Head & Neck Superficial Anatomy-Sievert Flashcards
What are the 3 main structures of the developing head & neck?
placodes
somites
branchial arches
What is another name for branchial arches? What are the 2 subtypes?
aka pharyngeal arches
clefts (come from the outside)
pouches (come from the inside)
What are placodes? What are the 3?
they are thickenings of the ectoderm that form structures for some of our special senses. Otic placode (ear) Lens Placode (eye) Olfactory Placode (nose)
What separates the bilateral placodes?
the neural tube.
Describe the location of the somitomeres (baby somites) in relation to the placodes.
There are 3 somitomeres above the otic placode. Called preotic somites. There are 3 somitomeres that are below the otic placode (postotic somites).
What do the preotic somites contribute to? What do the postotic somites contribute to?
preotic: extraocular muscles
postotic: tongue muscles
What does the olfactory placode form?
the primary olfactory epithelium (found in the superior nasal cavity). these are the cells of smell.
Where is the olfactory placode located?
near the forebrain the telencephalon part.
As the telencephalon develops you get something that induces the formation & thickening of the olfactory placode. What’s the deal with all of this?
the telencephalon develops & forms the olfactory bulb. This induces the olfactory placode to thicken
The cells of smell (primary neurosensory cells) of the olfactory placode meet up with the olfactory tract in the olfactory bulb. What must they penetrate to do this?
they have to get thru little holes in the cribriform plate of the ethmoid bone to get to the olfactory bulb.
Describe briefly how the lens placode forms.
an out pocketing of the forebrain (the diencephalon part) induces the surface ectoderm to thicken & form the lens placode.
How is the lens placode different from the otic & olfactory placodes?
it has nothing to do with neurons or receptors.
All that it is is something that thickens, invaginates, & breaks off to form the lens.
What does the lens placode help form?
the remaining surface ectoderm forms the cornea.
What are the 3 parts of the ear?
external
middle
inner
What does the otic placode form?
the inner ear
the membranous labyrinth
sensory neurons of cranial nerve 8
ganglion cells of cranial nerve 8
What are ganglion cells of cranial nerves?
they are very much like a DRG but they are located outside of the CNS
- *don’t have a synapse
- *have pseudo unipolar cells with a peripheral & central process
What should moms know about the ear’s development?
it is very slow to develop & therefore very susceptible to environmental defects
furthermore, it is difficult to tell when there are defects in an ear–have to specific tests w/ a baby.
What induces the otic placode?
the CNS induces the otic placode
it then invaginates creating the sensory neurons & inner ear.
What makes the external part of the ear?
the external auditory canal is formed by a cleft. an invagination of surface ectoderm
What makes the middle ear?
the middle ear is formed by 1st branchial pouch
an out pocketing of the endoderm of the pharynx
What’s cool about the tympanic membrane?
3 embryonic derivates live together!
T/F In the tympanic membrane you will find ectoderm, endoderm, and a little mesenchyme.
True.
What are somites?
masses of mesoderm that form skeletal muscles
T/F Preotic somites take care of the pupillary dilator & constrictor muscles.
False. Only extraocular muscles
muscles that move the eyeball & open eyelid NOT pupil or ciliary body stuff.
What nerves do we associate with somites?
GSE. General Somatic Efferents. So extraocular muscles (came from somites) are innervated by GSE fibers. Somatomotor.
What are GVE?
These are General Visceral Efferents. These are the fibers that innervate muscles that are smooth muscle, cardiac muscle etc. Visceromotor.
Branchiomotor nerve fibers innervate what?
muscles that came from branchial arches. This includes skeletal muscles, striated muscle. ??
What muscles come from postotic somites?
tongue muscles
Which cranial nerves are associated w/ the preotic somites?
3, 4, 6
Which cranial nerve is associated w/ the postotic somites?
Cranial Nerve 12–>hypoglossal nerve.
What are pharyngeal/branchial arches?
masses of mesenchymal tissue that flank the developing gut tube.
What does each pharyngeal arch have associated w/ it?
artery
nerve
block of tissue–>muscles
What direction do the pharyngeal arches develop in?
cranial–>caudal direction
Developmentally, when do the pharyngeal/branchial arches show up?
4th-5th week.
What does a pharyngeal arch look like in cross section?
it has a nerve, artery, & a part that becomes cartilage or bone
also has mesenchymal tissue & some neural crest cells
**outside lining is ectoderm. When this invaginates =cleft.
**inside lining is endoderm. When this invaginates=pouch.
What are the different derivates of the pharyngeal arches?
muscle
bone or cartilage
skin (from ectoderm)
gut lining (endoderm)
Describe the first pharyngeal arch. What does it give rise to?
So this arch has 2 parts. The maxillary arch & the mandibular arch.
