Flashcards in Head and Neck, Session 3 Deck (84):
What is the stomadaeum?
the site of the future mouth which is the first evidence of face development and is a depression in the ectoderm on ventral aspect of head
How do facial clefts and cleft lips occur?
failure of fusion of the paired mandibular prominences and laterally paired maxillary prominences consisting of mesenchyme and a covering of ectoderm
what does the frontonasal prominence go on to form?
forehead, bridge of nose, upper eyelids, centre of upper lip
what do the maxillary prominences go on to form?
middle 1/3 of face, upper jaw, most of lip and sides of nose
what do the mandibular prominences go on to form?
lower 1/3 of face, lower jaw and lip
what is the first evidence of nose formation?
appearance of nasal placodes- bilateral ectodermal thickenings on ventrolateral aspect of frontonasal prominence
formation of nasal pits?
inagination of nasal placodes to form deep pits
entrance of each pit= future nostril
what is the oronasal memebrane?
thin layer of cells separating the stomodaeum from the deepening nasal pits dorsally
what prominences are involved in palate development?
maxiallry and medial nasal
how does cleft palate occur?
failure of 1 or both palatal shelves which grom for each maxillary prominence to reach midline or fuse with its opposite number
what does the temporal fossa comprise?
the temporalis muscle and its neurovascular supply
what does the infratemporal fossa contain?
medial and lateral pterygoid muscles, inferior part of temporalis muscle, mandibular nerve (division of trigeminal), inferior alveolar nerve, lignual, buccal nerves, maxillary artery, pterygoid venous plexus, otic ganglion (where glossopharyngeal nerve supplying salivary glands synapses), and chorda tympani- branch of facial nerve
where does the infratemporal fossa lie?
beneath base of skull, between pharynx and ramus of mandible
what is the mandibular foramen?
superior opening of the mandibular canal on the medial aspect of the ramus of the mandible, which also forms the lateral wall of the infratemporal fossa
what passes through the mandibular foramen?
inferior alveolar nerve and vessels
what happens if anasesthetic is injected around the mandibular foramen?
anaesthetise all mandibular teeth on that side- inferior alveolar nerve block
what nerve is vulnerable to injury when traumatic dislocation of TMJ?
auriculotemporal nerve- branch of mandibular division of trigeminal nerve
what is the inferior alveolar nerve a branch of?
the mandibular division (mandibular nerbe) of the trigeminal nerve
gives rise to the mental nerve- supplies skin and mucous membrane of lower lip
what drives the development of the face?
expansion of cranial neural tube
appearance of complex tissue system assoc. with cranial gut tube and outflow of developing heart
development of sense organs and need to separate resp. from GI tract
what is a placode?
thickened plate of ectoderm from which a sense organ develops- lens(eye), otic(ear), nasal (nose)
number of pharyngeal cleft characterising 5wk embryo?
what do neural crest cells contribute to the development of?
head and neck structures
where do neural crest cells arise?
lateral border of the neuroectoderm along edges of neural folds
displaced and enter mesoderm, then migrate
how do neural crest cells contribute to development of CVS?
contribute to conotruncal endocardial cushions which separate outflow tract of heart into pulmonary and aortic channels, and regulation of secondary heart field
what prominences contribute to the formation of the face?
medial and lateral nasal
structures formed by lateral nasal prominences?
alae of nose
structures formed by maxillary prominences?
cheeks, lateral portion of upper lip
why might the palatine shelves fail to fuse?
smallness of shelves
failure of shelves to elevate
inhibition of fusion process itself
failure of tongue to drop from between shelves because of micrognathia- jaw undersized
what is formed by the 2 merged medial nasal prominences?
components of intermaxillary segement from medial nasal prominences?
labial part: philtrum
upper jaw: 4 incisors
importance of mandible initially being very small and then enlarging?
mandible grows large enough to allow tongue to drop, and so allow fusion of palatal shelves- if problem with this, can cause cleft palate
how do the ears come to lie in line with the eyes?
growth of mandible allows ears to ascend
how does maxillary prominence grow?
population by neural crest cells
otic placodes invaginate to form auditory vesicles, what do these vesicles give rise to?
membranous labyrinth: cochlea, semi-lunar canal system
what are the articulations of the TMJ?
2 articulatory surfaces on squamous temporal under surface: mandibular fossa- post and concave, articular tubercle- ant and convex
1 articulatory surface on each side of mandible: condyle of mandible
importance of mandible having a rounded superior edge and ellipsoid circumference with its major axis postero-medial?
not a simple hinge type movement produced, degree of medial and lateral displacement of the joint
how do we know where to palpate the TMJ?
found anter. and roughly level to the tragus of the ear
how is the fibrous capsule of the TMJ specialised to permit joint movements?
thin and loose
how is posterior dislocation of TMJ prevented?
by intrinsic lateral ligament- a thickened part of the joint capsule, which strengthens joint laterally, and with postglenoid tubercle, acts to prevent post. dislocation of joint.
where is the joint capsule of the TMJ attached?
to the circumference of the mandibular fossa and articular tubercle superiorly, and neck of condyle of mandible inferiorly
problem of looseness of TMJ capsule?
remains liable to sublaxation or complete displacement
how are the bony surfaces of the TMJ separated from one another?
by an articular disc/meniscus- fibrocartilage, creating 2 separate cavities: superior and inferior articular cavities within the TMJ capsule, each lined by separate S and I synovial membranes
why is having upper and lower articular cavities of the TMJ important?
allows for 2 separate types of independent movements of the joint: upper= gliding joint- protrusion and retrusion, lower= modified hinge joint, allowing rotational/pivoting and hinge movements
what are the articulating surfaces of the upper joint cavity of TMJ?
articulator surface of under surface of temporal bone, and upper surface of articular disc
articulating surfaces of lower joint cavity of TMJ?
inferior surface of articular disc and mandibular condyle
how does articular disc help stabilise TMJ?
makes the articulatory bony surfaces congruent, improving their fit
why is the TMJ unusual in the components of its synovial joint cavity?
articulatory surfaces lined with fibrocartilage, rather than hyaline cartilage
advantages and disadvantages of fibrocartilage lining articulatory surfaces of TMJ?
