Embryology 2 - Neurulation, Folding, and Development of Nervous System (Week 8) Flashcards by Stephanie South

What are the roles of the notochord?

1) Establishes the longitudinal axis of the embryo and gives it some rigidity

2) Provides signals for the development of axial MSK structures and the CNS

3) Contributes to the intervertebral discs

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How does the notochord form?

Note: this process occurs @ approx. day 16, 17, and 18

mesenchymal cells “dive” into the primitive pit, migrating towards the cephalad region
they stop at the prechordal plate (acts as “stop signal” from developing too far anteriorly)
in doing so, these cells form the notochordal process

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The notochordal process develops a lumen called the __________

Once this canal forms, the floor of the notochordal process fuses with the endoderm, replacing whatever endoderm was there with the notochord process.

notochordal canal

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Once the notochordal canal disappears and becomes the notochordal plate, we also get the ___________ canal, which allows for communication between the amniotic cavity and the umbilical vesicle.

neurenteric

Note: was once the primitive pit –> becomes neurenteric canal

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As the notochordal plate proliferates and folds into itself, it forms the ___________

@ ~ middle of 3rd week

notochord

Note: notochord is like a tube

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True or False: Notochord formation starts caudally and progresses cranially

False.

Notochord formation starts cranially (cephalad) and progresses caudally

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After the notochord is fully developed, the _____________ is fully obliterated

neurenteric canal

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True or False: The neural groove is a groove that is part of the ectoderm that is located on top of the notochord. On either sides of the groove, there are neural folds.

True

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What serves as the central axis of the embryo, dividing right from left?

the notochord

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What does the prechordal plate develop into?

the oropharyngeal membrane

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The oropharyngeal membrane is a two-layer membrane that includes an ________ and ________, but NO ____________

ectoderm and endoderm,

mesoderm

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What eventually becomes the future site of the anus?

cloacal membrane

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The cloacal membrane is a two layered membraned that includes an ____________ and ___________, but NO ___________

ectoderm and endoderm,

mesoderm

Note: similar to the oropharyngeal membrane

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True or False: The cloacal membrane forms caudal to the primitive streak

True

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A small, vascularized diverticulum (outpouching) from the caudal wall of the umbilical vesicle, extending into the connecting stalk

allantois

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What is the allantois involved with?

early blood formation
bladder development

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The ________ is a tube that extends from the bladder to the belly button (umbilical region) that closes after birth and becomes the ________________ in adults

urachus,

median umbilical ligament

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The notochord induces the overlying ectoderm to develop into the ____________

neural plate

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The process by which the neural tube is formed is called what?

neurulation

Note: begins with neural plate formation

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The neuroectoderm gives rise to what?

the CNS
retina
tissues that arise from the neural crest

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True or False: As the organism matures, the neural plate extends beyond the notochord

True

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On day 18, the neural plate invaginates to form the _____________, whereby neural folds are found on either side

neural groove

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When the neural folds fuse together, they form the ___________

neural tube

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When is neurulation complete?

By the end of the 4th week, when the tube becomes completely closed

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____________ are a subset of neuroectodermal cells that originate at the apex of the neural folds, lose affinity to the epithelium and neighbouring cells, and migrate widely on either side of the tube, throughout the mesenchyme

neural crest cells

What do the neural crest cells give rise to?

the peripheral nervous system (PNS)

What are some derivatives of the neural crest cells?

- ganglia of CN V, VII, IX, and X - spinal ganglia (dorsal root ganglia) - autonomic nervous system ganglia - neurolemma (Schwann) sheaths of peripheral nerves - contribute to arachnoid and pia mater - adrenal medulla - melanocytes - craniofacial bone and cartilage - portions of the heart

Intraembryonic mesoderm proliferates to form a thick column of mesoderm on either side of the notochord, called __________

paraxial mesoderm

The ____________ is found just lateral to the paraxial mesoderm

intermediate mesoderm

The ____________ is found just lateral to the intermediate mesoderm

lateral mesoderm

During the 3rd to 5th week, the paraxial mesoderm "bulks up" to form what?

somites

What are somites?

cuboidal masses of mesoderm on either side of the notochord, that give rise to most of the axial skeleton and associated musculature (e.g., erector spinae), as well as the dermis in those areas

During the 3rd week, mesenchymal cells migrate anteriorly, lateral to the notochordal process to eventually form the ____________

cardiogenic mesoderm Note: eventually gives rise to the embryonic heart primordia (aka the primordial heart)

REVIEW: what is a coelum?

a fluid-filled cavity

True or False: By about day 21, isolated coelomic spaces in the lateral mesoderm and cardiogenic mesoderm join together and form a single horseshoe-shaped intraembryonic coelom

True

The intraembryonic coelom is in the middle of and separates what two layers in the lateral mesoderm?

1) somatopleure (the somatic mesoderm and the overlying ectoderm; forms the body wall) 2) splanchnopleure (the splanchnic mesoderm and the underlying intraembryonic endoderm; forms the embryonic gut)

During the 2nd month, the intraembryonic coelom develops into what 3 body cavities?

