Head and neck anatomy pt2

TMJ

the only freely movable articulation, together with the ossicles of the middle ear

Enarthrosis (spherical structure rotating around a cavity)

limited, both joints are joined by a very robust mandible

What muscles move the TMJ

muscles of mastication (jaw movements)

Articular surfaces (TMJ)

Mandibular fossa: posterior articulating surface (temporal bone), which houses the mandibular condyle at rest

Articular eminence: anterior to the mandibular fossa (condyle translated)

Fibrocartilage: collagen with some chondrocytes

Condyle

Capsule

tough and fibrous

Above: anterior lip of the squamotympanic fissure to the squamous bone, slack (loose)

Below: neck of condyle, tighter

Where is the lateral pterygoid inserted *

into the anterior surface of the capsule

Lateral temporomandibular ligament:

extends obliquely downwards and backwards from the articular tubercle → lateral surface of the mandibular neck

Sphenomandibular ligament (accessory)

extends downward and forward from the spine of the sphenoid → lingula of the mandible, sling

Stylomandibular ligament (accessory)

extends from the styloid process to the angle of the mandible

Articular disc

divides the TMJ into upper and lower compartments

it’s dense fibrous tissue, a continuation of a tendon of attachment of the lateral pterygoid muscle through the joint cavity

Mandibular rest position

muscles maintain a low level of activity → interocclusal space or freeway space (no occlusion when resting)

Rotation movement (TMJ)

Rotation of the head of the condyle about a transverse axis

Depression of the mandible

Short movement → sliding movement

Sliding movement (TMJ)

Condyle and disc slide together forwards and downwards from the mandibular fossa onto the articular eminence

Condylar guidance angle → prosthetics

They are not naturally used in isolation

Depression (TMJ)

Smooth, progressive combination of rotation and sliding with the mandibular heads rotating against the undersurface of the disc as they slide forwards onto the articular eminences (lateral pterygoid, digastric and suprahyoid muscles are involved)

Elevation (TMJ)

Reverse sequence of movements during depression

Temporalis, masseter and medial pterygoid muscles are involved

Protrusion (TMJ)

Produced by symmetrical sliding forwards at the 2 TMJs

Medial and lateral pterygoids, bilateral contraction

Retrusion (TMJ)

Reverse movement

Temporalis muscles, posterior fibres

Lateral excursion (TMJ)

The head of the mandible on the side to which movement is taking place is retained in the mandibular fossa, while the contralateral head is translated forwards onto the articular eminence

Lateral and medial pterygoids, temporalis (compensation)

Working side (inside the fossa) and balancing side (out of the fossa)

Mandible to the left =

working side

(right side is balancing)

Dentition (deciduous + permanent)

develops from the interaction of oral epithelial cells and the underlying mesenchymal cells

Oral epithelial cells

from enamel organ → enamel

Mesenchymal cells

from dental papilla → dentin

Bud stage

initial stage, rounded localised growth of the epithelial cells surrounded by proliferating mesenchymal cells

Cap stage

epithelial cells now become the enamel organ

dental papilla

dental follicle

Bell stage

growth of the papilla and the enamel organ

morphodifferentiation and histodifferentiation

Morphodifferentiation

inner enamel epithelial cells are characterised by the shape of the tooth they form

Histodifferentiation

new cells layer, ameloblasts → amelogenesis,

odontoblasts → dentinogenesis

Deciduous teeth

erupt into the mouth at or around 6 months after birth → have erupted by 3 years of age - 20 teeth

Permanent teeth

The first permanent molar erupts at or around 6 years. Deciduous teeth are exfoliated one by one to be replaced by their permanent successors

Complete permanent dentition

when the third molars erupt at or around the age of 18-21 years - 32 teeth

Incisiforms

cutting teeth (incisors). Thin blade-like crowns

Caniniforms

canine, piercing or tearing teeth. Single, stout, pointed, cone-shaped.

