Face and oral cavity part 4 Flashcards
Describe the course of the facial nerve
The facial nerve [VII] exits the posterior cranial fossa through the internal acoustic meatus. It passes through the temporal bone, giving off several branches, and emerges from the base of the skull through the stylomastoid foramen (Fig. 8.63). At this point it gives off the posterior auricular nerve. This branch passes upward, behind the ear, to supply the occipital belly of the occipitofrontalis muscle of the scalp and the posterior auricular muscle of the ear.
The main stem of the facial nerve [VII] then gives off another branch, which innervates the posterior belly of the digastric muscle and the stylohyoid muscle. At this point, the facial nerve [VII] enters the deep surface of the parotid gland (Fig. 8.63B).
Once in the parotid gland, the main stem of the facial nerve [VII] usually divides into upper (temporofacial) and lower (cervicofacial) branches. As these branches pass through the substance of the parotid gland they may branch further or take part in an anastomotic network (the parotid plexus).
Ultimately, what are the 5 terminal branches of the facial nerve
Whatever types of interconnections occur, five terminal groups of branches of the facial nerve [VII]—the temporal, zygomatic, buccal, marginal mandibular, and cervical branches—emerge from the parotid gland
Summarise the typical pattern of distribution of the 5 terminal branches of the facial nerve
Temporal branches exit from the superior border of the parotid gland to supply muscles in the area of the temple, forehead, and supra-orbital area.
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Zygomatic branches emerge from the anterosuperior border of the parotid gland to supply muscles in the infra-orbital area, the lateral nasal area, and the upper lip.
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Buccal branches emerge from the anterior border of the parotid gland to supply muscles in the cheek, the upper lip, and the corner of the mouth.
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Marginal mandibular branches emerge from the anteroinferior border of the parotid gland to supply muscles of the lower lip and chin.
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Cervical branches emerge from the inferior border of the parotid gland to supply the platysma.
Summarise the sensory innervation of the face
Because the face is derived developmentally from a number of structures originating from the first pharyngeal arch, cutaneous innervation of the face is by branches of the trigeminal nerve [V].
The trigeminal nerve [V] divides into three major divisions—the ophthalmic [V1], maxillary [V2], and mandibular [V3] nerves—before leaving the middle cranial fossa (Fig. 8.61). Each of these divisions passes out of the cranial cavity to innervate a part of the face, so most of the skin covering the face is innervated solely by branches of the trigeminal nerve [V].
What is an exception to the sensory innervation of the face
The exception is a small area covering the angle and lower border of the ramus of the mandible and parts of the ear, where the facial [VII], vagus [X], and cervical nerves contribute to the innervation.
Where does each branch of the trigeminal nerve leave the skull
The ophthalmic nerve [V1] exits the skull through the superior orbital fissure and enters the orbit.
The maxillary nerve [V2] exits the skull through the foramen rotundum.
The mandibular nerve [V3] exits the skull through the foramen ovale
What are the two main branches of the mandibular branch of the trigeminal nerve?
Lingual Nerve
Inferior Alveolar Nerve
What are the functions of the lingual and inferior alveolar nerve?
Inferior Alveolar – innervates the lower teeth (this is the one that is stimulated in tooth ache)- terminates as the mental branch- at the mens (chin)
Lingual – sensation (touch and taste) to the anterior 2/3 of the tongue AND secretomotor to the sublingual and submandibular salivary glands-pre-ganglionic parasympathetic (fibres from chorda tympani which is a branch of the facial nerve)
What fibres join the lingual nerve?
Some fibres of the facial nerve via the Chorda Tympani (this is why the lingual nerve is responsible for taste)
Describe the motor root of the trigeminal nerve
The motor root of the trigeminal nerve also passes through the foramen ovale and unites with the sensory component of the mandibular nerve outside the skull. Thus the mandibular nerve is the only division of the trigeminal nerve that contains a motor component.