+ve: bettwe withstand large forces
-ve: wears thin more readily
which muscles elevate mandible at TMJ?
temporalis, masseter, medial pterygoid
muscles depress mandible at TMJ?
lateral pterygoid, suprahyoid and infrahyoid muscles- all active against resistance
prime mover= gravity
muscles that cause mandibular protrusion at TMJ
lateral pterygoid- prime mover, masseter and medial terygoid
muscles that cause mandibular retrusion at TMJ?
temporalis- post oblique and near horizontal fibres, and masseter
muscles that cause lateral movements of TMJ?
temporalis of same side, pterygoids of opposite side, and masseter
how does attachments of articular disc limit anterior displacement of jaw?
disc attached ti lateral pterygoid muscle anteriorly, but temporal bone posteriorly- limits displacement
when the jaw is closed, what is the condyle of the mandible articulating with?
mandibular fossa of temporal bone- posterior superior articular surface of cranium
accessory ligaments (extrinsic) of TMJ?
sphenomandibular and stylomandibular
describe structure and function of sphenomandibular ligament
primary passive support of mandible
remains constant in length and tension for all positions of mandible
prevents inferior dislocation of joint
function of stylomandibular ligament?
thickening of fibrous capsule of parotid gland
separates parotid from submandibular gland
does not contribute significantly to strength of TMJ
what must head of mandible and articular disc do to be able to open mouth wider than just to separate upper and lower teeth?
they must move anteriorly on articular surface until head lies inferior to articular tubercle- translation movement
how is TMJ stabilised by teeth when jaw closed?
teeth in occlussal contact
what occurs at TMJ for any movement to happen?
displacement of mandible
contribution of pterygoid venous plexus to yawning?
when bored, venous stasis occurs in this venous plexus, causing metabolites to accumulate, which then triggers yawning- pumps blood through the veins, but dislocation of TMJ may occur if excessive contraction of lateral pterygoids occurs!
muscular contents of infratemporal fossa?
lower part of medial pterygoid
lower part of lateral pterygoid
lower part of temporalis
clinical significance of openings of infratemporal fossa?
infections can spread!!
how do opening movements of TMJ occur?
condyles pulled forward- protrusion via lateral pterygoid muscles- prime mover
chin pulled downward and back- digastric muscles (suprahyoid)
what must happen to the mandible for us to close our mouths?
mandible must be elevated and retruded
how do closing movements of TMJ occur?
mandible retrusion: posterior fibres of temporalis pull mandible backwards.
mandible elevation: remainder of temporalis, masseter muscles
medial pterygoid muscles
anatomical factors aiding stability of TMJ?
post displacement limited by postglenoid tubercle
passive anterior displacement limited by articular tubercle
inferior displacement prevented by sphenomandibular ligament (internal lateral) and stylomandibular ligament (posteriorly)
where might the mandible dislocate during yawning?
head of mandible dislocates anteriorly- passing anterior to articular tubercles
muscles must be made tired- then relax, and TMJ can be reset
what is knacking?
loud sounds due to jaw displacing
what is bruxism?
grinding teeth when asleep, associated with expression of stress syndrome
what is the infratemporal fossa?
an irregularly shaped space deep and inferior to zygomatic arch, deep to ramus of mandible and posterior to maxilla.
how does the infratemporal fossa communicate with the temporal fossa?
through interval between the zygomatic arch- part of temporal bone, and cranial bones
branches of mandibular nerve?
what are the openings of the infratemporal fossa?
foramen ovale- mandibular nerve
foramen spinosum- middle meningeal artery
alveolar canal- inferior alveolar nerve enters mandibular process
inferior orbital fissure
problem of infratemporal fossa being a potential space?
tumours can grow here without detection for a long time, so are typically advanced when become symptomatic
deep arteries of infratemporal fossa?
middle meningeal, maxillary (larger terminal branch of external carotid)
superficial artery of infratemporal fossa?
superficial temporal- can feel temporal pulse
veins of infratemporal fossa?
middle meningeal veins
pterygoid venous plexus
describe a mandibular nerve block
anaesthetic injected near mandibular nerve where it enters infratemporal fossa- near foramen ovale. Extraoral approach: needle passes through mandibular notch of ramus of mandible, into infratemporal fossa. Injection anesthetises auriculotemporal, inferior alveolar, lingual and buccal branches of nerve
what is the mandibular foramen, and why might an injection occur around this site?
the opening into the mandibular canal on the medial aspect of the ramus of the mandible.
Canal gives passage to inferior alveolar nerve, artery and vein
Inferior alveolar nerve block: all mandibular teeth anaethetised to median plane.
Skin + mucous membrane of lower lip, labial alveolar mucosa, gingivae, and skin of chin also anaesthetised as supplied by mental nerve.
which compartment of TMJ responsible for elevating mandible to close mouth?
when does TMJ dislocation commonly occur?
Dislocation of the TMJ most commonly results from a side-ways blow to the chin when the mouth is open, dislocating the TMJ on the side that received the blow. Dislocation of the TMJ may also accompany fractures of the mandible.