(04) Development of the Nervous System

Question 1

The notochord induces overlaying ectoderm to become _________ and form a ________.

What are the stages of neural tube formation?

In the process of separating from overlaying ectoderm, some neural plate cells become detached from the tube and collect ___________ to it, forming __________.

Answer 1

• neuroectoderm, neural tube
• neural plate, ectodermal cells overlaying notochord become tall columnar producing thickened neural plate (surrounding ectoderm produces epidermis)
• neural groove - neural plate transformed into neural groove
• neural tube - dorsal margins of neural groove merge medially, forming a neural tube composed of columnar neuroepithelial cells surrounding a neural cavity
• bilateral, neural crest

Question 2

• Neural tube becomes _________, which consists of the ______ and ________. The neural cavity becomes the __________ of the brain and the ________ of the spinal cord.
• Neural crest cells become ______ of the _________ that have their cells bodies located in the ________. They also become ___________ of the PNS.

Answer 2

• CNS, brain, spinal cord, ventricles, central canal
• neurons, PNS, ganglia, neurolemmocytes (Schwann cells)

Question 3

• To ensure that all targets get sufficient innervation, ___________ produces an excessive number of neurons along with _____________.
• Neurons that fail to contact an appropriate target will ___________ (because ________).
• For the same reason, _________ of surviving neurons will undergo degeneration if they fail to _________ (______).
• __________ are released by target cells to nurture neurons (and are released by neurons to modify ________)

Answer 3

• initial neural development, profuse, random growth of neuronal processes
• degenerate and dissapear, they do not receive sufficient neurotrophic molecules
• processes, fail to contact an appropriate contact, (selective pruning).
• neurotrophic molecules, target cells

Question 4

What is a consequence of functional competition for neural targets?

• Neural targets that lead to more _______ and more ______ are preferred by neurons.
• Thus developmental remodeling is driven by _______, related to experiences/behavior. “Survival of the successful” is the neural theme.

Answer 4

• selective degeneration of neurons and neuronal processes
• excitation/conduction, neurotransmitter release
• neuronal activity

Question 5

What drives nervous system remodeling throughout life?

Are selective growth and pruning of neuronal synapses is the most common remodeling event in the adult?

Answer 5

• experiences
• yes

Question 6

• ________ represents stem cells that give rise to neurons, ______, and ________. Additionally, the CNS contains ______ and ________ derived from mesoderm.
• Some stem cell divisions are __________, producing _______ which give rise to neurons or ________ which give rise to ________.

Neuroblasts and most glioblasts lose contact with surfaces of the neural tube and migrate toward the center of the ________ where they accumulate in a ______. (Some _________ retain surface contacts to guide __________)

_______ are Derived from mesoderm associated with invading blood vessels.

Answer 6

• Neuroepithelium, glial cells, ependymal cells, blood vessels, microglial cells
• differential, neuroblasts, glioblasts (spongioblasts), glial cells
• neural tube, mantle layer
• glial cells, neuroblast migrations
• Microglial

Question 7

Answer 7

1 - mantle layer

2 - marginal layer

3 - alar plate

4 - basal plate

5 - gray matter

6 - white matter

Question 8

Accumulated neuroblasts and glioblasts form the ________, a zone of high cell ________ within the wall of the neural tube. Cells that remain lining the neural cavity are designated _________; they form an ________ layer. Surrounding the mantle layer, a cell-sparse zone where only ______ and some ________ are present is designated the ______ layer.

• The mantle layer becomes _______ and the marginal layer becomes ______ of the CNS.
• The wall of the neural tube is divided into regions (plates). A bilateral indentation evident in the neural cavity (the ________) serves as a landmark to divide each lateral wall into an ________ (dorsal) and a ________ (ventral). Midline regions dorsal and ventral to the neural cavity constitute, respectively, the ______ and the ____________.

The basal plate contains _________ that send _____ into the PNS.

The alar plate contain neurons that receive input from the ______.

Answer 8

• mantle layer, density, ependymal cells, ependymal, axons, glial cells, marginal layer
• gray matter, white matter
• sulcus limitans, alar plate, basal plate, roof plate, floor plate
• efferent neurons, axons
• PNS

Question 9

In general, neurons are ________ of cell divisions - so all neurons must be formed from _______ during nervous system development. However, in ________ and __________, some stem cells or neuroblasts persist and can give rise to a small number of new neurons postnatally.

