Development of the Brain (Dennis)

Question 1

Describe neurulation

Answer 1

Week 3: Notochord induces posterior aspect of embryo to form neural plate and neural groove
Week 4: Neural tube forms from 5th somite (neurulation)

Question 2

Cranial 2/3 (up to 4th pair of somites) part of the neural tube becomes …
Caudal 1/3 part of the neural tube becomes…

Answer 2

• future brain

- future spinal cord

Question 3

When does cranial neuropore close?

When does caudal neuropore close?

Answer 3

• 25 days

- 27 days

Question 4

How does the brain proper develop?

Answer 4

Neural folds in the cranial region will fuse while the rostral neuropore will close to form the primary brain vesicles

Question 5

What are the primary brain vesicles?

Answer 5

Forebrain (prosencephalon)
Midbrain (mesencephalon)
Hindbrain (rhombencephalon)

Question 6

What happens at week 5?

Answer 6

Secondary vesicles form

Question 7

Describe the development of secondary brain vesicles:

Answer 7

Forebrain divides into telencephalon and diencephalon

Hindbrain divides into metencephalon and myelencephalon

Question 8

Label the parts of the developing brain

Answer 8

OK

Question 9

What does the developing brain do morphologically at week 5?

Answer 9

-Grows rapidly and bends ventrally (unequal)
-The bending produces the midbrain/mesencephalic flexure (midbrain) and cervical flexure (midbrain-SC junction)
Unequal growth produces the pontine flexure

Question 10

What is the significance of these flexures?
Cervical
Pontine

Answer 10

• divides the hindbrain from the spinal cord

- divides the hindbrain into the metencephalon (rostral) and myelencephalon (caudal)

Question 11

What does the myelencephalon form?
What does the metencephalon form?
What does the cavity of the hindbrain form?

Answer 11

• medulla oblongata
• pons and cerebellum
• 4th ventricle and central canal in the medulla

Question 12

Describe what happens to the caudal part of the myelencephalon

Answer 12

Neuroblasts in alar plate migrate to the marginal zone to form the nuclei gracilus and cuneatus (sensory nuclei)
Pyramids with CST fibers form at the ventral side

Question 13

Describe what happens to the rostral part of the myelencephalon

Answer 13

Pontine flexure causes wall of medulla to move laterally and the roof plate is thinned
After this movement, alar plate becomes lateral to the basal plate (sensory is lateral to motor)

Question 14

What do the neuroblasts at the basal plate of medulla form?

Answer 14

Motor neurons form three separate circles/columns - GSE, SVE, GVE

Question 15

What do the neuroblasts of the alar plate of medulla form?

Answer 15

Sensory neurons form the lateral circles/columns: GVA, SVA, GSA, SSA

Question 16

Somatic efferent column

Answer 16

CNs: III (in mesenscephalon)

IV, VI, XII (in rhombencephalon)

Question 17

Special/branchial efferent column

Answer 17

Rhombencephalon has V, VII, IX, X, XI

Question 18

Visceral efferent column:

Answer 18

Rhombencephalon has salivatory and dorsal nucleus of vagus Mesencephalon has the Edinger-Westphal nucleus (III)

Question 19

General visceral afferent column:

Answer 19

Has the nucleus that receives info via CN IX and X

Question 20

Special afferent column:

Answer 20

Has the nucleus of the tractus solitarius, which receives taste impulses via CN VII, IX and X

Question 21

General afferent column:

Answer 21

Receives general facial sensation (CN V and VII)

Oral, nasal and auditory cavities (CN V, VII, IX and X)

Question 22

Special somatic afferent column:

Answer 22

Has cochlear and vestibular nuclei (VIII)

Question 23

Metencephalon forms the …

Answer 23

Pons and cerebellum

Question 24

What does the pontine flexure do specifically?

Answer 24

Pushes the walls of the pons laterally, spreads gray matter in floor of 4th ventricle
Each basal plate has neuroblasts that develop into motor nuclei

Question 25

Cerebellum development

Answer 25

Forms from the dorsal part of the alar plate | Cerebellar swellings project into the 4th ventricle and fuse in median plane

Question 26

Describe the formation of the choroid plexus

Answer 26

Ependymal roof of the 4th ventricle is covered by pia forming the tela choroidea. This structure invaginates the 4th ventricle to form the choroid plexus

Question 27

Epithelium of the choroid plexus is derived from … | Stroma of the choroid plexus is derived from …

Answer 27

Neuroepithelium | Mesenchymal cells

Question 28

What are the median and lateral apertures?

Answer 28

Evaginations of the 4th ventricle at 3 different locations. Formation of these apertures allow the CSF to enter the subarachnoid space from the 4th ventricle

Question 29

What happens to the Alar plate neuroblasts in the midbrain?

Answer 29

Migrate to the tectum to form the superior and inferior colliculi

Question 30

Cerebral peduncles are formed from … | Cerebral aqueduct formed from ….