Outside the skull, the motor fibres innervate the four muscles of mastication (temporalis, masseter, and medial and lateral pterygoids) as well as the tensor tympani, the tensor veli palatini, the anterior belly of the diagastric muscle and the mylohyoid muscle.
Describe the sensory innervation of the opthalamic nerve (V1)
The ophthalmic nerve [V1] carries sensory branches from the eyes, conjunctiva, and orbital contents, including the lacrimal gland. It also receives sensory branches from the nasal cavity, frontal sinus, ethmoidal cells, falx cerebri, dura in the anterior cranial fossa and superior parts of the tentorium cerebelli, upper eyelid, dorsum of the nose, and the anterior part of the scalp.
Describe the sensory innervation of the maxillary nerve (V2)
The maxillary nerve [V2] receives sensory branches from the dura in the middle cranial fossa, the nasopharynx, the palate, the nasal cavity, teeth of the upper jaw, maxillary sinus, and skin covering the side of the nose, the lower eyelid, the cheek, and the upper lip.
Describe the sensory innervation of the mandibular nerve (V3)
The mandibular nerve [V3] also receives sensory branches from the skin of the lower face, cheek, lower lip, anterior part of the external ear, part of the external acoustic meatus and the temporal region, the anterior two-thirds of the tongue, the teeth of the lower jaw, the mastoid air cells, the mucous membranes of the cheek, the mandible, and dura in the middle cranial fossa.
Describe the two components of the gag reflex
Afferent- Glossopharyngeal nerve
Efferent- Vagus nerve
Reflex: touching the posterior pharyngeal wall will lead to brief but brisk elevation of the soft palate and contraction of the pharyngeal muscles
The reflex helps prevent choking, as well as helping to moderate the transition from liquid to solid foods during infancy. By thrusting objects in the throat toward the opening of the mouth,
What are the branches coming off the inferior alveolar nerve?
Mental nerve – terminal branch (provides sensation to the front of the chin)
Nerve to mylohyoid
What is the vallecula
Depression just behind the root of the tongue – they serve as spit traps
Saliva is temporarily held in the valleculae to prevent initiation of the swallowing reflex
Summarise the oral cavity
The oral cavity is inferior to the nasal cavities (Fig. 8.243A). It has a roof and floor and lateral walls, opens onto the face through the oral fissure, and is continuous with the cavity of the pharynx at the oropharyngeal isthmus.
Summarise the roof of the oral cavity
Roof: hard / soft palates
The two maxillae contribute substantially to the architecture of the roof of the oral cavity. The parts involved are the alveolar and palatine processes
The parts of each L-shaped palatine bone that contribute to the roof of the oral cavity are the horizontal plate and the pyramidal process
The pterygoid processes and spines of the sphenoid bone are associated with structures related to the soft palate, which forms part of the roof of the oral cavity
What are the walls of the oral cavity formed by
The walls of the oral cavity are formed by the cheeks.
Each cheek consists of fascia and a layer of skeletal muscle sandwiched between skin externally and oral mucosa internally. The thin layer of skeletal muscle within the cheeks is principally the buccinator muscle.
Lateral walls: cheeks (converging anteriorly to form the oral fissure - the anterior opening)
Summarise the floor of the oral cavity
The floor of the oral cavity proper is formed mainly by three structures:
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a muscular diaphragm, which fills the U-shaped gap between the left and right sides of the body of the mandible and is composed of the paired mylohyoid muscles;
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two cord-like geniohyoid muscles above the diaphragm, which run from the mandible in front to the hyoid bone behind; and
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the tongue, which is superior to the geniohyoid muscles.
Also present in the floor of the oral cavity proper are salivary glands and their ducts. The largest of these glands, on each side, are the sublingual gland and the oral part of the submandibular gland.
Describe the posterior aperture of the oral cavity
oropharyngeal isthmus (opening to oral part of the pharynx)
Summarise the sensory innervation of the face
The upper parts of the cavity, including the palate and the upper teeth, are innervated by branches of the maxillary nerve [V2].
