Development Of The Brain Flashcards
When and where does the neural plate and neural groove develop?
Week 3
On posterior aspect of the Trilaminar embryo
What induces the development of the neural plate and neural groove?
Notochord
When does Neurulation begin?
Week 4
22-23 days
What does the cranial 2/3rds of the neural plate form?
Future brain
4th pair of somites
What does the caudal 1/3 of the neural plate form?
Future spinal cord
What does the 5th somite form?
Neural tube
When does the cranial neuropore close?
Day 25
When does the caudal neuropore close?
Day 27
What is the origin of the neural plate and neural groove?
Neuroectoderm
What does the brain develop from? And when?
3rd week from neural tube
What is the neural tube?
Cranial to 4th pair of somites
What are primary brain vesicles formed from?
Fusion of neural fold in cranial regions
&
Closure of rostral neuropore
What are the primary brain vesicles?
Forebrain (prosencephalon)
Midbrain (mesencephalon)
Hindbrain (rhombencephalon)
What happens during the 5th week?
Secondary brain vesicle form
What are the secondary brain vesicles?
Telencephalon Diencephalon Mesencephalon Metencephalon Myelencephalon
What secondary brain vesicles are formed from the
Forebrain?
Telencephalon
Diencephalon
What secondary brain vesicles are formed from the
Midbrain?
None - stays as the Mesencephalon
What secondary brain vesicles are formed from the
Hindbrain?
Metencephalon
Myelencephalon
What are the adult derivates that come from the
Telencephalon?
Walls: cerebral hemispheres
Cavities: lateral ventricles
What are the adult derivates that come from the
Diencephalon?
Wall: Thalami
Cavities: Third ventricle
What are the adult derivates that come from the
Mesencephalon?
Walls: midbrian
Cavities: aqueduct
What are the adult derivates that come from the
Metencephalon?
Walls: Pons & cerebellum
Cavities: upper part of 4th ventricle
What are the adult derivates that come from the
Myelencephalon?
Walls: medulla
Cavities: lower part of the fourth ventricle
What happens during the 5th week?
Secondary brain vesicles form
Embryonic brain grows rapidly
Bends ventrally with the head fold
What does the bending of the brain produce?
Midbrain flexure
Cervical flexure
What is the cervical flexure?
Hindbrain- SC junction
What produces the pontine flexure?
Unequal growth
What is the pontine flexure?
Meten - myelencephalon junction
This is what eventually moves cerebellum up and over the pons
What is the first flexure to form?
Mesencephalic flexure
Where is the junction of the cervical flexure?
At level of superior rootlet of C1
Roughly at foramen magnum
What does the pontine flexure do?
Divide the hindbrain into
Metencephalon (pons and cereb.)
&
Myelencephalon (medulla)
What does the cavity of the hindbrain produce?
Fourth ventricle
Central canal in medulla
In the caudal myelencephlon what do neuroblasts in the alar plate do?
Migrate into marginal zone
Form nuclei Gracilus & Cuneatus
What are nuclei Gracilus and Cuneatus?
Sensory nuclei that associate w/ paired, afferent tracts
What are the pyramids of the myelencephalon?
Ventrally located structures consisting of CST fibers
What does the pontine flexure do in the rostral myelencephalon?
Causes walls of medulla to move laterally, thinning the roof plate
Cavity is now made and will be part of future 4th ventricle
What are the alar plates of the myelencephalon compared to the basal plates?
Alar plates are more lateral
Makes motor nuclei develop medial to sensory
What do the neuroblasts in the basal plate of the medulla develop into?
Motor neurons
How do the nuclei of the basal plate organize?
GSE
SVE
GVE
(GVE - closest to sulcus limitans)
How are neuroblasts in the alar plates of the medulla arranged?
GVE
SVA
GSA
SSA
(SSA is farthest from sulcus limitans)
What will some neuroblasts of the alar plates do?
Migrate ventrally and form neurons in the Olivary nuclei *
Of the basal columns, what does the GSE column consist of?
- Nucleus of CN 12 in caudal most rhombencephalon
- CN 6 more cranially in rhombencephalon
• Cn 4 in most cranial rhombencephalon
◦ Will later be displaced into caudal midbrain
• CN 3 in mesencephalon
Of the basal columns, what does the SVE column consist of?
- 3 nuclei serving ns. 5, 7 ,9-11 confined in rhombencephalon
- Cn 5 and 7 = cranially located in rhombencephalon
- CNs 9, 10, 11 = caudally located in rhombencephalon, supplied by Nucleus Ambiguus
Of the basal nuclei, what does the GVE column consist of?
• 2 nuclei in rhombencephalon
◦ Salivatory nucleus
‣ Pre-g parasympathetic to salivary and lacrimal glands
◦ Dorsal Nucelus of vagus ‣ Caudal to salivatory nucelus ‣ Pre-g parasympathetic to CN 10 to innervate viscera
• In mesencephalon
◦ Edinger-WEstphal nucleus
‣ CN3 - constrict eye
Of the alar columns, what does the GVA column consist of?