Maxillary arch–>Upper jaw
Mandibular arch–>Lower jaw & small inner ear bones (malleus & incus) & part of temporal bone
**zygomatic bone formed by something in the 1st pharyngeal arch.
What is the 2nd pharyngeal arch called? What does it give rise to?
hyoid arch
**gives rise to part of the styloid process & the stapes & part of the hyoid bone
What does the 3rd pharyngeal arch give rise to?
the rest of the hyoid bone?
What does the 4th pharyngeal arch give rise to?
the cartilage of the larynx
What arch (aside from the 4th) helps contribute to the cartilage of the larynx? What’s the deal here?
the 6th arch contributes to the cartilage of the larynx, specifically the cricoid cartilage. The 4th specifically takes care of the thyroid cartilage.
These 2 arches fuse.
Which muscles arise from the 1st pharyngeal arch?
the muscles of mastication
Which muscles arise from the 2nd pharyngeal arch?
muscles of facial expression
Which muscles arise from the 3rd pharyngeal arch?
1 muscle. The stylopharyngeus muscle. Goes from the styloid process to the pharynx.
Which muscles arise from the 4th pharyngeal arch?
muscles of the pharynx, larynx, & palate.
Where do the pharyngeal arches get their sensory innervation?
the endodermal lining of the pharyngeal arches is innervated (cutaneous innervation) by the nerve of that arch.
What’s the deal with cutaneous innervation & the 1st pharyngeal arch?
so…the 1st pharyngeal arch forms the anterior 2/3 of the tongue. It overgrows the 2nd pharyngeal arch. This area of the tongue for some reason is more associated w/ ectoderm. Therefore, the cutaneous anterior 2/3 of the tongue (1st arch) is innervated by the 5th cranial nerve.
What’s the deal with cutaneous innervation to the 2nd pharyngeal arch?
remember, overgrown by the 1st arch! Poor guy.
What’s the deal with cutaneous innervation & the 3rd pharyngeal arch?
this covers the posterior 1/3 of the tongue. Behind the sulcus terminalis & the foramen cecum.
this area is more associated w/ endoderm.
This is innervated by the 9th cranial nerve. Cutaneous innervation, that is.
What’s the deal with cutaneous innervation & the 4th pharyngeal arch?
this forms the epiglottis
cutaneous innervation by cranial nerve 10
What are the important pharyngeal clefts & what do they give rise to?
really one 1 important cleft.
1st pharyngeal cleft gives rise to external auditory meatus
What happens to the other pharyngeal clefts?
they close off & can make cervical sinuses or cysts
How many important pharyngeal pouches are there?
4
What happens to the 1st pharyngeal pouch?
the 1st pouch merges w/ the 1st cleft & makes the auditory tube/eustachian tube. The pouch also makes the middle ear.
What happens to the 2nd pharyngeal pouch?
it forms the palatine tonsil
What happens to the 3rd pharyngeal pouch?
inferior parathyroid gland
thymus
Why is the inferior parathyroid gland formed by a higher pouch than the superior parathyroid gland?
b/c the thymus migrates downward. Eventually, the inferior parathyroid gland is in fact inferior.
What happens to the 4th pharyngeal pouch?
it forms the superior parathyroid gland & the ultimobranchial body (C cells of thyroid gland)
The olfactory placode is associate w/ which cranial nerve? What is the nature of this nerve?
Cranial Nerve 1–>Olfactory Nerve
sensory nerve
Lens placode. Associated w/ which cranial nerve? What is the nature of this nerve?
Cranial Nerve 2–>Optic Nerve
sensory nerve
**really talking about responding to an out pocketing of neural tube here
Preotic Somites. Associated w/ which cranial nerve? What is the nature of this nerve? Which embryonic derivative? Which muscles do they innervate?
Cranial Nerve 3-->Oculomotor Nerve Cranial Nerve 4-->Trochlear Nerve Cranial Nerve 6-->Abducens Nerve Somatomotor (think somites!) Mesoderm Extraocular Muscles
1st pharyngeal arch. Associated w/ which cranial nerve? What is the nature of this nerve?
Cranial Nerve 5–>Trigeminal Nerve
Both motor & sensory.
2nd pharyngeal arch. Associated w/ which cranial nerve? What is the nature of this nerve?
Cranial Nerve 7–>Facial Nerve
motor & sensory??
3rd pharyngeal arch. Associated w/ which cranial nerve?
Cranial Nerve 9–>Glossopharyngeal Nerve
4th pharyngeal arch. Associated w/ which cranial nerve?
Cranial Nerve 10–>Vagus Nerve
Postotic Somites. Associated w/ which cranial nerve?
All Cranial Nerve 12–>Hypoglossal Nerve
**does the muscles of the tongue
What’s the deal with Cranial Nerve 11?
Spinal Accessory Nerve. Innervates the trapezius. Controversy in terms of which primordial structure it came from.