Functional Anatomy of the Head and Jaw

Original Editor - Ewa Jaraczewska

Top Contributors - Ewa Jaraczewska and Jess Bell  

Introduction

The human head includes the skull, hyoid bone, and face. The skull contains cranial and facial structures. The face can be divided into upper and lower regions. The upper region consists of the forehead, eyes, and nose. The lower region contains the lips, chin, and jaw. The head and jaw are highly complex structures and have many functions. The skull provides protection and support for its inner contents and an attachment site for muscles. The muscles of this area are involved in expression, mastication and eye movements. This page discusses these muscles, as well as the bones, ligaments, and nerve and blood supply for the head and jaw.

Key Terms

Axes: lines around which an object rotates. The rotation axis is a line that passes through the centre of mass. There are three axes of rotation: sagittal passing from posterior to anterior, frontal passing from left to right, and vertical passing from inferior to superior. The rotation axes of the foot joints are perpendicular to the cardinal planes. Therefore, motion at these joints results in rotations within three planes. Example: supination involves inversion, internal rotation, and plantarflexion.

Bursae: reduce friction between the moving parts of the body joints. A bursa is a fluid-filled sac. There are four types of bursae: adventitious, subcutaneous, synovial, and sub-muscular.

Capsule: one of the characteristics of the synovial joints. It is a fibrous connective tissue which forms a band that seals the joint space, provides passive and active stability and may even form articular surfaces for the joint. The capsular pattern is "the proportional motion restriction in range of motion during passive exercises due to tightness of the joint capsule."

Closed pack position: the position with the most congruency of the joint surfaces. In this position, joint stability increases. For example, the closed pack position for the interphalangeal joints is full extension.

Degrees of freedom: the direction of joint movement or rotation; there is a maximum of six degrees of freedom, including three translations and three rotations.

Ligament: fibrous connective tissue that holds the bones together.

Open (loose) pack position: position with the least joint congruency where joint stability is reduced.

Planes of movement: describe how the body moves. Up and down movements (flexion/extension) occur in the sagittal plane. Sideway movements (abduction/adduction) occur in the frontal plane. The transverse plane movements are rotational (internal and external rotation).

Head and Jaw Structure

The skeletal structure of the human skull is composed of two parts: the neurocranium, which protects the brain and brainstem, and the facial skeleton, which supports the face. The neurocranium is made up of eight bones: the frontal, ethmoid, sphenoid, and occipital bones, as well as two temporal and two parietal bones. The facial skeleton contains six paired bones and two unpaired bones.

Neurocranium (Cranial Bones)

• Frontal bone: belongs to the forehead region of the face and houses the frontal sinuses. It forms the roof of the ethmoid sinuses, nose and orbit (for the eye)
• Parietal bones: sits on the top and sides of the skull. It has four articulations: the frontal bone, occipital bone, temporal bone and second parietal bone.
• Occipital bone: a single bone covering the back and base of the skull. It articulates with both temporal bones, the sphenoid bone, two parietal bones, and the upper cervical vertebra (i.e. the atlas).
• Temporal bones: located at the sides and base of the skull. It forms the external auditory canal and houses the cockles, canals, and hearing organs.
• Sphenoid bone: a single bone that connects the neurocranium with the facial bones. It is located posterior to the frontal bone and anterior to the occipital bone.
• Ethmoid bone: a single bone that separates the nasal cavity from the brain. It belongs to the anterior aspect of the cranium, forming the lateral boundaries of the orbit.

Facial Bones

• Two inferior nasal conchae: form part of the lateral wall of the nasal cavity.
• Two nasal bones: form the upper part of the nasal cavity - i.e. the bridge of the nose. They articulate with the maxilla and the frontal bone.
• Two maxillae bones: form the roof of the oral sinus, and house the upper teeth. They belong to the roof and lateral wall of the nasal cavity.
• Two palatine bones: form the hard palate with the maxillae.
• Two lacrimal bones: small, fragile bones located in the anteromedial part of the orbit.
• Two zygomatic bones: form the lateral rim and wall of the orbit, and create the anterior zygomatic arch.
• Mandible (jaw bone): the only mobile bone in the facial skeleton. It houses the lower teeth.
• Vomer: forms the inferior portion of the nasal septum.

Read more about the facial skeleton here.

Bones, Articulations and Kinematics of the Head and Jaw

This section focuses on the bones, articulations and kinematics of the temporomandibular joint (TMJ). The TMJ is formed between the mandibular fossa of the temporal bone and the condyloid process of the mandibular bone.

The TMJ is divided into superior and inferior compartments by the intra-articular disc of the TMJ. Each compartment acts as a joint. The superior compartment separates the glenoid fossa of the temporal bone from the disc and allows for translational movements. The inferior compartment separates the disc from the mandibular condyle and allows for rotational movements.

The disc is the central anatomic structure of the TMJ. It has three parts: the anterior and posterior articular bands and the intermediate zone in the centre. The lateral aspect of the disc connects to the joint capsule before inserting into the condylar neck. When the mouth is closed, the position of the articular disc can be assessed based on the position of the "location of the posterior band and intermediate zone in relation to the mandibular condyle.":

• The posterior band is near the 12 o’clock position on the sagittal projection
• The intermediate zone lies between the condyle and the temporal bone
• The medial and lateral corners of the disc are aligned with the condylar borders

During mouth opening, the following actions should occur:

• The condyle rotates in the inferior compartment
• The condyle then translates anteriorly in the superior compartment
• The disc moves between the condyle and the articular eminence

Bones and Articulations

Bones	Articulations	Characteristics	Key palpation points
Mandible, Temporal bone	Temporomandibular joint (TMJ)	The articulation between the upper and lower jaws. The right and left joints function together. They cannot act independently due to the connection between the TMJ and the mandible. Includes a fibrous capsule, intra-articular disc, synovial membrane, fluid, and ligaments. Plays an important role in breathing, eating, and speech.	Palpate the mandible with the patient in sitting. First, palpate the symphysis menti - the articulation between the left and right parts of the mandible. This articulation is felt as a small, vertical ridge in adults. Inferiorly, it divides and encloses a midline depression, which is called the mental protuberance. You can also palpate a mental tubercle on each side of the mental protuberance. Move your finger up to feel for the incisive fossa of the mandible. Place your finger in front of the ear to palpate the upper portion of the mandible. You will feel the round structure of the condylar process of the mandible, which is part of the temporomandibular joint (TMJ). To confirm your palpation, ask the patient to open their mouth slowly, and you should feel the condyle of the mandible moving.

Kinematics

Joint	Type of joint	Plane of movement	Motion	Kinematics	Closed pack position	Open pack position
Temporomandibular joint (TMJ)	Ginglymoarthrodial joint ( hinge and a gliding joint): Bilateral movement of the lower joint acts like a hinge joint Bilateral movement of the upper portion forms a plane gliding type of joint	Transverse (mouth opening) Sagittal (protrusion/retrusion) Frontal (lateral deviation)	The lower jaw: elevation depression lateral deviation protrusion retrusion	Jaw opening: approximately 40 to 50 mm movement; Transversal displacement: approximately 0.9 mm	Mouth closed with the teeth clenched. The heads of the condyles are in the posterior aspect of the joint.	Mouth slightly open, lips together, no contact between the teeth

Read about the physiology and biomechanics of the temporomandibular joint here.

Temporomandibular Joint Ligaments

Key ligaments	Origin	Insertion	Action/role	Key palpation points
Lateral temporomandibular ligament	Lower articular tubercle of the zygomatic arch	Lateral and posterior border of the neck of the mandible	Supports the capsule of the TMJ. Helps prevent posterior dislocation of the TMJ.	Find the zygomatic arch by palpating the bone extending forward from the temporal bone towards the opening of the ear. When you palpate the lateral part of the zygomatic arch, you will find a small bony projection known as the articular tubercle of the zygomatic arch. To palpate the neck of the mandible, find the head of the mandible. Place your finger in front of the ear to palpate the upper portion of the mandible. You will feel the round structure of the condylar process of the mandible, known as the head of the mandible. You can find the neck of the mandible just below the condylar process.
Stylomandibular ligament	Styloid process of the temporal bone	Angle of the mandible and posterior border of the mandible with a 30° angle of inclination	Connects the styloid process of the temporal bone to the mandible and limits excessive protrusion of the mandible.	Palpate the temporal bone located at the side and base of the skull. The temporal bone is located posterior to the frontal and inferior to parietal bones, just behind and underneath the ear. The sphenoid bone is anterior to the temporal fossa. Next, gently pull the ear forward to place your finger on the mastoid process located just behind the ear. The styloid process can be palpated in front of the mastoid process and directly below the ear. This is the attachment point for the stylohyoid muscle. To confirm the location, ask your patient to swallow. You should feel the hyoid bone move.
Sphenomandibular ligament	Spine of the sphenoid bone	Lingula	Provides passive support for the mandible by limiting its depression

Muscles of the Temporomandibular Joint

Muscles of the Temporomandibular Joint (Mastication muscles)

Accessory Mastication Muscles

The main functions of the mastication muscles are swallowing, chewing, and grinding. These muscles can also assist in mandibular movement. The mastication muscles are divided into the suprahyoid and the infrahyoid muscles.

The suprahyoid muscles are the following:

• Geniohyoid muscle
• Mylohyoid muscle
• Digastric muscle

The infrahyoid muscles include the following:

• Thyrohyoid
• Sternothyroid
• Sternohyoid
• Omohyoid

Muscle	Origin	Insertion	Innervation	Action
Geniohyoid	Inferior mental spine: the posterior surface of the mandible near the lower part of the mandibular symphysis	Superior border of the body of the hyoid bone	C1 via the hypoglossal nerve	Moves the larynx upwards and forwards during swallowing through the movement of the hyoid bone.
Mylohyoid	Mandible near the molars	Hyoid bone	Mylohyoid nerve of the inferior alveolar nerve (Mandibular division of the trigeminal nerve (Cranial nerve V, CN V)	Forms the floor of the oral cavity. Elevates the hyoid bone and floor of the mouth. Depresses the mandible.
Digastric (D): Anterior belly (DAB) Posterior belly (DPB)	DAB: digastric fossa of mandible DPB: mastoid notch of the temporal bone	DAB/DPB: Body of the hyoid bone	DAB: Mylohyoid nerve of the inferior alveolar nerve (Mandibular division of the trigeminal nerve (CN V) DPB: digastric branch of the facial nerve (CN VII)	Depresses the mandible. Assists with chewing and swallowing as it elevates the hyoid bone.
Thyrohyoid	Oblique line of thyroid cartilage	Inferior border of the body of the hyoid bone Greater horn of hyoid bone	Anterior ramus of spinal nerve C1 via hypoglossal nerve (CN XII)	Depresses the hyoid bone. Elevates the larynx.
Sternothyroid	Posterior surface of the manubrium of the sternum Costal cartilage of the first rib	Oblique line of the thyroid cartilage	Anterior rami of C1-3 (via the ansa cervicalis)	Depresses the larynx
Sternohyoid	Manubrium of sternum Medial end of the clavicle	Inferior border of the body of the hyoid bone		Depresses the hyoid bone
Omohyoid (O): Inferior belly (OIB) Superior belly (OSB)	OIB: superior border of the scapula near the suprascapular notch OSB: intermediate tendon	OIB: intermediate tendon OSB: body of the hyoid bone		Depresses and retracts the hyoid and larynx

Muscles of the Face

The muscles of the face are primarily involved in facial expressions.

