The Temporomandibular Joint

• This articulation is a modified hinge type of synovial joint.
• The articular surfaces are: (1) the head or condyle of the mandible inferiorly and (2) the articular tubercle and the mandibular fossa of the squamous part of the temporal bone.

• An oval fibrocartilaginous articular disc divides the joint cavity into superior and inferior compartments. The disc is fused to the articular capsule surrounding the joint.

• The articular disc is more firmly bound to the mandible than to the temporal bone.

• Thus, when the head of the mandible slides anterior on the articular tubercle as the mouth is opened, the articular disc slides anteriorly against the posterior surface of the articular tubercle

->The sides and base of the skull are formed partly by these bones.
->Each bone consists of four morphologically distinct parts that fuse during development (squamous, petromastoid, and tympanic parts and the styloid process).
->The flat squamous part is external to the lateral surface of the temporal lobe of the brain.
->The petromastoid part encloses the internal ear and mastoid cells and forms part of the base of the skull.
->The tympanic part contains the bony passage from the auricle (external ear), called the external acoustic meatus. The petromastoid part also forms a portion of the bony wall of the tympanic cavity (middle ear). The meatus and tympanic cavity are concerned with the transmission of sound waves.
->The slender, pointed styloid process of the temporal bone gives attachment to certain ligaments and muscles (e.g., the stylohyoid muscle that elevates the hyoid bone).
->The temporal bone articulates at sutures with the parietal, occipital, sphenoid, and zygomatic bones.
->The zygomatic process of the temporal bone unites with the temporal process of the zygomatic bone to form the zygomatic arch. The zygomatic arches form the widest part of the face.
->The head of the mandible articulates with the mandibular fossa on the inferior surface of the zygomatic process of the temporal bone.
->Anterior to the mandibular fossa is the articular tubercle.
->Because the zygomatic arches are the widest parts of the face and are such prominent facial features, they are commonly fractured and depressed. A fracture of the temporal process of the zygomatic bone would likely involve the lateral wall of the orbit and could injure the eye.

A. Anatomic position-erect body position with the arms at the sides and the palms  upward

B. Plane or section

1. Definition-imaginary flat surface formed by an extension through an axis

2. Median plane-a vertical plane. that divides a body into right and left halves

3. Sagittal plane

• Any plane parallel to the median plane
• Divides the body into right and left portions

4. Frontal plane

• Vertical plane that forms at right angles to the sagittal plane
• Divides the body into anterior and posterior sections
• Synonymous with the term coronal plane

5. Transverse plane

• Horizontal plane that forms at right angles to the sagittal and frontal planes
• Divides the body into upper and lower portions
• Synonymous with the term horizontal plane

C. Relative positions

1. Anterior

• Nearest the abdominal surface and the front of the body
• Synonymous with the term ventral
• In referring to hands and forearms, the terms palmar and Volar are used

2. Posterior

• Back of the body
• Synonymous with the term dorsal

3. Superior

• Upper or higher
• Synonymous with the term cranial (head)

4. Inferior

• Below or lower
• Synonymous with the term caudal (tail)
• In referring to the top of the foot and the sole of the foot. the terms dorsal and plantar are used respectively

5. Medial-near to the median plane

6. Lateral-farther away from the median plane

7. Proximal-near the source or attachment

8. Distal-away from the source or. attachment

9. Superficial-near the surface

10. Deep-away from the surface

11. Afferent-conducting toward a structure

12. Efferent-conducting away from a structure

Intrinsic muscles

    all innervated by recurrent laryngeal nerve except cricothyroid: external laryngeal nerve
    adductors of vocal folds: bring folds together at midline

    Transverse and oblique arytenoids: pull arytenoids together
    Lateral cricoartenoids: spin and slide arytenoids up
    only one abductor of vocal folds
    
    Posterior cricoarytenoids—down and up
    adjustors of shape and tension of vocal folds

    Cricothyroid muscle
    
o    superficial to lateral cricoarytenoid
o    tenses vocal folds by tilting thyroid cartilage forward and sliding forward

    Thyroartenoid and vocalis muscles
    
o    vocalis: sometimes treated as medial most fibers of thyroartenoid muscle
o    different fiber directions
    
    lateral: adduct
    medial: change shape of folds
    control voice by bring bringing together different parts of folds

o    as move from epithelium to vocalis muscle, fold becomes stiffer
o    near connections, vocal folds are stiffer
o    vocal fold: complex, multilayered vibrator

The Oral Cavity

• The oral cavity (mouth) consists of two parts: the vestibule and the mouth proper.

• The vestibule is the slit-like spaced between the cheeks and the lips and the teeth and gingivae.
• It is the entrance of the digestive tract and is also used for breathing.
• The vestibule communicates with the exterior through the orifice of the mouth.

• The oral cavity is bounded:
• Externally: by the cheeks and lips.
• Roof of oral cavity: formed by the palate.
• Posteriorly: the oral cavity communicates with the oropharynx.

The Medial Pterygoid Muscle

• This is a thick, quadrilateral muscle that also has two heads or origin.
• It embraces the inferior head of the lateral pterygoid muscle.
• It is located deep to the ramus of the mandible.

• Origin: deep head—medial surface of lateral pterygoid plate and pyramidal process of palatine bone, superficial head—tuberosity of maxilla.
• Insertion: medial surface of ramus of mandible, inferior to mandibular foramen.
• Innervation: mandibular nerve via medial pterygoid nerve.

• It helps to elevate the mandible and closes the jaws.
• Acting together, they help to protrude the mandible.
• Acting alone, it protrudes the side of the jaw.
• Acting alternately, they produce a grinding motion.