Embryology Week 5

What type of tumour can occur of the notochord fails to degenerate away?

Chordoma

What % of malignant bone tumours are chordomas?

2%

Which bones are chordomas found in?

The spine

What part of the spine is the most common site of chordomas?

Sacrum (50%)

What % of chordomas metastasize?

40%

What is the term for inward eye turning?

Esotropia

What is the term for outward eye turning?

Exotropia

What is the term for downward eye turning?

Hypotropia

What is the term for upward eye turning?

Hypertropia

What is the term for the overall process of forming the neural tube?

Neurulation

What week of gestation does neuralation occur in?

Week 3

What parts of the nervous system are formed by the neural tube?

Brain and spinal cord

What is the first structure to be formed in neuralation?

neural plate

What marks the end of neurulation?

Closure of the caudal neuropore

When does neurulation end?

End of week 4 gestation

What is the first stage of neurulation?

Formation of the neural plate

What germ layer does the neural plate arise from?

Ectoderm

What is the second stage of neurulation?

Elongation and shaping of the neural plate

What is the third stage of neurulation?

Lateral folding of the neural plate into neural folds and neural groove

What is the fourth stage of nuerulation?

Rolling up of the lateral folds and escape of the neural crest cells

What day does neuroectoderm formation begin on?

Day 18

Where do the neuroectoderm cells differentiate from?

Ectoderm

What is the AKA of the neuroectoderm?

Neural ectoderm

What is the term for the conversion of epithelial-type tissue into neural tissue in neurulation?

Neural induction

What 4 structures are involved in the conversion of ectodermal cells into neuroectoderm cells?

Notochord

Primitive node

Prechordal plate

Anterior visceral endoderm

What are the 2 main players in the conversion of ectodermal cells to neuroectoderm cells?

Notochord

Primitive node

What gene is turned off in neuroectoderm cells to allow for neural induction?

Bone morphogenetic protein-4 (BMP-4)

What is the default state of the ectoderm?

Neural tissue

What 3 genes inhibit BMP-4?

Noggin

Chordin

Cer-1

Where do noggin and chordin come from?

Primitive Node

Where does Car-1 come from?

Notochord, AVE cells, and prechordal plate cells

What does the neural plate become when it rolls up?

Neural tube

What structures arise from the neural tube?

Brain

Spinal cord

Neural crest cells (nerves)

What is the shape of the neural plate?

Key-shaped

Which end of the neural plate is wider?

Cranial portion

What is the term for the process of elongation of the neural plate?

Convergent extension

What does the wider portion of the neural plate form?

Brain

What does the narrow portion of the neural plate form?

Spinal cord

T or F: The elongated neural plate contains mostly neuroectoderm cells with deactivated BMP-4 genes

False (it is mostly ectoderm with active BMP-4)

What is the first step towards converting the neural plate into the neural tube?

Lateral folding

What is the shape of cells in the midline of the neural plate?

Narrow at the apex

Wider at the base

(pizza shaped)

What is created by the bending of the neural plate?

Right and left neural fold

What causes narrowing of the apex of cells at the median hinge point?

Shroom

What type of protein is shroom?

Actin-binding protein

What part of the midline neuroectoderm cells contracts to form the median hinge joint?

Apical region

What is the narrowest type of cytoskeletal protein?

Microfilament

What type of protein polymer are microfilaments made of?

2 Actin in a double helix

Where are microfilaments found in the cell?

Cytoplasm (endo/ectoplasm)

What is the function of microfilaments?

Provides structural strength to the cell

What type of forces are resisted by microfilaments?

Pulling forces

What movements are microfilaments responsible for?

Cytokinesis

Contraction

Gliding

Changing the shape of the cell

What is the term for the point in the midline which at which each side folds upward.

Median Hinge joint

What is the name of the newly created walls on either side of the median hinge point?

Neural folds

What is the term for the midline valley that is created between the folds?

Neural groove

What is the term for the shroom-activated cells in the middle of each lateral fold?

Lateral hinge points

What creates a more tube-like structure from the neural plate?

Lateral hinge joints

What new cell type forms at the lateral most region of the folding neural plate?

Neural crest cells

What is considered the fourth germ layer?

Neural crest cells

Where do neural crest cells arise from?

Junction of ectoderm and neural plate

What arises from the neural crest cells?

Nerves and ganglia

ON what day do the dorsal-most tips of the neural folds push together?

Day 21

What is formed from the neural folds joining?

Neural tube

What do neural crest cells morph into in order to escape the closure of the neural tube?

Mesenchymal cells

What is the term for migration of neural crest cells out of the neural tube?

Delamination

What type of transformation do neural crest cells perform before delimitation?

Epithelial-to-mesenchymal

What region of the neural tube closes first?

Middle region

What ends of the neural tube are left open for a long time?

Cranial and caudal ends

What is the AKA of the cranial neuropore?

Anterior neuropore

What is the AKA of the caudal neuropore?

Posterior/Rostral neuropore

Which neuropore closes first?

Cranial

When does the cranial neuropore close?

day 25 gestation

When does the caudal neuropore close?

Day 28

When is the process of neurulation complete?

When the neuropores are closed

What is the term for failure of the spinal cord portion of the neural tube to close?

Rachisichisis

Where are the neural crest cells derived from?

Ectoderm (from the epiblasts)

What causes the lateral most neuroectoderm cells to morph into neural crest cells?

Medium expression of BMP-4

Which genes are turned on by medium BMP-4 expression?

Foxd-3

Sox-10

Ets-1

GBX2 homeobox gene

What gene protects neural crest cells from damage and premature differentiation?

Sox-10

Where do crest cells migrate along?

Bottom of the ectoderm

Sides of the neural tube

What inhibits the migration of neural crest cells?

Chondriotin sulcate-containing proteoglycans

What structures do the neural crest cells give rise to?

PNS

ANS

DNRG

Adrenal medulla

T or F: Neural crest cells in the trunk give rise to the entire PNS of the trunk, while cranial neural crest cells only give rise to some of the peripheral nerves

True

What are the Merkel cells and discs derived from?

Ectoderm cells

What is the difference between a Merkel cella nd a Merkel disc?

Merkel disc = merkel cell + AB-afferent nerve endings

What is the neurilemma?

Plasma membrane of a Schwann cell

What are the epineurium, perineurium, and endoneurium derived from?

Mesoderm

What are the 4 parasympathetic ganglia?

Ciliary

Ethmoid

Sphenopalatine

Submandibular

What forms the outer skin covering in most places (epidermis)

Ectoderm

What forms the body's second layer of skin (dermis and hypodermis)?

Mesoderm

Where is most of the body's bone derived from?

Mesoderm

What makes up the leptomeninges?

Pia matera and arachnoid mater

What are the leptomeninges derived from?

Neural crest cells

Where is the dura mater derived from?

Mesoderm

Which parts of the skull are derived from the neural crest cells?

Squamous portion of calvarium

Parietal bone

Frontal bone

Maxilla

Mandible

Bones of the nasal cavity

Ethmoid bone and lacrimal

Middle ear ossicles

Auditory ossicles

What are the 3 auditory ossicles?

Malleus

Incus

Stapes

When is the primitive brain ready to be formed?

After the neuropores close, completing secondary neurulation

What are the 3 primary vesicles?

Prosencephalon

Mesencephalon

Rhombencephalon

What are the 5 secondary vesicles?

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon