Module 23: Skull and Muscles of the Face

Cranium

Skeletal structure of the head that supports the face and protects the brain, subdivided into facial bones and cranial bones

Facial bones functions

Underlie the facial structures, form the nasal cavity, enclose the eyeballs, support the teeth, form upper and lower jaws, form nose

Rounded cranium of the cranial bones function

Surrounds and protects the brain and houses the middle and inner ear structures

Orbit

Bony socket that houses the eyeball and muscles, cone shaped with narrow posterior region and large anterior opening, where bony margins are thickened and somewhat constricted to protect the eye

Supraorbital margin

Upper margin of the anterior orbit

Nasal cavity

Broad inferior space that narrows superiorly, divided into triangular halves by nasal septum, upper portion formed by perpendicular plate of the ethmoid bone, lower portion formed by vomer bone, includes the nasal concha

Nasal concha

Includes superior, which is part of the ethmoid, middle, which is part of the ethmoid, and inferior, which is an independent bone, attached to the lateral wall on either side of the nasal cavity, swirls incoming air to warm and moisturize it, allows mucus to trap incoming dust, pollen, bacteria, and viruses

Zygomatic arch

Bony arch on the side of the skull spanning from the area of the cheek to just above the ear canal that separates these areas formed by the junction of the temporal process of the zygomatic bone, which is short and anterior, and the zygomatic process of the temporal bone, which is longer and posterior.

Cranial cavity

Interior space of the cranium, bounded superiorly by the calvaria and lateral and posterior sides of the skull

Calvaria

Rounded top of the skull

“Flat” bones of the skull

Bones that form the top and sides

Floor of the cranium

Base of the skull, has numerous openings for passage and varies in depth, is subdivided into anterior, middle, posterior cranial fossae

Cranium bones

Paired parietal and temporal, unpaired frontal, occipital, sphenoid, and ethmoid bones

Parietal bone

Paired bones that forms most of the upper lateral side of the skull, right and left join together at the top of the skull, bounded anteriorly by the frontal bone, inferiorly by the temporal bone, and posteriorly by the occipital bone

Frontal bone

Single bone that forms the forehead, extends posteriorly inside the cranial cavity, forms both the roof of the orbit below and floor of the anterior cranial cavity above, contains supraorbital foramen

Supraorbital foramen

Where the supraorbital nerve exits

Temporal bone

Forms lower lateral side of the skull, includes external acoustic meatus, mandibular fossa, styloid process, mastoid process, stylomastoid foramen, carotid canal

External acoustic meatus

Large opening on the lateral side of the skull, allows air to vibrate the tympanic membrane

Mandibular fossa

Deep, oval-shaped depression located on the external base just in front of the external acoustic meatus where the mandible joins with the skull to form the TMJ

Temporomandibular joint

Joint where mandible and skull merge, moves mandible during the opening and closing of the mouth, as well as side-to-side and protraction or retraction of the mandible, involves articulation between mandibular fossa and articular tubercle of the temporal bone, with the condyle of the mandible

Styloid process

An elongated, downward bony projection that is posterior to the mandibular fossa on the external base of the skull, attachment site for several small muscles and a ligament that supports the hyoid bone

Mastoid process

Inferior portion of the mastoid portion and is an area for attachment of the sternocleidomastoid muscle

Stylomastoid foramen

Small opening located between styloid process and mastoid process, point of exit for CN VII

Carotid canal

Zig-zag shaped tunnel running anteromedially within the skull to open into the middle cranial cavity just above the foramen lacerum and near the posterior-lateral base of the sella turcica that provides passage through the base of the skull anteromedial to the styloid process for the internal carotid artery

Occipital bone

Single bone that forms the posterior skull and posterior base of the cranial cavity, has the foramen magnum, occipital condyle, and jugular foramen

Foramen magnum

Large opening in the posterior cranial fossa that allows for the passage of the spinal cord, CN XI, and vertebral arteries

Occipital condyle

On either side of the foramen magnum and forms joints with the first cervical vertebra to support the skull

Jugular foramen

Allows for CN IX, X, XI, and internal jugular veins to pass through immediately inferior to the acoustic meatus

Sphenoid bone

Single, complex bone of the central skull, “keystone” bone because it joins with almost every other bone of the skull, forms much of the base of the central skull and extends laterally to contribute to the sides, includes the right and left lesser wings, sella turcica, greater wings, optic canal, superior orbital fissure, and foramen ovale

Right and left lesser wings

Form the lip of a prominent ridge that marks the boundary between anterior and middle cranial fossa