Answer 9

• incapable, stem cells, hippocampus, olfactory bulb

Question 10

The cranial end of the neural tube forms three _______ (_______) that further divide into the ____ primary divisions of the brain. Caudal to the brain the neural tube develops into _______.

Answer 10

• vesicles (enlargements), five, spinal cord

Question 11

(SPINAL CORD DEVELOPMENT)

• the neural cavity becomes the ________, which is lined by _________
• Growth of ______________, but not roof and floor plates, results in symmetrical right and left halves separated by a _________ and a _________ (or septum).

The mantle layer develops into ________.

The marginal layer becomes _______. [note: funiculus = ________]

Enlargements of spinal cord segments that innervate limbs limbs (cervical and lumbosacral enlargements) are the result of greater numbers of _______ in those segments. Neurons are ______ numerous in enlargement segments because those segments underwent less ________, compared to segments that did not innervate _____ and thus offered _____ targets for developing neurons.

Answer 11

• central canal, ependymal cells
• alar and basal plates, ventral median fissure, dorsal median fissure
• gray matter
• white matter, slender rope
• neurons, more, neuronal degeneration, limbs, fewer

Question 12

(HINDBRAIN: Medulla Oblongata and Pons)

• _______ plates shift _______ and the cavity of the neural tube expands ________ forming a ________.
• The basal plate (containg _______ of cranial nerves) is positioned _______ to the alar plate and ________ to the fourth ventricle.
• White and gray matter (_____ and ______ layers) become __________ (unlike spinal cord): ________ adds extra structures.

Answer 12

• alar, laterally, dorsally, fourth ventricle
• efferent neurons, medial, ventral
• marginal, mantle, intermixed, cerebellar development

Question 13

(HINDBRAIN: Cerebellum)

Bilateral ________ are the first evidence of cerebellar development; the lips are expansions of the ______ in the ______.

Superfical and deep layers of neurons are evident within the _________ of the future cerebellum; the deep cells migrate (pass the more superficial cells) toward the _______ and become _________ of the __________: Meanwhile, neurons of the _______ layer migrate deeply and become _________.

• Neuroblasts located laterally in the ________ migrate along the outer surface of the ________, forming an __________ (which continues to undergo mitosis); subsequently, neurons migrate deep to the _________ and form the ______ cell layer of the _________.
• What does migration of neuron populations past on another allow?
• Neurons that fail to connect are destined to _______. Connections are made by _______ that subsequently elongate as _______ migrate during growth.

Answer 13

• rhombic lips, alar plate, roof plate
• mantle layer, cerebellar surface, Purkinje cells, cerebellar cortex, superficial, cerebellar nuclei
• rhombic lip, cerebellum, external germinal layer, Purkinje cells, granule, cerebellar cortex
• allows connections to be established between neurons of the respective populations.
• degenerate, axons, neurons

Question 14

(MIDBRAIN)

• The neural cavity of the midbrain becomes ______.
• alar plates form two pairs of dorsal _______ which become _______________.
• The basal plate gives rise to _______ and ______ nerves which innervate muscles that move the _______.

The midbrain is the rostral extent of the _______ (_______).

Answer 14

• mesencephalic aqueduct
• bulges, rostral and caudal colliculi
• oculomotor (III), trochlear (IV), eyes
• basal plate (efferent neurons).

Question 15

The forebrain: diencephalon and telencephalon are derived entirely from what?

Answer 15

• from alar plate

Question 16

(DIENCEPHALON)

• the neural cavity expands ________ and becomes the narrow ________.
• The floor of the third ventricle gives rise to the ________ (________).
• The _______ layer of the diencephalon gives rise to _________, _______, etc.
• The ______ and ______ develop as an outgrowth of the wall of the _________.

Answer 16

• dorsoventrally, third ventricle
• neurohypophysis (neural lobe of pituitary gland)
• mantle, thalamus, hypothalamus
• optic nerve, retina, diencephalon

Question 17

(TELECEPHALAON (CEREBRUM)):

• bilateral hollow outgrowths become right and left __________. The cavity of each hemisphere becomes a ______ a that communicates with the __________ via an interventricular foramen.
• at the midline, the ________ end of the telencephalon forms the rostral wall of the ______ ventricle.
• The mantle layer surrounding the lateral ventricle in each hemisphere gives rise to ______ and to the ______.