Muscle	Origin	Insertion	Innervation	Action
Occipitofrontalis (OF): Frontal belly (OFFB) Occipital belly (OFOB)	OFFB: epicranial aponeurosis OFOB: occipital and temporal bones	OFFB: subcutaneous tissue in the forehead and eyebrow region OFOB: epicranial aponeurosis	OFFB: temporal branch of the facial nerve (CN VII) OFOB: posterior auricular nerve	OFFB: elevates the eyebrows to show surprise and protracts the scalp creating a frown. OFOB: retracts the scalp.
Corrugator supercilii	Frontal bone	The skin above the middle of the supraorbital margin.	Temporal branch of the facial nerve (CN VII)	Moves the eyebrows medially. Creates vertical lines above the nose bridge, e.g. when frowning.
Orbicularis oculi: Palpebral part (PP) Lacrimal part (LP) Orbital part (OP)	Medial palpebral ligament Lacrimal bone	Lateral palpebral raphe	Temporal and zygomatic branches of the facial nerve (CN VII)	PP: closes the eyelids gently. LP: faciliates drainage of tears. OP: squeezes the eyelids tightly shut.
Procerus	Nasal bone	Skin over the bridge of the nose	Temporal, lower zygomatic or buccal branches of the facial nerve (CN VII)	Wrinkles the skin over the bridge of the nose (typical facial expression when exposed to strong, bright light).
Nasalis: Alar part (NAP) Transverse part (NTP)	NAP/NTP: maxilla	NAP: greater alar cartilage NTP: nasal bone, becomes continuous with the muscle on the opposite side	Buccal branch of the facial nerve (CN VII)	NAP: Flares nostrils. NTP: Compresses the nasal opening.
Levator labii superioris alaeque nasi	Maxilla	Nostril and upper lip	Buccal branch of the facial nerve‎ (CN VII)	Flares nostrils and elevates the upper lip.
Levator labii superioris	Zygomatic process of the maxilla Maxillary process of the zygomatic bone	Blends with muscles of the upper lip	Zygomatic and buccal branches of the facial nerve (CN VII)	Elevates the upper lip.
Orbicularis oris: Inner part Outer part	Medial aspects of the maxilla and mandible Perioral skin and muscles Modiolus at the corner of the mouth	Dermis of the upper and lower lips	The buccal and mandibular branches of the facial nerve (CN VII)	Enables the mouth to close.
Buccinator	Pterygomandibular raphe Maxilla Mandible	Orbicularis oris and the modiolus	The buccal branches of the facial nerve (CN VII)	Assists with mastication, sucking, and forcible expulsion of air or fluid.
Zygomaticus minor	Zygomatic bone	Upper lip	The zygomatic and buccal branches of the facial nerve (CN VII)	Elevates the upper lip, can contribute to smiling or expressions of disdain.
Zygomaticus major	Zygomatic arch	Modiolus	Buccal and zygomatic branches of the facial nerve (CN VII)	Elevates and pulls the corner of the mouth upwards, like when smiling.
Levator anguli oris	Maxilla		Buccal branch of the facial nerve (CN VII)	Elevates the corner of the mouth.
Risorius	Parotid gland			Pulls the corners of the mouth laterally.
Depressor labii inferioris	Mandible	Orbicularis oris	Mandibular branch of the facial nerve (CN VII)	Depresses the lower lip and pulls the lower lip laterally.
Mentalis		Skin of the chin		Moves the soft tissue of the chin upward-inward and raises the central portion of the lower lip.
Depressor anguli oris	Tubercle of the mandible‎	Orbicularis oris Modiolus	Marginal mandibular branch of the facial nerve (CN VII)	Depresses the corner of the mouth, like in frowning.
Platysma	Skin and fascia of the shoulder Superior thoracic regions	Mandible Lower lip Modiolus	Cervical branch of the facial nerve (CN VII) Transverse cervical nerve.	Pulls down the corner of the mouth, the lower lip, and the mandible.

Extraocular Muscles

These muscles are responsible for eye movement. Understanding their function is important for proper testing of the cranial nerves.

Muscle	Origin	Insertion	Innervation	Action
Superior rectus (SR), Inferior rectus (IR), Lateral rectus (LR) Medial rectus (MR)	Common annular tendon that surrounds the optic nerve	SR: superior aspect of the eyeball IR: inferior aspect of the eyeball LR: lateral aspect of the eyeball MR: medial surface of the eyeball	SR: superior branch of the oculomotor nerve (CN III) IR: inferior branch of the oculomotor nerve (CN III) LR: the abducens nerve (CN VI) MR: lower branch of the oculomotor nerve (CN III)	SR: elevates the eye IR: depresses the eye LR: abducts the eye MR: adducts the eye
Oblique: Superior oblique (SO) Inferior oblique (IO)	SO: the sphenoid bone IO: the maxilla	SO: superior aspect of the eye IO: lateral side of the eye	SO: trochlear nerve (CN IV) IO: the inferior branch of the oculomotor nerve (CN III)	SO: medial eye rotation (intorsion). Assists with eye depression and abduction. IO: lateral eye rotation (extorsion). Assists with eye elevation and abduction.
Levator palpebrae superioris	Sphenoid	Upper eyelid	Superior branch of the oculomotor nerve (CN III)	Lifts the eyelids

Innervation of the Head and Jaw

Twelve pairs of cranial nerves (CN) arise directly from the brain. Cranial nerves I and II begin at the cerebrum, and cranial nerves III to XII arise from the brainstem. The number of each cranial nerve reflects the following:

• location on the brainstem: starting superior to inferior, then medial to lateral
• the order of the cranial nerves exiting from the cranium (anterior to posterior)

The following is the list of cranial nerves:

• Olfactory nerve (CN I)
• Optic nerve (CN II)
• Oculomotor nerve (CN III)
• Trochlear nerve (CN IV)
• Trigeminal nerve (CN V)
  • Ophthalmic nerve (V1)
  • Maxillary nerve (V2)
  • Mandibular nerve (V3)
• Abducens nerve (CN VI)
• Facial nerve (CN VII)
• Vestibulocochlear nerve (CN VIII)
• Glossopharyngeal nerve (CN IX)
• Vagus nerve (CN X)
• Accessory nerve (CN XI)
• Hypoglossal nerve (CN XII)

You can read about cranial nerves here.