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The lower parts, including the teeth and oral part of the tongue, are innervated by branches of the mandibular nerve [V3]
Summarise the taste innervation of the face
Taste (special afferent [SA]) from the oral part or anterior two-thirds of the tongue is carried by branches of the facial nerve [VII], which join and are distributed with branches of the trigeminal nerve [V].
Summarise the autonomic innervation of the face
Parasympathetic fibers to the glands within the oral cavity are also carried by branches of the facial nerve [VII], which are distributed with branches of the trigeminal nerve [V].
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Sympathetic fibers in the oral cavity ultimately come from spinal cord level T1, synapse in the superior cervical sympathetic ganglion, and are eventually distributed to the oral cavity along branches of the trigeminal nerve [V] or directly along blood vessels.
Summarise the motor innervation of the face
All muscles of the tongue are innervated by the hypoglossal nerve [XII], except the palatoglossus, which is innervated by the vagus nerve [X].
All muscles of the soft palate are innervated by the vagus nerve [X], except for the tensor veli palatini, which is innervated by a branch from the mandibular nerve [V3]. The muscle (mylohyoid) that forms the floor of the oral cavity is also innervated by the mandibular nerve [V3].
What are the tonsils
Collections of lymphoid tissue in the mucosa of the pharynx surrounding the openings of the nasal and oral cavities are part of the body’s defense system. The largest of these collections form distinct masses (tonsils). Tonsils occur mainly in three areas
Describe the 3 areas of the tonsils
The pharyngeal tonsil, known as adenoids when enlarged, is in the midline on the roof of the nasopharynx.
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The palatine tonsils are on each side of the oropharynx between the palatoglossal and palatopharyngeal arches just posterior to the oropharyngeal isthmus. (The palatine tonsils are visible through the open mouth of a patient when the tongue is depressed.)
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The lingual tonsils refer collectively to numerous lymphoid nodules on the posterior one-third of the tongue.
Where do small lymphoid nodules also occur
Small lymphoid nodules also occur in the pharyngotympanic tube near its opening into the nasopharynx, and on the upper surface of the soft palate.
Describe the two regions of the oral cavity
The oral cavity is separated into two regions by the upper and lower dental arches consisting of the teeth and alveolar bone that supports them (Fig. 8.243B):
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The outer oral vestibule, which is horseshoe shaped, is between the dental arches and the deep surfaces of the cheeks and lips—the oral fissure opens into it and can be opened and closed by muscles of facial expression, and by movements of the lower jaw.
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The inner oral cavity proper is enclosed by the dental arches.
What are the full numbers in a typical permanent set of teeth?
32
16 upper and 16 lower
8 incisors, 4 canines, 8 premolars and 12 molars (including 4 wisdom teeth)
How many deciduous (baby) teeth are there?
20
Which teeth are missing in the deciduous set compared to the adult set?
No premolars nor wisdom teeth
When do the first deciduous teeth erupt
Around 6 months
When is the deciduous set usually complete
Around 20-24 months
What are the approximate starting and completion ages for the permanent set of teeth?
Starts around 7 years and usually completed by the age of 21
Why are the tonsils clinically important?
They are areas of lymphoid tissue so they can get infected and inflamed
What is the simplest test of the glossopharyngeal nerve
Test the patient’s gag reflex by sticking something down their throat
How is the hypoglossal nerve tested?
Ask the patient to stick their tongue out
How is the trigeminal nerve tested?
Sensory – touch the patient around the jawline, on the cheek and on the forehead (to test the three divisions)
Motor – ask the patient to clench their teeth and try to palpate the bulge of the masseter and temporalis
How is the facial nerve tested
Ask the patient to crease up their forehead by raising their eyebrows
Ask the patient to keep their eyes closed against resistance
What are the teeth attached to
The teeth are attached to sockets (alveoli) in two elevated arches of bone on the mandible below and the maxillae above (alveolar arches). If the teeth are removed, the alveolar bone is resorbed and the arches disappear
Describe the gums
The gingivae (gums) are specialized regions of the oral mucosa that surround the teeth and cover adjacent regions of the alveolar bone.