Sella turcica

Located at the midline of the middle cranial fossa and houses the pituitary gland

Greater wings

Extend laterally to either side away from the sella turcica, where they form the anterior floor of the middle cranial fossa

Optic canal

Passageway for the ophthalmic artery and CN II at the posterior apex of the orbit, specifically anterior lateral corner of the cella turcica

Superior orbital fissure

Passageway for CN III, IV, V1, and VI into posterior orbit on the anterior wall of the middle cranial fossa, lateral to the optic canal and under projecting margin of the lesser wing

Foramen ovale

Passageway for CN V3 in the floor of the middle cranial fossa

Ethmoid bone

Single, midline bone that forms the roof and lateral walls of the upper nasal cavity, the upper portion of the nasal septum, a portion of the medial wall of the orbit, and a portion of the floor of the anterior cranial cavity, includes crista galli, cribriform plates, cribriform foramina, small air-filled spaces, sueprior and middle nasal concha, and perpendicular plate

Crista galli

Small upward bony projection located at the midline that functions as an anterior attachment point for the falx cerebri

Cribriform plate

On either side of the crista galli, has small, flattened area with cribriform foramina

Cribriform foramina

Small openings on cribriform plate that create a passageway for CN I

Perpendicular plate

Makes up part of the nasal septum

Suture

Twisting, immobile joint between adjacent bones of the skull, has a narrow gap filled with dense fibrous connective tissue that unites the bones, tightly interlocks the adjacent bones to add strength to the skull

Coronal suture

Runs from side to side across the skull within the coronal plane, joins frontal bone to the right and left parietal bones

Sagittal suture

Extends posteriorly from the coronal suture, running along the midline at the top of the skull in the sagittal plane to unite the right and left parietal bones, terminates by joining the lambdoid suture

Lambdoid suture

Extends downward and laterally to either side away from its junction with the sagittal suture in a “V” shape to join the occipital bone to the right and left parietal and temporal bones

Squamous suture

Located on the lateral skull, unites the squamous portion of the temporal bone with the parietal bone

Pterion

Small, H-shaped suture line region that unites the frontal, parietal, squamous portion of the temporal, and greater wing of the sphenoid bone at the intersection, weakest part of the skull

Facial bones

Paired are maxilla, palatine, zygomatic, nasal, lacrimal, inferior nasal conchae. Unpaired are vomer and mandible

Maxillary bone

Paired bone that forms the upper jaw, much of the hard palate, medial floor of the orbit, and lateral base of the nose, contains the alveolar process, alveolus, infraorbital foramen, palatine process, and maxillary sinus

Alveolar process

Curved, inferior margin of the maxillary bone that forms the upper jaw and contains the upper teeth

Alveolus

Deep socket where a tooth is anchored

Infraorbital foramen

Point of exit for a sensory nerve that supplies the nose, upper lip and anterior cheek

Palatine process

Joins together at the midline to form the anterior three quarters of the hard palate

Hard palate

Bony plate that forms the roof of the mouth and floor of the nasal cavity, separating the oral and nasal cavities

Palatine bone

Pair of irregularly shaped bones that contribute small areas to the lateral walls of the nasal cavity and medial wall of each orbit, includes horizontal plate

Horizontal plate

Plates from the right and left palatine bones join together at the midline to form the posterior quarter of the hard palate

Zygomatic bone

Paired bones form much of the lateral walls of the orbit and lateral-inferior margins of the anterior orbital opening, includes short temporal process

Short temporal process

Projects posteriorly, where it forms the anterior portion of the zygomatic arch

Nasal bone

One of the two small bones that articulate with each other to form the bony base of the nose and support cartilages that form the lateral walls of the nose

Lacrimal bone

Small, rectangular bone that forms the anterior, medial wall of the orbit, includes the lacrimal fossa, nasolacrimal canal

Lacrimal fossa

Shallow depression formed from anterior portion of the lacrimal bone

Nasolacrimal canal

Extends inferiorly from the lacrimal fossa

Lacrimal fluid drainage

Drains at the medial corner of the eye into the nasolacrimal canal, then extends downward to open into the nsal cavity, behind the inferior nasal concha. Normally drains posteriorly, but some will drain anteriorly with an increased flow of tears to cause a runny nose.

