Development Anat. Block B

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Development Anat. Block B
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Developmental Anatomy Block B
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  1. primary vesicles
    • three expansions at rostral end of developing neural tube around 3 weeks of  development
    • prosenscephalon: forebrain
    • mesencephalon: midbrain
    • rhombencephalon: hindbrain
  2. secondary brain vesicles
    • 5 differentiated enlargements of primary vesicles of the brain around 5 weeks of development
    • prosencephalon becomes telencephalon and diencephalon
    • mesencephalon continues on as mesencephalon
    • rhombencephalon becomes metencephalon and myelencephalon
  3. telencephalon
    • walls form cerebral hemispheres, corpus striatum, & basal ganglion
    • cavity becomes lateral ventricles
  4. diencephalon
    • walls form thalamus and surrounding area (hypothalamus, epithalamus, metathalamus, etc.) - leads to development of optic nerve
    • cavity forms third ventricle
  5. mesencephalon
    • continues on as midbrain
    • cavity forms cerebral aqueduct (communication between 3rd & 4th ventricle)
    • undergoes the least amount of differentiation
  6. metencephalon
    • walls become pons (origin of trigeminal nerve) and cerebellum (motor learning)
    • cavity forms upper part of 4th ventricle
  7. myelencephalon
    • walls form the medulla (continuous with spinal cord at foramen magnum just above spinal nerve C1)
    • cavity forms lower part of 4th ventricle
  8. brain stem
    midbrain + pons + medulla
  9. brain flexures
    • brain bends ventrally with formation of head folds
    • formed during 4th week
    • cervical flexure
    • cephalic/mesencephalic/midbrain flexure
    • pontine flexure
  10. cervical flexure
    • level of foramen magnum (spinal nerve C1)
    • NOT seen in adults
    • between the rhombencephalon and hindbrain (myencephalon & spinal cord)
  11. midbrain flexure
    • AKA Cephalic/mesencephalic flexure
    • between mesencephalon & prosencephalon
    • Between axes of brainstem (vertical) & forebrain (horizontal)
    • Seen in adult
  12. pontine flexure
    • divides the hindbrain into myelencephalon (caudal) and metencephalon (rostral)
    • causes reorganization of motor & sensory components
    • causes neural tube walls to spread apart near 4th ventricle & thinning of the roof
  13. development of the metencephalon
    • develops from thickenings in the dorsal parts of the alar plates
    • cerebellar swellings enlarge & overgrow the rostral half of the 4th ventricle, the pons & the medulla
    • forms cerebellum
  14. development of the medulla
    • from myelencephalon
    • pontine flexure causes neural tube to spread apart at 4th ventricle
    • walls spread apart, roof thins out
    • alar plates - lateral sensory components (GSA, GVA, SSA, SVA)
    • basal plates - medial motor components (GSE, GVE, SVE)
    • sulcus limitans divides alar & basal plates
    • caudal portion of medulla is closed - central canal
    • rostral portion is open in the region of metencephalon
  15. functional components of brain stem
    • GSA
    • GVA
    • SSA: vision & hearing
    • SVA: taste & olfaction
    • GSE
    • GVE
    • SVE: motor component of muscles derived from pharyngeal arches
  16. development of telencephalon
    • cerebral hemispheres expand rapidly
    • cover diencephalon, midbrain, and hindbrain
    • floor of each cerebral hemisphere contains corpus striatum that expands more slowly than the cortical walls
    • force C shaped telencephalon, lateral ventricles, internal capsule & corpus striatum
    • grey matter on outside; white matter on inside
  17. alar plate
    becomes dorsal horn of spinal cord segments
  18. dorsal root ganglia
    • derived from NCC
    • central processes synapse on secondary sensory neurons in DRG
  19. basal plate
    becomes ventral horn &  IMLCC
  20. lissencephalic cerebral hemispheres
    • surface of hemispheres is smooth
    • initial development of telencephalon includes smooth surfaced cerebral hemispheres
    • as development proceeds, sulci (grooves) and gyri (elevations) develop
  21. sulci & gyri
    allow considerable increase in surface area of the cerebral cortex without requiring extensive increase in cranial size
  22. gyrancephalic cortex
