Branchial Arch Embryology Flashcards
Oral Cavity: Stomatodeum
Primitive oral cavity
- lined with surface ectoderm
- forms b/w developing brain and heart
- derivatives: oral mucosa, lips, gingiva, enamel, anterior pituitary
Oral Cavity: primitive pharynx
lined with endoderm
separated from stomatodeum by the buccopharyngeal membrane (disappears at the end of week 3)
Level of ectoderm-endoderm junction in adults
oral fauces (arches)
(back of throat)
Rathke’s Pouch
an ectodermal outpocketing from the stomatodeum
forms the anterior pituitary gland (adenohypophysis)
Posterior pituitary forms from
neural tube
(neurohypophysis)
Teeth begin to form during
week 6
Dental lamina
thick line of surface ectoderm along mandible and maxilla
dental buds
ectodermal primordial, forms enamel
dental papillae
neural crest derived mesenchyme, forms dentin and pulp
How many branchial arches form?
6 arches form around gut tube (visceral)
arch 5 degenerates (disappears)
How are bone, cartilage and connective tissue formed?
neural crest cells invade arches 1-3
laryngeal cartilages (arches 4,6) from LPM
How are muscle tissues created?
somites (paraxial mesoderm) invade to form muscle tissue
cranial somites (AKA somitomeres)
extrinsic eye muscles (CN III, IV, VI; GSE)
Occipital somites (AKA somitomeres)
tongue muscles (CN XII; GSE)
Myoblasts are from
cranial and occipital somites
migrate into branchial arch region, following NCC to form muscles of head and neck
CN V, VII, IX, X and XIc (SVE)
pharyngeal pouch
inside branchial arches, lined with endoderm
pharyngeal cleft
outside branchial arches, lined with surface ectoderm
Why are RLN’s found in the thorax even though they supply intrinsic muscles responsible for speech?
RLN is associated with branchial arch 6
Viscerocranium
(facial skeleton)
from branchial arch related neural crest
e.g. mandible, maxilla, zygoma, hyoid
Membranous neurocranium
from neural crest and somites (sclerotome)
flat bones of the braincase (crainial vault)
form through intramembranous ossification
e.g. frontal bone (NCC), parietal and occipital bones (PAM)
Neural chondocranium
from neural crest and somites (sclerotome)
bones of the skull base (basicranium)
form through endochondral ossification
e.g. sphenoid, ethmoid, petrous part of temporal bone
Sella Turcica
“Turkish Saddle”
depression in sphenoid bone
contains the hypophysis (pituitary gland)
basicranial bone posterior to the sella turcica is derived from sclerotome
basicranial bone anterior to the sella turcica is derived from NCC
Hyoid bone
develops from neural crest cells
arch 2: lesser horn and upper body
arch 3: greater horn and lower body
Laryngeal cartilages
(connective tissue from arches 4-6 comes from LPM)
thyroid
cricoid
arytenoid
corniculate
cuneiform
Tongue functions
- aids in ingestion of food (GSE)
- sensory organ
- tactile sensation (GSA)
- chemosensation/taste (SVA)
Muscles of tongue develop from
occipital somites
somatomotor (GSE) innervation from CN XII
2 major regions of tongue
oral tongue (anterior 2/3)
pharyngeal tongue (posterior 1/3)
foramen cecum
boundary between two regions of tongue
innervation of mucosa of tongue is
GSA (from oral ectoderm)
lateral lingual swellings
form mucosa of anterior 2/3 of tongue
arch 1 (CN V, GSA)
medial lingual swellings
- tuberculum impar from arch 1 (CN V, GSA)
- hypobranchial eminence (AKA copula lingulae) from arch 3 (CN IX, GSA)
- epiglottis from arch 4 (CN X, GVA)
Taste bud development
- taste buds come from endoderm lining the branchial arches
- oral tongue, pharyngeal tongue, and epiglottis have different cranial nerves for taste (SVA)
- Nerves that carry taste: CN VII, IX, and X
oral tongue innervations
- associated with arches 1-2
- sensation (GSA): CN V
- taste (SVA): CN VII
Pharyngeal tongue innervation
- associated with arch 3
- sensation (GSA): CN IX
- taste (SVA): CN IX
Epiglottis innervation
- associated with arch 4
- sensation (GVA): CN X
- taste (SVA): CN X
Thyroid gland develops from
- between arches 1 and 2
- follicular cells from endoderm
- parafollicular cells from NCC (pouch 4)
Thyroglossal duct
thyroid gland descends through the developing tongue
(may give rise to cyst or fistula)
foramen cecum marks
position of thyroglossal duct
Primordial structures of face
- frontonasal prominene
- forms the nasal placodes/pits (nasal cavities)
- placodes surrounded by medial and lateral nasal swellings
- maxillary swelling (arch 1, paired)
- mandibular swelling (arch 1, paired)
Trigeminal nerve
- CN V innervation of face
- CN V1-opthalmic nerve
- CN V2-maxillary nerve
- CN V3-mandibular nerve
Greater occipital nerve
C2-posterior scalp and neck
Greater auricular nerve
C2-C3-angle of mandible, external ear
Platysma Muscle- derived from and innervation
Derived from and completely surrounded by the superficial fascia
innervation: cervical branch, facial nerve (CN VII)
Aponeurosis
- flat, broad tendons
- epicranial aponeurosis: connects occipital, auricular and frontal muscles
- superficial muscular aponeurosis system (SMAS): distributes forces from superficial fascia muscles to the skin
Facial nerve emerges from
(CN VII)
emerges from parotid gland
Branches of facial nerve
temporal
zygomatic
buccal
mandibular
cervical
Muscles of facial expression
- facial modiolus: fibromuscular condensation
- convergence of 8 muscles
- orbicularis oris m.
- depressor anguli oris m.
- levator anguli oris m.
- levator labii superioris m.
- depressor labii inferioris m.
- buccinator m.
- risorius m.
- zygomaticus major m.
Bell’s Palsy
- paralysis (complete or partial) of facial nerve (CN VII)
- one-sided
- ideopathic, possibly related to inflammation in the facial canal
- loss of:
- branchial motor (SVE) innervation to muscles of facial expression
- taste to the anterior tongue
- lacrimation (tear production)
- salivation
Arches Chart
Pharyngeal Pouches and Cleft Chart
Aortic Arch/Artery
Prominence and Adult Structures
