Embryology Flashcards
What kind of structures are the pharyngeal arches
Solid structures
In what organisms do pharyngeal arches develop
In all vertebrates
When do the arches develop
Weeks 4 and 5
What are pharyngeal arches also known as
Branchial arches
What are the numbers of the arches in humans
1,2,3,4,6
What are the pharyngeal arches derived from?
All 3 germ layers - mesoderm, ectoderm and endoderm
What is the core of the mesenchyme derived from
Paraxial and lateral plate mesoderm
What does the paraxial and lateral plate mesoderm form
Musculature of the face and neck
What do the neural crest cells form
The skeletal components of the face
What is the name for the external indentations between one arch and the next
Cleft
What is the name for the internal indentations between one arch and the next
Pouch
What are the clefts lined with
Ectoderm
What are the pouches lined with
Endoderm
Why is the migration pathways of the neural crest important
They provide a pathway for the axons of the cranial nerves to follow
Cranial nerve 7 (facial) follows what arch
2
Cranial nerve 5 (trigeminal) follows what arch
1
Cranial nerve 9 (glossopharyngeal) follows what arch
3
Cranial nerve 10 (vagus) follows what arch
4 and 6
What nerve follows arch 4
superior laryngeal branch of the vagus nerve
What nerve follows arch 5
Recurrent laryngeal branch of the vagus nerve
What are the 2 main skeletal components of the first arch
Maxillary process (dorsal portion) and the mandibular process (ventral portion)
What is Meckel’s cartilage
An embryonic cartilage that is associated with the mandibular process but does not form bone
What does the maxillary process of the 1st arch contain
Maxilla, zygomatic and part of the temporal bone
What does the mandibular arch contain
Meckel’s cartilage –> incus, malleus and mandible
What muscles form form arch 1
Muscles of mastication, anterior belly of digastric mylohyoid, tensor tympani and tensor palatini
What nerve supplies the muscles from arch 1
V3
What sensory nerves supply what parts of the skin of the face that come from arch 1
V1 (ophthalmic)
V2 (maxillary)
V3 (mandibular)
What does the myohyloid muscle do
Forms the floor of the mouth
What are the muscles supplied by
The 3rd branch of the trigeminal nerve
What does the 2nd arch form
Skeletal components
What are the skeletal components of arch 2
Stapes styloid process of the temporal bone stylohyoid ligament Lesser horn Upper part of body of hyoid
What are the muscles that form form arch 2
Muscles of facial expression
stapedius
stylohyoid
posterior belly of digastric and auricular muscles
What nerve supplies the muscles from arch 2
The facial nerve (7)
Describe the auricular muscles in humans
Extremely rudimentary but in other species they are better developed (dogs perk their ears up whereas humans can barely move their ears)
What forms from the 3rd arch
Greater horn and lower part of body of hyoid
What is the only muscle formed from arch 3
Stylopharyngeus muscle
What nerve supplies the stylopharyngess muscle
Glossopharyngeal nerve
What is formed from the 4th and 6th arches
Laryngeal cartilages
What are the muscles formed from arch 4
Cricothyroid
Levator palatini
Pharyngeal constrictors
What nerve supplies the muscles from arch 4
Superior larygneal nerve of vagus nerve (X)
What are the muscles formed in arch 6
Intrinsic larygenal muscle
What are all the muscles and cartilages from arch 6 supplied by
The recurrent laryngeal nerve
What is formed from the 1st pouch
Middle ear
Eustachian tube
contributes to the Tympanic membrane
What is formed in the 2nd pouch
Palatine tonsil
What does the middle ear do during development
Engulfs the bony structures formed in the 1st arch
How does the palatine tonsil form
The endoderm of the 2nd pouch will proliferate and give rise to it
What structures are formed in the 3rd pouch
Inferior parathyroid gland
Thymus
What structures are formed in the 4th pouch
Superior parathyroid gland
Ultimobranchial body
Why is the thymus so important
T cells mature in here
What is the ultimobranchial body
A fancy name for the structure that give cells that populate the thyroid i.e. C cells
what does the foramen caecum make
the point of proliferation. It migrates down to the thyroid
what is the first thing to become associated with the foramen caecum
the structures from the 4th pouch
How does the anterior parathyroid move down?
