fertilized egg
- outer layer will become fetal contribution of placenta
- inner cells will become embryo(embryonic disk)
- implants into the endometrium of the uterus
embryonic disk
2 layers:
1) ectoderm
2) endoderm
embryonic stage
Day 15 to eighth week
- organs are formed
ectoderm
sensory organs, epidermis, nervous system
mesoderm
dermis, muscles, skeleton, excretory and circulatory
endoderm
gut, liver, pancreas, respiratory
Fetal
9th week to birth
- nervous system develops and myelination begins
Neural plate
longitudinal thickening of ectoderm
- forms on the surface of embryo(head to tail)
Neural fold
edges of the plate fold toward each other
Neural tube
formed when neural folds touch(day 21)
- first closes in cervical region
- rostrally –> caudally - neuropores = openings of the tube
- superior neuropore closes = day 27
- inferior neuropore closes = day 30
- neural tube(day 26):
1) marginal layer(outer) = white matter(axons and glial cells)
2) mantle layer(inner) = cell bodies and gray matter
Neural crest
adjacent cells that separate from tube and remaining ectoderm
- tube and crest go inside embryo and covered by ectoderm(epidermal skin)
schlerotome
anteromedial part of somites
- vertebrae and skull
myotome
posteromedial part
- muscles
dermatome
lateral part
- dermis
ventral section
motor plate –> ventral horn
- axons from cell bodies –> myotome
- myotome:
1) embryologic section of somite
2) group of muscles innervated by nerve- cell bodies in dorsal root ganglia
conus medullaris
end of the spinal cord(L1 to L2)
conus equina
lumbosacral nerve roots extending inferior to end of spinal cord
filum terminale
end of dura, pia, and glia
hindbrain
myelencephalon = lower section metencephalon = upper section
- medulla, pons, cerebellum
midbrain
connects 3rd and 4th ventricles
forebrain
diencephalon = thalamus and hypothalamus
midline cavity –> third ventricle
telencephalon = anterior part(cerebral hemispheres)
central cavity –> lateral ventricles
- hemispheres expand ventrolaterally –> temporal lobe
- C-shaped
neurons migrate by
1) sending process to brain surface and follow process
2) climb along radial glia
glia
long cells that stretch from center of brain to surface
growth cone
forward end process that samples environment
neuronal death
failed to make optimal connections or too inactive
myelin sheath
insulation for axons
- lipids and proteins
- begins fetal month 4 –> 3rd year of life
growing into deficit
nervous system damage that occurred earlier is not evident until damaged system would normally become functional
Nervous system disorders
CNS most susceptible from day 14 –> week 20
Anencephaly
Neural tube defect
- formation of brain stem without cerebral and cerebellar hemisphere(die before birth)
- cranial end of tube does not close and no forebrain
- detected by:
1) maternal blood 2) amniotic fluid 3) ultrasound - causes:
1) chromosome abnormalities 2) maternal nutrition deficiencies 3) hyperthermia
Arnold-Chiari malformation
deformity of hindbrain
- type 1 and 2
Type 1 Arnold-chiari malformation
herniation of cerebellar tonsils through foramen magnum
- mostly no symptoms
- if symptoms, in adolescence, head and neck pain
- hydrocephalus = excess of CSF
- sensory and motor disorders
- malformation of lower cranial nerves
- hydrocephalus = excess of CSF
Type 2 Arnold-chiari malformation
malformation of brainstem and cerebellum
- extension of medulla and cerebellum through foramen magnum
- associated with meningomyelocele = nonclosure of neural tube
Spina bifida
inferior neuropore does not close
- vertebrae do not close around tube = bony defect at distal end of tube
- maternal nutritional deficits
spina bifida cystica
meninges and spinal cord through posterior opening of vertebrae
3 types:
meningocele, meningomyelocele, myeloschisis
Meningocele
meninges through posterior opening
meningomyelocele
neural tissue with meninges protruding outside of the body
- abnormal growth of spinal cord
- LE dysfunction
- cognitive dysfunction(abstract, visual, visual-motor)
myoloschisis
neural folds do not close
- malformed spinal cord open to surface
Tethered spinal cord
spinal cord adheres to lower vertebrae causing traction
- dermatome and myotome deficits in LE
- pain in saddle region
signs:
- progressive LE weakness, deterioration in walking, back and leg pain, excessive muscle resistance to stretch, scoliosis, foot deformity
spinal muscular atrophy
autosomal recessive disorder - motor neurons with cell bodies in spinal cord degenerate Type 1(most severe) Type 2(intermediate) Type 3(less severe)
Forebrain malformation
1 cerebral hemisphere instead of 2
- facial abnormalities
- holoprosencephaly(genetic)
- genetic testing and ultrasound
Intellectual Disability
abnormalities of dendritic spines
cerebral palsy
movement and postural disorder caused by damage to developing brain
- types: spastic, dyskinetic, ataxic, hypotonic, mixed
