Session 1 - Embryology

Question 1

In what week does gastrulation begin?

Answer 1

Week 3

Question 2

Describe the formation of the neural tube.

Answer 2

Gastrulation produces the notochord.
The notochord then induces neurulation by causing the neural plate to form from overlying ectoderm.
Lateral edges of the neural plate elevate.
Forms a depressed region in the middle called the neural groove.
The neural folds gradually approach each other in the midline and fuse, producing the neural tube.

Question 3

What is the notochord?

Answer 3

A solid rod of cells running down the mid line of the embryo. Has an important signalling role as it directs the conversion of the overlying ectoderm to neurectoderm.

Question 4

The neural tube has completely formed by which day of development?

Answer 4

Day 28-32

Question 5

What causes neural tube defects?

Answer 5

Failure of the neural tube to fuse correctly. Failure can occur caudally or cranially.

Question 6

Cranial neural tube defects result in what abnormality?

Answer 6

Anencephaly

Question 7

Caudal neural tube defects result in what abnormality?

Answer 7

Spina bifida

Question 8

What is spina bifida?

Answer 8

Neural tube defect where the vertebrae of the spine don’t form correctly around the spinal cord.

Question 9

Spina bifida can occur anywhere along the length of the spine, but they are most common in which region?

Answer 9

Lumbosacral region

Question 10

What is a significant risk factor for the development of spina bifida?

Answer 10

Lack of folic acid before and in the early stages of pregnancy.

Question 11

What are the 3 main types of spina bifida?

Answer 11

Myelomeningocele - most severe. Spinal cord and meninges push out and form a sac in the baby’s back.
Meningocele - meninges push out but the spinal cord develops normally.
Spina bifida occulta - most common and mildest. Gap in spine is very small, doesn’t cause any problems, usually unaware of it.

Question 12

The majority of babies will develop what as a result of spina bifida?

Answer 12

Hydrocephalus

Question 13

What is hydrocephalus?

Answer 13

Build up of fluid on the brain. This excess fluid puts pressure on the brain which can damage it.

Question 14

What is anencephaly?

Answer 14

Anencephaly is the absence of a major portion of the brain, skull, and scalp that occurs during embryonic development. Due to failure of the neural tube to close cranially. It is incompatible with life.

Question 15

What is rachischisis?

Answer 15

Failure of neural fold elevation meaning there is no formation of the neural tube at all. This is not compatible with life.

Question 16

How can a neural tube effect be diagnosed?

Answer 16

Raised maternal serum alpha-fetoprotein (indicates an open defect)
Ultrasound scan

Question 17

Consumption of what substance by mothers before conception and during the first trimester of pregnancy reduces the incidence of neural tube defects?

Answer 17

Folic acid

Question 18

Before the 3rd month of development, the spinal cord is the same length as the vertebral column. What happens to the vertebral column after the 3rd month, and what does this mean for the spinal roots?

Answer 18

After the 3rd month, the vertebral column grows faster than the spinal cord. The spinal roots still exit at the intervertebral foramen, meaning they must elongate as the vertebral column grows. This forms the cauda equina.

Question 19

What are the three primary brain vesicles? When do they form?

Answer 19

Prosencephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)

Form after neural tube closure in the 4th week.

Question 20

What are the five secondary brain vesicles? When do they form?

Answer 20

Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon 

Form by the 5th week of development.

Question 21

Which secondary brain vesicles arise from the prosencephalon (forebrain)?

Answer 21

Telencephalon

Diencephalon

Question 22

Which secondary brain vesicles arise from the rhombencephalon?

Answer 22

Metencephalon

Myelencephalon

Question 23

What is the mature derivative of the telencephalon?

Answer 23

Cerebral hemispheres

Question 24

What is the mature derivative of the diencephalon?

Answer 24

Thalamus

Question 25

What is the mature derivative of the mesencephalon?

Answer 25

Midbrain

Question 26

What are the mature derivatives of the metencephalon?

Answer 26

Pons

Cerebellum

Question 27

What is the mature derivative of the myelencephalon?

Answer 27

Medulla oblongata

Question 28

What is the role of the ventricular system in the brain?

Answer 28

To cushion the brain and spinal cord within their bony cases.

Question 29

Blockage of the ventricular system e.g. due to a tumour or infection, can cause what abnormality?

Answer 29

Hydrocephalus

Question 30

What are the layers of the early neural tube?

Answer 30

From inside to out:

• neuroepithelial layer
• intermediate (mantle) layer (alar (sensory) and basal (motor) plates, formed by neuroblasts)
• marginal layer

Also has roof and floor plates which regulate dorsal and ventral patterning.

Question 31

What are neural crest cells?

Answer 31

Cells of the lateral border of the neuroectoderm tube which become displaced and enter the mesoderm. In the mesoderm they then undergo epithelial to mesenchymal transition.

Question 32

What neural crest cell derivatives are found in the nervous system?

Answer 32

Cranial nerve ganglia
Spinal (dorsal) root ganglia
Sympathetic ganglia (chain and pre-aortic)
Parasympathetic ganglia
Schwann cells
Glial cells
Leptomeninges (arachnoid and pia)

Question 33

What neural crest derivatives are found in the head, neck and midline?

Answer 33

Connective tissue and bones of the face and skull
Odontoblasts
Dermis
C cells of the thyroid gland

Question 34

What other neural crest cell derivatives are there?

Answer 34

Conotruncal septum (heart)
Melanocytes
Adrenal medulla

Question 35

Give examples of conditions caused by defects of neural crest cell migration.

Answer 35

Hirschsprung’s disease (aganglionic megacolon). - defect of migration/morphogenesis affecting one structure

DiGeorge syndrome (thyroid deficiency, immunodeficiency secondary to thyroid defect, cardiac defects, abnormal facies). - defect affecting multiple structures.