The thymus is in the anterior mesosynum and starts to migrate away and as it does it pulls the anterior parathyroid down and onto the posterior surface
What happens to the 2nd, 3rd and 4th clefts
They ultimately will be lost - they lose contact with outside and form the cervical sinus
The ectoderm will overgrow the structures.
What is eventually formed form the 1st cleft
The external auditory meatus
What are the 3 components of the ear
Inner
Middle
External
What do the Otic places give rise to
The inner ear which divides into 2 components:
semicircular canals and also the organ of corti
Describe the appearance of the Otic Placode
Very pronounced indentation
What makes up the Otic Placode
A thickening of the ectoderm will begin to invaginate on either side of the embryo
What gives rise to the inner ear
Otic Vesicles
Describe the process in which a otic placed becomes and otic vesicle
The ectoderm will pull in from either side of the invagination to form a pit which will then completely separate off and form a vesicle
What do the Utricular portion and saccular portion of the otic vesicle eventually connect via
A thin duct
What does the saccular portion give us
The cochlea
What does the Utricular portion give us
The semicircular canals
At what stage do the semicircular canals develop
Week 6
What are the semicircular canals filled with
Fluid
How will the 3 semicircular canals all connect eventually
Into the utricle
How do the 3 canals lie in relation to each other?
Why is this important?
90 degrees to one another
This is an organ of balance - having these 3 planes allows the semicircular canals to sense movement in all directions
What is the name for the dilated end of the semicircular canals
Crus Ampullare
What is the name for the non-dilated end of the semicircular canals
Nonampullare
What do the swollen ends of the semicircular canal do
They sense movement of fluid within the canal and respond to this by feeding information back to the brain which then alters us to keep us balanced
Describe how and when the cochlear duct grows
In a spiral (2.5 turns) between weeks 6-8
What does the surrounding mesenchyme of the cochlear duct become
Cartilaginous
What is the cochlear duct surrounded by
A basement membrane which grows a cartilaginous shell
What is the function of the bony strut
It provides support for the cochlear duct
Why is the modiolus an important structure
In terms of providing innervation into the cochlear duct
Describe the function of the vestibuli
It is in contact with the cochlear duct and will become the vestibular membrane
Describe the pathway of sound in terms of the scala vestibule and scala tympani
The sound wave will travel down the scala vestibule and once it reaches the tip of the scala vestibule, there is a communication where the sound waves will tavel back through the scala tympani
What innervated the inner hair cells
Auditory nerve fibres
What nerve sends information about sound back to the brain
The cochlear nerve
Where do the ossicles of the middle ear come from
The pharyngeal arches
What forms the cavity of the middle ear
The ossicles
What happens when the mesenchyme surrounding the auditory ossicles breaks down
The bones will expand to fill the space left behind
What develops to help stabilise the bones of the inner ear
Ligaments
How is the meatal plug formed
The epithelial cells rapidly proliferate to form the Meatal plug which then remains in place until the 7th month of development before then breaking down
How many mesenchymal proliferation are there?
6
Where do the mesenchymal proliferations come from
3 from arch 1 and 3 from arch 2
What fuses to form definitive Auricle
Hillocks
Where are the external ears initially formed
In the lower neck
How do the external ears ascend
Due to the development of the mandible
Name 4 abnormalities of the external ear
Microtia (anotia)
Microtia
Preauricular pit
Preauricular appendages
What is anti
No structures of the external ear can be seen
What is Microtia
relatively small ear
What is Periauricular appendiages
Additional appendages
What is Preauricular pit
Small indentation
