Embryology Screencasts Flashcards
When do the pharyngeal arches develop?
In weeks 4 and 5 = first arch by day 22, second and third arches by day 24, fourth and sixth arches by day 29
What direction do the pharyngeal arches develop?
In a cranial to causal direction
What do the three components of the pharyngeal arches relate to?
Each layer relates to a different layer of the trilaminate embryonic disc
What are the three components of the pharyngeal arch?
Core pharyngeal arch = mesenchymal tissue
External pharyngeal cleft = ectoderm
Internal pharyngeal pouch = endoderm
What separates arches?
Clefts and pouches
What is the difference between cleft/pouches and arches?
Clefts and pouches have a more epithelial organisation to their cells
What does each arch consist of?
Core of mesenchyme, neural crest cells, cranial nerve component, artery
Where is the core of mesenchyme present in each arch derived from?
The paraxial and lateral plate mesoderm = goes on to give rise to musculature
What do neural crest cells give rise to?
Skeletal components = from week 5 onwards
How many nerves innervate each arch?
Just one nerve
Where do the arteries that supply the arches come from?
The aortic arch
Which nerve supplies the first pharyngeal arch?
The trigeminal nerve = V2 and V3
Which nerve supplies the second pharyngeal arch?
Facial nerve (CN VII)
Which nerve supplies the third pharyngeal arch?
Glossopharyngeal nerve (CN IX)
Which cranial nerve supplies the fourth and sixth pharyngeal arches?
Vagus nerve (CN X) = superior laryngeal branch to fourth arch, recurrent laryngeal branch to sixth arch
What are the two sections of the first arch?
Maxillary process (cranial) and mandibular process (caudal)
What skeletal elements does the maxillary process of the first arch give rise to?
Maxilla, zygomatic bone, squamous portion of temporal bone
What skeletal elements does the mandibular process of the first arch give rise to?
Incus and malleus, mandible
Where is Meckel’s cartilage located?
In the mandibular process of the first pharyngeal arch
What occurs in Meckel’s cartilage?
Neural crest cells form cartilage = cartilage stimulates mesenchyme to ossify or produce components of the skull
What nerve supplies the musculature derived from the first pharyngeal arch?
CN V3
What musculature is formed from the first pharyngeal arch?
Muscles of mastication, anterior belly of digastric, mylohyoid, tensor tympani, tensor veli palatini
Which arch gives sensory innervation to the skin of the face?
First arch = via maxillary and mandibular divisions of CN V (CN V1 makes no contribution)
Which components does the first pharyngeal arch give rise to in general terms?
All components supplied by the trigeminal nerve (except those innervated by CN V1)
Where is Reichert’s cartilage located?
Second pharyngeal arch = extends from body of hyoid up towards styloid process
What are the skeletal derivatives of the second pharyngeal arch?
Stapes, styloid process of temporal bone, stylohyoid ligament, lesser horn of hyoid, upper part of hyoid bone
What supplies all the musculature derived from the second pharyngeal arch?
Facial nerve (CN VII)
What muscles are formed from the second pharyngeal arch?
Muscles of facial expression, posterior belly of digastric, stylohyoid, stapedius, auricular muscles
What are the skeletal components and muscles derived from the third pharyngeal arch?
Skeletal = greater horn and lower part of hyoid bone Muscles = stylopharyngeus (longitudinal pharyngeal muscle)
Which nerve supplies all components derived from the third pharyngeal arch?
Glossopharyngeal nerve (CN IX)
What skeletal components are derived from the fourth and sixth pharyngeal arches?
Laryngeal cartilages (e.g thyroid)
What muscles arise from the fourth pharyngeal arch?
Cricothyroid, levator veli palatine, pharyngeal constrictors
Which muscles are formed from the sixth pharyngeal arch?
Intrinsic muscles of larynx
What nerves supply the fourth arch?
Superior laryngeal nerve (CN X) and pharyngeal plexus
What is a cleft?
Invagination of ectoderm
What forms the pharyngeal membrane?
When the cleft connects with the mesenchyme of its opposite pouch
What structure is formed form the first cleft?
External acoustic meatus
What forms the cervical sinus?
Second to fourth clefts = lose contact with the outside to form sinus
What structures are formed from the first pouch?
Middle ear, tympanic membrane, Eustachian tube
Which pouch gives rise to the palatine tonsil?
Second pouch
What structure gives rise to the ossicles?
Formed from mesenchymal condensation
When is the mesenchyme covering the ossicles lost?
From 8 months gestation
What structures arise from the third pharyngeal pouch?
Inferior parathyroid gland, thymus
What does the fourth pharyngeal pouch go on to form?
Superior parathyroid gland, ultimobranchial body
What structures form from the ultimobranchial body?
Thyroid gland, C-cells
