Development of the Brain

Question 1

When does the brain develop?

Answer 1

During the 3rd week

Question 2

What does the brain develop from?

Answer 2

From the neural tube, cranial to 4th pair of somites

Question 3

How do the primary brain vesicles form?

Answer 3

Fusion of neural folds in cranial region and closure of rostral/cranial neuropore

Question 4

What are the primary brain vesicles?

Answer 4

Forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon)

Question 5

What secondary vesicles does the prosencephalon give rise to?

Answer 5

Telencephalon and diencephalon

Question 6

What secondary vesicles does the mesencephalon give rise to?

Answer 6

Mesencephalon

Question 7

What secondary vesicles does the rhombencephalon give rise to?

Answer 7

Metencephalon and myelencephalon

Question 8

What does the telencephalon give rise to?

Answer 8

Cerebral hemispheres and lateral ventricles

Question 9

What does the diencephalon give rise to?

Answer 9

Thalami (hypothalamus, epithalamus, thalamus) and 3rd ventricle

Question 10

What does the mesencephalon give rise to?

Answer 10

Midbrain and aqueduct

Question 11

What does the metencephalon give rise to?

Answer 11

Pons and cerebellum and upper part of 4th ventricle

Question 12

What does the myelencephalon give rise to?

Answer 12

Medulla and lower part of 4th ventricle

Question 13

What causes brain folding/flexures?

Answer 13

Unequal proliferation in different brain vesicles

Question 14

What is the first flexure to fold?

Answer 14

Midbrain flexure (mesencephalic flexure). Flattening/face down forward motion of telencephalon and diencephalon at junction with mesencephalon

Question 15

What is the second flexure to fold?

Answer 15

Cervical flexure. Forward bending at hindbrain/spinal cord junction creates positioning of brainstem underneath brain

Question 16

What is the third flexure?

Answer 16

Pontine flexure. Folds backward at metencephalon/myelencephalon junction. Positions cerebellum over/posterior to pons

Question 17

What forms in the caudal myelencephalon?

Answer 17

Nuclei gracilus and cuneatus (from alar plate)

Pyramids (basal plate)

Question 18

What forms in the rostral myelencephalon?

Answer 18

Alar plates (sensory/afferent inputs) and basal plates (motor/efferent outputs)

Question 19

How does the pontine flexure move the alar and basal plates?

Answer 19

Alar plate moves lateral to basal plate

Question 20

Neuroblasts in the basal plate develop into what?

Answer 20

Efferent neurons

Question 21

Neuroblasts in the alar plate develop into what?

Answer 21

Afferent neurons

Question 22

How are the olivary nuclei formed?

Answer 22

Alar neurons migrate anteriorly

Question 23

How does the cerebellum develop?

Answer 23

From the dorsal parts of alar plates. Cerebellar swellings arise which fuse over the median plate, overgrowing the posterior side of the 4th ventricle

Question 24

How does the choroid plexus form? (specifically in 4th ventricle)

Answer 24

Initially has a basic organization (pia + ependymal roof) without invaginations/layering called tela choroidea on roof of 4th ventricle. Then invaginates into 4th ventricle to form choroid plexus

Question 25

How do the median/lateral apertures form?

Answer 25

The roof of the 4th ventricle ruptures/evaginates in 3 locations to permit CSF to enter subarachnoid space

Question 26

In the midbrain, what is the tectum?

Answer 26

Forms from neuroblasts of the alar plate migrating together. Then forms superior (vision) and inferior (auditory) colliculi

Question 27

In the midbrain, what are tegmental nuclei?

Answer 27

Form from neuroblasts of basal plates (red nuclei, reticular nuclei, CN III/IV nuclei)

Question 28

What are the cerebral peduncles in the midbrain?

Answer 28

Also known as the crus cerebri, extensions of white matter. Fiber tracts from cortex to rest of body.

Question 29

How is the cerebral aqueduct formed?

Answer 29

Narrowing of neural canal in the midbrain

Question 30

What is the substantia nigra?

Answer 30

Nucleus important for movement, unsure whether alar or basal derivative

Question 31

How are the thalami formed?

Answer 31

Swellings in lateral walls of 3rd ventricles form the thalamus, hypothalamus, and epithalamus

Question 32

What separates the thalamus and epithalamus?

Answer 32

Epithalamic sulcus

Question 33

What separates the thalamus and hypothalamus?

Answer 33

Hypothalamic sulcus

Question 34

What structure is present in people whose thalamus have fused?

Answer 34

Massa intermedia (interthalamic adhesion/mass) connects R and L thalamic structures in 70% of people

Question 35

How is the hypothalamus formed?

Answer 35

Arises from neuroblasts in intermediate zone. Mammillary bodies form on the anterior surface

Question 36

Where does the pineal gland come from?

Answer 36

From the epithalamus

Question 37

How does the epithalamus form?

Answer 37

From roof/posterior portion of lateral wall of 3rd ventricle

Question 38

What does the pineal gland do?

Answer 38

Regulates sleep/wake cycles

Question 39

What is the infundibulum?

Answer 39

Attaches the posterior pituitary to the hypothalamus

Question 40

How is the anterior pituitary made?

Answer 40

Upgrowth of surface ectoderm from roof of stomodeum called the hypophyseal diverticulum (Rathke's pouch)

Question 41

How is the posterior pituitary made?

Answer 41

Downgrowth of diencephalon (neuroectoderm) called the neurohypophyseal diverticulum

Question 42

When does the pituitary gland develop?

Answer 42

3rd week

Question 43

When does the connection of the anterior pituitary to the oral cavity degenerate?

Answer 43

6th week

Question 44

What does the telencephalon divide into?

Answer 44

Two telencephalic/cerebral vesicles which then make the cerebral hemispheres

Question 45

What happens after rostral neuropore closes?

Answer 45

Optic vesicles appear

Question 46

Where does the falx cerebri come from?

Answer 46

Mesenchyme is trapped in the longitudinal fissure when cerebral hemispheres expand and meet each other in the midline

Question 47

What is holoprosencephaly?

Answer 47

Failure of telencephalon to divide into R/L cerebral vesicles (single-lobed brain). Impairs cholesterol synthesis and therefore SHH signaling

Question 48

What are commissures?

Answer 48

White matter tracts that connect different brain regions to each other (ex: corpus callosum)

Question 49

Where do commissures form?

Answer 49

In the lamina terminalis (rostral/inferior end of forebrain)

Question 50

What do anterior commissures connect?

Answer 50

R and L olfactory areas

Question 51

What do hippocampal commissures connect?

Answer 51

R and L hippocampi

Question 52

What do posterior commissures connect?

Answer 52

R and L temporal lobes

Question 53

What does the corpus callosum connect?

Answer 53

R and L hemispheres

Question 54

What is the septum pellucidum?

Answer 54

A thin plate of brain tissue that separates R and L lateral ventricles

Question 55

How does postnatal growth of the brain occur?

Answer 55

Neurons increasing in size and myelination of axons

Question 56

How does the cortex grow?

Answer 56

New neurons migrate through deeper layers to exit to the surface and establish more superficial layers ('inside out' development)

Question 57

What is lissencephaly?

Answer 57

Abnormal migration of new neurons onto surface. Smooth brain = decreased gyration of brain. Developmental and mental abnormalities and seizures

Question 58

What is microcephaly?

Answer 58

Calvaria and brain are underdeveloped