Development of the Nervous System

Question 1

What does the nervous system develop from? *

Answer 1

ectoderm

Question 2

What happens by the third week of development? *

Answer 2

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

Question 3

How is the neural plate formed? *

Answer 3

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

Question 4

How are the Neural Folds formed? *

Answer 4

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

Question 5

How is the neural tube formed? *

Answer 5

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.

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

Question 8

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

Primary vesicles: forebrain = prosencephalon
secondary vesicles
regions ventricles

Answer 8

secondary vesicles:
telencephalon
diencephalon

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

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

Question 9

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

Primary vesicles: midbrain = mesencephalon
secondary vesicles
regions ventricles

Answer 9

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

Question 10

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

Primary vesicles: hindbrain =rhombencephalon
secondary vesicles
regions ventricles

Answer 10

secondary vesicles:
metencephalon
myelencephalon

regions:
metencephalon- pons, cerebellum
myelencephalon- medulla

ventricles:
metencephalon - 4th ventricle
myelencephalon- central canal

Question 11

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

Answer 11

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

Question 12

Describe the 3 layers of the neural tube.

Answer 12

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

intermediate layer- Mantle layer

outer layer- Marginal layer

Question 13

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

Answer 13

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

Question 14

• Describe the formation of the Alar and Basal plates.

Answer 14

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)

Question 15

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

Answer 15

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

Question 16

How is the ventral root of the spinal cord formed?

Answer 16

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

Question 17

How are tracts in the spinal cord formed?

Answer 17

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

Question 18

What forms the dorsal roots of the spinal cord?

What forms the white matter of the cord?

Answer 18

axons arising from dorsal root ganglion cells form dorsal roots

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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)

Question 21

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

Answer 21

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

Question 22

Describe the 2 principle components of the metencephalon.

Answer 22

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)

Question 23

Describe the formation of the cerebellum and the vermis.

How many layers in cerebellar cortex vs cerebral cortex?

Answer 23

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

Question 24

Describe the the aqueduct of Sylvius or cerebral aqueduct.

Answer 24

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

Question 25

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

Answer 25

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.

Question 26

How does the diencephalon begin?

What displays the greatest amount of growth?

Answer 26

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

Question 27

What happens as the third ventricle expands?

Answer 27

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)

Question 28

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

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

Answer 28

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

Question 29

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

Answer 29

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.

Question 30

What does the hippocampal formation (archipallium) arise from?

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

Answer 30

medial surface of the telencephalic vesicel

ventral surface of telencephalon

Question 31

What fiber bundles (commissures) cross the midline and connect the left and right hemispheres?

Answer 31

corpus callosum
anterior commissure
posterior commissure

Question 32

*Describe neural tube defects (abnormalities).

How does it occur? Manifest? 3 types?

Answer 32

Spina bifida (myeloschisis) occurs when the posterior neuropore fails to close
manifests by a failure of the vertebral canal to close properly

3 types:
spina bifida occulta
spina bifida cystica (meningocele and meningomyelocele)
rachishisis

Question 33

*Describe the cranial defects (abnormalities).

Answer 33

Development of the NS occurs before the formation of the skull.
Ossification defects in the bones of the skull can lead to formation of a meningocele (can treat), meningoencephalocele (brain tissue in there) and meningohydroencephalocele (has ventricular lumen, CSF in there too)

Question 34

Describe axencephaly and anencephaly.

Answer 34

cranial defect

exencephaly is characterized by failure of the cephalic (rostral) neural tube to close, and results in failure of the skull to form, thus leaving the malformed brain exposed.

brain tissue typically becomes necrotic leading to anencephaly. incompatible with life even though the brainstem often remains intact, if defect continues into the spianl cord, called craniorachischisis

Question 35

*Describe hydrocephalus.

Answer 35

abnormal accumulation of CSF within the ventricular system can lead to hydrocephaly. in newborns it is typically due to blockage or narrowing (stenosis) of the aqueduct of Sylvius.

As a result fluid builds up in the lateral ventricles and presses outward on the cortex and developing skull. Since cranial sutures have not fused, skull expands.

Question 36

Describe Dandy- Walker syndrome. (hydrocephalus)

Answer 36

congenital abnormality of the fourth ventricle with failure of foramens Luschka and Magendie to form, resulting in an enlargement of the fourth ventricle; complete absence of the cerebellar vermis; and cyst formation near the internal base of the skull.

Can appear dramatic or develop unnoticed

Question 37

Describe Arnold-Chiari malformation.

Answer 37

is a caudal displacement (and herniation) of the posterior cranial fossa structures, namely the cerebellum, through the foramen magnum.

microcephaly describes a cranial vault that is smaller than normal. Normally due to a lack of brain development. Impaired mental development is associated with more than 50 percent of these cases

Question 38

Where are Purkinje cells located?

Answer 38

in metencephalon (morphogenesis of cerebellum)

Question 39

What is adenohypophysis and neurohypophysis?

Answer 39

adenohypophysis- develop from Rathke’s pouch, may give craniopharyngioma

neurohypophysis- develops from infundibulum (neuroectodermal diverticulum of hypothalamus)