Embryology of the Skull and its contents

Question 1

Head mesoderm versus Branchial (pharyngeal) Arch Mesenchyme:

Answer 1

BAM is a mixture of neural crest cells AND head mesoderm. Head mesoderm is rostral to the notocord and is a blend of many different kinds of mesoderm.

Question 2

Intracartilaginous versus intramembranous ossification (a review)

Answer 2

Intracartilaginous- Mesochyme condenses, forms chondroblasts which convert masses of mesenchyme into cartilage patterns of bones, then osteoblasts convert the cartilage model into bone.

Intramembranous Ossification: Mesochyme condenses and forms flat sheets; “membranes” of mesoderm, osteoblasts differenatiate and lay down bone spicules while membrane continues to grow. Over time, the flat sheet gets converted to flat bone. Continues past birth.

Question 3

Cartilaginous and membranous neurocranium:

Answer 3

Cartilaginous neurocranium forms the floor of the skull and is made through intracartilaginous ossification.

The membranous neurocranium forms the calvarium and is made through intramembranous ossification.

Both parts of the neurocranium are derived from head mesoderm.

Question 4

Cartilaginous and membranous viscerocranium:

Answer 4

There is a cartilaginous and a membranous viscerocranium- both derive from branchial arch mesenchyme.

The cartilaginous viscerocranium (formed from Cartilage Processes of ALL the branchial arches) forms middle ear bones, hyoid bone, and thyroid and laryngeal cartilages.

The Membranous viscerocranium (formed only from maxillary/mandibular processes or the 1st branchial arch) forms the upper and lower jaw, squamous temporal bone, nasal bone.

Question 5

Craniosynostosis :

Answer 5

Premature ossification of sutures- can cause twisting and deformities of the skull bones.

Question 6

Encephalocele:

Answer 6

Part of the brain is forced out of the skull.

Question 7

Neuroepithelium

Answer 7

(forms the neural tube): Will proliferate to form all neurons and glia in the brain.

Question 8

Central canal and ventricles:

Answer 8

Arises from the neural canal

Question 9

Cerebral Spinal Fluid (CSF):

Answer 9

Produced by the choroid plexus. Acts to protect, circulate growth factors, helps with signaling . . .

Question 10

Spina Bifida Occulta; Spina Bifida Cystica; Spina Bifida with Myeloschisis

Answer 10

Occulta: Incomplete fusion of vertebral arche (can be asymptomatic)
Cystica: Larger defect, permits cyst like protrusions of the spinal cord
Myeloschisis: Severe disruption of neural tube closure, vertebral arch fails to form and the neural tube is split open to outside world.

Question 11

Telencephalon, Diencephalon, Mesencephalon, Metencephalon, Myelencephalon:

Answer 11

These make up the 5 secondary brain vesicals

Question 12

Choroid Plexus :

Answer 12

Comes from a mixture of piamater, mesoderm and neural crest cells that Produce CSF. Is the roof of the 4th ventrical.

Question 13

Hydrocephalus:

Answer 13

Caused by a disruption of CSF transit

Question 14

Cerebral Hemispheres, Sulci, Gyri :

Answer 14

Formed from the telencephalon. Important for more surface area. (The telencephalon forms the giant round portion of the brain)

Question 15

Rathke’s Pouch and Infundibulum of the brain:

Answer 15

Rathke’s pouch is a dorsal diverticulum off the stomodeum. Infundibulum is a ventral diverticulum off diencephalon. They make the pituitary which is formed from 2 sources of ectoderm (the neural tube and the stomodeum).

Question 16

Adenohypophysis

Answer 16

= anterior pituitary, formed from rathke’s pouch

Question 17

Neurohypophysis

Answer 17

= posterior pituitary, derived from infundibulum

Question 18

Cranium Bifidum:

Answer 18

a split skull

Question 19

Meningocele, Meningoencephalocele (= Encephalocele) :

Answer 19

Herniation of meninges or brain from the skull.

Question 20

Meroanencephaly
Anencephaly
Exencephaly

Answer 20

Meroanencephaly (partial abscense of brain), Anencephaly (complete absence of brain), and Exencephaly (Brain forms outside of skull)

Question 21

Polyhydramnios :

Answer 21

Excessive amniotic fluid, a red flag that something is wrong with the nervous syndrome.

Question 22

The developmental origins and major divisions of the neurocranium

Answer 22

The neurocranium is derivied from head mesoderm where the viscerocranium is derived from branchial arch mesenchyme. The neurocranium has 2 major divisions, the cartilagenous neurocranium which is formed from Intracartilagenous ossification and forms the floor of the skull. And the membranous neurocranium which is made through intramembranous ossification and forms the calvarium.

Question 23

The developmental origins and major divisions of the viscerocranium:

Answer 23

Likewise, there is a cartilaginous and a membranous viscerocranium- both derive from branchial arch mesenchyme. The cartilaginous viscerocranium (formed from Cartilage Processes of all branchial arches) forms middle ear bones, hyoid bone, and thyroid and laryngeal cartilages. The Membranous viscerocranium (formed from maxillary/mandibular processes) forms the upper and lower jaw, squamous temporal bone, nasal bone.

Question 24

The contribution of the branchial arch mesenchyme to the skull:

Answer 24

Forms ALL the viscerocranium, where as the neurocranium forms from head mesoderm.

Question 25

Formation of the primary and secondary brain vesicles, and what they give rise to

Answer 25

Primary vesicles are the forebrain, midbrain and hindbrain

Secondary vesicles:
Telencephalon (contains ventricals 1 and 2) and Diencephalon (contains third ventrical) of the forebrain.
Mesencephalon (contains cerebral aquaduct) of the midbrain.
Metencephalon (forms the pons and the cerebellum) and Myelencephalon (forms the medulla and the brainstem, contains the 4th ventrical) of the hindbrain.

Question 26

What the neural canal gives rise to in the brain and spinal cord:

Answer 26

Give rise to the ventricles of the brain which contain CSF and the central canal of the spinal cord.

Question 27

What can happen when the caudal or rostral neuropore fails to close?:

Answer 27

Spina bifida.

Question 28

The general location of the four ventricles (in which regions of the brain?)

Answer 28

Telencephalon contains ventricle 1 and 2.
Diencephalon contains ventricle 3.
Myelencephalon contains ventricle 4.

Question 29

What happens if the flow of CSF through the ventricles is disrupted:

Answer 29

You can get brain swelling, results in hydrocephalus and compression of the neural tube.

Question 30

What the Telencephalon and Diencephalon form (to the extent we cover them in class):

Answer 30

Telenecephalon forms the cerebral hemispheres and makes us human. Diencephalon forms the optic nerves and retina, infundibulum(ventral diverticulum) and pineal gland (dorsal diverticulum).

Question 31

How the pituitary (hypophysis) forms from two sources of ectoderm:

Answer 31

The two sources are the stomodeum and the diencephalon.

Question 32

What types of defects occur when the cranial sutures close prematurely:

Answer 32

Craniosynostosis

Question 33

What types of defects can occur when the skull bones fail to close correctly

Answer 33

Meningiocele, encephalocele