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DPT 736 Neuroanatomy > Embryology > Flashcards

Flashcards in Embryology Deck (26)
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1

3 Stages of Embryonic Development

-pre-embryonic: conception-day 14
-embryonic: day 14-end of 8th week
-fetal: end of 8th week to birth

2

Pre-embryonic

-fertilization
-ovum released from ovary
-fertilization of ovum divides as it moves down the uterine tube into uterus
-morula (solid ball of cells) forms and then forms a cavity inside
-cells are now called blastocyst (hollow ball)
-blastocyst cavity: will become yolk sac which nourishes embryo until placenta is fully formed
-outer layer: trophoblast will become placenta
-inner layer: inner cell mass will become embryo; develops into embryonic disc which has 2 cell layers (ectoderm, endoderm, and a third layer later forms between as the mesoderm)
-blastocyst implants into endometrium
-mother doesn't know she's pregnant

3

Embryonic Stage

-organs formed
-ectoderm: sensory organs, epidermis, and nervous system
-mesoderm: dermis, muscles, skeleton, excretory and circulatory systems
-endoderm: gut, liver, pancreas, and respiratory system
-neurulation occurs: folding process where neural plate forms neutral tube

4

Fetal Stage

-nervous system develops more and myelination begins

5

Formation of Nervous System

-occurs during embryonic stage
-two phases: phase 1-neural tube forms (day 21), develops into brain and spinal cord; phase 2-brain formation, begins when neural tube closes

6

Neurulation

-neural plate: thickening of ectoderm, forms on surface of embryo and extends from head to tail, floor of amniotic sac and therefore bathed in amniotic fluid
-neural folds: 3rd week after fertilization
-neural tube: commences in neck region
-neuropores: closed off by end of 4th week, superior closes at 27 days, inferior closes at 30 days, closure coincides with establishment of blood supply
-neural crest: cells from neural folds; becomes cranial and spinal nerves and schwann cells

7

Mantle

-by day 26 neural tube differentiates into 2 layers
-mantle layer: inner wall, contains cell body and becomes gray matter
-marginal layer: outer wall, contains processes of cells whose bodies are in gray and develops into white matter: axons and glial cells

8

Neural Tube Defects

-anterior neural tube defect: anterior neuropores fail to close results in anencephaly
-posterior neural tube defect: posterior neuropores fail to close results in spina bifida or myelomeningocele

9

Neurulation Pt 2

-walls of neural tube thicken to become the brain and spinal cord
-lumen becomes ventricular system and central canal

10

Spinal Cord

-dorsal tube=alar plate: sensory neurons, receive dorsal nerve roots growing in from spinal ganglia, becomes dorsal horn
-ventral tube=basal plate: motor neurons, ventral nerve roots, becomes ventral horn

11

Brain Vesicles

-prosencephalon: forebrain-made up of telencephalon (cerebral cortex, corpus stratum) and diencephalon (thalamus, hypothalamus, optic outgrowth)
-mesencephalon: midbrain-4th week=primitive brain folds at mesencephalon
-rhombencephalon: hindbrain made up of metencephalon (pons, cerebellum) and myelencephalon (medulla)

12

Ventricular System

-neural canal dilates and forms ventricular system (next 4 parts)
-hemispheres=lateral ventricles 1 and 2
-diencephalon=3rd ventricle
-midbrain=cerebral aqueduct, for CSF
-hindbrain=4th ventricle anterior to pons, posterior to cerebellum
-choroid plexus: secretes CSF

13

Cerebral Hemispheres

-by 14th week the frontal, parietal, temporal, and occipital lobes are identifiable
-insula only grows so much
-superior operculum (upper hat) covers insula top and inferior operculum covers bottom
-by 28th week the lateral, central and calcarine sulci are noticeable

14

Hydrocephalus

-water on the brian
-excessive CSF in ventricular system
-imbalance between production and absorption of CSF
-congenital aqueductal stenosis
-obstruction of foramina from 4th ventricle to subarachnoid space: arnold-chiari malformation=herniation of part of cerebellum and brainstem into foramen magnum
-meningitis: adhesions may compromise CSF flow
-increased fluid leads to increased pressure on neural structures
-thinning of the bones of calvaria, prominence of forehead, atrophy of cerebral cortex and white matter, and compression of basal ganglia and diencephalon
-tx: early identification, pressure sensitive catheter or shunt into internal jugular vein
-shunt: can go into jugular vein or into peritoneum; can get blocked can lead to H/A, vomiting, memory impairment

