lec 3 - nervous system development

Question 1

Pre-embryonic period

Answer 1

Begins with fertilization and ends at implantation

weeks 1 & 2

how embryo develops

before nervous system

Question 2

Embryonic/Critical period

Answer 2

Characterized by cell differentiation and organogenesis

weeks 3-8

1st trimester = most sensitive - susceptible to environment toxins

Question 3

Fetal period

Answer 3

Characterized by growth of fetus

weeks 9+

Question 4

Pre-Embryonic Period: Week 1

Answer 4

Fertilization
Cleavage
Blastocyst formation
Implantation

Question 5

Fertilization:

Answer 5

sperm penetrates a secondary oocyte/mature egg

A zygote is formed when sperm fertilizes an egg

Question 6

Cleavage:

Answer 6

stage characterized by a series of cell divisions

Question 7

Blastocyst formation:

Answer 7

a fluid-filled cavity is formed

organizes the cells into an inner (embryoblast) and outer (trophoblast) cell mass

Question 8

Implantation:

Answer 8

the blastocyst implants into the uterine wall

Question 9

Pre-Embryonic Period: Week 2

Answer 9

During week 2, a bilaminar embryonic disc forms

The embryoblast differentiates into 2 layers:
> Epiblast
> Hypoblast

Question 10

Epiblast:

Answer 10

dorsal row of cells that will develop into the entire embryo and all adult structures

A fluid-filled cavity forms in the epiblast cells, which is called the amniotic cavity

Question 11

Hypoblast:

Answer 11

ventral row of cells that form supporting structures of the embryo

Hypoblast cells migrate down to line the inner surface of the cytotrophoblast cells, and ultimately line a fluid filled space called the yolk sac

Question 12

The epiblast and hypoblast together form a flat, ovoid shaped disk called the ____

Answer 12

bilaminar embryonic disc

Question 13

Embryonic Period: Week 3 – Gastrulation

Answer 13

process that transforms the bilaminar embryonic disc into a trilaminar embryonic disc

cells rapidly divide to replace hypoblast cells and create a middle layer of cells, called mesoblasts

results in the 3 primary germ layers, which will form all adult structures:
> ectoderm
> mesoderm
> endoderm

Question 14

Surface ectoderm will form:

Answer 14

the skin, hair, and nails

Question 15

neuroectoderm will form the:

Answer 15

nervous system

Question 16

Mesoderm is a major precursor for:

Answer 16

muscles and connective tissues of the adult body

Question 17

Embryonic Period: Week 4 – Neurulation

Answer 17

embryonic process that forms the nervous system

occurs during week 4

Ectodermal cells rapidly divide, forming a thickened plate of cells, called the neural plate

The neural plate invaginates down into underlying mesoderm and pinches off, forming the neural tube and neural crest

Question 18

Neural tube and neural crest (collectively, neuroectoderm) are located in the ___

Answer 18

underlying mesoderm

Question 19

Ectoderm thickens to form the neural plate due to cell division:

Answer 19

Ectoderm invaginates because it rapidly divides, causing it to buckle in on itself and invaginate down into the underlying mesoderm

Question 20

Neurulation begins in the middle of the embryo and extends cranially and caudally =

Answer 20

This forms an anterior/cranial neuropore and posterior/caudal neuropore as these are the final regions to complete neurulation and close

By day 28, the neuropores have completed neurulation and are closed

If the neuropores do not close, it may lead to nervous system deficits

Question 21

Failure of anterior neuropore closure results in ___

Answer 21

anencephaly

cerebrum development affected

Question 22

Failure of posterior neuropore closure results in ___

Answer 22

spina bifida

tail of spinal cord doesn’t close properly = outpocket into skin

Question 23

Chiari II malformation

Answer 23

A condition in which brain tissue extends into the spinal canal, present at birth

It occurs when part of the skull is abnormally small or misshapen

Question 24

Result of neurulation:

Answer 24

Neuroectoderm is in the underlying mesoderm and forms the nervous system

Neural tube forms the CNS

Neural crest forms the PNS, connective tissues of the head, and others

Surface ectoderm overlies the neural tube and neural crest and forms surface structures of the body
> Forms epidermis, hair, nails, enamel, and parts of the ears and eyes

Question 25

The neural tube forms:

Answer 25

Brain (cerebrum, cerebellum, brainstem) Spinal cord Other CNS structures (e.g., pineal gland, part of pituitary gland, retina)

Question 26

The neural tube forms neurons and glial cells of the CNS:

Answer 26

Neuroepithelial cells differentiate into neurons or glia Neuroblasts form neurons Gliablasts form glia

Question 27

The only glia in the CNS that are not formed from the neural tube are ___

Answer 27

microglia Microglia are formed from the mesodermal germ layer

Question 28

Neural tube:

Answer 28

consists of neuroepithelial cells that extend over the entire thickness of the wall and form a thick pseudostratified epithelial layer Neuroepithelial cells divide rapidly and differentiate into neuroblasts, which form neurons, and gliablasts, which form glial cells

