embryology of the head neck and face grayscale condensed slides

7/27/2019 Embryology of the Head Neck and Face Grayscale Condensed Slides

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EmbryologyEmbryology

Alex ForrestAssoci ate Profess or of For ensic Od ontol ogyForensic Science Research & Innovation Centre, Griffith UniversityConsultant Forensic Odontologist,Queensland Health Forensic and Scientific Services,

39 Kessels Rd, Coopers Plains, Queensland, Australia 4108

Oral Biology

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Learning ObjectivesLearning Objectives

1. You should be able to understand and explain the basic

embryological formation of the face, including the times

at which crucial events occur.

2. You should understand and be able to identify the

major possible causes of interruption to the formation

of the face, and to explain the clinical consequences

that result.

3. You should be able to describe and explain the fates of

the derivatives of branchial arches I,II,III,IV and VI in

man.

Learning ObjectivesLearning Objectives

4. You should be able to relate your embryologicalknowledge to recognition of patterns in the head and

neck, such as the innervation of the palate, and the

innervation of major muscle groups in the head.


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Early DevelopmentEarly Development


As you will remember, the embryo

develops from the original fertilized

cell, and as cell numbers increase,

they become specialized in different

regions to form tissues and organs.

Developing neural and bloodsystems provide communications

between the different cells and

groups of cells.

From:

http://www.luc.edu/depts/biol

ogy/devf.htm

Recall that the embryo

develops into a three-

layered plate shape that

folds into a tube to createthe primitive gut, and

curves at the head and tail

to end up with a C-shaped

form that curves around

the developing heart.

Ten Cate, AR, Oral Histology, Development, Structure &

Function, St. Louis, CV Mosby, 1980, p. 14


Initially, however, the

embryo forms a two-

layered (or bilaminar)embryonic disk.

Mesoderm develops in the

third week.



What about the Germ Layers?What about the Germ Layers?


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At week three, a structure called the primitive streak

develops.

Modified from https://reader008.{domain}/reader008/html5/0417/5ad58baf78150/5ad58bb192631.jpg

Formation of MesodermFormation of Mesoderm

Ectodermal cells migrate towards this primitive streak, and

then invaginate beneath it and spread between the ectoderm

and endoderm to form the third layer.



This process continues until mesoderm separates the

ectoderm and endoderm, except at the head end and down at

the far tail end.



Clearly, however, in the head of a developed organism we still

have mesoderm. But to understand where it comes from, we

need to examine the formation of the nervous system.




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The nervous system

begins its development

towards the head end of

the embryo.

It begins as a thickening in

the ectoderm in this areacalled the neural plate.

Modified from

https://reader008.{domain}/reader008/html5/0417/5ad58baf78150/5ad58bb343ba6.jpg

Development of Nervous SystemDevelopment of Nervous System

The edges of the neural plate now begin to thicken, producing

raised margins to the structure. Between the raised edges lies

the neural groove.

Modified from http://publish.uwo.ca/~jkiernan/nrltub.gif

Development o f Nervous SystemDevelopment o f Nervous System

The neural folds continue to develop until they meet on top of

the neural fold to produce a neural tube. This will become the

ventricles and central canal of the nervous system.



Notice however the group of cells that develop alongside the

growing neural folds called the neural crest, and shown in the

diagram above.


Development o f Nervous SystemDevelopment o f Nervous System


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As you can see, the neural crest cells separate from the

remainder of the neural tube to form a group of cells in their

own right.



There is ongoing debate in the literature as to whether the

neural crest cells really are a derivative of the developing

nervous cell population or are a distinct group themselves.

e.g: Weston JA, Yoshida H, Robinson V, Nishikawa S and Fraser ST (2004). Neural crest and the origin of

ectomesenchyme: neural fold heterogeneity suggests an alternative hypothesis. Dev Dyn. 229: 118-30.


Development of EctomesenchymeDevelopment of Ectomesenchyme

Either way, these cells are most important to the continued

development of the embryo.

