Mandible Movement and Jaw Closure

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Questions and Answers

What is the shape of the upper surface of the disc?

Concavoconvex (correct)

Convexoconcave

Flat

Convex

What is the characteristic of the retrodiscal tissue?

Fibrous and poorly innervated

Avascular and poorly innervated

Vascular and highly innervated (correct)

Cartilaginous and avascular

What connects the articular disc to the tympanic plate of the temporal bone?

Synovial membrane

Inferior retrodiscal layer

Superior retrodiscal layer (correct)

Articular capsule

Which nerve branch supplies the TMJ?

Auriculotemporal and masseteric branches Signup and view all the answers

What is the main blood supply to the TMJ?

Deep auricular artery and superficial temporal artery Signup and view all the answers

What type of movement can occur in the TMJ?

Rotation, elevation, depression, protrusion, and retraction Signup and view all the answers

What is the function of the synovial membrane?

To line the capsule in the upper and lower cavities of the joint Signup and view all the answers

What is the venous drainage of the TMJ?

Superficial temporal vein and maxillary vein Signup and view all the answers

What is the primary function of the lateral temporomandibular ligament?

To limit the movement of the mandible in a posterior direction Signup and view all the answers

What type of joint is the temporomandibular joint?

Synovial joint Signup and view all the answers

Where is the sphenomandibular ligament attached above?

To the spine of the sphenoid bone Signup and view all the answers

What is the function of the fibrous bands that attach the articular disc to the head of the mandible?

To ensure that the disc moves forward and backward with the head of the mandible Signup and view all the answers

What is the articular disc composed of?

Fibrocartilage Signup and view all the answers

What is the function of the stylomandibular ligament?

To provide additional support to the joint Signup and view all the answers

Where is the capsule of the temporomandibular joint attached above?

To the articular tubercle and the margins of the mandibular fossa Signup and view all the answers

What is the attachment of the articular disc in front?

To the tendon of the lateral pterygoid muscle Signup and view all the answers

What is the primary function of the lateral pterygoid muscle during depression of the mandible?

To pull the neck of the mandible and the articular disc forward Signup and view all the answers

Which muscles are responsible for elevation of the mandible?

Temporalis, masseter, and medial pterygoids Signup and view all the answers

What happens to the head of the mandible during protrusion of the mandible?

It is pulled forward onto the anterior tubercle Signup and view all the answers

Which muscle is responsible for pulling the articular disc backward during elevation of the mandible?

Fibroelastic tissue Signup and view all the answers

What is the primary movement of the mandible during depression?

Rotation of the head of the mandible on the undersurface of the articular disc Signup and view all the answers

Which muscle is responsible for pulling the head of the mandible backward during elevation of the mandible?

Temporalis Signup and view all the answers

What is the primary function of the fibroelastic tissue during depression of the mandible?

To limit the forward movement of the articular disc Signup and view all the answers

During which movement of the mandible does the articular disc move backward into the mandibular fossa?

Retraction Signup and view all the answers

What is the primary function of the posterior fibers of the temporalis muscle?

Retract the mandible Signup and view all the answers

Which muscle is responsible for elevating the mandible and also plays a role in retracting the mandible?

Temporalis Signup and view all the answers

What is the origin of the anterior belly of the digastric muscle?

Body of the mandible Signup and view all the answers

Which nerve supplies the masseter muscle?

Mandibular nerve Signup and view all the answers

What is the function of the lateral pterygoid muscle?

Pulls the neck of the mandible forward Signup and view all the answers

What is the insertion of the medial pterygoid muscle?

Oblique line on the lamina of the thyroid cartilage Signup and view all the answers

Which structure is located anterior to the temporomandibular joint?

Mandibular notch Signup and view all the answers

What is the primary function of the geniohyoid muscle?

Elevates the hyoid bone Signup and view all the answers

What structure lies immediately in front of the external auditory meatus?

Temporomandibular joint Signup and view all the answers

What is the clinical significance of the lateral temporomandibular ligament?

It prevents the head of the mandible from passing backward and fracturing the tympanic plate Signup and view all the answers

What is the result of the articular disc becoming partially detached from the capsule?

The joint movement becomes noisy and produces an audible click Signup and view all the answers

What is the movement that causes the head of the mandible and the articular disc to move forward until they reach the summit of the articular tubercle?

Depression of the mandible Signup and view all the answers

What is the position of the head of the mandible in bilateral cases of dislocation?

In front of the articular tubercle Signup and view all the answers

What is the method used to reduce the dislocation of the temporomandibular joint?

Pressing the gloved thumbs downward on the lower molar teeth and pushing the jaw backward Signup and view all the answers

What muscles are overcome by the downward pressure during the reduction of the dislocation?