Question 29

The neuroblasts are formed first, followed by ___

Answer 29

gliablasts

Question 30

The gliablasts migrate into the mantle and marginal layers of the neural tube to form ___

Answer 30

astrocytes which are located near blood vessels and neurons and provide support and metabolic functions to neurons

Question 31

Gliablasts also form __, which migrate to the marginal layer to form ___

Answer 31

oligodendrocytes the myelin sheath around axons in the CNS

Question 32

Microglia =

Answer 32

glial cells that form from the mesodermal layer not derived from ectoderm phagocytic cells that develop later than other glia cells and migrate into the CNS

Question 33

Prosencephalon

Answer 33

Forebrain (1°) > (2°) telencephalon forms 2 large lateral outpocketings that develop into the cerebral hemispheres, basal ganglia, and lateral ventricles > (2°) diencephalon is characterized by the outgrowth of the optic vesicles and forms deeper brain structures, including the thalamus and hypothalamus and the third ventricle

Question 34

Mesencephalon

Answer 34

Midbrain (1°) > mesencephalon (2°) forms the midbrain > mesencephalon does not change name and forms the midbrain and cerebral aqueduct

Question 35

Rhombencephalon

Answer 35

Hindbrain (1°) > forms the secondary vesicles named the - metencephalon - myelencephalon > The metencephalon (2°) forms the pons and cerebellum and the superior part of the fourth ventricle > The myelencephalon (2°) forms the medulla and lower part of the fourth ventricle

Question 36

CNS Development: Brain

Answer 36

> cranial end of the neural tube forms the brain and brainstem > rest of the neural tube forms the spinal cord > at the cranial end, named vesicles form that create the walls and spaces/cavities in the brain and brainstem > cranial end of the neural tube first forms 3 primary vesicles, called the prosencephalon, mesencephalon, and rhombencephalon (from cranial to caudal) > the 3 primary vesicles then develop into 5 secondary vesicles

Question 37

CNS Development: Spinal Cord

Answer 37

spinal cord develops inferior to the rhombencephalon marginal layer mantle layer neuroepithelial layer neuroblasts form the mantle and marginal layers of the neural tube cell bodies of the neuroblasts form the mantle layer and the axons of the neuroblasts form the marginal layer

Question 38

Myelination of the neuroblast axons by ___ makes the appearance of the marginal layer ___, thus, forming the ___

Answer 38

oligodendrocytes white white matter of the CNS

Question 39

The outer layer of the neural tube is called the ___, which forms the ___

Answer 39

marginal layer white matter of the spinal cord

Question 40

The middle layer of the neural tube is called the ___ and forms the ___

Answer 40

mantle layer gray matter of the spinal cord

Question 41

The inner layer of the neural tube is called the ___ and forms the ependymal cells that line the ____

Answer 41

neuroepithelial layer central canal of the spinal cord

Question 42

The mantle layer differentiates into ____

Answer 42

alar plates = dorsal and basal plates, which are ventral

Question 43

The alar plates form the ___, while the basal plates form the ____

Answer 43

dorsal gray horn (sensory) ventral gray horn (somatic motor)

Question 44

The ____ forms in the region between the alar and basal plates

Answer 44

lateral/intermediate horn (visceral motor)

Question 45

As a result of continuous addition of neuroblasts to the mantle layer, each side of the neural tube forms thickenings: a ventral thickening called the ___ and a dorsal thickening called the ____

Answer 45

basal plate alar plate

Question 46

The basal plate contains somatic motor neuron cells that form the ____ The alar plate contains cell bodies of interneurons that form the ____ The lateral (intermediate) horn develops between the ventral and dorsal horns at thoracolumbar spinal levels and contains cell bodies for ____

Answer 46

ventral horn of the spinal cord dorsal horn of the spinal cord preganglionic sympathetic motor neurons

Question 47

A longitudinal groove, called the ____, serves as the boundary between the alar and basal plates. The roof plate and floor plate form at the midline of the neural tube, with the roof plate being the ___ and the floor plate being the ____.

Answer 47

sulcus limitans dorsal midline ventral midline

Question 48

The floor plates are regions that do not contain ___, but instead serve as pathways for nerve fibers crossing from one side of the spinal cord to the other side of the spinal cord.

Answer 48

neuroblasts

Question 49

The neural crest forms:

Answer 49

Peripheral and cranial nerves and their ganglia Face and skull bones Connective tissues in the head Some other structures in the body as well

Question 50

PNS Development

Answer 50

Neural crest cells migrate to form PNS structures, including: > cranial nerve ganglia > dorsal root ganglia > spinal nerves > sympathetic trunk > collateral ganglia > adrenal medulla > enteric nervous system Neural crest cells also form Schwann cells which create the myelinate sheath around PNS axons

Question 51

neural crest cells forming the dorsal root ganglia contain the cell bodies of ____ sensory neurons

Answer 51

pseudounipolar The central process of these sensory neurons grows into the dorsal horn to from the dorsal root, while the peripheral process grows toward the periphery somatic motor neuron axons grow out of the ventral horn to form the ventral root