They migrate extensively and give rise to components of the

peripheral nervous system including sensory ganglia,

sympathetic neurons, Schwann cells, meninges and pigment

cells.


They also give rise to the embryonic connective tissue of the

facial region and to the cartilages of the branchial arches.

This embryonic connective tissue is known as

ectomesenchyme, to differentiate it from the mesenchyme

produced at the primitive streak.



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It has been regarded as a fourth germ layer by some authors,

and there are cogent reasons for thinking of it in this way.


It has properties slightly different to those of mesenchyme

elsewhere in the body.

For instance, the bones of the face and cranium (but not of the

base of the skull, which derive from conventional mesoderm)form by intramembranous ossification rather than the

endochondral method common in other bones.


You should look up Treacher Collins Syndrome, which results

from interference in the migration of neural crest cells in the

facial area.

Treacher Collins SyndromeTreacher Collins Syndrome

http://www.dental.mu.edu/oralpath/lesions/treachercollins/treachercollins.htm

Note that the skeletal muscles of the head and neck do not

derive from the ectomesenchyme. They develop from somites

or somitomeres which migrate into the branchial arches or thefrontonasal process.

(Somitomeres are similar to somites but derived from paraxial

mesoderm. They arise as 7 pairs and give rise to facial

muscles, muscles of mastication, extraocular muscles and

some muscles of the pharynx.)

Origin of MusclesOrigin of Muscles


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Facial DevelopmentFacial Development

Facial DevelopmentFacial Development

The face develops from five embryonic tissue

masses, also known as processes. They all arise by

rapid multiplication of neural crest cells which

originate from ectoderm:

Frontonasal Process

Mandibular Processes (paired)

Maxillary Processes (paired)

Modified from Ten Cate, AR, Oral Histology, Development, Structure &Function, St. Louis, CV Mosby, 1980, p. 24

MouthMouth

The developingmouth is given a

special name: the

stomodeum or

stomatodeum.

From http://www.llk.ie/cleftpalate/embryology.shtml


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MouthMouth

It appears as a

depression in the

embryonic surface

at about the fourth

week of

development, so itis an early feature.

From http://www.llk.ie/cleftpalate/embryology.shtml

Eventually, the stomatodeum will give rise to the oral

cavity.

At first, it is lined with oral ectoderm, which will give rise

to the teeth and finally become the oral epithelium.

MouthMouth

The floor of this depression

pushes against the

developing gut, and the wall

that separates them is

termed the buccopharyngeal

membrane.

It represents the meeting of

ectoderm and endoderm.

MouthMouth

Modified from http://www.bartleby.com/107/241.html

This soon breaks down so that the stomatodeum can open

directly into the primitive pharynx of the foregut.

MouthMouth

Ten Cate, AR, Oral Histology, Development, Structure & Function , St. Louis, CV Mosby, 1980, p. 29


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At the sides, the

stomatodeum

becomes limited by

the formation of the

first pair of branchial

arches, which give

rise to the lower part

of the face.

MouthMouth

Modified from Berkovitz, BKB et al. Color Atlas of Oral Anatomy, Histology &

Embryology, London, Mosby-Wolfe, 2nd Ed 1992, p. 231

NeckNeck

Development of the neck begins at the same time as

development of the face, in the fourth week of embryonic

life.

It is completed before birth. It arises from the branchial

arches and the primitive pharynx, which is part of thedigestive tube.

The caudal part of the

primitive pharynx

forms the

oesophagus, and aventral outgrowth

leads to formation of

the larynx, and

trachea, which end at

the developing lungs.

NeckNeck

Arey, Developmental Anatomy, Philadelphia, WB Saunders, 4 th

Ed 1941, p 218

Branchial ArchesBranchial Arches

The branchial arches

are bulges on the

embryo visible

immediately beneaththe developing brain

mass.

The first one will form

the lower part of the

face.

Modified from: Arey, Developmental Anatomy, Philadelphia, WB

Saunders, 4th Ed 1941, p. 145


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Of the six branchial

arches, only five

survive in man.