Nerve	Origin	Branches	Motor fibres	Sensory fibres
Mandibular nerve (Cranial nerve V3)	Trigeminal nerve (CN V)	Buccal nerve Mental nerve Auriculotemporal nerve	Primary muscles of mastication Mylohyoid muscle Anterior belly of the digastric muscle	Skin of the buccal region Sensory supply to the tongue (anterior two-thirds) Temporal region
Ansa cervicalis	Superior root (anterior rami of C1-C2) Inferior root (anterior rami of C2-C3)	Muscular branches	Infrahyoid muscles, except for the thyrohyoid muscle
First cervical spinal nerve (C1)		Ansa Cervicalis Other Muscular Branches Greater Auricular Nerve Transverse Cervical Nerve Lesser Occipital Nerve Supraclavicular Nerves	Thyrohyoid muscle Geniohyoid muscle	Dura around the foramen magnum
Hypoglossal nerve (CN XII)	Hypoglossal nucleus in the medulla oblongata of the brainstem		The extrinsic and intrinsic muscles of the tongue, except the palatoglossus muscle Thyrohyoid muscle	No sensory function
Facial nerve (CN VII)	Pons of the brainstem	Temporal branch Zygomatic branch Buccal branch Marginal mandibular branch Cervical branch	Muscles of facial expression Posterior belly of the digastric Stylohyoid and stapedius muscles	Small area around the concha of the external ear Taste sensation to the anterior two-thirds of the tongue via the chorda tympani
Oculomotor nerve (CN III)	Midbrain of the brainstem	Superior branch Inferior branch	Extraocular muscles, except for the superior oblique and the lateral rectus muscle
Trochlear nerve (CN IV)	The posterior aspect of the midbrain (trochlear nucleus of the brain)		Superior oblique	No sensory function
Abducens nerve (CN VI)	The pons of the brainstem (the abducens nucleus)		Lateral rectus	No sensory function

Vascular Supply of the Head and Jaw

Artery	Origin	Branches	Supply
Occipital artery	External carotid artery	Meningeal branch Mastoid branch	Back of the skull
Maxillary artery		Deep auricular artery, anterior tympanic artery, middle meningeal artery, inferior alveolar artery, accessory meningeal artery	TMJ, maxilla, and parts of the orbital region
Superficial temporal artery		Parotid branch, transverse facial artery, anterior auricular branches, zygomatic-orbital artery, middle temporal artery, frontal branch, parietal branch	TMJ, frontal, parietal, and temporal regions of the skull
Facial artery		Ascending palatine artery, tonsillar branch, submental artery, glandular branches.	Superficial areas of the face
Ophthalmic artery	Internal carotid artery	Supratrochlear (or frontal) artery and the dorsal nasal artery	The orbital region, forehead and scalp

Clinical Relevance

1. Impairment of the TMJ can cause orofacial pain / temporomandibular disorders (TMD). You can learn more about TMJ disorders by completing the Aetiology, Symptoms and Clinical Classifications of Temporomandibular Disorders course.
2. Bruxism or teeth grinding is a condition characterised by grinding, gnashing or clenching the teeth. Read more about it here.
3. Paralysis or weakness on one side of the face can be a symptom of facial palsy. You can learn more about the facial nerve here and facial palsy rehabilitation here.

Resources

• Romano N, Federici M, Castaldi A. Imaging of cranial nerves: a pictorial overview. Insights Imaging. 2019 Mar 15;10(1):33.
• Hutto JR, Vattoth S. A practical review of the muscles of facial mimicry with special emphasis on the superficial musculoaponeurotic system. AJR Am J Roentgenol. 2015 Jan;204(1):W19-26.
• Bony Landmark Palpation - Mandible (Skull).