Embryology Flashcards
What does the neural tube form from
Ectoderm forms a tube
Describe neural crest cells
They can break off from the neural crest and travel to different parts of the foetus
Some form nerves such as sympathetic ganglia
Form many other structures
How many pharyngeal arches are there
5
Numbered 1,2,3,4,6
5 is missing
What (in general) do the pharyngeal arches form
Most of the head and neck
In which week do the pharyngeal arches first develop
Week 4 and 5
Develop in numerical order = 1 to 6
What are the 3 components of the pharyngeal apparatus
Core pharyngeal arch - mesenchyme
External cleft - exoderm
Internal pouch - endoderm
Cleft and pouch separate arches
What does each pharyngeal arch consist of
Core of mesenchyme that forms musculature
Neural crest cells which from skeletal components
Cranial nerve for innervation
Artery - one of the aortic arch arteries
Which cranial nerves supply each pharyngeal arch
1 =Trigeminal (V2,3)
2 = facial
3 = glossopharyngeal
4&6 = vagus (superior and recurrent laryngeal)
What skeletal elements are formed by the first arch
Maxillary process - maxilla, zygomatic bone and squamous part of temporal bone
Mandibular process - Meckel’s cartilage which then forms incus, malleus and the mandible
Which muscles are formed in the first arch
Muscles of mastication Anterior belly of digastric Mylohyoid Tensor tympani Tensor veli palatini
All innervated by V3
Which nerve supplies the 1st arch structures
CNV - trigeminal
All 3 branches of this nerve give sensory supply to skin of the face
What skeletal elements are formed by the 2nd arch
Stapes Styloid process of temporal bone Stylohyoid ligament Lesser horn of the hyoid Upper part of hyoid body
Which cartilage is found in the 2nd arch
Reichert’s Cartilage
Starts as a bar then splits up and ossifies to form the skeletal elements
Which muscles are formed in the 2nd arch
Muscles of facial expression Posterior belly of digastric Stylohyoid Stapedius Auricular muscles
Which nerve supplies the structures of the 2nd arch
CNVII - facial nerve
What skeletal elements are formed by the 3rd arch
Greater horn of hyoid
Lower part of hyoid body
Which muscles are formed in the 3rd arch
Stylopharyngeus
Longitudinal pharyngeal muscle
Which nerve supplies the structures of the 3rd arch
CNIX - glossopharyngeal
What skeletal elements are formed by the 4th and 6th arches
Laryngeal cartilages
Which muscles are formed in the 4th arch
Cricothyroid
Levator veli palatini
Pharyngeal constrictors
Which muscles are formed in the 6th arch
Intrinsic laryngeal muscles
Which nerve supplies the structures of the 4th and 6th arches
CNX - vagus nerve
Arch 4 = superior laryngeal branch and pharyngeal plexus
Arch 6 - recurrent laryngeal branch
What does the 1st pharyngeal cleft form
external acoustic meatus
What is formed by pharyngeal clefts 2-4
The cervical sinus
Arch 2 falls down to cover these clefts
They lose contact with the outside and form the sinus
What is formed from the 1st pharyngeal pouch
Middle ear
Tympanic membrane
Eustachian tube
What is formed from the 2nd pharyngeal pouch
Palatine tonsils
Starts as 2 little buds that become invaded by lymphoid tissue
What is formed from the 3rd pharyngeal pouch
Inferior parathyroid gland
Thymus
What is formed from the 4th pharyngeal pouch
Superior parathyroid gland
Ultimobranchial body = thyroid and C cells
Describe how the parathyroid glands reach their final position
Inferior set of glands actually develops above the superior ones
As the thymus tracks down to it’s position in the thorax, it drags the inferior glands down with it
They jump over the superior ones and bud off to imbed in the thyroid
This occurs around week 7
What structures make up the middle ear
Tympanic cavity and ossicles
What structures make up the external ear
External auditory meatus
Auricle
What structures make up the internal ear
Semi-circular canals - for balance
Organ of corti - hearing
Describe how the otic vesicles form and what they give rise to
Starts as otic placode which pinches inwards to form the otic pit
This further closes off to form the hole that is the otic vesicles
This gives rise to the inner ear
Describe how the shape of the vesicles develop
Vesicle stretches out and becomes tear shaped
Further shape changes form a small sac at the very top with a long thin duct that connects it to two other circular (ish) areas
These are the pars superior and inferior
These develop into the utricular portion and saccular portion of the otic vesicle
What does the utricular portion of the otic vesicle give rise to
The semi-circular canals
The structure regresses in sections to change the sac into a series of canals
Responsible for balance
What does the saccular portion of the otic vesicle give rise to
The cochlear
Main part for hearing
Name the semi-circular canals
Superior
Lateral
Posterior
S and P connected by crus commune nonampullare
What is found within the crus ampullae of the semi-circular canal
Crista ampullaris
This contains the sensory cells needed for balance and the fibres of CNVIII
In which weeks does the cochlear duct begin to form its spiral shape
between weeks 6 and 8
Describe the development of the external ear
6 mesenchymal proliferations form around the 1st cleft
3 come from arch 1 and 3 from arch 2 (3 above and below)
They then fuse to form the auricle
How does the postion of the external ear change with development
Initally form in the lower neck
Ascend due to development of the mandible
If development is stunted it often leads to low set ears (feature of some congenital diseases)
An abnormality in the shape of the external ear suggests what
Error with the neural crest cells elsewhere in the body
e.g. heart or gut
How many facial swelling are present in week 4 of development
5
The frontonasal prominence
2 maxillary and 2 mandibular prominences
What is the name for the primitive oral cavity
Stomodeum
Surrounded by the facial swellings
How many facial swelling are present by week 5
The 5 initial ones and then 4 additional nasal swellings (2 medial and 2 lateral)
What is the nasolacrimal groove and what will it form
Groove between the maxillary prominence and lateral nasal prominence
Connect the corner of nose to eye
Will form the lacrimal system
Which facial prominences form the upper lip
2 medial nasal prominences
2 maxillary prominences
Which facial prominences form the lower lip
Mandibular prominence
Which facial prominences form the nose
Frontonasal prominence - bridge and septum
Medial prominences - crest and tip
Lateral - alae
What forms the intermaxillary segment
Fusion of the medial nasal prominences
What does the intermaxillary segment contain
Portion of the upper jaw - 4 incisors
Has a labial portion that forms the philtrum of upper lip
Palatal component forms part of the primary palate
What forms the primary palate
Intermaxillary segment and two sides of the maxillary process
U shaped
Eventually fuse to form the secondary palate
How do the nasal cavities form
Nasal pits deepen (move into the face) and frontal nasal prominence moves forward
Intermaxillary process moves forward and connecting nasal fin will eventually thins and disappears, leading to one big connected sac
Communicates with oral cavity initially
As the palate develops, this connection shifts back until the nasal cavity meets the pharynx
Error of palate fusion can lead to what pathology
Cleft palate and lip