    cerebral hemispheres in relatively confined space (skull) develop sulci & gyri to allow increased area of cerebral cortex & greater number of neurons without increasing brain size greatly
  23. meroanencephaly
    missing all or part of brain
  24. anencephaly
    • missing cerebral cortex
    • due to failure in closure of anterior neuropore
    • occurs in ~5/10000
    • the brain is not formed
    • the surrounding meninges & skull may be absent
    • facial abnormalities may be present
    • defect extends from level of lamina terminalis to foramen magnum
    • neonatal death is inevitable
    • lack of development of fetal cranial vault
  25. congenital anomalies of the brain
    • meroanencephaly
    • anencephaly
    • defects in ventral induction
    • cerebral palsy
    • cranium bifidum
    • meningoencephalocele
    • meningohydroencephalocele
    • exencephaly
    • hydrocephalus
  26. lamina terminalis
    • demarcates site of anterior neuropore closure
    • visible on adult brain
  27. types of hydrocephalus
    • obstructive/noncommunicating hydrocephalus
    • nonobstructive/communicating hydrocephalus
  28. congenital aqueductal stenosis
    X linked genetic problem OR fetal viral infection (cytomegalovirus, toxoplasma gondii, etc.)
  29. obstructive/noncommunicating hydrocephalus
    • cerebral aqueductal stenosis
    • Physical obstruction of flow of CSF (produced in lateral 3rd ventricle & 4th ventricle)
  30. foramen of Luschka
    • lateral aperature 
    • CSF absorbed through arachnoid villi
  31. nonobstructive/communicating hydrocephalus
    • Problem with absorption of CSF through arachnoid villi to sagittal sinus
    • Metabolic problem
  32. CSF reabsorption
    • CSF produced in lateral ventricles, roots of 3rd & 4th ventricles
    • flows out of ventricles into holes on caudal aspect of medulla
    • foramen of Magenti: single midline communication between ventricular system & subarachnoid space
    • foramne of Luschka: lateral aperatures (paired)
    • CSF percolates through subarachnoid space
    • CSF reabsorbed into sagittal sinus through arachnoid villi
  33. encephalocele
    • herniation of intracranial contents through a defect in the cranium
    • cranium bifidum
    • usually occur in the occipital region, but may occur in front or parietal locations
    • meningocele: meninges only
    • meningoencephalocele: meninges + brain
    • meningohydroencephalocele: meninges + brain + part of ventricular system
  34. prosencephalization
    • sequences of events by which the prosencephalon differentiates into the diencephalon & telencephalon
    • normally - telencephalon divides into two cerebral hemispheres
  35. holoprosencephaly
    • results from failure of cleavage of the prosencephalon into right & left cerebral hemispheres, telencephalon, & diencephalon
    • little to no brain function
    • associated with chromosomal anomalies (trisomy 13) and maternal diabetes mellitus
  36. alobar holoprosencephaly
    one big ventricular space
  37. semilobar holoprosencephaly
    small cleft representing an attempt to separate the hemispheres
  38. pituitary gland
    • sits in hypophyseal fossa
    • functions in production of various hormones
    • pars nervosa: anterior lobe
    • pars tuberalis: posterior lobe
  39. developmental source of pituitary gland
    • neural ectoderm: diencephalon gives rise to diverticulum & pars nervosa
    • superficial ectoderm: from roof of oral cavity (stomodeum); gives rise to pars tuberalis
  40. hypophyseal pouch
    evagination of dorsal aspect of stomodeum (roof of mouth) which meets the infundibulum of diencephalon
  41. oropharyngeal membrane
    • closes off the oral cavity
    • composed of superficial ectoderm & endoderm of the foregut
    • under normal circumstances - gives rise to primitive stomodeum
  42. neural crest cells
    • neuroectodermal origin
    • leave the future brain well before closure of neural folds
    • differentiate into mesenchyme in the head region
    • migrate into pharyngeal arches
    • participate in the formation of bones & CT of craniofacial structures
  43. types of bone formation
    • endochondral bone formation
    • membranous bone formation
  44. endochondral bone formation
    • majority of bone forms this way
    • mesenchymal cells first give rise to hyaline cartilage
    • cartilagenous models become ossified
  45. membranous bone formation
