Chapter 17
Head and
neck
Outline
• Origin of head structures.
• Definition: pharyngeal arch, pouch, and cleft.
• The derivatives of the first and second arches,
• The first cleft and pouch, and the remaining pouches give rise to
the parenchyma of numerous glands.
• The nerves associated with each arch.
• The origin of the tongue, including its nerve supply.
• The origin of the thyroid gland, how it assumes its final position in
the adult, and the formation of thyroglossal cysts.
• Definition: facial prominences and their role in formation of the
face.
• Definition: primary and secondary palate and the origins of clefts in
these structures and the upper lip.
Origin of mesenchyme in head region
• Origin of mesenchyme in head region:
– Paraxial mesoderm (somites and somitomeres) form:
• Cartilaginous & membranous neurocranium
• All voluntary muscles of craniofacial region
• Dermis & connective tissue in dorsal region of head
• Meninges caudal to prosencephalon
– Lateral plate mesoderm:
• laryngeal cartilages and connective tissue.
– Neural crest from forebrain, midbrain & hindbrain form:
• All vicerocranium (face) and parts of membraneous &
cartilaginous neurocranium(skull)
• All other tissues in these regions (cartilage, bone, tendon,
dermis, pia & aracnoid, sensory neurons & glandular
connective tissue).
– Cells from ectodermal placodes (with Neural Crest) form
neurons of V, VII, IX, X cranial sensory ganglia.
Skeletal structures of the head and face. Mesenchyme for these
structures is derived from neural crest (blue), lateral plate mesoderm
(yellow), and paraxial mesoderm (somites and somitomeres) (red).
• Migration pathways of neural crest cells from forebrain, midbrain, and
hindbrain regions into their final locations (shaded areas) in the
pharyngeal arches and face.
• Regions of ectodermal thickenings (placodes), which will assist crest cells
in formation of the fifth (V), seventh (VII), ninth (IX), and tenth (X) cranial
sensory ganglia are also illustrated.
Pharyngeal arches
Pharyngeal arches
• (branchial arches) like gills
• Appear in 4
th
& 5
th
weeks
• In lateral wall of pharynx
• mesoderm core, endoderm
(inside), ectoderm
(outside), blood vessel
(aortic arch), and cranial
nerve.
Nerves for Pharyngeal arches
Trigeminal nerve (V) (three branches: ophthalmic, maxillary &
mandibular): supply 1
st
Ph arch
Facial nerve (VII): supply 2
nd
Ph arch
Glossopharyngeal nerve (IX): supply 3
rd
Ph arch
Superior laryngeal branch of Vagus nerve (X) : supply musculature of 4
th
arch
Recurrent branch of vagus nerve: supply 6
th
arch
First arch = maxillary and mandibular prominences
First arch bones: maxilla and mandible and (malleus and incus)
1
st
ph. Arch
Muscles of mastication
NERVE SUPPLY;motor: mandibular branch of trigeminal nerve
Sensory to skin of face: 3 branches of TG nerve
• Second arch = stapes and hyoid bones, muscles of facial expression, facial
nerve.
• Third arch = hyoid bone, glossopharyngeal nerve.
• Fourth to sixth arches =
• Constrictor muscles of pharynx, Vagus (superior laryngeal branch)
• Laryngeal cartilages
• Intrinsic muscles of larynx, Vagus (recurrent branch)
Pharyngeal pouches
• One auditory tube, middle
ear.
• Two palatine tonsils.
• Three inf parathyroid and
thymus.
• Four superior parathyroid
and ultimobranchial body
(parafollicular (C) cells of
thyroid which secrete
calcitonin).
Pharyngeal clefts
• One = external auditory meatus.
• Second, third & fourth clefts disappear
BIRTH DEFECTS INVOLVING THE PHARYNGEAL
REGION
• Ectopic thymic & parathyroid tissue
BRANCHIAL FISTULAS & LATERAL CERVICAL CYSTS
remnants of pharyngeal clefts
LATERAL CERVICAL CYST
Neural crest cells and craniofacial
defects
• Neural crest cells form much of the craniofacial region
• Disruption of crest cell development results in craniofacial malformations
• Since neural crest cells also form conotruncal endocardial cushions: many
infants with craniofacial defects also have cardiac abnormalities (
persistent truncus arteriosus, tetralogy of Fallot and transposition of great
vessels).
• Neural crest cells are vulnerable cell population and are easily killed by
compounds such as alcohol and retinoic acid.
NEURAL CREST CELLS &
CRANIOFACIAL DEFECTS
Tongue
• Appears in 4
th
week
• Two lateral lingual swellings and a medial swelling (tuberculum impar):
originate from 1
st
ph arch
• Another median swelling (copula or hypobranchial eminence): arise from
mesoderm of 2
nd
, 3
rd
& 4
th
arches.
• A third median swelling make the epiglottis arise from 4
th
arch.
• Tongue:
• ant two thirds = first arch = mandibular nerve;
• post third = mostly third arch = glossopharyngeal n;
• line between the two = terminal sulcus.
• Muscles = occipital somites = hypoglossal n;
• taste = facial n (chorda tympani).
• Thyroid gland = forms from an epithelial proliferation at the base of
tongue; descends in midline along thyroglossal duct: remnants or cysts
may remain = midline.
Ankyloglossia (tongue-tie)
THYROID GLAND
Thyroglssal cyst
thyroglssal fistula
abberant thyroid tissue
• Face = prominences = maxillary, mandibular, frontonasal, medial and
lateral nasal (around nasal placodes, pits).
Face
• Face: 4
th
week: appearance of nasal (olfactory) placodes
5
th
week: formation of nasal pits & nasal promenances
Upper lip = fusion of two
medial nasal prominences and
maxillary.
Lower lip = fusion of
mandibular prominence.
Nasolacrimal groove
Nasolacrimal duct = between
maxillary and lateral nasal
prominences.
• PRIMARY PALATE
• Intermaxillary segment = medial nasal prominences merge = philtrum,
incisor part of jaw, primary palate.
• Secondary palate = shelves off maxillary prominence elevate and fuse
(incisive foramen = fusion of primary and secondary palates).
Formation of secondary palate
Fusion of primary & secondary palates &
nasal septum
NOSE
• Nose = frontal prominence
(bridge), medial nasal (crest and
tip), lateral (alae).
• FACIAL CLEFTS:
• Median cleft lip = medial nasal prominences = often mentally retarded
associated with holoprosencephaly = lacking midline of face and brain.
• Lateral cleft lip = between medial nasal and maxillary prominences.
• Oblique clefts = between maxillary and lateral nasal prominences.
• Cleft palate = maxillary prominence (palatal shelves).
Median cleft lip
CLET LIP &
CLEFT PALATE