Development of Nervous System

Development of Nervous system occurs starting week ____ until _____

week 4 until adulthood

the brain weighs how many grams at birth?

800g

Weight of the brain at 6 y.o

1,200g

Weight of the brain of an adult

1,400g

Manifestations of abnormalities

1. Malformation

2. Growth retardation

3. Functional Defect

4. Death

Pre-embryonic stage is AKA

Conceptus

True/False: Abnormalities can be seen as early as the Conceptus stage

False

Embryonic stage span what weeks of development

Weeks 3-8

Process by which the blastula becomes a gastrula

Gastrulation

Gastrulation marks the start of the formation of these cells

Ectoderm, mesoderm, endoderm

Neural tissue appears at ____ week of development

3rd week

Establishes basic body plans of vertebrates

Primitive Streak

Defines the rostral direction; notochordal process develops above and somites from beside the notochord

Primitive Node / Hensen’s Nodes

Induces epiblast cells to form neuroectoderm

Notochord

Process of cell to cell signaling; Mesoderm induces the ectoderm to become neuroectoderm & form the neural plate

Neural Induction

Neural induction starts when?

16th-17th day of intrauterine life

The Notochord defines the longitudinal axis of the embryo by production of _________

cell adhesion molecules

the notochord determines the orientation of the __________

vertebral columnT

the notochord persists as the _______ of the IVD

nucleus pulposus

Slipper shaped plate of thickened ectoderm

Neural plate

The neural plate forms at day __

day 18

The neural plate is located in the?

mid dorsal region in front of the primitive gut

this part of the neural plate becomes the neural folds

Lateral edges

The neural folds form at day ____

day 20

At 21 days, the neural folds become the _______

neural tube

The primitive streak emerges as a groove at the ________

caudal part of the embryo

Primitive streak initiates _____

gastrulation

Closure of the neural tube proceeds in what direction

Bidirectionally

Unclosed part of the neural tubes are called _____

Anterior and Posterior Neuropores

Cranial / Anterior neuropore closes at day ___

24

Caudal / Posterior neuropore closes at day ___

day 26

A process by which the neural plate folds over on itself and fuses in a zipperlike fashion to become a neural tube

Neurulation

Process by which the brain and the cervical, thoracic, upper lumbar part of the spinal cord are formed

Primary neurulation

Neurulation begins and ends at what days?

Begins at day 18 and ends by Day 28

Process by which the caudal part of the spinal cord (lower lumbar, sacral, & coccygeal segments) are formed

Secondary Neurulation

Mass of cells that develop in the caudal part of the neural tube and it enlarges eventually to become continuous with the neural tube

Caudal Eminence

When does secondary neurulation occur?

Days 20-42

Primary Neurulation vs Secondary Neurulation

Primary	Secondary
Starts at ectoderm	starts at mesenchyme
Forms a tube	condenses and hollows; undergoes epithelial transition; Cavitation

Neural Tube related birth defects

Anterior Neuropore	Posterior Neuropore
Anencephaly	Spina bifida occulta
Encephalocoele/Cranium bifidum	Spina bifida aperta
Chiari I malformation	Spina bifida cystica

Failure to close of the anterior neuropore causes

Anencephaly, encephalocoele, Chiari I malformation

Failure to close of the posterior neuropore causes

Spina bifida oculta, aperta, cystica

Defective Primary Neurulation

Dysraphic Defects

Minor fusion failure of the posterior vertebral arches unaccompanied by herniation of meninges or neural tissue

Spina bifida occulta

Collectively designates meningocele, myelomeningocele, and other cystic lesions

Spina bifida cystica

Anencephaly is 37 times more common in _____

females

Prevention of Anencephaly

Folic acid

The rostral end of the neural tube undergoes __________ giving rise to three primary brain vesicles

Cephalization

Cephalization begins when?

Week 4

Between the 4th and 8th weeks, the brain tube folds sharply at 3 locations:

1. Mesencephalic flexure

2. Pontine flexure

3. Cervical flexure

Primary brain vesicles

1. Prosencephalon

2. Mesencephalon

3. Rhombencephalon

Further subdivision of the brain vesicles created how many secondary vesicles?