    mesenchymal cells differentiate directly into bone
  46. skull
    • develops from mesenchyme around the developing brain
    • neurocranium: protective case for the brain
    • viscerocranium: skeleton of the face/jaws
  47. neurocranium
    • membranous neurocranium: undergoes intramembranous bone formation; upper portion of skull
    • cartilagenous neurocranium (chondrocranium): undergoes endochondral ossification; makes up base of skull
  48. cranial chondrification
    • begins in the 2nd month
    • initially consists of cartilaginous base of the developing skull
    • forms as fusion of several cartilages
    • by the end of 3rd month, the base of the skull is a unified mass of cartilage
    • endochondral ossification forms the bones of the base of the skull
    • ossification commences before the chondrocranium has fully developed
  49. cartilages that give rise to cartilaginous neurocranium
    • parachordal cartilage: base of occipital bone, foramen magnum
    • hypophyseal cartilage: body of sphenoid bone
    • trabeculae cranii: midline portions of the ethmoid bone
    • orbitosphenoid: lesser wing of the sphenoid
    • alisphenoid: greater wing of the sphenoid
    • otic capsule: petrous & mastoid parts of the temporal bone
    • nasal capsule: ethmoid, ethmoid air cells, inferior nasasl concha, nasal bone
  50. bones formed (at least in part) by endochondral bone formation
    • occipital bone: multiple ossification centers
    • petromastoid temporal bone: multiple ossification centers
    • sphenoid bone: >16 ossification centers
    • ethmoid bone: 3 ossification centers
    • inferior nasal concha: 1 ossification center
    • nasal bone: 1 ossification center
  51. synchondroses
    • present between bones and/or ossification centers before bones fuse together
    • analagous to epiphyseal plates
    • cartilaginous joints
    • union of two bones separated by hyaline cartilage
    • most common type of joint in developing bone
    • bony epiphysis + body are united by epiphyseal cartilage
  52. bones formed by intramembranous bone formation
    • frontal
    • parietal
    • squamous occipital
    • squamous temporal
    • lacrimal
  53. membranous neurocranium
    • induced by specifica parts of the developing brain
    • intramembranous ossification occurs in the mesenchyme at sides & top of the brain forming the calvaria
  54. sutures
    dense connective tissue that separates the flat bones of the calvaria
  55. fontanelles
    • anterior
    • posterior
    • mastoid/ posterolateral (2)
    • sphenoid/anterolateral (2)
  56. anterior fontanelle
    • largest fontanelle
    • at the junction of sagittal, coronal & frontal sutures
    • closes at the middle in 2nd yr of life
  57. fontanelle closure
    • posterior & lateral fontanelles: 1-2 months
    • anterior: 2nd year
  58. meitopic suture
    • continuous with frontal suture
    • may not close in oriental individuals
  59. palpation of fontanelles
    • determines progress of growth in surrounding bones
    • determines degree of hydration of baby (if dehydrated, fontanelles will be depressed)
    • determines state of intracranial pressure
  60. cartilaginous viscerocranium
    • cartilages of the first two pharyngeal arches
    • 1st pharyngeal arch, dorsal end: malleus + incus
    • 2nd pharyngeal arch, dorsal end: stapes + styloid process
    • 2nd pharyngeal arch, ventral end: lesser horn & upper body of hyoid bone
    • 3rd pharyngeal arch: greater horn & lower body of hyoid bone
  61. membranous viscerocranium
    • intramembranous ossification occurs in the maxillary prominence
    • maxillary bone
    • zygomatic bone
    • palatine bone
    • vomer
    • pterygoid laminae
    • nasal bone
  62. development of mandible
    mesenchyme in the mandibular prominence of the 1st arch condenses around its Meckel's cartilage and undergoes intramembranous ossification
  63. skull at birth
    • large in proportion to other parts of the skeleton
    • facial portion of cranium is small (equals 1/8 the bulk of the skull in the new born, 1/2 the bulk in adults)
    • nasal cavities lie almost entirely between the orbits
    • lower border of anterior nasal aperture is only a little below the level of the orbital floor
    • mastoid process is not developed - facial nerve is close to surface and may be damaged by forceps
  64. why is the face small at birth?