1) pericardial cavity 2) pleural cavity 3) peritoneal cavity

REVIEW: The bilaminar embryonic disc --> trilaminar embryonic disc during gastrulation. What are the layers?

bilaminar (epiblast and hypoblast) --> trilaminar (ectoderm, mesoderm, endoderm) Note: When the endoderm forms, the hypoblast goes away. Everything in the middle becomes mesoderm. Everything left in the epiblast becomes the ectoderm.

What are the two general planes of embryonic folding ?

1) median plane folding (aka cranial-caudal folding) 2) horizontal plane folding (aka lateral folding)

the anterior and posterior ends of the embryo move ventrally

median plane folding/cranial-caudal folding

the lateral edges of the embryonic disk move ventrally, whereby the edges roll ventrally towards the umbilical vesicle

horizontal plane folding/lateral folding

When does embryonic folding begin?

By the end of the 3rd week, but is more prominent in the 4th week

As embryo folds cranially, what appears?

- brain vesicles - some somites

As embryo folds laterally, what forms?

the body wall

The foregut lies between the ________ and _________

forebrain, primordial heart

True or False: Part of the endoderm of the umbilical vesicle is incorporated into the embryo as the foregut

True

The __________ is the primordium of the mouth

stomodeum

The ___________ separates the foregut from the stomodeum

oropharyngeal membrane

The _____________ lies caudal to the heart and develops into the central tendon of the diaphragm, separating the abdominal cavity from the thoracic cavity

septum transversum

The pericardial coelom lies __________ (ventral/dorsal) to the heart

ventral (tummy side)

True or False: Part of the endodermal germ layer is incorporated into the embryo as the hindgut

True Note: similar to foregut

The connecting stalk is the primordium of what?

the umbilical cord

As the tail folds, the connecting stalk moves from caudal to _________ and the allantois becomes part of the embryo

ventral

True or False: During lateral folding, as the abdominal walls form, part of the endoderm germ layer is incorporated into the embryo as the midgut

True

The foregut and hindgut form during ____________ and the midgut forms during ___________

cephalad/caudal folding, lateral folding

After lateral folding, the midgut and umbilical vesicle are connected by the _________

omphaloenteric duct

What does the endoderm give rise to?

- epithelial lining of the digestive and respiratory tracts - parenchyma of the tonsils - thyroid and parathyroid glands, thymus - liver, pancreas - epithelial lining of the urinary bladder and most of urethra - epithelial lining of the tympanic cavity, tympanic antrum, and eustachian tube

What does the mesoderm give rise to?

- connective tissue (cartilage, bone) - striated and smooth muscle (heart, blood, lymphatic vessels) - ovaries, testes, genital ducts - serous membranes lining the body cavities (pericardial, pleural, peritoneal) - spleen - cortex of suprarenal glands

What does the ectoderm give rise to?

- CNS, PNS - sensory epithelia of the eyes, ears, nose - epidermis and its appendages (hair and nails) - mammary glands - subcutaneous glands - enamel of teeth - pituitary gland - neural crest cells

True or False: By the end of neurulation, after the neuropores close, a basic blood circulation has been established

True

The cranial 2/3 of the neural tube forms what?

the brain

The caudal 1/3 of the neural tube forms what?

the spinal cord

What are the three zones that develop during spinal cord development?

1) ventricular zone 2) intermediate zone 3) outer marginal zone

True or False: During spinal cord development, the outer marginal zone is the first of the three layers to develop

False The ventricular zone is the first to develop

What does the ventricular zone give rise to?

all neurons and macroglia

What does the intermediate zone become populated with?

primordial neuroblasts

What does the outer marginal zone develop into?

white matter tracts

Glioblasts are precursors to what?

glial cells

Alar plates eventually develop into?

dorsal gray horn (afferent/sensory nuclei)

Basal plates eventually develop into?

ventral gray horn (efferent/motor nuclei)

What are the spinal meninges derived from?

mesenchyme

Neuroepithelium (neuroectoderm) derivatives

- glioblasts - astroblasts - oligodendrocytes - ependymal cells (provide CSF) - neuroblasts --> eventually make neurons

Brain development occurs when?

beginning ~ week 5

What are the three primary brain vesicles?

1) forebrain (prosencephalon) 2) midbrain (mesencephalon) 3) hindbrain (rhombencephalon)

What two SECONDARY brain vesicles does the prosencephalon divide into?

1) telencephalon 2) diencephalon

What does the telencephalon give rise to?

cerebral hemispheres

What does the diencephalon give rise to?

thalami (thalamus, hypothalamus, epithalamus)

What does the midbrain give rise to?

midbrain (easy to remember!)

What secondary vesicles does the hindbrain (rhombencephalon) divide into?

1) metencephalon 2) myelencephalon

What does the metecephalon give rise to?

pons and cerebellum

What does the myelencephalon give rise to?

medulla

During week 4, lateral outgrowths/optic vesicles give rise to what?

retinae and optic nerves

Telencephalic vesicles give rise to what?

cerebral hemispheres and their cavities become the lateral ventricles

Three swellings develop in the lateral walls of the third ventricle, which go on to become what?

1) thalamus 2) hypothalamus 3) epithalamus Note: these are prevalent by week 7