Answer 30

Fibers growing from the cerebral cortex | Narrowing of the neural canal

Question 31

Describe how the diencephalon develops:

Answer 31

Lateral walls of the 3rd ventricle will have swellings that form the thalamuses (thalamus, hypo and epi)

Question 32

Functions of the epithalmic sulcus and hypothalmic sulcus

Answer 32

Separates the thalamus from the epithalamus and hypothalamus respectively

Question 33

Describe how the thalamus develops

Answer 33

Bulges from the walls of the 3rd ventricle, fuses at midline and forms the interthalamic adhesion

Question 34

Describe how the hypothalamus develops

Answer 34

It arises from neuroblasts in the intermediate zone . Develops endocrine and homeostatic nuclei and forms Mammillary bodies on the ventral surface

Question 35

Describe how the pineal gland develops:

Answer 35

Forms a median diverticulum at the caudal part of the roof of diencephalon Cells proliferate and form the cone shaped gland

Question 36

Describe the development of the pituitary gland

Answer 36

Rathke's pouch (hypophyseal diverticulum) grows upward from the stomedeum while the neurohypophyseal diverticulum grows downward from the diencephalon > cells of both diverticulum proliferate to form certain parts > Neuroepithelial cells differntiate into pituicytes and nerve fibers grow into the pars nervosa from the hypothalamus

Question 37

Parts of the hypophyseal diverticulum: | Parts of the neurohypophyseal diverticulum:

Answer 37

Pars anterior and pars tuberalis | Median eminence, infundibulum and pars nervosa

Question 38

Hypophyseal diverticulum comes from which lobe and which tissue type? Neurohyophyseal diverticulum comes from which lobe and which tissue type?

Answer 38

- Anterior lobe, oral ectoderm | - Posterior lobe, neuroectoderm

Question 39

Telencephalon: What do the telencephalic/cerebral vesicles become? What does the median cavity of the Telencephalon become>

Answer 39

Median cavity of the telencephalon forms the 3rd ventricle while the two telencephalic/cerebral vesicles are the primordia of the cerebral hemispheres.

Question 40

What does the closure of the rostral neuropore induce?

Answer 40

Appearance of the optic vesicles (primordia of the retinae and optic nerves)

Question 41

How doe the hemispheres and the 3rd ventricle communicate?

Answer 41

Via the interventricular foramina

Question 42

Describe the development of the hemispheres:

Answer 42

From the primordia, hemispheres become more C shaped. Medial wall of the hemisphere becomes very thin and choroid plexus appears at this site. Hemispheres expand and cover the entire thing and meet at midline

Question 43

Falx cerebri develops from …

Answer 43

Mesenchyme trapped in the longitudinal fissure as the hemispheres develop

Question 44

Holoprosencephaly (HPE): Cause Clinical

Answer 44

Incomplete separation of the hemispheres caused by defects in forebrain development = facial anomalies Could result in cyclopia, premaxillary agenesis and other facial deformities

Question 45

Cerebral commissures are

Answer 45

Nerve fibers connecting the cerebral hemispheres

Question 46

Lamina terminalis forms

Answer 46

Septum pellucidum as it is stretched

Question 47

Anterior commissure connects | Hippocampal commissure connects

Answer 47

Olfactory bulb with hemispheres | Hippocampal formations

Question 48

Corpus callosum connects

Answer 48

Hemispheres along their length | Anterior develops before posterior

Question 49

Agenesis of corpus callosum:

Answer 49

Absence of corpus callosum | Seizures and mental deficiency, but can be asymptomatic. Mostly associated with congenital syndromes

Question 50

Describe the growth of cerebral hemispheres into sulci and gyri:

Answer 50

Cortex is smooth at first. It infolds and forms the gyri which basically increases surface area Birth brain is only at 25% volume, reaches final size at age 7

Question 51

Zones of the cerebral hemisphere:

Answer 51

Ventricular, intermediate and marginal. Subventricular appears later

Question 52

Describe the histogenesis of the cerebral cortex:

Answer 52

Neurons migrate from deeper layers to form the superficial layers to form cortical layers (inside out development)

Question 53

Lissencephaly

Answer 53

Incomplete neuronal migration to cerebral cortex at month 3 or 4 Smooth cerebral surface with gyri abnormality. Enlarged ventricles and malformed corpus callosum. Patient is normal at first but later develop seizures, mental deficiency and spastic quadriplegia

Question 54

Pachygyria Agyria Neuronal heterotopia

Answer 54

- broad, thick gyri - lack of gyri - cells in weird positions compared to normal brain

Question 55

Microcephaly

Answer 55

Reduction of brain growth due to inadequate pressure from growing brain. Caused by genetics, radiation, infection or alcohol abuse. Calvaria and brain is small but face is normal sized.