    • rudimentary condition of maxilla & mandible
    • non-eruption of the teeth
    • small size of the maxillary air sinuses and nasal cavities
  65. postnatal growth of skull
    • fibrous sutures permit skull to enlarge during infancy & childhood
    • skull rapidly grows from birth to 7th year
    • calvaria normally increases in capacity until 15-16 years of age
    • after 16 yrs, the calvaria usually increases in size for 3-4 years because of thickening of bone
  66. suture closure
    • sagittal suture: 22 yrs
    • sphenofrontal suture: 22 yrs
    • coronal suture: 24 yrs
    • lambdoidal suture: 26 yrs
    • occipito-mastoid suture: 26 yrs
    • sphenoparietal suture: 29 yrs
    • sphenotemporal suture: 30 yrs
    • parietomastoid suture: 37 yrs
    • squamous suture: 37 yrs
  67. craniofacial anomalies
    • account for 1/3 of skull malformations
    • most are multifactorial
    • stem from interaction of environment or outside influences with individual's own genetic determinants
    • individuals show different susceptibilities to the actions of a given teratogen
  68. teratogens known to cause craniofacial malformations
    • alchohol
    • toluene
    • smoking
    • hyperthermia
    • hydantoin
    • accutane
    • ionizing radiation
  69. secondary disturbances to brain development
    • acrania/anencephaly: congenital defective development of the brain with absence of bones of the cranial vault
    • microcephaly: size of cranial vault accomodates to very small brain
    • hydrocephaly: greatly enlarged cranial vault that represents excessive build up of CSF
  70. craniosynostosis
    • congenital anomaly characterized by premature closure of skull sutures
    • pathogenesis unknown - probably genetic
    • may result from environmental insults (trauma, drugs, intrauterine infections)
  71. primary craniosynostosis
    • fusion of suture present at brth (defect occurred in utero)
    • lack of growth of skull perpendicular to affected suture
    • overgrowth of skull parallel to affected suture
  72. theories regarding craniosynostosis
    • abnormality centered in skull base
    • skull base deformity (especially in sphenoid) results in premature fusion of calcified structures due to transmission of abnormal forces from skull base through the dura to sutures themselves
    • calvarial sutures fuse prematurely & skull bone deformities occurred secondarily
    • abnormality centered in mesenchymal cells of embryo - affected both calvarial & basilar structures
    • fetal head constraint: premature descent of fetus into pelvis
  73. secondary craniosynostosis
    • results from failure of brain growth & expansion
    • sickle cell anemia: inherited disorder of hemoglobin metabolism
    • hyperthyroidism: low CSF pressure caused by ventricular-peritoneal shunt
  74. non-syndromic craniosynostoses
    • scaphocephaly: sagittal suture fused; boat skull
    • trigonocephaly: metopic suture fused; triangular skull
    • plagiocephaly: unilateral coronal suture fused; asymmetric skull
    • brachycephaly: bilateral coronal suture fused; short skull
    • plagiocephaly: lambdoid suture fused; asymmetric skull
  75. scaphocephaly
    • most frequent non-syndromic craniosynostosis
    • occurs more commonly in males
    • sagittal suture closes prematurely
    • compensatory anteroposterior growth
    • skull becomes narrow & wedge shaped - boat skull du to frontal & occipital bossing
  76. syndromic craniosynostoses
    • Saethre-Chotzen Syndrome
    • Crouzon Syndrome
    • Apert Syndrome
    • Pfeiffer Syndrome
  77. developmental source of eye
    • neuroectoderm + neural crest cells
    • superficial ectoderm
    • mesenchymal mesoderm
  78. optic sulcus/groove
    • at 22 days, cranial end of neural tube is still open
    • invagination of neural folds
    • becomes evagination of rostral part of brain with closure of neural folds
  79. opticoele I
    • original cavity of the optic vesicles (from prosencephalon)
    • associated with diencephalon (division of prosencephalon)
    • becomes intraretinal space
  80. optic stalk
