Embryology Flashcards
Briefly explain how the mesoderm is formed?
- Embryo begins as 2 layers
- epiblast layer invaginates
- brings new cells between the layers (mesoderm)
WHat layer comes together to form the neural tube?
Ectoderm (neural cells)
All neural crest cells go on to form nerves or neural structures such as the brain and spinal cord. TRUE/FALSE?
False
Some form skeletal structures in head and neck
How many pharyngeal arches develop in humans?
6 arches
but 5th usually disappears
On what day of development do each of the pharyngeal arches form?
Arch 1 – Day 22
Arch 2 + 3 – Day 24
Arch 4 + 6 – Day 29
What are the 3 components to the pharyngeal arches?
- Core pharyngeal arch (Mesenchymal tissue)
- External pharyngeal CLEFT (Ectoderm)
- Internal pharyngeal POUCH (Endoderm)
What cranial nerve is associated with each pharyngeal pouch?
1 - CN V2 and V3
2 - CN VII
3 - CN IX
4 and 6 - CN X
What are the 2 sections of the 1st pharyngeal arch?
Maxillary portion
Mandibular portion
What does the maxillary portion of the 1st pharyngeal arch give rise to?
Maxilla
Zygomatic bone
Squamous portion of temporal bone
What does the mandibular portion of the 1st pharyngeal arch give rise to?
Forms Meckel’s cartilage
Incus and Malleus (ear ossicles)
Mandible
What is Meckel’s cartilage?
embryological structure which eventually splits to form various other structures in the head and neck
All musculature associated with the 1st pharyngeal arch is innervated by which cranial nerve?
CN V3
What muscles are associated with the 1st pharyngeal arch?
Muscles of mastication Anterior belly of digastric Mylohyoid Tensor Tympani Tensor veli Palatini
What is the function of the tensor tympani and stapedius?
Dampen sound
What cartilage is developed in the 2nd pharyngeal arch?
Reichert’s Cartilage
What are the skeletal derivatives of Reichert’s Cartilage?
- Stapes (ear ossicle)
- Styloid process of temporal bone
- Stylohyoid ligament
- Lesser horn of Hyoid
- Upper part of Hyoid body
What cranial nerve supplies the muscles associated with the 2nd pharyngeal arch?
CN VII
Muscles of facial expression
What are the muscles of facial expression associated with the 2nd pharyngeal arch?
- Posterior belly of digastric
- Stylohyoid
- Stapedius
- Auricular muscles
What cranial nerve supplies the stylopharyngeus (associated with the 3rd pharyngeal arch)?
CN IX Glossopharyngeal
What skeletal structures are developed from the third pharyngeal arch?
Greater horn
Lower part of hyoid bone
What skeletal structures do the 4th and 6th pharyngeal arches give rise to?
Laryngeal cartilages
What muscles are associated with the 4th pharyngeal arc and what cranial nerve supplies them?
Cricothyroid
Levator veli palatini
Supplied by Superior Laryngeal from CN X
What muscles are associated with the 6th pharyngeal arc and what cranial nerve supplies them?
Intrinsic laryngeal muscle
Supplied by recurrent laryngeal from CN X
What do each of the pharyngeal clefts become during development?
1st cleft becomes = acoustic meatus
2nd, 3rd and 4th come inwards and form cervical sinus
If cervical sinuses are not formed properly what can result?
Cysts and fistulae
- either pre-auriculr or anterior to sternocleidomastoid
What do the first 2 pharyngeal pouches become?
1st:
Middle ear
Tympanic membrane
Eustachian tube
2nd:
Palatine Tonsils
What does the 3rd pharyngeal pouch split into?
Upper part = inferior parathyroid gland
Lower part = thymus
What does the 4th pharyngeal arch divide into?
Superior parathyroid gland Ultimobranchial body (c-cells containing calcitonin in thyroid)
What is the otic placode and what does it give rise to?
- Collection of ectoderm which develops near the hindbrain
- Pinches in to from pit and eventually vesicle
- vesicle gives rise to inner ear
What are the 2 parts to the otic vesicle and what do they develop into?
Pars Superior (Utricular) = semicircular canals
Pars inferior (Saccular) = cochlear
How do the semicircular canals develop?
- Flattened outpocketings of utricular part
- Central part of the walls appose each other and break down
What is the name given to the dilated end of the semicircular canal?
Crus ampullare
What is the name for the non-dilated end of the semicircular canals?
Crus Nonampullare
What is the crista ampullaris found inside the ampullae of the semi-circular canals?
Sensory cells for balance
Describe how the saccule forms the cochlear duct
tubular outgrowth spirals around 2.5 times to form duct
remains joined to saccule by ductus reuniens
Where are the outer and inner hair cells found in the ear?
Organ of Corti
What mechanical stimuli is converted into the sound we hear?
Fluid moving over the outer and inner hair cells
Most sound is conducted in the inner hair cells. TRUE/FALSE?
FALSE
outer hair cells conduct most sound (and there’s more of them)
How is the middle ear formed?
- Mesenchymal cells come together and condense to form ossicles
- ossicles attached to bony wall by ligaments to allow vibration of sound
What is the meatal plug?
- Proliferated epithelium present during embryonic development
- Regresses before birth to form ear drum
What can occur if the meatal plug does not regress?
Congenital deafness
Requires surgical thinning
What helps to develop the external ear?
6 mesenchymal proliferations
3 from Arch 1
3 from Arch 2
What causes the ears to ascend during development?
Development of the mandible
Why are the ears normally low set in genetic disorders?
Stunt in development has caused ascending of ears to halt.
