Development of the Brain

Question 1

Neural tube development

Answer 1

Neural plate and neural groove first develop from neuroectoderm, induced by notochord in week 3
Neurulation begins in week 4
Cranial end–>4th pair of somites-future brain
Caudal end- future spinal cord
Neural tube forms at 5th somite

Question 2

Brain develops from the

Answer 2

Neural tube during the 3rd week, from cranial end to the 4th pair of somites

Question 3

Forebrain gives rise to

Answer 3

Telencephalon, diencephalon - these are considered the secondary vesicles
Forebrain/prosencephalon, midbrain/mesencephalon, hindbrain/rhombencephalon are primary vesicles

Question 4

Hindbrain gives rise to

Answer 4

Metencephalon, myelencephalon - also considered secondary vesicles

Question 5

Telencephalon derivatives

Answer 5

Walls- Cerebral hemispheres

Cavities- Lateral ventricles, anterior 3rd ventricle

Question 6

Diencephalon derivatives

Answer 6

Walls- thalami

Cavities- third ventricle

Question 7

Mesencephalon derivatives

Answer 7

Walls- midbrain

Cavities- aqueduct

Question 8

Metencephalon derivatives

Answer 8

Walls- pons, cerebellum

Cavities- upper part of fourth ventricle

Question 9

Myelencephalon derivatives

Answer 9

Walls- medulla

Cavities- lower part of fourth ventricle

Question 10

Cervical flexure

Answer 10

Demarcates the hindbrain from the spinal cord

Flexures form during the 5th week

Question 11

Pontine flexure

Answer 11

Formed by unequal growth

Divides hindbrain into the metencephalon and myelencephalon

Question 12

Alar plate neuroblasts

Answer 12

Form nuclei gracilus and cuneatus
GVA
SVA
GSA
SSA

Question 13

Basal plate neuroblasts

Answer 13

Develop into motor neurons
GSE
SVE
GVE

Question 14

Olivary nuclei

Answer 14

Formed from alar/basal plate neuroblasts

Question 15

Cerebellum derived from

Answer 15

Dorsal parts of alar plates

Question 16

Tela choroidea

Answer 16

Sheet of pia/ependymal roof covering lower 4th ventricle

Invaginates 4th ventricle to form choroid plexus

Question 17

Epithelia and stroma of choroid plexus are derived from

Answer 17

Epithelial lining- neuroepithelium

Stroma- mesenchymal cells

Question 18

Median and lateral apertures formed by

Answer 18

Evaginations of 4th ventricle, permit the CSF to enter subarachnoid space from 4th ventricle

Question 19

Superior and inferior colliculi derived from

Answer 19

Neuroblasts of alar plates

Question 20

Tegmental nuclei include what and are formed by

Answer 20

Include red, reticular, CN III, CN IV nuclei

Neuroblasts of basal plates

Question 21

Epithalamus development

Answer 21

Roof and dorsal portion of the lateral wall of the 3rd ventricle form epithalamus

Question 22

Pineal gland development

Answer 22

Formed by median diverticulum of the roof of diencephalon (epithalimus)

Question 23

Pituitary gland development- hypophyseal and neurohypophyseal diverticuli

Answer 23

Hypophyseal diverticulum: forms anterior lobe, glandular tissue
- formed by upgrowth of roof of surface ectoderm from stomodeum (mouth)
Neurohypophyseal diverticulum: posterior lobe, nervous tissue
- formed by downgrowth of neuroectoderm from diencephalon
Hypophyseal diverticulum lies near floor of diencephalon in 3rd week, connection to oral cavity degenerates in 6th week

Question 24

Telencephalon and formation of optic vesicles

Answer 24

As closure of rostral neuropore occurs, optic vesicles appear which form retinae and optic nerves
Cerebral hemispheres communicate with 3rd ventricle via interventricular foramina
Hemispheres become C-shaped because cortex rapidly proliferates while deeper nuclei do not

Question 25

Falx cerebri formed by

Answer 25

Mesenchyme trapped in longitudinal fissure

Question 26

Holoprosencephaly

Answer 26

Incomplete separation of cerebral hemispheres
Defects in forebrain development cause facial anomalies resulting from reduction of the forebrain FNP
-Clyclopia, premaxillary agenesis, proboscis, single-nostril, hypotelorism, facial clefts
- Many genes involved inhibit cholesterol synthesis- which leads to lack of sonic (Hedgehog?) signaling

Question 27

Cerebral commissures

Answer 27

Groups of nerve fibers interconnecting the cerebral hemispheres
Anterior & hippocampal commissures form first
Anterior connects olfactory bulb w/hemispheres
Hippocampal connects hippocampal formations
Anterior corpus callosum forms before posterior
Lamina terminalis is stretched forming the septum pellucidum- thin plate of brain tissue dividing right and left lateral ventricles

Question 28

Agenesis of corpus callosum

Answer 28

Complete or partial absence of corpus callosum
Condition may be asymptomatic, but seizures and mental deficiency are common
Associated with more than 50 congenital syndromes

Question 29

Brain reaches final size at age

Answer 29

7

Question 30

Histogenesis of the cerebral cortex

Answer 30

Cortical layers are laid down in a sequence from deep to superficial
Neurons migrate through deeper layers and exit, to establish more superficial layers
This causes earliest born neurons to be deepest in the brain

Question 31

Lissencephaly

Answer 31

Incomplete neuronal migration to cerebral cortex during 3-4 months of gestation
Cerebral surface exhibits pachygyria (broad, thick gyri), agyria, neuronal heterotopia (cells in aberrant positions), enlarged ventricles and malformation of corpus callosum
Patient initially appears normal but later develops seizures, profound mental deficiency and mild spastic quadriplegia

Question 32

Microcephaly

Answer 32

Calvaria and brain are small but face is normal size
Significant mental deficiency due to brain underdevelopment
Caused by autosomal recessive gene
Ionizing radiation
Cytomegalovirus, rubella, toxoplasma gondii
Maternal alcohol use

Question 33

Cranial and caudal neuropores close when

Answer 33

At 25 and 27 days, respectively

Question 34

Hypothalamus development

Answer 34

Arises from neuroblasts in the intermediate zone

Mamillary bodies form on ventral surface