    originates from the more proximal part of the optic vesicle due to differential growth between the prosencephalon & the optic vesicle
  81. lens placode
    optic vesicle/ opticoele induces superficial ectoderm to thicken and form the lens placode
  82. lens pit
    invagination of central region of lens placode
  83. optic cup
    superficial ectoderm cause invagination of optic vesicle (opticoele I)
  84. opticoele II
    • cavity of optic cup
    • formed by invagination of optic vesicle
  85. layers of optic cup
    • outer/proximal wall: becomes pigmented layer of retina
    • inner/distal wall: forms sensory layer of retina
  86. choroid fissure
    • AKA retinal or optic fissure
    • groove formed along the ventral part of the optic cup
    • extends back along the optic stalk
    • contains the hyaloid artery & vein
    • directing pathway for axons of ganglion cells of the retina that will eventually form the optic nerve
  87. central artery of the retina
    formed from proximal parts of hyaloid artery within choroid fissure
  88. floaters
    • distal parts of hyaloid artery & vein degenerate
    • pieces may break off and occlude vision temporarily
  89. retinal detachment
    most likely to occur at intraretinal space (originally opticoele I) if layers of optic cup are not tightly fused
  90. lens development
    • frontal wall of lens vesicle remains cuboidal - become lens epithelium
    • epithelial cells produce an elastic, non cellular lens capsule
    • back wall differentiates into tall columnar cells which lose their nuclei, become transparent - become lens fibers
    • lens fibers continually produced at the equator
  91. pars optica
    • thicker portion of optic cup; back 4/5 of cup
    • forms photosensitive retina
    • outer layer - pigmented layer of retina (RPE)
    • inner layer - sensory layer of retina
  92. pars caeca
    • anterior 1/5 of optic cup that remains thin
    • forms non-photosensitive retina
    • pars iridica: forms iris
    • pars ciliaris: forms ciliary body & processes
  93. ora serrata
    point of junction between pars optica and pars caeca of optic cup
  94. pars iridica
    • part of pars caeca (nonphotosensitive retina) from optic cup
    • becomes iris
    • pupillary membrane undergoes apoptosis to expose pupil
    • dilator & constrictor pupillae muscles derive from pars iridica (neuroectoderm of outer layer of optic cup)
    • stroma of iris develops from mesenchyme
  95. pars ciliaris
    • part of pars caeca (nonphotosensitive retina) from optic cup
    • becomes ciliary body & processes
    • ciliary muscle derives from mesenchyme
    • choroid derives from mesenchyme adjacent to the optic cup (becomes pigmented & vascular)
    • sclera derives from superficial mesenchyme
  96. development of cornea
    • substantia propria: develops from mesenchyme between superficial ectoderm & optic cup in front of developing eye
    • corneal epithelium: develops from superficial ectoderm
    • conjunctiva: develops from superficial ectoderm
  97. development of eyelids
    • from superficial ectoderm + mesoderm
    • start as folds
    • fuse around 10 weeks
    • separate again around 26 weeks
  98. persistant iridopupillary membrane
    • failure of iridopupillary membrane to undergo apoptosis within pars iridica
    • congenital atresia of the pupil: trabeculae across pupil
    • Rx - laser removal
  99. congenital glaucoma
    • genetic defect
    • may result from maternal Rubella
    • incomplete formation of canals of Schlemm or spaces of Fontana/trabecular meshwork
  100. symptoms of congenital glaucoma
    • Excessive tearing
    • Sensitivity to light (photophobia)
    • Large appearing eye (excessive fluid)
    • Cloudiness of eyes
    • May result in blindness
  101. congenital cataract
    may result from maternal Rubella
  102. coloboma
    • abnormal cleft in either eyelid (palpebral) or iris (iridis)
    • may be genetic or environmental
  103. coloboma iridis
    • pupil has keyhole appearance
    • results from failure of choroid fissure to close properly
  104. cyclopia
