Embryology and development

Question 1

What are the 3 germ layers?

Answer 1

1. ectoderm
2. mesoderm
3. endoderm

Question 2

What is formed in the body from the Ectoderm?

Answer 2

Skin

Nervous system

Question 3

What is formed in the body from the Mesoderm?

Answer 3

Bone
Kidney
Blood
Heart
Muscle

Question 4

What is formed in the body from the Endoderm?

Answer 4

Gut
Liver
Lungs

Question 5

What is formed first during neural tube formation?

Answer 5

Notochord - cylinder of mesoderm

Question 6

What is formed as the neural fold moves inwards?

Answer 6

The neural groove which fuses to form the neural tube

Question 7

What does the overlying surface ectoderm form?

Answer 7

Skin

Question 8

What is formed from the neural tube?

Answer 8

Brain and spinal cord (CNS)

Question 9

When does neural tube closure occur during development?

Answer 9

3rd week of embryogenesis

Question 10

In what direction does neural tube closure progress?

Answer 10

Rostrally and caudally

Question 11

How many vesicles are present at the start and end of brain development?

Answer 11

start = 3 
end = 5

Question 12

What 3 parts of the brain form from the prosencephalon?

Answer 12

• telencephalon
• diencephalon
• optic cup

Question 13

What occurs as a result of a caudal neural tube close defect?

Answer 13

Spina bifida - vertebrae are incomplete

Question 14

What are the 3 layers of the neuroepithelium?

Answer 14

• germinal
• mantle
• marginal

Question 15

What is the purpose of selective pruning?

Answer 15

All neurons are formed during development, which produces an excess
Pruning reduces the number of neurons and selects for the ones that are needed

Question 16

What do the mantle and marginal form in the brain?

Answer 16

mantle = grey matter
marginal = white matter

Question 17

Compare where afferent and efferent nerves originate from

Answer 17

Afferent (sensory) - from neural crest, cell bodies in ganglia

Efferent (motor) - from neural tube basal plate, cell bodies in CNS

Question 18

How does development of the medulla occur?

Answer 18

Alar plates move laterally and the cavity of the neural tube expands dorsally forming the fourth ventricle

Question 19

How does the development of horses, cows and sheep differ to cats and dogs?

Answer 19

Horses, cows, sheep:

• Have young with good motor function at birth
• well developed cerebellum

Cat and dog:

• young have poor motor function
• poorly developed cerebellum at birth
• thick germinal layer

Question 20

Where is the forebrain developed from?

Answer 20

Alar plate

Question 21

How many cranial nerves are there?

Answer 21

12 pairs - each has a dorsal and ventral branch

Question 22

Name the 12 cranial nerves in order

Answer 22

I	Olfactory
II	Optic
III	Occulomotor
IV	Trochlear
V	Trigeminal
VI	Abducent
VII	Facial
VIII	Vestibulo-cochlear
IX	Glosso-pharyngeal
X	Vagus
XI	Accessory
XII	Hypo-glossal

Question 23

How are bodies cavities formed in the trunk?

Answer 23

Belts of mesoderm in the trunk contain spaces where cavitation occurs

Question 24

Why does cavitation not occur in the head?

Answer 24

Intermediate mesoderm fails to develop

Lateral plate mesoderm remains as solid belt of tissue surrounding gut tube

Question 25

What do the 7 segments in the head consist of?

Answer 25

- Ectoderm - Somites - Endoderm - Lateral plate mesoderm - Segmental arteries - Neuraxis - Nerves

Question 26

Is conscious control somatic or autonomic?

Answer 26

Somatic

Question 27

In what direction does afferent supply?

Answer 27

Towards the brain

Question 28

What are the lateral indentations that mark the segments externally? Which segment does not have this?

Answer 28

Pharyngeal clefts | 1st segment

Question 29

What is the outer epithelial covering (ectoderm) innervated by?

Answer 29

Somatic afferents

Question 30

What is the inner epithelial covering (endoderm) innervated by?

Answer 30

Autonomic afferents/efferents

Question 31

Where is the lateral plate mesoderm located?

Answer 31

Belt of striated skeletal muscle that surrounds pharynx of all segments except segment 1 - referred to as pharyngeal arch

Question 32

What is the lateral plate mesoderm innervated by?

Answer 32

Special visceral efferents

Question 33

Which is obliterated as the brain/head continues to develop?

Answer 33

- Somites 4 and 5 - Pharyngeal arch 5 - Arterial arches 1 and 2 - Pharyngeal clefts/pouches 5 and 6 - Ectoderm of segments 6 and 7

Question 34

Which somites migrate, and where do they migrate to?

Answer 34

6 and 7 | to the floor of the mouth

Question 35

Describe the lining of the mouth

Answer 35

Front part of the mouth is lined with ectoderm, the back is lined with endoderm

Question 36

What is the tongue innervated by?

Answer 36

Somatic efferents

Question 37

What develops from the depression in the floor of arches 4 and 6 (laryngo-tracheal groove)?

Answer 37

Trachea and lungs which then become part of the thorax

Question 38

Which clefts/pouches form the different parts of the ear?

Answer 38

Cleft 1 = external ear | Pouch 1 = middle ear cavity

Question 39

From which segments does most of the skin of the head come from?

Answer 39

1 and 2

Question 40

What do somites 1-7 go on to form?

Answer 40

1-3 = extrinsic muscles of the eye 4 and 5 = disappear 6 and 7 = muscles of the tongue