1.2.1 Development of the CNS

Question 1

What is gastrulation?

Answer 1

Process where the outer layer of the bilayer germ disc invaginates at the primitive streak to produce a 3 layered disc

Question 2

What are the 3 layers of the embryonic disc after gastrulation takes place?

Answer 2

Ectoderm
Mesoderm
Endoderm

Question 3

What tissues does the ectoderm form?

Answer 3

Skin and neural tissue as well as neural crest

Question 4

What tissues does the mesoderm form?

Answer 4

Heart
Vessels
Muscles
Notochord

Question 5

What tissues does the endoderm form?

Answer 5

Gut and accessory lining
Inner linings of tubes

Question 6

How does the notochord induce the formation of the neural tube?

Answer 6

Notochord releases chemicals to the overlying ectoderm to form the neural tube

Question 7

What is neurulation?

Answer 7

The process of formation of the neural tube

3rd week

Question 8

Describe the process of neurulation

Answer 8

1. Induced by the notochord
2. Elevation of the neural folds
3. Fusion of the folds at the mid cervical level
4. When folds fuse, neural crest cells detach and migrate to their ultimate destinations
5. Neural tube zips up rostrally and caudally

Question 9

Why are the swellings on the rostral neural tube significant?

Answer 9

Swellings will develop and become major parts of the adult brain

Question 10

What are the 3 major parts of the brain called?

Answer 10

Prosencephalon-forebrain (remember prose means first)

Mesencephalon -midbrain (mes- means middle)

Rhombencephalon- hindbrain (4th ventricle shaped like a rhombus)

Question 11

How do the eyes start to develop?

Answer 11

Outgrowths of the forebrain forming optic vesicles which then later form optic nerves

Question 12

What are the two parts of the prosencephalon?

Answer 12

Telencephalon
Diencephalon

Question 13

What do the telencephalon and diencephalon become?

Answer 13

Telencephalon-becomes most of cerebral hemisphere

Diencephalon-becomes thalamus,hypothalamus and optic nerve/retina (eyes-two-di)

Question 14

What are the two parts of the rhombencephalon?

Answer 14

Metencephalon- forms the pons and cerebellum

Myelencephalon- forms the medulla

Question 15

Where do motor structures tend to sit in relation to sensory structures?

Answer 15

Motor tends to sit anteriorly, motor in a car is in the front

Sensory is posterior, think of parking sensors at the back

Question 16

Why do sensory and motor structures tend to develop in this way?

Answer 16

Due the development of the basal (floor) and alar (roof) plates in the neural tube

Notochord inducts the ventral (anterior) portion of the neural tube to become the basal (floor) plate

Question 17

What does the basal plate give rise to?

Answer 17

Motor neurones

Question 18

How does the alar (or roof) plate form?

Answer 18

In the absence of influence from the notochord

Question 19

What does the alar plate give rise to?

Answer 19

Inter- and sensory neurones

Question 20

What is the pattern of sensory and motor function in the spinal cord?

Answer 20

Same as the brain, dorsal roots are sensory while ventral roots are motor

Dorsal horn contains sensory neurones and dorsal columns sit posteriorly

Ventral horn contains motor neurons and the corticospinal (motor) tract sits anteriorly

Question 21

What is the pattern of sensory and motor function in the medulla?

Answer 21

Lemnisci (sensory) posterior

Pyramids (motor) anterior

Question 22

What is the pattern of sensory and motor function in the midbrain?

Answer 22

Colliculi (sensory) posterior

Cerebral peduncles (motor) anterior

Question 23

What is the pattern of sensory and motor function in the cerebral cortex?

Answer 23

Primary sensory cortex posterior to pre-central gyrus

Question 24

How does the cauda equina develop?

Answer 24

Initially there is a one to one relationship between spinal nerves and vertebrae

The spine grows faster than the spinal cord, especially at the lumbar level

Lower portions of the cord are stretched, drawing out the cauda equina

Starts at L2

Question 25

How can neural tube defects cause hydrocephalus?

Answer 25

May be caused by tethering of the cord at the site of the defect

As the spine grows the cord cannot move within the vertebral canal, brainstem (containing 4th ventricle) is pulled down through foramen magnum becoming occluded