    • Eyes are partially or completely fused into a single median eye
    • Tubular nose or proboscis is above eye
    • Autosomal recessive
    • ex. Trisomy 13 - Patau syndrome
  105. congenital ptosis
    • failure of development of the levator palpebrae superioris muscle
    • may result for incomplete innervation of muscle
    • hereditary
  106. anopthalmia
    • absence of eyeball
    • results from the failure of the optic vesicle to form
  107. micropthalmos
    • arrested development of the optic vesicle
    • genetic: recessive or sex linked
    • environmental: Rubella, Herpes simplex, Toxoplasma gondii viruses
  108. congenital detachment of the retina
    failure of layers to fuse due to unequal growth of optic cup
  109. congenital aphakia
    • congenital absence of lens
    • results from failure of lens placode to form OR degeneration of the lens during fetal development
  110. cryptopthalmos
    failure of eyelids to form
  111. pharyngeal arches
    • condesations of mesodermal mesenchyme and neural crest cell mesenchyme
    • transverse swellings of mesenchyme that flank the foregut
    • contribute to the formation of the face, nasal cavities, mouth, larynx, & neck
    • originally have core of mesodermal mesenchyme
    • NCCs migrate into pharyngeal arches
  112. pharyngeal pouches
    diverticulum of the endoderm from foregut
  113. pharyngeal grooves
    invaginations of the superficial ectoderm towards the pharyngeal pouches
  114. pharyngeal membranes
    combination of endoderm of pouch wth ectoderm of grooves
  115. components of pharyngeal apparatus
    • pharyngeal arches
    • pharyngeal pouches
    • pharyngeal grooves
    • pharyngeal membrane
  116. pharyngeal arch development
    • 23 days: first signs of pharyngeal arches
    • 24 days: 1st and 2nd arches visible with 1st pharyngeal groove
    • 26 days: 3rd arch is visible
    • 28 days: 4th arch visible (4 weeks = 4 arches)
    • 5th & 6th arches are rudimentary
  117. oropharyngeal membrane
    • surrounded by first arch
    • ruptures via apoptosis
    • becomes oral cavity (stomodeum)
  118. contents of typical pharyngeal arch
    • aortic arch - from truncus arteriosus
    • cartilagenous rod
    • muscular component
    • nerve - from primordial brain
  119. developmental source of skeletal muscle & vascular endothelia
    mesodermal mesenchyme
  120. cranial neural crest derivatives
    • bone
    • dentin
    • cartilage
    • pigment cells
    • glandular stroma - thyroid (C cells); parathyroid; thymus; salivary glands
  121. neural crest cells
    • neuroectodermal origin
    • leave the future brain well before closure of the neural folds
    • differentiate into mesenchyme in the head region
    • participate in the formation of bones & CT of craniofacial structures
  122. defects of migration/morphogenesis of NCC
    • trunk neural crest: Hirschsprung's disease (aganglionic colon)
    • cranial neural crest: aorticopulmonary septation defects of heart; anterior chamber defects of eye; cleft lip and/or palate; frontonasal dysplasia; DiGeorge syndrome; dental anomalies
    • trunk & cranial neural crest: CHARGE syndrome; Waardenburg syndrome
  123. CHARGE syndrome
    • coloboma: failure of choroid fissure to close
    • heart defects: tetralogy of Fallot
    • atresi choanae: blocking of airway, cannot breath through nose
    • retardation of growth & development: sensory deficits, mental retardation
    • genitourinary problems: genital hypoplasia, undescended testes, small labia
    • ear abnormalities: unusually shaped ears, sensory or conductive hearing loss
  124. Waardenburg syndrome
    • autosomal dominant
    • defect in migration of neural crest cells
    • family history of parent with Waardenburg syndrome
    • extremely pale blue eyes or heterochromia
    • partial albinism - white forelock (poliosis) of hair; early greying of hair
    • deafness (variable degree)
  125. tumors & proliferation defects of NCCs
    • pherochromocytoma: tumor or chromaffin tissue of adrenal medulla
    • neuroblastoma: tumor of adrenal medulla and/or autonomic ganglia
