Face and oral cavity part 4

Question 1

Describe the course of the facial nerve

Answer 1

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).

Question 2

Ultimately, what are the 5 terminal branches of the facial nerve

Answer 2

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

Question 3

Summarise the typical pattern of distribution of the 5 terminal branches of the facial nerve

Answer 3

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.

Question 4

Summarise the sensory innervation of the face

Answer 4

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].

Question 5

What is an exception to the sensory innervation of the face

Answer 5

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.

Question 6

Where does each branch of the trigeminal nerve leave the skull

Answer 6

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

Question 7

What are the two main branches of the mandibular branch of the trigeminal nerve?

Answer 7

Lingual Nerve

Inferior Alveolar Nerve

Question 8

What are the functions of the lingual and inferior alveolar nerve?

Answer 8

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)

Question 9

What fibres join the lingual nerve?

Answer 9

Some fibres of the facial nerve via the Chorda Tympani (this is why the lingual nerve is responsible for taste)

Question 10

Describe the motor root of the trigeminal nerve

Answer 10

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.

Question 11

Describe the sensory innervation of the opthalamic nerve (V1)

Answer 11

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.

Question 12

Describe the sensory innervation of the maxillary nerve (V2)

Answer 12

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.

Question 13

Describe the sensory innervation of the mandibular nerve (V3)

Answer 13

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.

Question 14

Describe the two components of the gag reflex

Answer 14

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,

Question 15

What are the branches coming off the inferior alveolar nerve?

Answer 15

Mental nerve – terminal branch (provides sensation to the front of the chin)
Nerve to mylohyoid

Question 16

What is the vallecula

Answer 16

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

Question 17

Summarise the oral cavity

Answer 17

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.

Question 18

Summarise the roof of the oral cavity

Answer 18

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

Question 19

What are the walls of the oral cavity formed by

Answer 19

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)

Question 20

Summarise the floor of the oral cavity

Answer 20

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.

Question 21

Describe the posterior aperture of the oral cavity

Answer 21

oropharyngeal isthmus (opening to oral part of the pharynx)

Question 22

Summarise the sensory innervation of the face

Answer 22

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]

Question 23

Summarise the taste innervation of the face

Answer 23

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].

Question 24

Summarise the autonomic innervation of the face

Answer 24

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.

Question 25

Summarise the motor innervation of the face

Answer 25

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].

Question 26

What are the tonsils

Answer 26

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

Question 27

Describe the 3 areas of the tonsils

Answer 27

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.

Question 28

Where do small lymphoid nodules also occur

Answer 28

Small lymphoid nodules also occur in the pharyngotympanic tube near its opening into the nasopharynx, and on the upper surface of the soft palate.

Question 29

Describe the two regions of the oral cavity

Answer 29

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.

Question 30

What are the full numbers in a typical permanent set of teeth?

Answer 30

32
16 upper and 16 lower
8 incisors, 4 canines, 8 premolars and 12 molars (including 4 wisdom teeth)

Question 31

How many deciduous (baby) teeth are there?

Answer 31

20

Question 32

Which teeth are missing in the deciduous set compared to the adult set?

Answer 32

No premolars nor wisdom teeth

Question 33

When do the first deciduous teeth erupt

Answer 33

Around 6 months

Question 34

When is the deciduous set usually complete

Answer 34

Around 20-24 months

Question 35

What are the approximate starting and completion ages for the permanent set of teeth?

Answer 35

Starts around 7 years and usually completed by the age of 21

Question 36

Why are the tonsils clinically important?

Answer 36

They are areas of lymphoid tissue so they can get infected and inflamed

Question 37

What is the simplest test of the glossopharyngeal nerve

Answer 37

Test the patient’s gag reflex by sticking something down their throat

Question 38

How is the hypoglossal nerve tested?

Answer 38

Ask the patient to stick their tongue out

Question 39

How is the trigeminal nerve tested?

Answer 39

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

Question 40

How is the facial nerve tested

Answer 40

Ask the patient to crease up their forehead by raising their eyebrows
Ask the patient to keep their eyes closed against resistance

Question 41

What are the teeth attached to

Answer 41

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

Question 42

Describe the gums

Answer 42

The gingivae (gums) are specialized regions of the oral mucosa that surround the teeth and cover adjacent regions of the alveolar bone.

Question 43

Describe the incisor teeth

Answer 43

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The incisor teeth are the “front teeth” and have one root and a chisel-shaped crown, which “cuts.”

Question 44

Describe the canine teeth

Answer 44

The canine teeth are posterior to the incisors, are the longest teeth, have a crown with a single pointed cusp, and “grasp.”

Question 45

Describe the premolar teeth

Answer 45

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.”

Question 46

Describe the molar teeth

Answer 46

The molar teeth are behind the premolar teeth, have three roots and crowns with three to five cusps, and “grind.”

Question 47

Summarise the arteries and veins of the thyroid gland

Answer 47

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

Question 48

What protects the carotid sheath when the head is turned

Answer 48

The sternocleidomastoid

Question 49

What does each branch of the ECA supply

Answer 49

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

Question 50

Which muscle forms the inferior limit of the oral cavity

Answer 50

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.

Question 51

Describe the AFI of the mylohyoid muscle

Answer 51

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]

Question 52

Describe the AFI of the geniohyoid muscle

Answer 52

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

Question 53

Describe the oropharyngeal triangle

Answer 53

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.

Question 54

Which structures pass through the oropharyngeal triangle

Answer 54

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.

Question 55

What is the hypoglossal muscle of the tongue an important landmark for

Answer 55

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.