6. Development of the nervous system

Question 1

What are the early developmental stages of the nervous system? i.e. day 19

Answer 1

Plate of ectoderm will make a tube in neurulation
At day 19+ a midline groove is apparent
Neurulation is induced by the notochord which is deep to the neural epithelium

Question 2

At day 20-21 (so end of the 3rd week) what happens?

Answer 2

Cells on plate edge thicken forming folds and a groove

Question 3

Going in to the 4th week what stage is the development at?

Answer 3

The edges roll over and the cells fuse to make a tunnel

Question 4

Summarise the development of the nervous system

Answer 4

Day 19: Plate of ectoderm will make a tube in neurulation. A midline groove is apparent. Neurulation is induced by the notochord which is deep to the neural epithelium
Day 20-21: Cells on plate edge thicken forming folds and a groove
Day 22: The edges roll over and the cells fuse to make a tunnel
Day 25: Rostral neuropore closure
Day 27: Caudal neuropore closure

Question 5

At which days do the rostral and caudal neuropore close?

Answer 5

Rostral neuropore closure= Day 25

Caudal neuropore closure = Day 27

Question 6

What is anencephaly?

Answer 6

A type of neural tube defect where there is failure of neural tube to close at the rostral neuropore.
Leads to:
-Infants are born without a forebrain
-Usually unreactive to light and sound
-Usually stillborn
-Some infants may exhibit respiration and respond to touch and sound

Question 7

Risk factors for NTDs?

Answer 7

Previous anencephaly, diabetes, epilepsy drugs

Question 8

NTD?

Answer 8

Neural tube defect

Question 9

Disease when caudal neuropore doesn’t close?

Answer 9

Spina bifida so that the spinal cord protrudes outwith the spinal column

Question 10

Spina bifida:
Ways to reduce risk?
Associated with what old illness?
Disease marker?

Answer 10

Supplementing maternal diet with folate reduces risk of neural tube defects

Associated with displaced cerebellum with hydrocephalus

Alpha fetoprotein (AFP) is a disease marker for neural tube defects/some cancers/liver disease

Question 11

Which 3 swellings of neural tube form the brain?

Answer 11

Forebrain= prosencephalon
Midbrain= Mesencephalon
Hindbrain= Rhombencephalon

Question 12

What does the forebrain form?

Answer 12

Grows two lateral expansions connected to a central slit like space

Lumen forms: 2 x lateral ventricles and the 3rd ventricle

Walls form:

• Telencephalon (the endbrain)
• Cerebral hemispheres (x2)
• Diencephalon (“between brain” includes thalamus)

Question 13

what does the mid brain form?

Answer 13

Grows slower than forebrain and remains as a single central tube
Lumen forms: Cerebral aqueduct

Question 14

What does the hindbrain form?

Answer 14

Develops into the (rest of the) brain stem and cerebellum with a central ventricle expanding.

Lumen forms: Fourth ventricle

Walls form: The caudal end i.e. the brainstem and cerebellum

• Metencephalon (so the pons and cerebellum)
• Myelencephalon (medulla)

Question 15

When does the c -shape develop?

Answer 15

By 16 weeks and the insula is exposed (Later is buried)

Question 16

What splits the basal ganglia?

Answer 16

Internal capsule ascending and descending bundles

Question 17

What structures make up the basal ganglia?

Answer 17

Caudate and lentiform nucleus

Question 18

What makes up the lentiform nucleus?

Answer 18

Putamen and globus pallidus

Question 19

How does the opening out the back of the brainstem change?

Answer 19

The roof of the IVth V widens
EARLY: Sensory grey matter is in dorsal position before IV ventricle forms
LATER: Sensory grey matter tends to be more lateral after the IV Ventricle forms

Question 20

Where does the cerebellum develop?

Answer 20

In the dorsal wall of the neural tube (adjacent to the IV ventricle.)

Question 21

Where does the choroid plexus develop?

Answer 21

Within the IV ventricle on the dorsal surface

Question 22

Where do most of the cranial nerves exit?

Answer 22

Ventrally (with X from the brainstem dorsal grey matter)

Question 23

What are the 3 layers of the developing spinal cord from the caudal neural tube?

Answer 23

VENTRICULAR LAYER: Progenitor cells, neurons/glia
MANTLE LAYER:
Neurons and glia devised from the deeper ventricular layer
MARGINAL LAYER:
Processes of neurones devised from the ventricular layer. Most outer layer

Question 24

How are the dorsal and ventral roots formed?

Answer 24

Ingrowth of neurites from dorsal root ganglion cells (DRG) forms dorsal root

Outgrowth from neurons motor grey forms ventral root

Question 25

What induces the neural tube formation and nerve cell specialisation?

Answer 25

1. Notochord important for inducing neural plate
2. Bone morphogenetic protein (BMP) inhibits neural ectoderm, promoting skin
   Noggin, chordin, follistatin produced in the notochord BLOCK BMP allows default differentiation of neural ectoderm
3. These neural crest specialised cells migrate away from the neural tube epithelium. Then produce a variety of cell types:
   - Skull
   - Sensory and autonomic nervous system
   - Pigment cells

Question 26

Neural crest cells become migratory and move into the mesoderm.
Form a wide range of cells……

Answer 26

• Cranial nerve ganglia
• Dorsal root ganglia
• Autonomic ganglia
• Adrenal medulla
• Schwann cells
• Smooth muscle of cardiac outflow
• Odontoblasts,
• Craniofacial skeleton
• Thyroid parafollicular cells
• Melanocytes

Question 27

Name 2 conditions that are a result of defective neural crest development?

Answer 27

Waardenburg’s Syndrome (autosomal dominant 1/50,000)

Treacher Collins Syndrome (autosomal dominant 1/50,000)

Question 28

Features of Treacher Collins Syndrome ?

Answer 28

Defective protein called Treacle (TCOF1 gene) Failure of formation/apoptosis of neural crest cells
Abnormal eye shape Micrognathia,
Conductive hearing loss,
Underdeveloped zygoma, Malformed ears

DUE TO: Defective Neural Crest development

Question 29

Features of Waardenburg’s Syndrome ?

Answer 29

Some types have Pax73 gene deletion Pigment abnormalities (even albinism)
Deafness
Constipation Heterochromia of eyes Telecanthus

DUE TO: Defective Neural Crest development