    • medullary carcinoma of thyroid: tumor of parafollicular (calcitonin secreting) cells of the thyroid
    • carcinoid tumors: tumors of enterochromaffin cells of digestive tract
    • neurofibromatosis: von Recklinghausen; peripheral nerve disease
  126. albinism
    • neural crest cell defects
    • lack of RPE allows visualization of choriovessels
  127. cervical sinus
    • 2nd pharyngeal arch enlarges and overgrows the 3th & 4th arches
    • disappears by end of 7th week (2nd and 4th grooves disappear) to give neck a smooth appearance
  128. derivatives of first arch cartilage
    • dorsal end: malleus & incus
    • middle part: regresses; perichondrium forms anterior ligament of malleus & sphenomandibular ligament
    • ventral part: primordium of mandible
  129. mandibular arch
    • first pharyngeal arch
    • plays a major role in facial development
    • maxillary prominence & mandibular prominence produced by migration of neural crest cells into the first arch
  130. maxillary prominence gives rise to:
    • maxilla
    • zygomatic arch
    • squamous portion of temporal bone
  131. mandibular prominence
    sets up precursor of Meckel's cartilage (primordium of mandible)
  132. nasal placode
    gives rise to the nose
  133. stomodeum
    invaginates to lead to oropharyngeal membrane (composed of foregut & superficial ectoderm of stomodeum)
  134. Rathke's pouch
    superior evagination of the ventral diverticulum of the foregut at the level of the 2nd pharyngeal pouch
  135. second arch cartilage derivatives
    • dorsal end: stapes; styloid process of temporal bone; stylohyoid ligament (from intermediate perichondrium)
    • ventral part: lesser cornu & superior part of body of hyoid bone
  136. meckel's cartilage
    first arch cartilage
  137. Reichert cartilage
    second arch cartilage
  138. third arch cartilage derivatives
    • greater cornu
    • inferior part of body of hyoid
  139. forth & sixth arch cartilage derivatives
    • laryngeal cartilages (except epiglottis)
    • epiglotic cartilage forms from the mesenchyme in the hypopharyngeal eminence
  140. fifth arch derivatives
    arch is rudimentary - NO derivatives
  141. derivatives of first pharyngeal arch muscle
    • muscles of mastication - temporalis, lateral and medial pterygoids, masseter
    • tensor veli palatini
    • tensor tympani
    • anterior belly of digastric
    • mylohyoid
  142. derivatives of second pharyngeal arch muscle
    • stapedius
    • stylohyoid
    • posterior belly of the digastric
    • all muscles of facial expression (including buccinator and auricular muscles)
  143. derivatives of third pharyngeal arch muscle
    stylopharyngeus
  144. derivatives of 4th pharyngeal arch muscle
    • cricothyroid
    • levator veli palatini
    • constrictors of the pharynx
  145. derivatives of 5th pharyngeal arch muscle
    intrinsic muscles of the larynx
  146. pharyngeal arch nerves
    • each pharyngeal arch is associated by its own cranial nerve
    • each nerve supplies the muscles derived from its associated pharyngeal arch muscle
    • each nerve supplies the dermis & mucous membranes derived from its associated pharyngeal arch
  147. derivatives of 1st pharyngeal pouch
    • lateral aspect: tubotympanic recess; tympanic cavity & mastoid antrum
    • proximal portion: pharyngotympanic tube
    • membrane: tympanic membrane
  148. derivatives of 2nd pharyngeal pouch
    tonsillar sinus/fossa (mostly obliterated by palatine tonsil)
  149. derivatives of third pharyngeal pouch
    • dorsal: inferior parathyroid gland
    • ventral: thymus
  150. derivatives of 4th pharyngeal pouch
    • superior parathyroid gland
    • with remnants of 5th pouch - ultimopharyngeal body (parafollicular or C cells of thyroid)
  151. abnormalities of pharyngeal apparatus
    • fistulas
    • sinuses
    • cytes
    • ectopic glands or glandular tissue
  152. first branchial cleft cysts: type I
    • located near the external auditory canal
    • commonly inferior & posterior to the tragus (base of ear)