15

Microcephaly

-normal or slightly small calvaria
-fontanelles close during early infancy and sutures close during first year, brain is underdeveloped
-gross mentally impairments
-suture lines between skull plates not closed until 12-14 months

16

Anencephaly

-failure of rostral neuropore to close during 4th week
-forebrain abnormal and calvaria defective
-due to abnormal structure and vascularization the nervous tissue undergoes degeneration
-brain is spongy mass consisting mostly of hindbrain structures with no bone or skin covering
-lethal
-accounts for 1/2 of severe neural tube defects: most common severe anomaly seen in stillborn fetuses
-causes: genetic factors; high exposure to nickel, chromium, lead, mercury; higher in areas where depleted uranium and man-made isotopes; can be induced in rats by teratogenic agents
-prevention: folic acid .4 mg/day before pregnancy
-dx: ultrasound, alpha-fetoproteins in amniotic fluid
fetal counterpart to serum albumen, increased in neural tube defects, decrease in down syndrome

17

Naturally Occurring Folate

-beans and legumes
-citrus fruits and juices
-wheat bran and other whole grains
-dark green leafy vegetables
-poultry, pork, shellfish
-liver

18

Arnold-Chiari Malformation

-most common congenital anomaly involving the lower brainstem and cerebellum
-structural defect of the cerebellum with herniation of the medulla and part of cerebellum through foramen magnum
-may cause hydrocephalus
-occurs 1+/1000 births and is frequently associated with spina bifida and syringomyelia
-S&S: neck pain, balance problems, muscle weakness, numbness of other abnormal feelings in arms or legs, dizziness, vision problems, difficulty swallowing, ringing or buzzing ears, hearing loss, vomiting, insomnia, depression, or H/A made worse by coughing or straining
-hand coordination and fine motor skills may be affected

19

Spina Bifida

-nonfusion of embryonic halves of vertebral arches during 4th week
-types: spina bifida occulta, spina bifida cystica (with meningocele, or with myelomeningocele), spina bifida with myelocele

20

Spina Bifida Occulta

-usually clinically unimportant
-occurs in L5 or S1 in about 10% of otherwise normal people
-small dimple with tuft of hair
-small percentage may have functional deficits
-vertebra don't close completely

21

Spina Bifida Cystica

-cystlike sac: covered by skin or a thin, easily ruptured membrane; most common in lumbar region
-causes: combo of genetic and environmental factors-DM and anticonvulsant medication, fever or external temperature during neural tube development, obesity
-75% have latex allergies
-1/1000 births
-10% cyst in meningocele
-90% cyst is myelomenigocele

22

Spina Bifida with Meningocele

-protrusion of meninges through a defect in the vertebral arch
-varying levels of functional deficits depending on lesion site and extent of herniation
-high alpha-fetoproteins

23

Spina Bifida with Myelomeningocele

-protrusion of the meninges and spinal cord through a defect in vertebral arch
-marked neurologic deficit inferior to the level
-more serious than meningocele
-paralysis=lower limb, bladder and bowel
-learning disability common
-prevention: folic acid prior to conception

24

Spina Bifida with Myelocele

-most severe form of spina bifida
-neural folds have remained open
-CSF leaks out
-clinical outlook poor

25

Cranium Bifidum

-herniation of brain and/or meninges

26

Factors Affecting Brain Development

-genetic: down syndrome; brachycephaly (flat head on back)
-maternal infection: congenital rubella-mental retardation; toxoplasmosis-microcephaly, hydrocephalus, cerebral calcification
-plagiocephaly: flat head on one side
-environmental factors: radiation (cell depletion), steroids, chemical substances-alcohol (microcephaly), smoking (smaller frontal lobes and cerebellar volumes), marijuana (impairs nerve development and guidance-permanent cognitive deficits, concentration disorders, hyperactivity)