Temporalis and masseter muscles Signup and view all the answers

What is the structure that the parotid gland lies laterally to?

Skin Signup and view all the answers

Study Notes

Temporomandibular Joint

The temporomandibular joint is a synovial joint that articulates between the articular tubercle and the anterior portion of the mandibular fossa of the temporal bone above and the head (condyloid process) of the mandible below.
The articular surfaces are covered with fibrocartilage.
The joint is divided into upper and lower cavities by the articular disc.

Capsule and Ligaments

The capsule surrounds the joint and is attached above to the articular tubercle and the margins of the mandibular fossa and below to the neck of the mandible.
The lateral temporomandibular ligament strengthens the lateral aspect of the capsule and limits the movement of the mandible in a posterior direction, protecting the external auditory meatus.
The sphenomandibular ligament lies on the medial side of the joint and represents the remains of the first pharyngeal arch in this region.
The stylomandibular ligament lies behind and medial to the joint and is a band of thickened deep cervical fascia that extends from the apex of the styloid process to the angle of the mandible.

Articular Disc

The articular disc is an oval plate of fibrocartilage that is attached circumferentially to the capsule.
The disc is also attached in front to the tendon of the lateral pterygoid muscle and by fibrous bands to the head of the mandible.
These bands ensure that the disc moves forward and backward with the head of the mandible during protraction and retraction of the mandible.

Retrodiscal Tissue

The retrodiscal tissue is vascular and highly innervated, making it a major contributor to the pain of Temporomandibular Disorder (TMD) when there is inflammation or compression within the joint.
The retrodiscal zone (bilaminar zone) of the TMJ is located between the posterior band of the articular disc and the posterior part of the articular capsule.
The superior retrodiscal layer of the TMJ joint is a lamina composed of connective tissue and elastic fibers that continues the posterior part of the articular disk and connects the disc to the tympanic plate of the temporal bone.
The inferior retrodiscal layer of the TMJ joint is a lamina composed of collagen fibers that continues the posterior part of the articular disk and inserts into the condylar neck.

Nerve and Vascular Supply

The TMJ is supplied by the auriculotemporal and masseteric branches of the mandibular nerve.
The TMJ is supplied mainly by three arteries: the deep auricular artery (from the maxillary artery), the superficial temporal artery (a terminal branch of the external carotid artery), and the anterior tympanic artery (a branch of the maxillary artery).
The venous drainage of the TMJ is via the superficial temporal vein and the maxillary vein.

Movements

The mandible can be depressed or elevated, protruded or retracted, and rotated.
Depression of the mandible is brought about by contraction of the digastrics, geniohyoids, and mylohyoids, with the lateral pterygoids playing an important role in pulling the mandible forward.
Elevation of the mandible is brought about by contraction of the temporalis, masseter, and medial pterygoids.
Protrusion of the mandible is brought about by contraction of the lateral pterygoid muscles of both sides, assisted by both medial pterygoids.
Retraction of the mandible is brought about by contraction of the posterior fibers of the temporalis.

Muscles

Masseter: originates from the zygomatic arch, inserts into the lateral surface of the ramus of the mandible, and elevates the mandible to occlude teeth.
Temporalis: originates from the floor of the temporal fossa, inserts into the coronoid process of the mandible, and elevates the mandible while posterior fibers retract the mandible.
Digastric: has two bellies, posterior and anterior, which depress the mandible or elevate the hyoid bone.
Mylohyoid: originates from the mylohyoid line of the mandible, inserts into the body of the hyoid bone, and depresses the mandible or elevates the floor of the mouth and hyoid bone.
Geniohyoid: originates from the inferior mental spine of the mandible, inserts into the body of the hyoid bone, and depresses the mandible or elevates the hyoid bone.
Lateral pterygoid: originates from the greater wing of the sphenoid and lateral pterygoid plate, inserts into the neck of the mandible and articular disc, and pulls the neck of the mandible forward.
Medial pterygoid: originates from the tuberosity of the maxilla and lateral pterygoid plate, inserts into the oblique line on the lamina of the thyroid cartilage, and elevates the mandible.

Clinical Notes

The temporomandibular joint lies immediately in front of the external auditory meatus.
The great strength of the lateral temporomandibular ligament prevents the head of the mandible from passing backward and fracturing the tympanic plate when a severe blow falls on the chin.
Dislocation of the temporomandibular joint can occur when the mandible is depressed, and the joint is unstable.
Reduction of the dislocation can be achieved by pressing the gloved thumbs downward on the lower molar teeth and pushing the jaw backward.

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Description

This quiz covers the movement of the mandible and jaw closure, including the roles of the articular disc, lateral pterygoid muscle, and surrounding structures.