    • may also be in the parotid gland or angle of mandible
    • may be difficult to distinguish from a solid parotid mass on clinical examination
  153. first branchial cleft cyst: type II
    associated with submandibular gland or found in the anterior triangle of the neck
  154. second branchial cleft cysts
    • accounts for 95% of branchial anomalies
    • congenital cyts that arise in the lateral aspect of the neck when the second branchial cleft fails to close during embryonic development
    • cysts are identified along the anterior border of the upper third of the SCM (adjacent to the muscle)
    • may present anywhere along the course of the lateral neck between the internal & external carotid arteries and into the palatine tonsil
  155. third branchial cleft cysts
    • RARE
    • extends from lateral neck posterior to the carotid arteries and pierces the thyrohyoid membrane to enter the larynx
    • usually located deep to the SCM
    • sometimes mistaken for retropharyngeal abscesses
  156. fourth branchial cleft cysts
    • RARE
    • arise from lateral neck, parallel to course of recurrent laryngeal nerve (around aorta on the left and around the right subclavian artery)
    • terminate in pyriform sinus
    • may arise in mediastinum
  157. congenital auricular sinuses & cysts
    • usually located in area of skin anterior to auricle
    • classified as minor anomalies - no serious medical consequence
  158. branchial sinus/fistula
    • incomplete closure of cervical sinus
    • can appear anywhere along SCM
    • courses in between internal & external carotid arteries
  159. first arch syndrome
    • results from insufficient migration of neural crest cells into the first arch during the fourth week
    • treacher collins syndrome: main manifestation
  160. Treacher Collins Syndrome
    • mandibulofacial dysostosis
    • autosomal dominant gene
    • malar hypoplasia
    • downslanting palpebral fissures
    • defects of the lower lids
    • deformed external ears
    • abnormalities of middle & internal ears
  161. development of thyroid gland
    • ventral endodermal thickening in floor of pharynx (thyroid diverticulum) at level of 2nd pharyngeal pouch
    • thyroglossal duct opens at foramen cecum of tongue
    • thyroglossal duct courses anterior to hyoid bone until it reaches tracheal cartilage due to differential growth
  162. thyroglossal duct cysts
    • can occure anywhere along the course followed by the thryoglossal duct during descent of the primordial thryoid gland from the tongue
    • painless, progressively enlarging movable mass
    • with infection, perforation of the skin occurs (thyroglossal duct sinus)
  163. ectopic thyroid tissue
    • lingual thyroid tissue
    • sublingual thyroid gland
    • substernal thryoid gland
  164. lingual thyroid
    • hot potato speech
    • difficulty in breathing & swallowing
    • four times more common in females than in males
    • cannot remove if it is the only thyroid tissue available
  165. sublingual thryoid mass
    • ectopic thyroid tissue
    • stays high in neck
  166. substernal thyroid gland
    • ectopic thyroid tissue
    • migrates too far in the mediastinum
  167. first indication of tongue development
    median tongue bud (tuberculum impar)
  168. development of the tongue
    • END OF 4th WEEK
    • median lingual swelling (tuberculum impar): disappears and makes no contribution to the adult tongue
    • median sulcus: point of fusion of two distal tongue buds
    • lateral lingual swelling: overgrow median lingual swelling to form anterior 2/3 of tongue
    • posterior 1/3 of tongue: from rostral part of hypopharyngeal eminence (3rd & 4th arches)
    • tongue musculature: from occipital myotomes
  169. tongue abnormalities
    • ankyloglossia: tongue-tie
    • macroglossia: large tongue
    • microglossia: small tongue
    • bifid tongue: split tongue
  170. anklyglossia
    • tongue-tie
    • short frenum - extends to tip of tongue
    • inferferes with protrusion of tongue
    • may make breastfeeding difficult

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