- Nucleus receiving interocetpive info
* Via CN 9 and 10
Of the alar columns, what does the SVA column consist of?
• Nucleus of Tractus Solitarius
◦ Taste impulses
◦ Via CN 7, 9, 10
Of the alar columns, what does the GSA column consist of?
• Neurons receiving impulses from general sensation from:
◦ CN 5 - areas of face
◦ Cn 7 - areas of face
◦ Cn 5, 7, 9, 10 - oral, nasal, external auditory, and pharyngeal/laryngeal cavities
Of the alar columns, what does the SSA column consist of?
• Cochlea and Vestibular Nuclei ◦ Cn 8
◦ Special senses of balance and hearing
In the Metencephalon what does the pontine flexure do?
Forces walls of pons laterally, spreading grey matter in floor of 4th ventricle
How does the cerebellum develop?
From the metencephalon’ s dorsal parts of alar plates
Cerebellar swellings project into the fourth ventricle and fuse in median plane
Overgrown rostral 4th ventricle and overlaps pons and medulla
What covers the ependymal roof of the fourth ventricle?
What is this derived from?
Pia mater
Hindbrain Mesenchyme
What forms the tela choroidea?
Pia + ependymal roof
What is the tela choroidea?
Sheet of Persia covering the lower part of the 4th ventricle that invaginates the 4th ventricle to form the choroid plexus
What is the epithelial lining of the choroid plexus derived from?
Neuroepithelium
What does the stroma of the choroid plexus develop from?
Mesenchymal cells
Where do plexuses similar to the choroid plexus develop?
Roof of 3rd ventricle
Medial walls of lateral ventricles
What forms the median and lateral apertures?
Invagination of the 4th ventricle’s roof in 3 location and the subsequent rupture of it
What is the function of the median and lateral apertures?
Permit CSF to enter subarachnoid space from the 4th ventricle
How do the superior and inferior colliculi form?
From midbrain neuroblasts of alar plates migrating into the tectum (Roof)
What do neuroblasts of the basal plate of the midbrain form?
Tegmental nuclei
What are the tegmental nuclei in the midbrain?
Red nuclei
Reticular nuclei
CN 3 and 4 nuclei
What is the superior colliculi pathway?
Superior colliculi —> branchium of the sup. Colliculi —> lateral genicular nucleus —> sight
What is the inferior colliculi pathway?
Inferior colliculi —> branchium of the inferior colliculi —> medial geniculate nucleus —> hearing
What forms the substantia nigra?
EITHER basal or alar plates of midbrain
Still debated
How does the crus cerebri form?
Fibers growing form the cerebral cortex form the cerebral peduncles
How does the cerebral aqueduct form? What does it do?
Neural canal narrows
Connects 3rd and 4th ventricles
What odes the diencephalon form?
Thalami from 3 swellings in the lateral walls of the third ventricle
(Thalami = thalamus, epi, hypo)
What does the epithalamus sulcus do?
Separates thalamus and epithalamus
What does the hypothalamic sulcus do?
Separates thalamus and hypothalamus
How does the thalamus develop?
Develops on each side of third ventricle and fuses at midline forming interthalamic adhesion or Mass Intermedia
How often does the interthalamic adhesion form?
70% of the time
20% of the time, Massa Intermedia is absent
What forms the hypothalamus?
Neuroblasts in the intermediate zone of the diencephalon
What develops in the hypothalamus?
Endocrine and homeostatic nuclei develop
Mammillary bodies form on ant. Surface
What makes the majority of the 3rd ventricle?
Diencephalon
How does the epithalamus develop?
From roof and dorsal portion of the lateral walls
Swelling originally quite large but become small
How does the pineal gland develop?
Develops as a median diverticulum of the caudal part of the roof of the diencephalon
Will proliferate in its walls, converting it into a solid, cone-shaped gland
What does the pineal gland do?
Regulate sleep and wake cycles
What two diverticulum does the pituitary gland develop from?
Hypophyseal diverticulum
Neurohypophyseal diverticulum
What is the hypophyseal diverticulum derived from?
Surface ectoderm since it is an upgrowth of roof of stomodeum
What is the neurohypophyseal diverticulum derived from?
Neuroectoderm since it is a downgrowth from the diencephalon
Where is the hypophyseal diverticulum located during week 3?
Wk 3 = near floor of diencephalon
What is the infundibulum?
Stalk that passes between the developing bones of the cranium to the posterior pituitary gland
How is the anteiror pituitary gland attached to the brain?
It’s not!
When does the hypophyseal diverticulum’s connection to the oral cavity degenerate?
Week 6
How does sella turcica develop?
Forms around the pituitary gland and makes that nice little saddle
What two things will the hypophyseal diverticulum make?
