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DPT 736 Neuroanatomy > Embryology > Flashcards

Flashcards in Embryology Deck (26)
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1
Q

3 Stages of Embryonic Development

A
  • pre-embryonic: conception-day 14
  • embryonic: day 14-end of 8th week
  • fetal: end of 8th week to birth
2
Q

Pre-embryonic

A
  • 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
Q

Embryonic Stage

A
  • 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
Q

Fetal Stage

A

-nervous system develops more and myelination begins

5
Q

Formation of Nervous System

A
  • 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
Q

Neurulation

A
  • 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
Q

Mantle

A
  • 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
Q

Neural Tube Defects

A
  • 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
Q

Neurulation Pt 2

A
  • walls of neural tube thicken to become the brain and spinal cord
  • lumen becomes ventricular system and central canal
10
Q

Spinal Cord

A
  • 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
Q

Brain Vesicles

A
  • 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
Q

Ventricular System

A
  • 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
Q

Cerebral Hemispheres

A
  • 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
Q

Hydrocephalus

A
  • 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
Q

Microcephaly

A
  • 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
Q

Anencephaly

A

-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
Q

Naturally Occurring Folate

A
  • beans and legumes
  • citrus fruits and juices
  • wheat bran and other whole grains
  • dark green leafy vegetables
  • poultry, pork, shellfish
  • liver
18
Q

Arnold-Chiari Malformation

A
  • 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
Q

Spina Bifida

A
  • 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
Q

Spina Bifida Occulta

A
  • 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
Q

Spina Bifida Cystica

A
  • 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
Q

Spina Bifida with Meningocele

A
  • 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
Q

Spina Bifida with Myelomeningocele

A
  • 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
Q

Spina Bifida with Myelocele

A
  • most severe form of spina bifida
  • neural folds have remained open
  • CSF leaks out
  • clinical outlook poor
25
Q

Cranium Bifidum

A

-herniation of brain and/or meninges

26
Q

Factors Affecting Brain Development

A
  • 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)