Embryology

Question 1

How is the neural tube formed?

Answer 1

Some of Ectoderm in midline folds in on itself to form neural tube

Question 2

What does the neural tube form?

Answer 2

Brain and spinal cord

Question 3

How is the neural crest formed?

Answer 3

Some cells at crest of neural fold of ectoderm (after formation of neural tube) seperate to form crest.

Question 4

What does the neural crest do?

Answer 4

Migrates from on top of the neural tube to the mesoderm- only in head and neck region of neural tube.
It later gives rise to various structures

Question 5

Which germ layer is the origin of somites?

Answer 5

Derived from paraxial mesoderm

Question 6

What do the somites help form?

Answer 6

axial skeleton and muscles (etc)

Help in cranial development

Question 7

How many somites are in an embryo?

Answer 7

Around 33

Question 8

Where are somites found?

Answer 8

Head region of embryo- help in cranial development.

Question 9

What 4 things need to develop in Head and neck embryology?

Answer 9

1- Face to house the special sense organs
2- Skull cap and base of skull to protect growing brain
3- Palate to seperate nose and mouth
4- Muscles, skeletal elements to support neck region

Question 10

What embryological tissue makes up the pharyngeal (branchial) arches?

Answer 10

Ectoderm lines outside- also forms clefts inbetween arches
Mesoderm (and neural crest cells) in the middle- Form cartilage and muscles.
Endoderm on the inside- Also forms pouches inbetween arches

Question 11

What are the pharyngeal arches?

Answer 11

Arches which develop around future mouth (stomatodeum) and pharynx. Supports primitive pharynx.

Question 12

What makes up the primitive pharynx?

Answer 12

Devloping mesoderm from mouth to respiratory diverticulum

Question 13

What do the pharyngeal arches do?

Answer 13

Face and neck develop from them.

Support primitive pharynx

Question 14

How many pharyngeal arches are there?

Answer 14

6 arches start to develop but the 5th arch disappears.
So there are 5 pharyngeal arches.
REMEMBER 5!

Question 15

What is the pharyngeal arch that disappears?

Answer 15

Arch 5

Question 16

What are the nerves of the pharyngeal arches?

Answer 16

1st- Mandibular branch of Trigeminal nerve (CNV3)
2nd- Facial Nerve (CNVII)
3rd- Glossopharyngeal nerve (CNIX)
4th- Superior laryngeal branch of vagus nerve (CNX)
5th- Arch disappears- no nerve.
6th- Recurrent laryngeal branch of vagus nerve (CNX)

Question 17

What is the pharyneal arch(s) is the origin of the muscles of the face?

Answer 17

Muscles of the face- innervated by facial nerve (CNVII)
2nd Pharyngeal arch is origin of facial nerve.

Answer is 2nd.

This applies to all muscles- answer is where the nerve originates from. KNOW NERVE SUPPLY OF MUSCLES

Question 18

What pharyngeal arch(s) is the origin of the digastric muscle?

Answer 18

Anterior belly of digastric- innervated by mandibular branch of trigimal nerve (CNV3). So 1st pharyngeal arch

Posterior belly of digastric- innervated by facial nerve. So second pharyngeal arch (CNVII).

Answer is CNV3 and CNVII.

This applies to all muscles- answer is where the nerve originates from. KNOW NERVE SUPPLY OF MUSCLES

Question 19

What happens to the pharyngeal cartilages?

Answer 19

Cartilages form the template for the formation of bone .

1st arch- Meckel’s cartilage over mandible
2nd arch- stylohyoid cartilage
3rd arch- Hyoid bone
4th arch- Thyroid cartilage
6th arch- Thyroid cartilage and cricoid cartilage.

(Might need more detail?)

Question 20

When does the pharyngeal arches form in utero?

Answer 20

4th to 6th week.

Question 21

Which non-skeletal/muscle structures form from the pharyngeal arches (4)

Answer 21

1- Tongue (all)
2- Thyroid (2nd arch endoderm)
3- Parathyroid (3rd and 4th arch endoderm and neural crest)
4- Part of pituatry gland

Don’t know if I need to know specific contributions

Question 22

Which 5 processes does the face develop from?

Answer 22

1 Frontonasal process (mesenchyme superior to future mouth)
2 maxillary processes (maxillary part of 1st pharyngeal arch mesoderm)
2 mandibular processes (also 1st arch mesoderm) fuse in the midline

Question 23

What happens to the frontonasal process?

Answer 23

Ectodermal thickening (nasal placode) of part of frontonasal process. Pushes inwards to form nasal pit- nostril

Medial nasal process further grows downwards (after nasal placode) and laterally, to form a process called
the philtrum.

Medial nasal process- nasal septum and philtrum
Lateral nasal process- nostrils of the nose.

Question 24

How does the palate form?

Answer 24

1- Medial nasal process grows downward and forms philtrum. This forms primary palate.
2- From the maxillary processes, two palatine shelves grow inwards
3- The palatine shelves meet in the midline to form the secondary palate.

This seperates the nasal and oral cavity.

A cleft palate is an congenital abnormality in the formation of the palate

Question 25

How is the cranial vault formed?

Answer 25

The cranial vault is made up of flat bones. These membranous bones are formed by intramembraneous ossification calvaria.

Mesenchyme derived from mesoderm that lies above the surface of developing brain and ossifies directly
It isn’t fully formed at birth. Sutures between bones are soft allowing deformation during passage through birth canal.

The 6 membrane covered anterior fontanelle (soft spot) is clinically important. closes at 1.5 years.

Craniosynostosis- a condition in which one or more of the fibrous sutures in an infant (very young) skull prematurely fuses by turning into bone (ossification), thereby changing the growth pattern of the skull.

Question 26

How is the base of the skull formed?

Answer 26

The base of the skull is made up of irregular bones. Formed by endochondral ossification (cartilage model replacement).

Mesenchyme around notochord is derived predominantly from neural crest cells.

Question 27

How is the viscerocranium formed?

Answer 27

Viscerocranium- skeleton of the face. Partly from branchial (pharyngeal) arches, partly by sensory (special sense) capsules.

Question 28

What is a congenital abnormality associated with the formation of the cranial vault?

Answer 28

Craniosynostosis:
A condition in which one or more of the fibrous sutures in an infant (very young) skull prematurely fuses by turning into bone (ossification), thereby changing the growth pattern of the skull.

Question 29

What are sensory (special sense) capsules derived from?

Answer 29

Derived from mesoderm of somites in head and neck region.

Question 30

What do the sensory (special sense) capsules form?

Answer 30

These preform in cartilage and ossify to form bones around the sense organs i.e. ears, eyes and nose.
They form partly base of skull, partly viscerocranium.

Question 31

How does the skull cap form?

Answer 31

Membranous bones over brain form skull cap.

Question 32

What do pharyngeal arches form?

Answer 32

Branchial arches form skeletal and muscular structures in neck region around pharynx. Also structures like tongue, endocrine glands.
Muscles of arch migrate and take their nerves with them

Question 33

What is the name for 1st pharyngeal arch deformity and what does it mean?

Answer 33

Treacher Collins syndrome:

Treacher Collins syndrome (TCS) is an autosomal dominant congenital disorder characterized by craniofacial deformities, typically involving the ears, eyes, cheekbones, and jawbone. Those affected have normal intelligence.

Corrective surgery can improve situation and hearing.