nsci 2101 exam 1 lec 3 (brain development)

zygote

fertilized egg

~2-3 days

zygote divides several times into itself, forming the morula (Latin for mulberry)

• stays the same volume but divides into itself, forming smaller cells

~4 days

morula fills with fluid which allows it to embed it the uterus and grow

• still not adding any matter to it, dividing smaller into itself

gestational age

time after last menstrual period (embryonic age + ~2 weeks)

clinicians typically talk in terms of ______ age

gestational

biologists generally talk in terms of ______ age

embryonic

6-15 days

embryo invades uterus SUPER AGGRESSIVELY

• hasn’t gained any mass but mass has been redistributed a little

embryonic age

time after fertilization

embryonic disk

the flattened inner cell mass that arises at the end of the blastocyst stage and from which the embryo begins to differentiate

primitive streak

initially forms via a thickening of cells near the connecting stalk. As cells proliferate and migrate toward the midline of the embryo, the thickening elongates to become linear in shape

ectoderm forms what?

skin and nervous system

mesoderm forms what?

bone, muscle, and some organs

endoderm forms what?

gut, glandular organs, and liver

what are the three primary germ layers called?

• ectoderm

• mesoderm

• endoderm

how does cell migration happen?

ectoderm migrates medially to the primitive streak → comes down through the primitive streak and into the interior space between endoderm and ectoderm → becomes mesoderm

what primary germ layer makes the nervous system?

ectoderm

what primary germ layer induces the beginning of transformation of ectoderm into neural tissue?

mesoderm

days 15-21

underlying mesoderm induces some ectoderm to become neural plate

what exists in the middle of the neural plate?

the neural groove

the neural plate closes up around the neural groove to form what?

the neural tube

what becomes the peripheral system?

the neural crest and neurogenic placodes

neural crest

what forms the CNS?

the neural tube

alar plate

• dorsal half of the neural tube

• forms sensory neurons

• sensory axons go in here

basal plate

• ventral half of the neural tube

• forms motor axons

• motor axons go out of here

spina difida

• a neural tube defect

• might result in spinal cord failing or being exposed

• might result in neural tube not closing entirely

• caused by vitamin b7 deficiency

the formation of the nervous system relies on what two processes?

• mitosis (cell division)

• cell migration

mitosis

allows cell growth and differentiation

cell migration

cells moving to their destinations

what are the four phases of the cell cycle?

• G1 or “gap” (pause: factors that initiate or block cell division are expressed)

• S (DNA is replicated and synthesized)

• G2 (pause: proteins needed for mitosis are expressed)

• M (cell divides into two)

what happens when a cell no longer needs to divide?

the cell enters a G0 phase, and mitosis ends

neural crest

• formed from the neural tube folding up near the lips of the neural fold

• can develop into dorsal root ganglion neurons

• can develop into autonomic ganglia

• located in the developing spinal column

neurogenic placodes

• areas of thickening adjacent to the neural plate

• induce the differentiation and creation of neural tissue

• located in the developing head

what can develop from the neural crest?

• sensory ganglia

• autonomic ganglia

• schwann cells

• enteric nervous system

• melanocytes

what can develop from the neurogenic placodes?

• sensory ganglia

• olfactory epithelium in nose

• hair cells of inner ear

• anterior pituitary gland

• lens of eye

• anterior pituitary cells

lens placode

the placode that forms the eye

• retina is formed of CNS tissue that grows out into the eye

olfactory placode

the placode that forms the nose and olfactory system

how do we get a brain from a neural tube?

• vesicles form where different regions will develop

• open spaces in those vesicles become the open spaces in the brain like ventricles

• different regions grow to different extents and develop different neurons

how many vesicles form at the end of the 4th week?

• three

• prosencephalon

• mesencephalon

• rhombencephalon

which secondary neural vesicles form at 40 days?

• telencephalon

• diencephalon

• metencephalon

• myelencephalon

the prosencephalon splits into which secondary vesicles?

• telencephalon

• diencephalon

the rhombencephalon splits into which secondary vesicles?

• metencephalon

• myelencephalon

telencephalon becomes what?

cerebral cortex

diencephalon becomes what?

thalamus and hypothalamus and pineal gland

metencephalon becomes what?

pons and cerebellum

mesencephalon becomes what?

midbrain

pontine flexure

allows the fourth ventricle to form

how does the cerebellum form?

starts forming off the rostral end of the pons (rhombic lip) → tissue expands and attaches intimately to the pons

what region enlarges more than any other region?

telencephalon

• expands in a C shaped structure

what lobe grows over the insular cortex?

the temporal lobe