Answer 17

• cerebral hemispheres, lateral ventricle, third ventricle
• rostral, third
• basal nuclei, cerebral cortex

Question 18

(TELECEPHALON CONT)

• cellular migrations that form the cerebral cortex….
• From the _____ layer, cells migrate radially to the surface of the _______, guided by _____ that extend from the ____ surface to the ______ surface of the cerebral wall (thus each locus of the mantle gives rise to a specific area of the ______):
• Migration occurs in ______; the first wave (which becomes the ______ layer of th cortex) migrates to the surface of the ______.

The second wave (which forms the _____ layer of the cortex) migrates to the _____ surface, passing through the first wave neurons which are displaced to a deeper position; the third wave etc. (the cerebral cortex has ___ layers)

• ________ are established withing the cerebral cortex as waves of newly arriving _____ migrate thorugh populations of neurons that arrived earlier.

Answer 18

• mantle, cerebral hemisphere, glial cells, venricular, outer, cerebral cortex
• waves, deepest, cortex
• next deepest, cortical, six
• Cell connections, neurons

Question 19

(PNS)

• neurolemmocytes (Schwann cells) arise from _____ and migrate through the PNS, _______ and _______ axons and forming _______ in ganglia:
• afferent neurons originate from ______ as _____ cells that subsequently become _______.
• Postganglionic visceral efferent neurons arise from _____. _______ migrate to form autonomic ganglia in the _____, or beside ______ (sympathetic trunk ganglia), or near the ______, or within the ____.
• somatic efferent neurons and preganglionic visceral efferent neurons arise from the ________ of the _______. Their cell bodies remain in the _____ and their axons join ______.
• Peripheral nerves establish contact early with the nearest _____, ____, _______, or _______ and innervate ________.

Innervation continuity is ______, even when the embryonic targets are _____ or when _____. The early establishment and maintenance of an innervation connection is _______, which explains why some nerves extended distances and including detours to reach distant inaccessible targets.

Answer 19

• neural crest, ensheathing, myelinating, satellite cells
• neural crest, bipolar, unipolar
• neural crest, head, vertebrae, aorta, gut wall
• basal plate, neural tube, CNS, peripheral nerves
• somite, somitomere, placode, pharyngeal arch, derivatives of these embyronic structures.
• retained, widely displaced, other structures obstruct the pathway. essential….

Question 20

(FORMATION OF MENINGES)

• meninges surround the ___ and the roots of ____ and ____ nerves

Three meningeal layers (____, ______, and ______) are formed as follows…

• ___ surround the neural tube aggregates into ___ layers
• the ____ layer forms _____
• _____ develop and ____ within the inner layer, dividing it into ____ and ____. The cavity between them becomes ________ (which contains ________)

Answer 20

• CNS, spinal, cranial
• dura mater, arachnoid, pia mater
• mesenchyme, two
• outer, dura mater
• cavities, coalesce, arachnoid, pia mater, subarachnoid space, CSF

Question 21

(FORMATION OF THE EYE)

• both eyes are derived from ______field of the ______. The single field separates into ____ fields associated with the ______. The following events produce each eye…
• a lateral diverticulum from the ______ forms an ________ attached to the diencephalon by an _______.

A _____ develops in the surface _____ where it is contacted by the ______; the lens placode induces the ______ to invaginate and form an _____ while the placode invaginates to form a ______ that invades the concavity of the optic cup.

Answer 21

• single, neural plate, bilateral, diencephalon
• diencephalon, optic vesicle, optic stalk
• lens placode, ectoderm, optic vesicle, optic vesicle, optic cup, lens vesicle

Question 22

(Formation of the eye COnT (note))

• the optic cup forms the ___ and contributes to formation of the ____ and ____. The outer wall of the cup forms the outer _______ layer of the ____, and the inner wall forms _____ layers of the retina.
• the optic stalk becomes the ____ as it fills with axons traveling from retina to the _____.
• The lens vesicle develops into the ___, consisting of layers of lens fibers enclosed within an _____.
• The vitreous compartment develops from the concavity of the _____, and the ____ is formed from ectomesenchyme that enters the compartment through the optic fissure.

Answer 22

• retina, ciliary body, iris, pigmented, retina, neural
• optic nerve, brain
• lens, elastic capsule
• optic cup, vitreous body

Question 23

(FORMATION OF THE EYE 2)