Pars anterior
Pars tuberalis
What will the neurohypophyseal diverticulum make?
Median eminence
Infundibulum
Pars nervosa
What is the derivation of the anteiror pituitary gland?
Oral surface ectoderm
What is the derivation of the posterior pituitary gland?
Neuroectoderm
What does the telencephlonconsist of?
Median part
2 telencephalic/cerebral vesicles
What do the telencephalic/cerebral vesicles give rise to?
Cerebral hemispheres
What does the median cavity of the telencephalon form?
Anterior 3rd ventricle
What appears at the closure of the rostral neuropore?
Optic vesicles appear; will give rise to retina and optic nerves
How do cerebral hemispheres communicate with the 3rd ventricle?
Intervetnricular foramina
Why do the cerebral hemispheres become C -shaped?
Due to cortex rapidly proliferating while deep nuclei do not
Thus impacting shape of ventricles
What forms at the medial wall of the cerebral hemisphere where is it continuous with the roof of the third v?
Choroid plexus
What covers the diencephalon, midbrain and hindbrain?
Cerebral hemispheres will meet each other int he midline and medial surfaces flatten
What gives rise to the falx cerebri?
Mesenchyme trapped in the longitudinal fissure after the cerebral hemispheres meet each other medially
What is holoprosencephaly (HPE)?
What can it cause?
Incomplete separation of the cerebral hemispheres
Defect in forebrain development causing facial anomalies bc reduction of the FNP
What are the facial anomalies seen with Holoprosencephaly?
Cyclopes Premaxillary agenesis Proboscis Single nostril Hypotelorism (close set eyes) Facial clefts
How common is holoprosencephaly?
Severe and common defect
1: 250 fetuses (although most spont. Abort)
1: 15,000 neonates
What can cause Holoprosencephaly?
Over 12+ genetic loci have been implicated
All inhibit cholesterol synthesis
What are the cerebral commissures?
Groups of nerve fibers interconnecting the cerebral hemispheres
(White matter tracts)
What is the lamina terminalis found int he cerebral commissures?
At rostral end of forebrain
Where most of the white matter commissures form
Which commissures form first?
Anterior commissure
Hippocampal commissure
What does the anteiror commissure do?
Interconnects olfactory bulb w/ hemispheres
What does the hippocampal commissure do?
Connects hippocampal formations
How does the corpus callosum form?
What does it do?
Anterior portions form first, posterior portions form in fetal life
Links hemispheres along their length
What does the lamina terminalis form?
Stretched and forms septum pellucidum
What is the septum pellucidum?
Thin plate of brain tissues containing nerve cells and fibers that separates the R and L lateral ventricles
What is the posterior commissure?
White matter tract connecting R and L temporal lobes
What is agenesis of corpus callosum?
Sxs?
Complete or partial absence of the corpus callosum
May be asymptomatic, seizure and mental deficits common
Assoc. w/ over 50 human congenital syndromes
How is gyri formed?
From infolding of the cortex
How do sulci and gyri develop?
Growth of cortex
What do sulci and gyri allow?
Increased surface area without increased the volume of the neurocranium
The brain at birth is only about what % of its adult volume?
25%
How does the brain grow postnatally?
Neurons increase in size
Myelination of axons
Additional growth and infolding if you learn to play musical instruments, etc.
When does the brain reach its final size?
7 years old
What are the zones of histogenesis for the cerebral cortex?
Ventricular
Intermediate
Marginal
&&&
*subventricular (!!!)
How are cortical layers of the cerebral cortex layer down?
From deep to superficial
Neurons will migrate thru deep and establish more superficial layers
Inside out development
What is lissencephaly?
Incomplete neuronal migration to cerebral cortex during 3-4 mos. gestation
Abnormal migration of those subventricular layers to outside
What is the incidence of Lissencephaly?
1:100,000 live births
What are the characteristics of Lissencephaly?
Smooth cerebral surface w/
Pachygyria
Agyria
Neuronal heterotopia
Enlarged ventricles and malformation of corpus callosum too
What is pachygyria?
Broad, thick gyri
What is agyria?
Lack of gyri
What is neuronal heterotopia?
Cell in aberrant positions compared to a normal brain
How does Lissencephaly present?
Initially - appear normal
Later - develop seizure, profound mental deficiency, and mild spastic quadriplegia
What is microcephaly?
Neurodevelopmental disorder where calvaria and brain are small but face is normal sized
What is the result of microcephaly?
Significant mental deficiencies due to brain underdevelopment
What does microcephaly result from?
Reduction in brain growth
No brain growth = no pressure of bones = small neurocranium
What is the incidence of microcephaly?
1:25,000 infants/yr in the US
What are the causes of microcephaly:?
Automakers recessive primary microcephaly
Ionizing radiation
Infectious agents (cytomegalovirus, rubella virus, toxoplasma gondii)
Maternal alcohol abuse
What do neural crest cells contribute to the development of?
Schwann cells