From:

https://reader008.{domain}/reader008/html5/0417/5ad58baf78150/5ad58bb6e7b6d.jpg

Branchial ArchesBranchial Arches Branchial ArchesBranchial Arches

Each branchial arch

contains a portion of

primitive striated muscle

tissue, some nervous

tissue from the neural

crest, some vascular

tissue, and a bar of

cartilage in its

mesodermal core.

Each arch therefore

contains an artery and a

nerve.

Ten Cate, AR, Oral Histology, Development, Structure & Function, St.

Louis, CV Mosby, 1980, p. 20

The branchial arches are

covered on the external

surface by ectoderm, andon the internal surface by

endoderm, and support

the lateral wall of the

primitive pharynx.

Modified from:

https://reader008.{domain}/reader008/html5/0417/5ad58baf78150/5ad58bb6e7b6d.jpg


The first two arches

are mainly involved

in the formation of

the face, and theremaining arches

are more involved

in the formation of

structures within

the neck.

Modified from Arey, Developmental Anatomy, Philadelphia, WB

Saunders, 4th Ed 1941, p 146



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Called the mandibular arch.

Cartilage is termed Meckel's

cartilage, after the anatomist

who first described it.

It forms the mandible and themaxillae, the muscles of

mastication and the mandibular

division of the trigeminal nerve.

Modified from: Grays Anatomy, London, Longman,

35th Ed, 1973, p.117

1st Branchial Arch1st Branchial Arch

The cartilage of the mandibular arch gives rise to the

incus and malleus bones, the anterior ligament of the

malleus and the sphenomandibular ligament, but the

bones of the mandible and maxilla do not form from it.

Instead they form by intramembranous ossification

following degeneration of the cartilage.


The nerve becomes mandibular division of the trigeminal

nerve, and migrates with the muscles.

Modified from: Grays Anatomy, London, Longman, 35 th Ed, 1973, p.132


The muscle tissue becomes the muscles of mastication,

tensor tympani and tensor veli palatini as well as the

mylohyoid muscle and the anterior belly of the digastric.All of these muscles take their motor nerve supplies from

branches of the mandibular division of the trigeminal

nerve.

The artery of the first arch does not survive.



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The second arch is

called the hyoid arch.

Its cartilage is termed

Reichert's cartilage,

again after the anatomistwho first described it.

Modified from: Grays Anatomy, London, Longman,

35th Ed, 1973, p.117

2nd Branchial Arch2nd Branchial Arch

Its muscle tissue forms the muscles of facial expression,

and its nerve is the facial nerve (VII).


2nd Branchial Arch2nd Branchial Arch

The Muscles of Facial Expression therefore all share acommon motor nerve supply the facial nerve.

Its muscle tissue also forms the stapedius muscle, the

stylohyoid and the posterior belly of digastric.

2nd Branchial Arch2nd Branchial Arch 2nd Branchial Arch2nd Branchial Arch

Its cartilage contributes to the stapes, styloid process of

the temporal bone, and some of the hyoid bone including

the upper part of its body and the lesser cornu (to which

the stylohyoid ligament attaches), as well as the

stylohyoid ligament.

The artery of the second arch also degenerates and

cannot be recognized in the adult.


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The cartilages of the remaining arches are not named.

The cartilage of the third arch contributes to the hyoid bone. Its muscle

becomes the stylopharyngeus muscle, and its nerve becomes the

glossopharyngeal nerve (IX).


3rd Branchial Arch3rd Branchial Arch

3rd Branchial Arch3rd Branchial Arch

Its artery becomes the common carotid artery and it alsocontributes to the proximal part of the internal carotid

artery.

The fourth and sixth arches fuse.

Their cartilages contribute to most of the laryngeal

cartilages (thyroid, cricoid, arytenoid, corniculate and

cuneiform cartilages).

