S6) Development of the Head, Neck and Face Flashcards
Describe the structure of the pharyngeal arches
Pharyngeal arches are comprised of a system of mesenchymal proliferations in the neck region of the embryo
How many pharyngeal arches are there?
5 in total, numbered 1 to 6 (5th does not form in humans)
Identify the components which constitute the building blocks for the head and neck region
- Pharyngeal arches
- Frontonasal prominence (FNP)
Describe the association of the cranial nerves with the pharyngeal apparatus
- Cranial nerves – CN V, CN VII, CN IX & CN X
- Functions:
I. Mixed sensory & motor functions
II. Supply the derivatives of the pharyngeal arches
Describe how the muscles of the face are derived from the pharyngeal arches
- Ph Arch 1: muscles of mastication
- Ph Arch 2: muscles of facial expression
State the 3 muscles derived from the 4th pharyngeal arch
Ph Arch 4:
- Cricothyroid
- Levator palatini
- Constrictors of the pharynx
State the muscles derived from the 3rd and 6th pharyngeal arches
- Ph Arch 3: stylopharyngeus
- Ph Arch 6: intrinsic muscles of the larynx
Each of the pharyngeal arches develops a neural crest.
Identify the cartilages of the 1st & 2nd pharyngeal arches
- Ph Arch 1 – Meckel’s cartilage: malleus, incus + a template for formation of the mandible
- Ph Arch 2 – Reichert’s cartilage: stapes + upper part hyoid bone
Each of the pharyngeal arches develops a neural crest.
Identify the cartilages of the 3rd, 4th & 6th pharyngeal arches
- Ph Arch 3 – remainder of hyoid bone
- Ph Arch 4 & 6 – cartilages of the larynx
The aortic sac lies in floor of the pharynx.
Hence, in light of this describe the derivatives of the pharyngeal arch arteries
- Ph arch 1&2 arteries disappear
- Ph arch 3 artery = internal carotid artery
- Ph arch 4 artery = arch of aorta (L) & subclavian artery (R)
- Ph arch 6 artery = pulmonary arteries
What is a pharyngeal pouch?
Pharyngeal pouches are endoderm lined pockets in the pharynx
The first pharyngeal pouch is the largest.
What is its derivative?
Pharyngotympanic tube and middle ear cavity
What is the derivative of the second pharyngeal pouch?
Palatine tonsils
What are the derivatives of the third pharyngeal pouch?
- Inferior parathyroid
- Thymus gland
What are the derivatives of the fourth pharyngeal pouch?
- Superior parathyroid gland
- C cells of thyroid gland
What is a pharyngeal cleft?
Pharyngeal clefts are grooves which form in the lateral ectodermal surface of the neck region to separate the arches
Describe the fate of the first pharyngeal cleft
1st pharyngeal cleft is remains and becomes the external acoustic meatus
What happens to the other pharyngeal clefts (besides 1)?
Ph arch 2 grows down to cover others, obliterating all other clefts
Which conditions can occur if there are remnants of other pharyngeal clefts?
Branchial cysts or fistulae can occur
Identify 5 muscular derivatives of pharyngeal arch 1
- Muscles of mastication
- Mylohyoid
- Anterior belly of digastric
- Tensor tympani
- Tensor veli palatine (soft palate)
Identify 5 skeletal derivatives of pharyngeal arch 1
- Maxilla
- Zygoma
- Meckel’s cartilage: mandible, malleus, incus
Identify 4 muscular derivatives of pharyngeal arch 2
- Muscles of facial expression
- Stapedius
- Stylohyoid
- Posterior belly of digastric
Identify 4 skeletal derivatives of pharyngeal 2
Reichert’s cartilage:
- Superior part of hyoid
- Stapes
- Styloid process
- Stylohyoid ligament
What is the muscular derivative of pharyngeal arch 3?
Stylopharyngeus muscle
What is the skeletal derivative of pharyngeal arches 3 and 4?
