Embryology

Question 1

what is mesenchyme?

Answer 1

embryonic connective tissue which develops into bone, cartilage, blood vessels etc

Question 2

how many branchial arches are there?

Answer 2

5

begins as 6 but one disappears (5th one so you are left with 1,2,3,4 & 6)

Question 3

name a condition that is caused by an abnormality of one of the branchial arches, which branch is affected, and the effect this has on the person.

Answer 3

treacher collins syndrome
1st phalangeal arch
abnormal development of structures supplied by the trigeminal nerve V3 - mandible, ears ect

Question 4

what makes up the branchial / phalangeal arches?

Answer 4

endoderm (also forms clefts between arches)
mesoderm + neural crest cells (cartilage and muscle
ectoderm (also forms pouches between arches)

Question 5

what are the nerves of the brachial arches?

Answer 5

1st = mandibular branch of trigeminal (CN V3)
2nd = facial (CN VII)
3rd = glossopharyngeal (CN IX)
4th = superior laryngeal (CN X)
6th = recurrent laryngeal (CN X)

Question 6

if there is abnormal development of the 2nd branchial arch, name a few things that will be affected?

Answer 6

muscles of facial expression
posterior belly of digastric
anterior half of EAC
stapes of the middle ear

Question 7

from what branch in the branchial arches/phalangeal arches does the ossicles develop from?

Answer 7

malleus and incus - 1st branch

stapes - 2nd branch

Question 8

why is the nerve supply of the tongue so complex and what is the nerve supply?

Answer 8

complex because it is formed from 3 branchial rings
sensory - lingual and chord tympani branches of facial (VII) (anterior) & glossopharyngeal (IX) (posterior)
motor for both - hypoglossal (XII)

Question 9

what does the face develop from?

Answer 9

5 processes;
one frontonasal processes
two maxillary processes
two mandibular processes

Question 10

which process which forms the face fuses?

Answer 10

mandibular

Question 11

what forms the palate?

Answer 11

medial nasal process forms Philtrum which forms primary palate
The palatine shelves grow from the maxillary process and meet inward

Question 12

what forms the nostrils?

Answer 12

nasal placode from the frontonasal process

Question 13

how are the cranial vault bones formed?

Answer 13

membranous ossification calabria

Question 14

how are the bones of the base of the skull formed?

Answer 14

endochondral ossification

Question 15

how is the viscerocranium developed?

Answer 15

partly from branchial arches and partly from sensory capules

Question 16

after birth what is clinically significant in terms of the membranous ossification of the cranial vault?

Answer 16

doesn’t full form at birth

the 6 membrane covered fontanelle is of clinical significance as it is a ‘soft spot’

Question 17

what is a contidion associated with abnormal development of the cranial vault?

Answer 17

craniosynostosis

fusion of the sutures too quickly

Question 18

what does the layers of the retina develop from?

Answer 18

the optic cup
outer 10th layer from the outer layer of optic cup
inner 9 layers from the inner layer of the optic cup

Question 19

why is the development of the retina of clinical significance?

Answer 19

because theoretical layers is formed from the inner and outer layers of the optic cup this creates a potential space between the 10th layer and the inner 9 layers.
retinal detachment can occur when fluid fills in this space separating the layers

Question 20

what forms from the mesenchyme of the developing eye?

Answer 20

choroid
storm of cornea
sclera
extra ocular msucles

Question 21

how does the lens become transparent in the developing eye?

Answer 21

the lens fibres form the epithelium of the lens vesicle

the epithelium then loses its nuclei to become transparent

Question 22

what forms from the surface ectoderm of the developing eye?

Answer 22

eyelids
conjunctiva
corneal epithelium

Question 23

where does the eye develop from?

Answer 23

the neural tube

its an extension of the brain

Question 24

optic vesicles which form the eye grow outwards from which part of the neural tube?

Answer 24

diencephalon

Question 25

how does the optic cup form?

Answer 25

as the optic vesicles grow outwards they reach the surface ectoderm
the cells of the surface ectoderm thicken creating a lens placode
this lens placode invaginates creating the optic cup

Question 26

where is the choroid fissure found?

Answer 26

within the developing retina and optic nerve

Question 27

what artery pierces into the optic cup creating the choroid fissure? and why is this of anatomical importance in the adult?

Answer 27

the central retinal artery

the fissure closes off but the artery remains within the substance of the optic nerve

Question 28

where does the optic nerve develop from?

Answer 28

the optic cup