4th - 6th Branchial Arch4th - 6th Branchial Arch


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The muscles of the fourth arch are innervated

by its nerve, the superior laryngeal branch of

the vagus nerve (X)

The nerve of the sixth arch becomes the

recurrent laryngeal branch of vagus (X),

which supplies the intrinsic muscles of the

larynx.


The artery of the fourth arch becomes the arch of the

aorta on the left side, and contributes to the right

subclavian and brachiocephalic arteries.

The artery of the sixth arch contributes to the pulmonary

arteries.


5th Branchial Arch5th Branchial Arch

The fifth arch degenerates and becomes

unrecognizable in man.

Branchial Pouches & CleftsBranchial Pouches & Clefts

A branchial pouch is the fold seen on the inside aspectof the branchial complex between adjacent arches.

Branchial cleft is the name given to the fold seen on the

outside.


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The first pharyngeal pouch becomes the auditory tube

and middle ear.

The first pharyngeal cleft becomes the external auditory

meatus, and the tympanic membrane remains as the

structure resulting from their meeting.


The second pharyngeal pouch becomes the tonsillar

fossa between the palataglossal and palatopharyngeal

folds.

As development of the embryo continues, this develops a

mass of lymphoid tissue called the palatine tonsil.

Formation of the FaceFormation of the Face

The face develops

between the 24th and

38th day of gestation.

In the early stages, the

development of the face

is dominated by the

changes that create the

primitive nasal cavities.




At about 24 days, the first

branchial arch starts to bud

off a process called the

maxillary process.The stomatodeum is now

limited by the developing

brain rostrally, by the first

branchial arch caudally,Modified from Ten Cate, AR, Oral Histology, Development,

Structure & Function, St. Louis, CV Mosby, 1980, p. 24

and by the newly formed maxillary process laterally.

The first arch also contains the mandibular process, and

contains Meckel's cartilage.


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The frontonasal process

develops two nasal pits,

and tissue builds up

around them in a horse-

shoe shape to form the

lateral and medial nasal

processes.

Modified from Ten Cate, AR, Oral Histology, Development,


The maxillary process

grows medially and

approaches the lateral

and medial nasal

processes.

At this stage, it remainsseparated from them by

a groove.

Modified from Berkovitz, BKB et al. Color Atlas of

Oral Anatomy, Histology & Embryology, London,

Mosby-Wolfe, 2nd Ed 1992, p. 232



The continued central growth of the maxillary process

pushes the medial nasal process towards the midline.

From Ten Cate, AR, Oral Histology, Development, Structure & Function, St. Louis, CV Mosby, 1980, p. 27


Here they fuse to create the middle part of the nose, the

middle part of the upper lip, the anterior part of the maxilla

and the primary palate.

Modified from: Arey, Developmental Anatomy, Philadelphia, WB Saunders, 4 th Ed 1941, p. 199


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This is known as the premaxilla, and it carries the

odontogenic epithelium for the maxillary incisors.


Formation of the PalateFormation of the Palate

It is, however, only after the formation of the secondary

palate that the distinction between the oral and nasal

cavities can be made clearly.



The formation of the

secondary palate takes

place between the 7thand 8th weeks of

development. It results

from the fusion of

shelves which arise from

the maxillary processes.

Modified from: Berkovitz, BKB et al. Color Atlas of


Mosby-Wolfe, 2nd Edition 1992, p. 234


The nerve of the

primary palate is

the incisive branch

of the long

nasopalatine

branch of the

maxillary division

of the trigeminal

nerve (V).

From Jamieson, EB, Illustrations of Regional Anatomy, Section II Head and

Neck, Edinburgh, Livingstone Ltd, 8th Edition, p 35.


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The nerve of the

secondary palate

is the greater

palatine branch of

the maxillary

division of V.

From Jamieson, EB, Illustrations of Regional Anatomy, Section II Head and Neck,

Edinburgh, Livingstone Ltd, 8th Edition, p 35.


This photograph shows the portions of the adult palate

derived from the primary and secondary palates. Correlate

this with the palatal nerve supply.