Molariforms

molar and premolars. Grinding teeth, Posses several cusps. Flattened biting surface. Premolars are bicuspid and restricted to the permanent dentition

Labial or buccal

adjacent to the lips or cheeks

Lingual or palatal

adjacent to the tongue or palate

Cranial nerves

routes by which the brain receives information from, and controls the functions of, structures by which are located mainly within the head and neck

Lowest numbers of the cranial nerves

arise from the most anterior aspect of the brain (forebrain)

Highest numbers of the cranial nerves

arise from the lowest part of brain (medulla)

the 3rd to 12th nerves are…

true peripheral nerves

the 1st and 2nd nerves are…

components of CNS not PNS, develop as outgrowths from brain

Trigeminal nerve (V)

most important, 2nd largest after optic nerve

3 divisions: ophthalmic, maxillary + mandibular

a large sensory and a small motor root arise from lateral aspect of pons

The mandibular division of the trigeminal nerve contains what type of axons *

motor axons

The ophthalmic and maxillary division of the trigeminal contains what type of axons *

purely sensory

What does the trigeminal nerve convey

proprioceptive info from muscles of mastication, TMJ, to the CNS

motor neurons to muscles derived from 1st pharyngeal arch (mastication)

Where does the trigeminal nerve receive sensory processes from

skin of the face, conjunctiva and cornea, eyeball, nasal cavity and paranasal sinuses, oral cavity, teeth, dura mater

Trigeminal ganglion

contains most of the sensory cell bodies. Located within the dural trigeminal cave in the middle cranial fossa (intracranial)*

Ophthalmic division (of trigeminal) 1st

leaves the cranial cavity and enters the orbit through superior orbital fissure

Maxillary division (of trigeminal) 2nd

exits through the foramen rotundum into the pterygopalatine fossa

Mandibular division (of trigeminal) 3rd

passes through the foramen ovale into the infratemporal fossa

What does the maxillary division cross

the floor of the orbit → infraorbital nerve → anterior and middle superior alveolar nerves (anterior upper teeth)

Ganglionic branches of maxillary division

pterygopalatine ganglion → greater palatine nerve (greater palatine foramen) → lesser palatine nerve (lesser palatine foramen)

Maxillary division

nasal and nasopalatine nerves: enter nasal cavity through the sphenopalatine foramen

pharyngeal nerves: posterior aspect of the pterygopalatine ganglion

posterior superior alveolar nerves: enter the maxilla through the small posterior alveolar foramina (molars and maxillary sinus)

Mandibular division has both…

mixed motor and sensory branches: nervus spinosus (meninges), nerve to medial pterygoid, tensor veli palatini and tensory tympani

Branches of mandibular division

from anterior trunk: buccal nerve, masseteric nerve, deep temporal nerve, nerve to lateral pterygoid

from posterior trunk: auriculotemporal nerve, lingual nerve, chorda tympani nerve, mylohyoid nerve, inferior alveolar nerve enters the mandibular canal (mandibular foramen)

mental nerve (mental foramen), incisive branch

Facial nerve (VII)

motor neurons → most numerous, muscles of facial expression (2nd pharyngeal arch)

parasympathetic preganglionic secretomotor axons → supply the lacrimal gland, submandibular and sublingual glands

special sensory processes → convey taste sensations from taste buds on tongue

Where does the facial nerve arise from

arise from the lateral aspect of the brainstem at the junction of the pons and medulla (2 roots) *

the 2 roots enter the internal auditory meatus (petrous temporal bone) along with the vestibulocochlear nerve

genu runs across medial wall of middle ear cavity (geniculate ganglion)

chorda tympani supplies taste buds in anterior tongue + salivary glands

facial nerve travels through the parotid and…

branches into 5 divisions for muscle of facial expression

before entering the gland, the facial nerve…

posterior auricular branch: occipitofrontalis and auricular muscles

branch for the posterior belly of the digastric and stylohyoid

within the gland, 5 divisions of facial nerve

temporal division: external ear + frontalis

zygomatic division: orbicularis oculi + frontalis

buccal division: buccinator + upper lip

mandibular division: muscles of lower lip

cervical division: platysma

main nerve of facial nerve

contains only motor axons → stylomastoid foramen

Facial paralysis or palsy

motor components of facial nerve, clinical testing

Bell’s palsy

viral infection, slow recovery, asymmetry in fave

Facial nerve damage

loss or impairment of taste, decrease in salivary output, impaired secretion of tears, sore and ulcerated cornea

The vestibule

contains the roof and floor of the mouth, buccal and labial sulci, frenulum, parotid duct, oropharyngeal isthmus and palatoglossal arch

