Early Embryonic Development 3

Question 1

Describe the formation of the neural tube

Answer 1

• Notochord signals the overlying ectoderm to thicken forming the neural plate
• Edges of the neural plate ELEVATE out and CURL towards eachother forming the neural tube

Question 2

Where is the intraembryonic coelom located?

Answer 2

Between the SOMATIC and SPLANCHNIC mesoderm

Question 3

Describe the organisation of the mesoderm

Answer 3

• PARAXIAL MESODERM at the centre surrounding notochord
• INTERMEDIATE MESODERM
• SOMATIC MESODERM adjacent to the ectoderm
• SPLANCHNIC mesoderm adjacent to the endoderm

Question 4

Describe the formation of somites

Answer 4

• SEGMENTATION OF PARAXIAL MESODERM
• PAIRS either side of the neural tube region
• 1st appear in the OCCIPITAL REGION (back of head) and more appear in a cranio aural sequence until there is 42-44 pairs
• Some disappear leaving 31 pairs in total

Question 5

How many pairs of somites are formed in total?

Answer 5

31 pairs

Question 6

When does segmentation of the PARAXIAL mesoderm occur?

Answer 6

Day 20

Question 7

What is derived from the somites?

Answer 7

• DERMATOME which forms the skin
• MYOTOME which forms the muscle
• SCLEROTOME which forms the bone

Question 8

What is a somite?

Answer 8

Regular block of mesoderm cells arranged around a small cavity

Question 9

How is the sclerotome formed?

Answer 9

VENTRAL WALL of somite breaks down and cells migrate to form the sclerotome

Question 10

What is the dermomyotome formed from?

Answer 10

DORSAL WALL OF THE SOMITE

Question 11

Explain how the dermomyotome separates into the DERMATOME and the MYOTOME

Answer 11

• Cells forming the MYOTOME proliferate and migrate

- Cells forming the DERMATOME disperse

Question 12

What does the sclerotome form?

Answer 12

Vertebrae and ribs

Question 13

What is the role of segmentation of the mesoderm?

Answer 13

• ORGANISATION into somites to give rise to repeating units

- Guides INNERVATION

Question 14

What repeating units are formed from the somites?

Answer 14

• Vertebrae
• Ribs
• Intercostal muscles
• Spinal cord segments

Question 15

What is the difference between the epimere and the hypomere?

Answer 15

• EPIMERE is the dorsal side of the mesoderm

- HYPOMERE is the ventral side of the mesoderm

Question 16

Explain how the mesoderm is innervated

Answer 16

• Epimere is innervated by dorsal branch of the spinal nerve for that segment
• Hypomere is innervated by the ventral branch of the spinal nerve for that segment

Question 17

What does the intermediate mesoderm form?

Answer 17

UROGENITAL SYSTEM including the kidneys, ureters and gonads

Question 18

What does the lateral plate of the mesoderm consist of?

Answer 18

• SOMATIC region
• SPLANCHNIC region
• INTEREMBRYONIC COELOM

Question 19

What does the somatic mesoderm form?

Answer 19

Connective tissue of limbs

Question 20

What does the splanchnic mesoderm form?

Answer 20

• Smooth musculature

- Connective tissue and vasculature of the gut wall

Question 21

What is the role of the notochord during NEURALATION?

Answer 21

• IMPORTANT SIGNALLING ROLE
• Signals overlying ectoderm to thicken, forming NEURAL PLATE
• Neural plate folds creating the NEURAL TUBE which ultimately forms the CNS

Question 22

What does the paraxial mesoderm form?

Answer 22

• Axial skeleton
• Dermis
• Muscles of A/L body wall
• Some limb muscles

Question 23

Where is the cardiogenic area (future heart) of the mesoderm located?

Answer 23

Above the buccopharyngeal membrane (site of future mouth)

Question 24

Describe the process of embryonic folding

Answer 24

• CEPHALOCAUDAL folding of the trilaminar disc

- LATERAL folding enclosing the endoderm

Question 25

What is the purpose of folding?

Answer 25

• Draws together the margins of the disc, forming a ventral body wall
• Pulls amniotic cavity around the embryo
• Pulls connecting stalk ventrally (forms umbilical cord)