Epiglottis
Identify the 3 muscular derivatives of pharyngeal arches 4-6?
- Constrictor muscles of pharynx and muscles of soft palate (levator veli palatine)
- Muscles of the larynx
- Striated muscle of upper oesophagus
What is the skeletal derivative of pharyngeal arches 4-6?
Cartilages of the larynx
Which 4 events drive the development of the face?
- The expansion of the cranial neural tube
- The appearance of a complex tissue system
- The development of the sense organs
- The need to separate the respiratory tract from the GI tract
What is associated with the appearance of a complex tissue system in the development of the face?
- The cranial gut tube
- The outflow of the developing heart
Identify and describe 2 structures which form in the early development of the face
- Facial primordia
I. Derived from Ph arch 1
II. Contains FNP
- Primordia of eyes
What does the FNP do in the facial primordia?
Frontonasal prominence surrounds ventro-lateral part of the forebrain
Identify the 4 components of the developing face
- Frontonasal prominence
- Maxillary prominence (PhA 1)
- Mandibular prominence (PhA 1)
- Stomatodeum (depression in buccopharyngeal membrane)
Identify 4 major facial features
- Palpebral fissures
- Oral fissure
- Nares
- Philtrum
Identify the 4 components of the frontonasal prominence
- Forehead
- Bridge of nose
- Nose
- Philtrum
Identify the 3 components of the maxillary prominence
- Cheeks
- Lateral upper lip
- Lateral upper jaw
Identify 2 components of the mandibular prominence
- Lower lip
- Lower jaw
In 5 steps, describe the embryological development of the nose
⇒ Nasal placodes appear on the FNP & sink to become the nasal pits
⇒ Medial and lateral nasal prominences form on either side of the pits
⇒ Maxillary prominences grow medially, pushing the nasal prominences closer together in the midline
⇒ Maxillary prominences fuse with medial nasal prominences
⇒ Medial nasal prominences then fuse in the midline
In 2 steps, describe the development of palatal shelves
⇒ Maxillary prominence give rise to two palatal shelves
⇒ These grow vertically downwards into the oral cavity on each side of developing tongue
In 2 steps, explain how the oral and nasal cavities are separated
⇒ Fusion of medial nasal prominences creates the intermaxillary segment
⇒ The secondary palate is derived from palatal shelves
State the 3 components of the intermaxillary segment
- Labial component: philtrum
- Upper jaw: 4 incisors
- Palate: primary palate
In 3 steps, explain how the nasal septum is formed
⇒ The mandible grows large enough to allow the tongue to “drop”
⇒ The palatal shelves then grow towards each other and fuse in the midline
⇒ The nasal septum develops as a midline down-growth & ultimately fuses with palatal shelves
How does a cleft lip occur?
Lateral cleft lips are due to the failure of fusion of the medial nasal prominence with the maxillary prominence
How does a cleft lip and cleft palate occur?
- Failure of fusion of medial nasal prominence & maxillary prominence
- Failure of palatal shelves to meet in midline
Describe the development of the following structures in the ear:
- External auditory meatus
- Middle ear cavity
- Ossicles
- Auricles
- External auditory meatus develops from the 1st Ph cleft
- Middle ear cavity develops from 1st pharyngeal pouch
- Ossicles develop from cartilages of 1st and 2nd arches respectively
- Auricles develop from proliferation within the Ph Arches 1&2
Explain how the ears are positioned
- Initially, external ears develop in the neck
- As the mandible grows, the ears ascend to the side of the head to lie in line with the eyes
Explain the effect of alcohol on embryological development
- The facial skeleton is derived from neural crest cells in the Ph arches
- Neural crest migration as well as development of the brain are known to be extremely sensitive to alcohol
What is the incidence of Foetal Alcohol Syndrome?
Incidence of FAS = 1 / 100 births
Describe the effects of Foetal Alcohol Syndrome on the development of the face:
What is ARND?
Alcohol-related neurodevelopmental delay