5 secondary brain vecicles

At week ___, the 3 primary vesicles becomes 5 secondary vesicles

Week 5

Lateral expansions of the telencephalon

telencephalic vesicles (become the cerebral hemispheres)

The pontine flexure is found between the _____ and ____

between mesencephalon (midbrain) and metencephalon (pons)

Process of forebrain development

ventral induction

Adult derivatives of the Telencephalon

1. Cerebral cortex

2. Subcortical white matter

3. Olfactory bulb

4. Basal ganglia

5. Amygdala

6. Hippocampus

Adult derivatives of the Diencephalon

1. Thalamic nuclei and associated structures

2. Optic nerve and retina

Congenital Dysgenesis of the Diencephalon characterized by underdevelopment (hypoplasia) of the optic nerves, abnormal formation of structures along the midline of the brain, and pituitary hypoplasia.

Septo-optic Dysplasiya

Lumen of the neural tube persists as the _____________

ventricular system of the adult brain

Cavities of the telencephalic vesicles become what ventricles

Lateral ventricles

Diencephalic cavity become what ventricles

Third ventricle

Rhombencephalus cavity become what ventricles

fourth ventricle

Mesencephalon cavity become what ventricles

Aqueduct of Sylvius

channels that connect the paired lateral ventricles with the third ventricle at the midline of the brain

Interventricular Foramen (Foramen of Monro)

an opening of the fourth ventricle at the caudal portion of the roof of the fourth ventricle

medial aperture or foramen of Magendie

Function of the foramen of magendie

allows flow of cerebrospinal fluid (CSF) from the fourth ventricle into the cisterna magna

paired apertures located in the lateral recesses of the fourth ventricle, within the posterior cranial fossa

Foramen of Luschka

The primary site of cerebrospinal fluid (CSF) production is

choroid plexi located within the lateral, third, and fourth ventricles of the brain

Choroid plexus develops where?

Where pia mater and ependyma are in direct contact

Occurs when flow of CSF is disrupted during development

Congenital Hydrocephalus

Likely site of blockage that leads to Congenital Hydrocephalus

Aqueduct of Slyvius

True/False: Congenital Hydrocephalus can be heredited

True

Peak time period of Neuronal proliferation

3-4 months

Sites of Neuronal Proliferation

Ventricular zone and subventricular zone

During neuronal proliferation, proliferative units are produced by?

Symmetrical divisions of stem cells

During neuronal Proliferation, what happens to proliferative units before migration?

Proliferative units later enlarge by asymmetrical division of the stem cells before migration

___________ multiply in the periventricular region producing neuroblasts & glioblasts

Blast cells (pluripotential)

Layers of the wall of the neural tube

Stages of Neuron development

Stages of Neuroglia development

_______ guide migration of developing neurons

Radial Glia

Peak time period of Neuronal Migration

3-5 months

Major events of Neuronal Migration in the Cerebrum

radial migration of the cerebral cortex, deep nuclei

Major events of Neuronal Migration in the Cerebellum

radial migration: purkinje cells, dentate nuclei

tangential migration: external—internal granule cells

The most common form of cell transit

Radial migration

Number of neurons that go into apoptosis

40%-60%

Development of Axons is facilitated by ________

neuronal growth cones

Development of dendrites is driven by ________

genes controlling calcium regulated transcription process

Point of contact between two brain cells

Synapse

First synapses are generally observed when?

23rd week / second trimester of pregnancy

Peak of production of synapses

1st year of life

True/False: Massive production of synapses if followed by sudden reduction

False; Gradual reduction

Process of removal of redundant or otherwise unnecessary synaptic connections

Synapse pruning

Until synaptogenesis, stages of brain development is largely driven by?

gene driven

Once brain reaches point where synapses are reduced, process of pruning becomes driven by?

Experience

process in which axons are wrapped with fatty cells

Myelination

Regions involved in _______ myelinate later than other regions

regions involved in higher cognitive ability