Development of the hEad and Neck- Week 1

Question 1

3 parts of the branchial appartus

Answer 1

THE BRANCHIAL (PHARYNGEAL) APPARATUS
(branchial and pharyngeal are equivalent terms)

The Branchial (Pharyngeal) Apparatus consists of:

1. Grooves (clefts). These are on the outside and they are lined with ectoderm.
2. Arches. Each arch has unique skeletal, muscle, nerve and arterial elements.
3. Pouches, These are on the inside and they are lined with endoderm

Question 2

Why is the 1st phayngeal cleft special

Answer 2

It reamins open to make the external ear canal

Question 3

Arch 1 components

Skeletal

Muscle

Nerve

Artery

Answer 3

Skeletal- MAxilla, mandible, malleus, incus

Muscles- Muscles of Masticatin- Mylohyoid, anterior digastric, tensor palatini and tensor tympani

Nerves- CN 5

Arteries- Regresses

Question 4

Arch 2 components

Answer 4

Skeletal- Stepes (3rd bone of middle ear), styloid process, hyoid bone

Muscles- Facial expression, Posterior belly of diagastric, Stylohyoid, Stapedius

Nerve- CN 7

Artery- regress

Question 5

Arch 3 components

Answer 5

Skeletal- lower part of hyoid bone

Muscle- stylopharyngeus

Nerve- CN 9 Glossopharyngeal

Arteries- Carotids

Question 6

Arch 4-5 componenets

Answer 6

Skeltal- laryngeal cartilage

Muscle- circothyroid, levator palatini, pharyngeral constrictors, intrinsic laryngeal mm.

Nerve- vagus

Arteries- Aorta, Subclvian

Question 7

What is mesenchymal? What arches derived from named cartilage?

Answer 7

Mesenchymal refers to loosely organized embryonic connective tissue regardless of origin.

• 1st arch. Meckel’s cartilage gives rise to the malleus, incus and future mandible.
• 2nd arch. Reichert’s cartilage gives rise to the stapes of the middle ear, the styloid processand upper part of the hyoid bone.
• 3rd arch. No named cartilage. Gives rise to the lower part of the hyoid bone.
• 4th– 6th arches. No named cartilage. Give rise to the cartilages of the larynx.

Question 8

Discuss the embrological origin of the msucles in the branchial arches

Answer 8

Myoblasts migrate from the occipital myotomes to the branchial arches. Cells then migrate to various parts of the head
and neck to form the muscles of arches.

Question 9

Nerves of each cranial arch

Answer 9

1st arch- CN 5- Trigemical and its 3 branches (Opthalmic, Maxillary, mandibular)

Arch 2- CN 7 Facial

Arch 3- CN 9- Glossopharyngeal

Arch 4- CN 10- Vagus

Question 10

Discuss the arteries of the arches

Answer 10

Key concept :Each branchial arch contains an artery called an aortic arch. Only certain aortic arches remain in the adult. We will focus on what remains.

Not all aortic arches are present at the same time.
By the time the sixth pair of arches has developed, the first two pairs have degenerated Only aortic arches that remain in an altered form in the adult are the 3rd , 4th and 6 th

Aorta reminas in 4th arch along with subclavian

Arch 3= carotids

Question 11

What happens to the pharygeal pouches?

Answer 11

What happens to the Pharyngeal Pouches?
1 st Pouch. This depression forms the Eustachian tube ,tympanic cavity (middle ear) and the mastoid cavity.

2nd pouch. Located in this depression are the palatine tonsils which develop from local accumulations of lymphocytes.

3rdpouch.This is not a typo.The inferior parathyroid and thymus develop and descendto their adult positions.

4th pouch.This is not a typo. The superior parathyroid is derived from the 4thpouch

Question 12

Thyroid gland

Beginning site?

What does it intially lie between?

Where can pieces of the thyroid gland possibly appear?

Answer 12

The site of the beginning of the thyroid is the foramen cecum which lies between the tuberculum impar and the copula.
•
The thyroid may maintain a connection with the foramen cecum by thyroglossal duct.

:
Pieces of the epithelial downgrowth which forms the thyroid may appear anywhere along the tract it takes to reach its adult location.

Question 13

Basic concept of development of the face

Discuss where the primitive mouth begins from?

Answer 13

The development of the face follows a general pattern of structures on either side meeting in the midline. Any midline defect must take these structures into account and most always includes neural crest cells

The primitive mouth begins as a depression of surface ectoderm called the stomodeum
The face develops from five primordia:
1 unpaired frontonasal prominence.
2 paired maxillary prominences.
2 paired mandibular prominences