Embryology Screencasts

Question 1

When do the pharyngeal arches develop?

Answer 1

In weeks 4 and 5 = first arch by day 22, second and third arches by day 24, fourth and sixth arches by day 29

Question 2

What direction do the pharyngeal arches develop?

Answer 2

In a cranial to causal direction

Question 3

What do the three components of the pharyngeal arches relate to?

Answer 3

Each layer relates to a different layer of the trilaminate embryonic disc

Question 4

What are the three components of the pharyngeal arch?

Answer 4

Core pharyngeal arch = mesenchymal tissue
External pharyngeal cleft = ectoderm
Internal pharyngeal pouch = endoderm

Question 5

What separates arches?

Answer 5

Clefts and pouches

Question 6

What is the difference between cleft/pouches and arches?

Answer 6

Clefts and pouches have a more epithelial organisation to their cells

Question 7

What does each arch consist of?

Answer 7

Core of mesenchyme, neural crest cells, cranial nerve component, artery

Question 8

Where is the core of mesenchyme present in each arch derived from?

Answer 8

The paraxial and lateral plate mesoderm = goes on to give rise to musculature

Question 9

What do neural crest cells give rise to?

Answer 9

Skeletal components = from week 5 onwards

Question 10

How many nerves innervate each arch?

Answer 10

Just one nerve

Question 11

Where do the arteries that supply the arches come from?

Answer 11

The aortic arch

Question 12

Which nerve supplies the first pharyngeal arch?

Answer 12

The trigeminal nerve = V2 and V3

Question 13

Which nerve supplies the second pharyngeal arch?

Answer 13

Facial nerve (CN VII)

Question 14

Which nerve supplies the third pharyngeal arch?

Answer 14

Glossopharyngeal nerve (CN IX)

Question 15

Which cranial nerve supplies the fourth and sixth pharyngeal arches?

Answer 15

Vagus nerve (CN X) = superior laryngeal branch to fourth arch, recurrent laryngeal branch to sixth arch

Question 16

What are the two sections of the first arch?

Answer 16

Maxillary process (cranial) and mandibular process (caudal)

Question 17

What skeletal elements does the maxillary process of the first arch give rise to?

Answer 17

Maxilla, zygomatic bone, squamous portion of temporal bone

Question 18

What skeletal elements does the mandibular process of the first arch give rise to?

Answer 18

Incus and malleus, mandible

Question 19

Where is Meckel’s cartilage located?

Answer 19

In the mandibular process of the first pharyngeal arch

Question 20

What occurs in Meckel’s cartilage?

Answer 20

Neural crest cells form cartilage = cartilage stimulates mesenchyme to ossify or produce components of the skull

Question 21

What nerve supplies the musculature derived from the first pharyngeal arch?

Answer 21

CN V3

Question 22

What musculature is formed from the first pharyngeal arch?

Answer 22

Muscles of mastication, anterior belly of digastric, mylohyoid, tensor tympani, tensor veli palatini

Question 23

Which arch gives sensory innervation to the skin of the face?

Answer 23

First arch = via maxillary and mandibular divisions of CN V (CN V1 makes no contribution)

Question 24

Which components does the first pharyngeal arch give rise to in general terms?

Answer 24

All components supplied by the trigeminal nerve (except those innervated by CN V1)

Question 25

Where is Reichert's cartilage located?

Answer 25

Second pharyngeal arch = extends from body of hyoid up towards styloid process

Question 26

What are the skeletal derivatives of the second pharyngeal arch?

Answer 26

Stapes, styloid process of temporal bone, stylohyoid ligament, lesser horn of hyoid, upper part of hyoid bone

Question 27

What supplies all the musculature derived from the second pharyngeal arch?

Answer 27

Facial nerve (CN VII)

Question 28

What muscles are formed from the second pharyngeal arch?

Answer 28

Muscles of facial expression, posterior belly of digastric, stylohyoid, stapedius, auricular muscles

Question 29

What are the skeletal components and muscles derived from the third pharyngeal arch?

Answer 29

``` Skeletal = greater horn and lower part of hyoid bone Muscles = stylopharyngeus (longitudinal pharyngeal muscle) ```

Question 30

Which nerve supplies all components derived from the third pharyngeal arch?

Answer 30

Glossopharyngeal nerve (CN IX)

Question 31

What skeletal components are derived from the fourth and sixth pharyngeal arches?

Answer 31

Laryngeal cartilages (e.g thyroid)

Question 32

What muscles arise from the fourth pharyngeal arch?

Answer 32

Cricothyroid, levator veli palatine, pharyngeal constrictors

Question 33

Which muscles are formed from the sixth pharyngeal arch?

Answer 33

Intrinsic muscles of larynx

Question 34

What nerves supply the fourth arch?

Answer 34

Superior laryngeal nerve (CN X) and pharyngeal plexus

Question 35

What is a cleft?

Answer 35

Invagination of ectoderm

Question 36

What forms the pharyngeal membrane?

Answer 36

When the cleft connects with the mesenchyme of its opposite pouch

Question 37

What structure is formed form the first cleft?

Answer 37

External acoustic meatus

Question 38

What forms the cervical sinus?

Answer 38

Second to fourth clefts = lose contact with the outside to form sinus

Question 39

What structures are formed from the first pouch?

Answer 39

Middle ear, tympanic membrane, Eustachian tube

Question 40

Which pouch gives rise to the palatine tonsil?

Answer 40

Second pouch

Question 41

What structure gives rise to the ossicles?

Answer 41

Formed from mesenchymal condensation

Question 42

When is the mesenchyme covering the ossicles lost?

Answer 42

From 8 months gestation

Question 43

What structures arise from the third pharyngeal pouch?

Answer 43

Inferior parathyroid gland, thymus

Question 44

What does the fourth pharyngeal pouch go on to form?

Answer 44

Superior parathyroid gland, ultimobranchial body

Question 45

What structures form from the ultimobranchial body?

Answer 45

Thyroid gland, C-cells