Formation of the TongueFormation of the Tongue

A mesenchymal swelling

arises in the midline in the

mandibular process of the first

branchial arch. It is called the

tuberculum impar.

Two other swellings appear,

one on either side of the

tuberculum impar, and these

enlarge rapidly and merge

with each other and with the

tuberculum to form a large

mass.Modified from: Berkovitz, BKB et al. Color Atlas of




The mucous membrane of

the anterior two-thirds of

the tongue is formed from

this mass.

This is why the anteriortwo-thirds of the tongue

have the mandibular

division of the trigeminal

nerve (via the lingual

nerve) as their sensorynerve supply.





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The nerve of the second arch contributes taste fibres to

the anterior two-thirds of the tongue, via the chorda

tympani.


The posterior part of the

tongue arises from the

hypobranchial

eminence, a large

midline swelling from the

third branchial arch, the

nerve of which becomes

the glossopharyngeal.

Therefore, the posteriorthird of the tongue

comes to be supplied by

IX.




Formation of the MandibleFormation of the Mandible

The mandible develops in the mandibular process, which we

have already mentioned. The cartilage of the first arch is

called Meckel's cartilage.

From Ten Cate, AR, Oral Histology, Development, Structure & Function, St. Louis, CV Mosby, 1980, p. 36


It is important to

realize that, while this

cartilage is in close

proximity to the

developing mandible,

it does not make a

large contribution to

it.

Modified from Ten Cate, AR, Oral Histology, Development,



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The two mandibular

processes fuse in the

midline to form a

mandibular arch.

Now, the bone of the

mandible begins to form in

the mesenchymal tissue

that condenses laterally to

the cartilage, and the

cartilage begins to

disappear.From Ten Cate, AR, Oral Histology, Development,



The bone forms a trough which contains the

inferior dental nerve.

From: Grays Anatomy, London, Longman, 35 th Ed, 1973, p.283


The bone above this forms a series of compartments

for the individual teeth, and finally closes over the tooth

germs to form a roof over the trough.

From http://www.usc.edu/hsc/dental/ohisto/Cards/odev/17_bb.html


By 10 weeks of age, the rudimentary mandible is formedalmost entirely from intramembranous ossification with

little direct involvement by Meckel's cartilage.


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The cartilage does, however, contribute to the development

of the malleus of the middle ear and its ligament, and to the

sphenomandibular ligament.

From: Grays Anatomy, London, Longman, 35th Ed, 1973, p.283


There is some evidence that Meckel's cartilage may

contribute to a small extent to the formation of the mandible

forwards of the position of the mental foramen.

From: Grays Anatomy, London, Longman, 35th Ed, 1973, p.283

Formation of the MaxillaFormation of the Maxilla

The maxilla also develops from a condensation of

mesenchyme from the first branchial arch.

There is no branchial arch cartilage in the maxillary

process, so the bone formation is entirely by

intramembranous ossification.

The maxillary sinus forms in the 16th week.

Origin

Unknown


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Congenital DefectsCongenital Defects

You will by now be aware that the development of a

person is a very complicated and finely-balanced

process.

Malfunctions of this process at different points can

produce congenital defects.

Some of these will be genetic in origin, but environmental

factors including drugs can also be responsible.


The types of environmental factors that can affect the

embryo can be classified into five groups:

1. Infectious agents

2. Ionizing radiation

3. Drugs

4. Hormones

5. Nutritional deficiencies


Among the most common of the defects that occur are

the orofacial clefts.

These constitute approximately 13% of the reported

anomalies and are the second most common reported

malformation.

Modified from Ten Cate, AR, Oral Histology,

Development, Structure & Function, St. Louis, CV

Mosby, 1980, p. 43



Mosby, 1980, p. 45


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Origin

Unknown Modified from Ten Cate, AR, Oral Histology,


Mosby, 1980, p. 43



Mosby, 1980, p. 45

Origin

Unknown

Origin

Unknown


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The End

embryology of the head neck and face grayscale condensed slides

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