Embryology of Cranium

Question 1

What is Head Mesoderm? How does it differ from Branchial Arch Mesencyme?

Answer 1

Head Mesoderm = rostral to the notocord, all types of mesoderm merge together (i.e. axial mesoderm of notocord and intermediate mesoderm of lateral plate); Branchial Arch Mesenchyme forms when neural crest cells migrate down.

Question 2

What cell type forms the neurocranium?

Answer 2

Head Mesoderm

Question 3

What cell type forms the viscerocranium?

Answer 3

Branchial Arch Mesenchyme

Question 4

What is the neurocranium?

Answer 4

Brain case (frontal bone, occipital bone, parietal bones)

Question 5

What is the viscerocranium?

Answer 5

Facial bones and cartilage

Question 6

How does the Cartilaginous Neurocranium form?

Answer 6

Intercartilaginous Ossification

Question 7

How does the Membranous Neurocranium form?

Answer 7

Membranous Ossification

Question 8

How does the Cartilaginous Viscerocranium form?

Answer 8

Cartilaginous Ossification

Question 9

How does the Membranous Viscerocranium form?

Answer 9

Membranous Ossification

Question 10

What is intercartilaginous ossification?

Answer 10

Mesenchyme gathers in regions of bone formation –> Mesenchyme lays down chondrocytes –> changes mesenchyme into patterns of future bones –> osteoblasts come and convert model to bone. “intercartilaginous ossification” b/c cartilage forms in bone.

Question 11

What’s intramembranous ossification?

Answer 11

Mesenchyme gathers in regions of bone formation –> membranes of mesoderm –> osteoblasts lay down spicules –> spicules of bone continue to be laid down and grow together to form flat bones

Question 12

Why is it important that ossification be completed after birth?

Answer 12

So the baby’s head can fit through the birth canal and so the head can continue to grow after birth

Question 13

What two disorders can occur if ossification occurs to early?

Answer 13

Craniosynostosis, Encephalocele

Question 14

Craniosynostosis

Answer 14

Ossification occurs too early; brain continues to grow but skull does not. Can decrease brain function / retardation

Question 15

Encephalocele

Answer 15

Ossification occurs too early; brain continues to grow, skull does not; part of the brain grows outside the skull

Question 16

What is the type of cartilage in cartilaginous viscerocranium?

Answer 16

Gill Arch Cartilage

Question 17

What does the Gill Arch Cartilage lead to?

Answer 17

Stapes, Incus, thyroid cartilage, thyroid cartilage

Question 18

Cartilage from which arches make up the Cartilaginous Viscerocranium?

Answer 18

All of them

Question 19

Mesenchyme from which arch forms the Membranous Viscerocranium?

Answer 19

1st arch only

Question 20

What bones make up the Cartilaginous Neurocranium?

Answer 20

ethmoid, sphenoid, occipital

Question 21

What bones make up the Membranous Neurocranium?

Answer 21

Frontal, Parietal

Question 22

What bones make up the Cartilaginous Viscerocranium?

Answer 22

Thyroid cartilage

Question 23

What bones make up the Membranous Viscerocranium?

Answer 23

Maxilla, mandible, nasal bone

Question 24

What cell type is the notocord made of?

Answer 24

Axial Mesoderm

Question 25

How is the notocord made?

Answer 25

Axial mesoderm secretes SHH --> Neural Plate --> overlying ectoderm changes fate to neural crest cells --> neural crest cells fold together --> Notocord

Question 26

Neural tube is ______________

Answer 26

Hollow and has CSF running through it

Question 27

Spinal Bifida Occulta

Answer 27

The neural tube does not close completely caudal; often sub-clinical.

Question 28

Spina Bifida Cystica

Answer 28

More serious than Spina Bifida Occulta; Vertebral Arch does not close all the way and spinal cord bulges out (risk of incontinence, paralysis)

Question 29

Spina Bifida with Myeloschisis

Answer 29

Most severe; Neural tube is open to the world... poses no problem in the womb but does after birth.

Question 30

What two regions comprise the forebrain?

Answer 30

The Telencephalon and Diencephalon

Question 31

Telencephalon (which ventricles?)

Answer 31

Most rostral; 1st and 2nd ventricles

Question 32

Diencephalon (which ventricles?)

Answer 32

3rd

Question 33

What is the mid-brain called? / Ventricle?

Answer 33

Mesencephalon / Cerebral Aquaduct

Question 34

What makes up the hind brain?

Answer 34

Metencephalon and Myencephalon

Question 35

What comprises the metencephalon?

Answer 35

Pons and Cerebellum

Question 36

What comprises the Myencephalon?

Answer 36

Brainstem and 4th ventricle

Question 37

What does the Choroid Plexus do?

Answer 37

Dangles down into each ventricle and pumps out CSF

Question 38

CSF's role?

Answer 38

Protection, carries growth factors and is important in terms of signaling btw different parts of CSF

Question 39

What does the Telencephalon form?

Answer 39

The neocortex; seat of higher cognition; most of what you're holding when you hold the brain

Question 40

What define the Telencephalon?

Answer 40

Sulci and Gyri

Question 41

What is the role of sulci and gyri?

Answer 41

Surface area; billions and billions of neurons need somewhere to go

Question 42

What is the sign of mental retardation?

Answer 42

Smooth brain

Question 43

Hydrocephalus

Answer 43

"Water in the brain"; caused by CSF blockage which compresses the growth of the brain; abnormal accumulation of CSF in the ventricles

Question 44

What is Rathke's Pouch?

Answer 44

Foregut; part of the stomodeum (ectoderm lined pit)

Question 45

What forms the pituitary gland?

Answer 45

Stalk pushes Rathke's Pouch (foregut) toward the infundibulum of the diencephalon (floor of forebrain); stalk regresses and Rathke's pouch forms anterior pituitary (adenohypophysis)

Question 46

Posterior Pituitary

Answer 46

formed by outgrowth of Diencephalon

Question 47

Meningocele

Answer 47

Protrusion of meninges through the skull or spinal column

Question 48

What is special about the 1st Branchial Arch? (4)

Answer 48

1) Contributes to both divisions of the Viscerocranium, 2) Splits into 2 distinct prominences, 3) contributes to middle and external ear, 4) plays essential role in palate formation

Question 49

Polyhydramnios

Answer 49

Excessive amniotic fluid; fetus does not control swallowing

Question 50

Anencephaly

Answer 50

No brain = Meroanencephaly,

Question 51

Exencephaly

Answer 51

Brain is located outside the skull