Describe the incisor teeth
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The incisor teeth are the “front teeth” and have one root and a chisel-shaped crown, which “cuts.”
Describe the canine teeth
The canine teeth are posterior to the incisors, are the longest teeth, have a crown with a single pointed cusp, and “grasp.”
Describe the premolar teeth
The premolar teeth (bicuspids) have a crown with two pointed cusps, one on the buccal (cheek) side of the tooth and the other on the lingual (tongue) or palatal (palate) side, generally have one root (but the upper first premolar next to the canine may have two), and “grind.”
Describe the molar teeth
The molar teeth are behind the premolar teeth, have three roots and crowns with three to five cusps, and “grind.”
Summarise the arteries and veins of the thyroid gland
Superior thyroid artery – from the external carotid artery
Inferior thyroid artery – from the thyrocervical trunk
Superior thyroid vein – to the internal jugular vein
Middle thyroid vein – to the internal jugular vein
Inferior thyroid vein – to the brachiocephalic vein
What protects the carotid sheath when the head is turned
The sternocleidomastoid
What does each branch of the ECA supply
Superior thyroid: thyroid and muscles
Ascending pharyngeal: palate and pharynx
Lingual: tongue, epiglottis and mouth
Facial: face
Occipital: sternocleidomastoid and meninges
Posterior auricular: parotid gland and ear
Superficial temporal: masseter and lateral face
Maxillary: large supply
Which muscle forms the inferior limit of the oral cavity
The two thin mylohyoid muscles (Table 8.20), one on each side, together form a muscular diaphragm that defines the inferior limit of the floor of the oral cavity (Fig. 8.248A). Each muscle is triangular in shape with its apex pointed forward.
Describe the AFI of the mylohyoid muscle
origin- mylohyoid line of mandible
insertion- Median fibrous raphe and adjacent part of hyoid bone
function- Supports and elevates floor of oral cavity; depresses mandible when hyoid is fixed; elevates and pulls hyoid forward when mandible is fixed
innervation- Nerve to mylohyoid from the inferior alveolar branch of mandibular nerve [V3]
Describe the AFI of the geniohyoid muscle
origin-inferior mental spines of mandible
insertion- body of hyoid bone
innervation- C1
function- Elevates and pulls hyoid bone forward; depresses mandible when hyoid is fixed
Describe the oropharyngeal triangle
In addition to defining the lower limit of the floor of the oral cavity, the free posterior border of the mylohyoid muscle on each side forms one of the three margins of a large triangular aperture (oropharyngeal triangle), which is a major route by which structures in the upper neck and infratemporal fossa of the head pass to and from structures in the floor of the oral cavity (Fig. 8.249). The other two muscles that complete the margins of the aperture are the superior and middle constrictor muscles of the pharynx.
Which structures pass through the oropharyngeal triangle
Most structures that pass through the aperture are associated with the tongue and include muscles (hyoglossus, styloglossus), vessels (lingual artery and vein), nerves (lingual, hypoglossal [XII], glossopharyngeal [IX]), and lymphatics.
A large salivary gland (the submandibular gland) is “hooked” around the free posterior margin of the mylohyoid muscle and therefore also passes through the opening.
What is the hypoglossal muscle of the tongue an important landmark for
The hyoglossus muscle is an important landmark in the floor of the oral cavity:
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The lingual artery from the external carotid artery in the neck enters the tongue deep to the hyoglossus, between the hyoglossus and genioglossus.
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The hypoglossal nerve [XII] and lingual nerve (branch of the mandibular nerve [V3]), from the neck and infratemporal fossa of the head, respectively, enter the tongue on the external surface of the hyoglossus.
