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What does the nervous system develop from? *



What happens by the third week of development? *

the notochord (of mesodermal origin) induces the development of the neural plate via a high rate of cell proliferation


How is the neural plate formed? *

By the third week of development the anterior portion of the notochord begins to thicken and form the neural plate


How are the Neural Folds formed? *

as the notochord thickens it forms the neural plate, as it continues to thicken it expands laterally where the faster growing lateral edges accumulate in a dorsal position as Neural folds


How is the neural tube formed? *

As the neural plate widens, it begins to form a shallow groove in its longitudinal aspect called the neural groove. The narrower, posterior end will become the spinal cord, while the broader, anterior end will become the brain. As it grows, the groove deepens, and some of the cells in the lateral margin separate and migrate to a dorsal position to become the neural crest. Eventually the neural folds fuse along the midline to form the neural tube.


What will neural crest cells differentiate into during early aspects of development? *

distinct neurons such as cranial nerve sensory ganglion cells and dorsal root ganglion cells, postganglionic autonomic ganglion cells (sympathetic and parasympathetic), chromaffin cells of the adrenal medulla, Schwann cells, and melanocytes


What will mesodermal cells alongside the neural tube begin to form in early aspects of development (neural crest)? *

somites, which will form skeletal muscle, vertebrae and the dermis


*Describe the early aspects of development- vesicles and terminal structures:

Primary vesicles: forebrain = prosencephalon
secondary vesicles
regions ventricles

secondary vesicles:

telencephalon- cerebral cortex, basal ganglia, amygdala, hippocampus
diencephalon- thalamus, hypothalamus, pituitary (neurohypophysis) pineal gland

telencephalon- lateal (foramen of Monro)
diencephalon- 3rd


*Describe the early aspects of development- vesicles and terminal structures:

Primary vesicles: midbrain = mesencephalon
secondary vesicles
regions ventricles

secondary vesicles- mesencephalon
regions- midbrain
ventricles- cerebral aqueduct (cont. of neural tube)


*Describe the early aspects of development- vesicles and terminal structures:

Primary vesicles: hindbrain =rhombencephalon
secondary vesicles
regions ventricles

secondary vesicles:

metencephalon- pons, cerebellum
myelencephalon- medulla

metencephalon - 4th ventricle
myelencephalon- central canal


*Describe the flexures in early aspects of development.
Where is increased growth greatest?
What are main flexures?

continued proliferation of cells results in distinct flexures of the developing nervous system

increased growth is greatest in the cerebral hemispheres (telencephalon) and brainstem (myelencephalon) areas

cephalic flexure, pontine flexure (where cerebellum comes from), and cervical flexure


Describe the 3 layers of the neural tube.

inner layer- ventricular zone, which is in direct contact with the neural tube, most proliferative layer

intermediate layer- Mantle layer

outer layer- Marginal layer


*During proliferation what are the groves that appear at the midpoints of the neural canal called?

sulcus limitans - grooves that appear at the midpoints of the neural canal


* Describe the formation of the Alar and Basal plates.

Neurocytes migrating dorsal to sulcus form alar plate
those migrating ventral to it form basal plate

those that lie in the intermediated position will form the autonomic neurons (intermediolateral cell column)


*What do neurons in the alar plate contribute? Basal plate?

neurons in alar plate contribute to sensory pathways
neurons in basal plate are motor pathways

(above sulcus limitans) sensory coming in
(below sulcus limitans) motor going out


How is the ventral root of the spinal cord formed?

axons situated more ventrally within the mantle will invade adjacent somites, thus becoming functionally linked by nerve fibers and form the ventral root of the spinal cord


How are tracts in the spinal cord formed?

axons in the marginal zone (white matter) grow toward the brain or spinal cord, forming tracts


What forms the dorsal roots of the spinal cord?
What forms the white matter of the cord?

axons arising from dorsal root ganglion cells form dorsal roots

axons added rapidly during development become the white matter of the cord


*What are the functional components of the spinal cord?/ What fibers do the developing spinal nerves contain?

GSA (pain temp touch)
GVA (visceral info)
GSE (alpha motor neurons!)
GVE (sympathetic to periphery)


*Describe the morphogenesis of the medulla (myelencephalon) in regards to how the divisions (alar/basal plate) come in.

While the neural canal remains small in the cord, that is NOT the case in the brainstem. As the brainstem develops, it expands laterally, forming the fourth ventricle. The roof plate expands greatly so that the alar plate becomes located LATERAL to the basal plate

(motor-middle, sensory-lateral)


*Describe the lateral and medial foramen that develop in the myelencephalon.

pair of foramina develop in the roof laterally and are called lateral apertures or foramen of Luschka

another foramen becomes situated medially and is known as the median aperture or the foramen of Magendie


Describe the 2 principle components of the metencephalon.

pons and cerebellum

pons has 2 basic division (dorsal tegmentum which is direct extension of the myelencephalon, and ventral region known as the basilar pons)


Describe the formation of the cerebellum and the vermis.

How many layers in cerebellar cortex vs cerebral cortex?

cerebellum derived from dorsal aspect of alar plate
cells in central region are called vermis, those in lateral regions form the cerebellar hemispheres (little growth occurs in the vermis while the hemispheres will expand considerably)

cerebellar cortex- 3 layers
cerebral cortex- 6 layers


Describe the the aqueduct of Sylvius or cerebral aqueduct.

cavity of the midbrain vesicle remains narrow and channels CSF from the forebrain ventricles to the fourth ventricle


Describe the morphogenesis of the forebrain at the 4th week.

the prosencephalon begins to differentiate. Optic vesicles form a ventral aspect. The vesicle expands outward while while its connection to forebrain becomes constricted (optic stalk). The fibers within the stalk are the optic nerves, which terminate in the diencephalon.

Each optic vesicle contributes to inductive interactions with the overlying ectoderm, thus forming the non-neural parts of the eye (such as the lens and cornea). The part of the forebrain rostal to the optic vesicle will form the telencephalon, while the remainder (lying medially) becomes the diencephalon.


How does the diencephalon begin?

What displays the greatest amount of growth?

begins as lateral swellings of neural canal

thalamus displays the greatest amount of growth, and differentiates into many small groups, thus forming the various nuclei of the thalamus. Growth is often so rapid that a "bridge" between the two thalami forms, called the massa intermedia 34


What happens as the third ventricle expands?

the ventral region does so at a slower rate, forming the hypothalamus. Other structures form on ventral surface of the hypothalamus (optic chiasm, mamillary bodies, tuber cinerum, and infundibulum)


What does the telencephalon form from? What does it consist of?

How do the lateral ventricles communicate with the lumen of diencephalon (third ventricle)?

forms from the most rostral ventricles
consists of 2 lateral outpockings (cerebral hemispheres) and median lamina terminalis

lateral ventricles communicate with lumen of diencephalon (third ventricle) via the interventricular foramen of monro


What happens as the cerebral hemispheres expand (morphogenesis of the cerebral cortex/ telencephalon)

roof plate fuses with pia mater which contains vascular mesodermal tissue which forms the choroid plexus of the lateral ventricles. Ventricles expand with the developing hemispheres, and thus elongate as the hemispheres continue to grow.

as they expand the hemispheres cover the lateral aspect of the diencephalon, mesencephalon, and cephalic portion of the metencephalon.


What does the hippocampal formation (archipallium) arise from?

What does the entorhinal and pyriform cortices (paleopallium) arise from?

medial surface of the telencephalic vesicel

ventral surface of telencephalon