Hard palate

bony partition between the nasal and oral cavity (anterior 2/3)

palatine process (maxillae) and horizontal process (palatine bone)

Soft palate

projects posteriorly, separating nasopharynx and oropharynx

uvula

Incisive papilla

small elevation overlying the incisive fossa, nasopalatine nerve

Greater palatine foramen

greater palatine nerve exits here

Palatine rugae

transverse ridges of mucosa

Terminal sulcus of the tongue

V-shaped

anterior 2/3 and posterior 1/3

Filiform papillae

most numerous, 2-3mm long with pointed ends

rough surface and no taste buds

Fungiform papillae

anterior tongue, bright red towards the sides and tip

has taste buds

Circumvallate papillae

12 large (2mm in diameter), anterior to the terminal sulcus

taste buds + minor salivary glands

Foliate papillae

several vertical folds on the posterior part of the lateral margins

has taste buds

Lingual tonsils

posterior third

numerous elevations of nodules of lymphoid tissue

Intrinsic muscles of the tongue

4 groups:

• superior longitudinal fibres: make dorsum concave

• inferior longitudinal fibres: give dorsum convex shape

• transverse fibres: narrow and elongate tongue

• vertical fibres: flatten and broaden tongue

Extrinsic muscles of the tongue

4 pairs:

• genioglossus

• hypoglossus

• styloglossus

• palatoglossus

Nerve supply of tongue

glossopharyngeal nerve: posterior 1/3 of dorsum

internal laryngeal branch (vagus): small area in front of epiglottis

lingual nerve (trigeminal): anterior 2/3

chorda tympanic (facial nerve): taste

hypoglossus nerve: instrinsic + extrinsic (palatoglossus innervated by vagus)

Blood supply of the tongue

lingual artery → runs forwards above the greater cornu of the hyoid to turn upwards at the anterior border of the hyoglossus muscle

Floor of the mouth

formed by the mylohyoid muscle

sublingual papillae: elevations either side of the lingual frenulum

sublingual folds: posteriorly from each papilla as a ridge (sublingual gland)

submandibular gland: lies partly on the floor of mouth and partly in neck

sublingual glad: entirely in floor of mouth

Nerve supply of the floor of the mouth

lingual nerve (medial surface of mandible, overlying roots of 3rd molar. Runs forwards, downwards and between mylohyoid and hypoglossus)

glossopharyngeal nerve

hypoglossal nerve

Blood supply of the floor of the mouth

lingual artery

Lips

orbicularis muscle and loose CT

skin externally + lining mucosa internally

sensory innervation of UL = infraorbital nerve

sensory innervation of LL = mental nerve

blood supply: mental and facial artery

facial vein venous drainage

lymph: submental nodes

Cheek

buccinator muscle

sensory innervation of upper cheek = posterior superior alveolar nerve

sensory innervation of lower cheek = buccal nerve

mental and facial artery blood supply

facial vein venous drainage

lymph: submental and submandibular nodes

Parotid gland

largest of 3 major salivary gland

wedges between mandibular ramus and its associated muscles in front of mastoid process

triangular outline

base: zygomatic arch and overlaps masseter

apex: angle of mandible

Parotid capsule

deep cervical fascia

Parotid duct

from anterior border, running forwards across the masseter. it turns medially, at the front edge of the masseter and pierces the buccinator to open into oral cavity

Structures within the parotid gland ****

External carotid artery: divides into its 2 terminal branches, maxillary and superficial temporal artery

Retromandibular vein: superficial to the external carotid artery and splits into the anterior and posterior divisions

Facial vein: superficial to retromandibular vein

Submandibular gland

superficial lobe: superficial to mylohyoid muscle, submandibular fossa

deep lobe: lying in the floor of the mouth between mylohyoid and hypoglossus muscle on the lateral aspect of the tongue

Submandibular duct

begins in the superficial lobe. Runs forwards firstly medial to the lingual nerve and then lateral, arches up to the tongue → sublingual papilla

Sublingual gland

smallest of 3 major glands

situated between mylohyoid laterally and the genioglossus medially in the front of the deep lobe of the submandibular gland

extends from 2nd molar to premolar region

in the sublingual fold

the lingual nerve and submandibular duct cross the medial surface of the gland

opens onto the surface of the sublingual fold through 15 small ducts