Embryology Review

Question 1

Define apical ectodermal ridge?

Answer 1

Layer of thickened ectoderm at the distal tip of the limb that controls outgrowth of the limb by maintaining a rapidly proliferating population of adjacent mesoderm cells, called the progress zone

Question 2

Define dermamyotome

Answer 2

The dorsolateral part of the ventromedial head region.

• differentiated from somites

Question 3

Define dermatome

Answer 3

Dorsal portion of each somite that forms the dermis of the skin of the back.

Dermatomes are segmented and supplied by spinal nerves from the segments at which they originated.

Question 4

Define endochondral bone formation

Answer 4

Mechanism for forming bone by first establishing a cartilaginous model followed by ossification.

This type of bone formation is characteristic of the bones of the limbs and base of the skull.

Question 5

Define epimere

Answer 5

Dorsal portion of a somite, frim which is formed muscles innervated by the dorsal ramus of a spinal nerve

Question 6

Define fontanel

Answer 6

Wide sutures in the skull created where more than two bones meet.

The largest is the anterior fontanelle, sometimes called the “soft spot,” located where the two parietal and two frontal bones meet

Question 7

Define myotome

Answer 7

Muscle forming region of a somite formed by myocytes derived from the ventrolateral and dorso-medial regions that coalesce beneath the dermatome.

They remain in the primaxial domain and form intrinsic back muscles, intercostal and cervical muscles and some muscles of the upper limb girdle

Question 8

Define membranous bone formation

Answer 8

Process of forming bone directly from mesenchyme.

This process is characteristic of the flat bones of the cranial vault.

Question 9

Define neurocranium

Answer 9

Part of the skull that forms a protective case around the brain.

It consists of two parts:

1. membranous neurocranium, or flat bones of the skull
2. cartilaginous neurocranium, or chondrocanium, forming base of the skull

Question 10

Define sclerotome

Answer 10

Ventromedial part of each somite that forms the vertebrae

Question 11

Define somite

Answer 11

epithelial balls of cells formed in segmental pairs along the neural tube from paraxial mesoderm.

Differintiate into vertebrae, muscles of the back and body wall, and dermis of the skin

Question 12

Define somitomere

Answer 12

loosely organized segmented collections of paraxial mesoderm in the cranial region.

form muscles and bones of the face and skull

Question 13

Define viscerocranium

Answer 13

Part of the skull that comprises the bones of the face