Development Flashcards
In which week does the neural tube form?
3
Where does the pharynx extend from and to?
Base of skull to inferior border of cricoid cartilage of the larynx
Where are the oropharyngeal, nasal and the laryngeal parts of the pharynx?
Nasal - superior to soft palate Oropharynx - soft palate to larynx Laryngeal pharynx - posterior to larynx
What are the pharyngeal arches?
System of mesenchymal proliferations in the neck region of the embryo
How many arches are there in total and how are they numbered?
5 1, 2, 3, 4, 6
What is each arch associated with?
A nerve, artery and cartilage bar
What does the mesoderm of the pharyngeal arches give rise to?
Muscle, cartilaginous structures, CVS components
What does the ectoderm of the pharyngeal arch give rise to?
Epidermis of skin
How does the neural tube form?
Notochord signals overlying ectoderm to thicken to give a slipper shaped neural plate Edges elevate out of the plane of the disk and curl towards each other creating the neural tube
Which part of the neural tube forms the brain and what three sections can it be divided into?
The anterior part
Prosencephalon - forebrain
Mesencephalon - midbrain
Rhombencephalon- hindbrain
Where are most of the cranial nerves derived from and which are the exceptions?
Mid or hind brain I and II
What groups can the cranial nerves be classified into?
Somatic efferent
Special sensory
Nerves of pharyngeal arches
Which cranial nerves have mixed sensory and motor functions and supply the derivatives of the pharyngeal arches?
V - trigeminal
VII - facial
X - vagus
Which cranial nerves have a relationship with the pharyngeal arch system?
Accessory (XI) Hypoglossal (XII)
What is the facial skeleton derived from?
The frontonasal prominence
First pharyngeal arch
Which pharyngeal arch are the muscles of facial expression derived from and therefore which nerve are they innervated by?
2
Facial nerve
Which pharyngeal arch are the muscles of mastication derived from and therefore which cranial nerve are they innervated by?
1 Trigeminal nerve (V) branch - the mandibular nerve
Which muscles does the third pharyngeal arch give rise to?
Stylopharyngeus
Which muscles does the 4th pharyngeal arch give rise to?
Cricothyroid Levator palatini Constrictors of the pharynx
Which muscles does the sixth pharyngeal arch give rise to?
Intrinsic muscles of the larynx
Which is the nerve of the first pharyngeal arch?
Trigeminal nerve (V)
Function of the trigeminal nerve?
Mixed
Principal sensory nerve of the head - skin and inside of mouth and nose
Motor: muscles of mastication, muscles derived from mandibular process
Which is the nerve of the second pharyngeal arch?
Facial (VII)
Function of the facial nerve?
Mixed Motor - muscles of facial expression and muscles from second pharyngeal arch Sensory - anterior two thirds of the tongue
Nerve of the third pharyngeal arch?
Glossopharyngeal (IX)
Function of the glossopharyngeal nerve?
Stylopharyngeus muscle
Sensory - posterior third of the tongue
Nerve of the fourth and sixth pharyngeal arches?
Vagus nerve (X) -4th arch branch is the superior laryngeal nerve -6th arch branch is the recurrent laryngeal nerve
What are the neural crest-derived cartilage bars of each of the pharyngeal arches?
1 = Meckel’s
2 = Reichert’s
4+6 = cartilages of the larynx
What can the first pharyngeal arch be divided into?
Maxillary and mandibular prominences
What does Meckel’s cartilage go onto form?
Malleus and incus of the ear
Template for mandible which forms by membranous ossification
What does Reichert’s cartilage go onto form?
Stapes in middle ear
Styloid process
Hyoid bone (part of it)
What does the cartilage of the third pharyngeal arch form?
Remainder of the hyoid bone
What do the cartilages of the 4th and 6th pharyngeal arches go onto form?
Epiglottis Thyroid, arytenoid, cricoid cartilages
Which artery is derived from each of the aortic arches?
1st and 2nd arch arteries disappear
3rd - internal carotid
4th - arch of aorta (L) and brachiocephalic trunk (R)
6th - pulmonary arch
Where do the aortic arches come from?
The aortic sac which lies in the floor of the pharynx
How many pharyngeal pouches are there?
4 pairs
Which part of the pharyngeal pouches give rise to organs?
The epithelial endodermal lining
What does pouch 1 give rise to?
Middle ear cavity
Eustachian tube
Lining of tympanic cavity
Tympanic membrane (ear drum)
What does pouch 2 give rise to?
Palatine tonsils Invaded by lymphoid tissue in third and fifth months
What does pouch three give rise to?
Inferior parathyroid
Thymus
What does pouch four give rise to?
Superior parathyroid
Which pouch is the parathyroid gland derived from?
3rd and 4th
How many pharyngeal clefts are there?
4, but only one contributes to a definitive structure
What is formed from the pharyngeal clefts? How?
External auditory meatus and part of the eardrum Dorsal part of the first cleft penetrates underlying mesenchyme and becomes the above
How are the clefts obliterated?
Second pharyngeal ARCH proliferates and covers third and fourth arches.
Merges with the epicardial ridge in the lower part of the neck.
Obliterates the other clefts
What can happen if the clefts are not obliterated?
Can have cysts or fistulae anywhere along the anterior border of the SCM