Inferior nasal conchae

Form a curved bony plate that projects into the nasal cavity space from the lower lateral wall, largest of the nasal conchae

Vomer bone

Triangular-shaped and forms the posterior inferior part of the nasal septum

Mandible

Forms the lower jaw and is the only moveable bone in the skull, includes a horizontal body, posteriorly a ramus, the angle, alveolar process, flattened coronoid process, condyler process, oval-shaped condyle, mandibular fossa, mandibular condyle, mental foramen, and mandibular foramen

Ramus

Has two upward-going bony projections, the flattened coronoid process and the condylar process

Coronoid process

More anterior projection that is the site for attachment for muscles of mastication

Condylar process

Topped by the condyle

Condyle

Articulates with the maxilla, mandibular fossa and articular tubercle of the temporal bone to form the TMJ

Alveolar process

Upper border of the body and serves to anchor the lower teeth

Mental foramen

Opening on each side of the anterior-lateral mandible, which is the exit site for a sensory nerve that supplies the chin

Mandibular foramen

Tunnel on the medial side of the ramus of the mandible that leads down the entire length of the body for the sensory nerve and blood vessels that supply the lower teeth

Orbit bones

Roof is frontal, lateral wall and floor is zygomatic, medial floor is maxilla and palatine, medial wall is ethmoid and lacrimal, posterior is sphenoid

Nasal septum

Consists of both bone and cartilage components, upper portion is perpendicular plate of ethmoid bone, lower and posterior parts is vomer bone, anterior is septal cartilageC

Cranial fossae

Increase in depth from anterior to posterior, shape of each conforms to the shape of the brain regions it contains, each has anterior and posterior boundaries and is divided at the midline into right and left areas by a significant bony structure of opening

Anterior cranial fossa

Most anterior and shallowest, overlies the orbits and contains the frontal lobes, bounded by frontal bone which forms the majority of the floor, lesser wings form ledge that marks the boundary between the anterior and middle cranial fossae, contains frontal lobes, olfactory bulb, olfactory tract

Middle cranial fossa

Deeper and situated posterior to the anterior fossa, extends from the lesser wings to the petrous ridges posteriorly, contains temporal lobe, pituitary gland, optic canal, superior orbital fissure, foramen rotundum, foramen ovale, foramen spinosum, carotid canal

Foramen rotundum

Passageway for a major sensory nerve that supplies the cheek, nose, and upper teeth in the floor of the middle cranial fossa just inferior to the superior orbital fissure

Foramen spinosum

Passageway for an artery that supplies the covering layers surrounding the brain posterior-lateral to the foramen ovale

Posterior cranial fossa

Most posterior and deepest portion of the cranial cavity, bounded anteriorly by petrous ridges, occipital bone forms the floor and posterior wall, foramen magnum divides it at the midline, contains the cerebellum, internal acoustic meatus, hypoglossal canal, and jugular foramen

Internal acoustic meatus

On medial wall of the petrous ridge in the posterior cranial fossa that provides for passage of the nerve from the hearing and equilibrium organs of the inner ear and the nerve that supplies the muscles of the face

Hypoglossal canal

At the anterior-lateral margin of the foramen magnum emerging on the inferior aspect of the skull at the base of the occipital condyle to provide passage for an important nerve to the tongue

Flexible articular disc

Between the bony structures in the TMJ to fill the gap between the skull and mandible, smooths movements between the temporal bone and mandibular condyle

Muscles of facial expression

Originate at the surface of the skull, specifically superficial fascia, insertions have fibers intertwined with connective tissue and the dermis of the skin, all innervated by CN VII except for the levator palpebrae superioris, which is innervated by CN III

Occiptofrontalis frontal belly

Elevate eyebrows, wrinkle forehead

Occiptofrontalis occipital belly

Retract scalp

Occiptofrontalis epicranial aponeurosis

Connects the two muscle bellies

Corrugator supercilii

Pull eyebrow inferior and medial, wrinkle superior nose vertically

Orbicularis oculi

Close eyelids

Levator palpebrae superioris

Elevate superior eyelid, innervated by CN III

Procerus

Depress medial eyebrow, wrinkle superior nose horizontally

Nasalis

Depress nasal cartilage

Levator labii superioris

Opens lips, elevates and furrows upper lips

Levator labii superioris alaeque nasi

Elevate upper lip, dilates nostrils

Levator anguli oris

Widens mouth, elevates corner of the mouth

Buccinator

Compresses cheek, draws corner of mouth laterally

Risorius

Draws corner of lip laterallyO

Orbicularis oris

Closes lip, purses, and protrudes lips

Zygomaticus major

Raises lateral corner of mouth

Zygomaticus minor

Raises lateral corner of mouth