CNS development

Question 1

what are the three distinct layers of the embryo?

Answer 1

endoderm, mesoderm and ectoderm

Question 2

what do each of the three layers of the embryo give rise to?

Answer 2

endoderm- lining of many of the internal organs (viscera)
mesoderm- bones of the skeleton and muscles
ectoderm- nervous system and skin

Question 3

what part of the ectoderm gives rise to the nervous system?

Answer 3

neural plate

Question 4

how do the neural tube and neural crest develop?

Answer 4

• The primitive embryonic CNS begins as a thin sheet of ectoderm.
• Then there is formation of the neural groove.
• The walls of the groove, called neural folds, come together and fuse, forming the neural tube.
• The bits of neural ectoderm that are pinched off when the tube rolls up is called the neural crest, from which the PNS will develop.

Question 5

what do the mesoderm somites develop into?

Answer 5

the 33 individual vertebrae of the spinal column and the related skeletal muscles.
(The nerves that innervate these skeletal muscles are therefore called somatic motor nerves.)

Question 6

what is neurulation and when does it occur?

Answer 6

The process by which the neural plate becomes the neural tube.
occurs around 22 days after conception.

Question 7

what nutrient consumed by the mother can prevent the incidence of neural tube defects by up to 90%?

Answer 7

folic acid.

Question 8

how does anencephaly (fatal) and spina bifida arise?

Answer 8

anencephaly- Failure of the anterior neural tube to close
spina bifida- Failure of the posterior neural tube to close

Question 9

what essential role does folic acid play in many metabolic pathways?

Answer 9

the biosynthesis of DNA, which naturally must occur during development as cells divide.

Question 10

what is the first step of differentiation in brain development?

Answer 10

at the rostral end of the neural tube, of three swellings called the primary vesicles. (The entire brain derives from the three primary vesicles of the neural tube.)

Question 11

what are the names of the three primary vesicles?

Answer 11

forebrain, midbrain and hindbrain

Question 12

what structures arise during differentiation of the forebrain?

Answer 12

secondary vesicles- optic vesicles and the telencephalic vesicles (two of each)
The central structure that remains after the secondary vesicles have sprouted off is called the diencephalon, or “between brain”

Question 13

what do the optic vesicles develop into?

Answer 13

The optic vesicles grow and invaginate (fold in) to form the optic stalks and the optic cups, which will ultimately become the optic nerves and the two retinas in the adult.

(The important point is that the retina at the back of the eye, and
the optic nerve containing the axons that connect the eye to the diencephalon and midbrain, are part of the brain, not the PNS)

Question 14

in what four ways does the telencephalon develop?

Answer 14

1. The telencephalic vesicles grow posteriorly so that they lie over and lateral to the diencephalon.
2. Another pair of vesicles sprout off the ventral surfaces of the cerebral hemispheres, giving rise to the olfactory bulbs and related
   structures that participate in the sense of smell.
3. The cells of the walls of the telencephalon divide and differentiate into various structures.
4. White matter systems develop, carrying axons to and from the neurons of the telencephalon.

Question 15

what tissue surrounds the lateral ventricles and the third ventricle?

Answer 15

lateral ventricles- telencephalon
third ventricle- diencephalon

Question 16

what two types of grey matter form in the telencephalon?

Answer 16

cerebral cortex and basal telencephalon

Question 17

what two structures does the diencephalon divide into?

Answer 17

thalamus and hypothalamus

Question 18

The neurons of the developing forebrain extend axons to communicate with other parts of the nervous system. what are the three axon bundles that develop?

Answer 18

• cortical white matter
• corpus callosum
• internal capsule

Question 18

The neurons of the developing forebrain extend axons to communicate with other parts of the nervous system. what are the three axon bundles that develop?

Answer 18

• cortical white matter
• corpus callosum
• internal capsule

Question 19

how are the cortical white matter, corpus callosum and internal capsule linked?

Answer 19

• The cortical white matter contains all the axons that run to and from the neurons in the cerebral cortex.
• The corpus callosum is continuous with the cortical white matter and forms an axonal bridge that links cortical neurons of the two cerebral hemispheres.
• The cortical white matter is also continuous with the internal capsule, which links the cortex with the brain stem, particularly the thalamus.

Question 20

sensory pathways from where relay through the thalamus to the cerebral cortex via the internal capsule?

Answer 20

eyes (vision), ears (audition) and skin (somatic sensory)

Question 21

how can the cortex command voluntary movement?

Answer 21

by sending signals down the corticospinal tract or by communicating with the basal ganglia (part of the basal telencephalon)

Question 22

how does the midbrain differentiate?

Answer 22

The midbrain differentiates into the tectum and the tegmentum.
The CSF-filled space at the core of the midbrain is the cerebral aqueduct.

Question 23

which important structures differentiate from the hindbrain?

Answer 23

the cerebellum, the pons, (metencephalon) and the medulla oblongata (myelencephalon)