Muscles acting on the Temporomandibular Joint

• Movements of the temporomandibular joint are chiefly from the action of the muscles of mastication.
• The temporalis, masseter, and medial pterygoid muscles produce biting movements.
• The lateral pterygoid muscles protrude the mandible with the help from the medial pterygoid muscles and retruded largely by the posterior fibres of the temporalis muscle.
• Gravity is sufficient to depress the mandible, but if there is resistance, the lateral pterygoid, suprahyoid and infrahyoid, mylohyoid and anterior digastric muscles are activated.

• Articulations

  Classified according to their structure, composition,and movability
  •    Fibrous joints-surfaces of bones almost in direct contact with limited movement
      o    Syndesmosis-two bones united by interosseous ligaments
      o    Sutures-serrated margins of bones united by a thin layer of fibrous tissue
      o    Gomphosis-insertion of a cone-shaped process into a socket

  •    Cartilaginous joints-no joint cavity and contiguous bones united by cartilage
      o    Synchondrosis-ends of two bones approximated by hyaline cartilage
      o    Symphyses-approximating bone surfaces connected by fibrocartilage

  •    Synovial joints-approximating bone surfaces covered with cartilage; may be separated by a disk; attached by ligaments 
      o    Hinge-permits motion in one plane only
      o    Pivot-permits rotary movement in which a ring rotates around a central axis
      o    Saddle-opposing surfaces are convexconcave. allowing great freedom of motion
      o    Ball and socket - capable of movement in an infinite number of axes; rounded head of one bone moves in a cuplike cavity of the approximating bone

  Bursae
  •    Sacs filled with synovial fluid that are present where tendons rub against bone or where skjn rubs across bone
  •    Some bursae communicate with a joint cavity 
  •    Prominent bursae found at the elbow. hip, and knee'

  Movements
  •    Gliding
      o    Simplest kind of motion in a joint
      o    Movement on a joint that does not involve any angular or rotary motions
  •    Flexion-decreases the angle formed by the union of two bones
  •    Extension-increases the angle formed by the union of two bones
  •    Abduction-occurs by moving part of the appendicular skeleton away from the median plane of the body
  •    Adduction-occurs by moving part of the appendicular skeleton toward the median plane of the body
  •    Circumduction
      o    Occurs in ball-and-socket joints
      o    Circumscribes the conic space of one bone by the other bone
  •    Rotation-turning on an axis without being displaced from that axis
   

• U-shaped bone
• Body
• Greater horn
• Lesser horn

• Suspended by ligaments from the styloid process

The Medial Wall of the Orbit 

• This wall is paper-thin and is formed by the orbital lamina or lamina papyracea of the ethmoid bone, along with contributions from the frontal, lacrimal, and sphenoid bones (L. papyraceus, "made of papyrus" or parchment paper).

• There is a vertical lacrimal groove in the medial wall, which is formed anteriorly by the maxilla and posteriorly by the lacrimal bone.
• It forms a fossa for the lacrimal sac and the adjacent part of the nasolacrimal duct.

• Along the suture between the ethmoid and frontal bones are two small foramina; the anterior and posterior ethmoidal foramina.
• These transmit nerves and vessels of the same name.

Appendicular Skeleton
Upper extremity
•    Shoulder-clavicle and scapula

Clavicle
    Articulates with the manubrium at the sternal end
    Articulates with the scapula at the lateral end
    Slender S-shaped bone that extends horizontally across the upper part of the thorax
    
Scapula

    Triangular bone with the base upward and the apex downward
    Lateral aspect contains the glenoid cavity that articulates with the head of the humerus
    Spine extends across the upper part of the posterior surface; expands laterally and
    forms the acromion (forms point of shoulder) 
    Coracoid process projects anteriorly from the upper part of the neck of the scapula
    
Arm (humerus)

Consists of a shaft (diaphysis) and two ends (epiphyses)
Proximal end has a head that articulates with the glenoid fossa of the scapula
Greater and lesser tubercles lie below the head

Intertubercular groove is located between them; long tendon of the biceps attaches here
Surgical neck is located below the tubercles

    o    Radial groove runs obliquely on the posterior surface; radial nerve is located here

    o    Deltoid muscles attaches in a V-shaped area in the middle of the shaft. called the deltoid tuberosity
    
Distal end has two projections. the medial and lateral epicondyles
Capitulum-articulates with the radius
Trochlea-articulates with the ulqa

Forearm

Radius
Lateral bone of the forearm
Radial tuberosity is located below the head on the medial side
Distal end is broad for articulation with the wrist: has a styloid process on its lateral side

Ulna

    Medial side of the forearm
    Conspicuous part of the elbow joint (olecranon)
    Curved surface that articulates with the trochlea of the humerus is the trochlearnotch
    Lateral ide is concave (radial notch); articulates with the head of the radius Distal end contains the styloid process 
    Distal end contains the styloid process

Hand

Carpal bones (8)
    Aranged in two rows of four
    Scaphoid. lunate. triquetral. and pisiform  proximal row); trapezium. trapezoid.
    capitate. and hamate (distal row)
    
Metacarpal bones (5)
    Framework of the hand
    Numbered 1 to 5 beginning on the lateral side
    
Phalanges (14)
    Fingers
     Three phalanges in each finger; two phalanges in the thumb

Ligaments of the Joint

• The fibrous capsule is thickened laterally to form the lateral (temporomandibular) ligament. It reinforces the lateral part of this capsule.
• The base of this triangular ligament is attached to the zygomatic process of the temporal bone and the articular tubercle.
• Its apex is fixed to the lateral side of the neck of the mandible.

• Two other ligaments connect the mandible to the cranium but neither provides much strength.

• The stylomandibular ligament is a thickened band of deep cervical fascia.
• It runs from the styloid process of the temporal bone to the angle of the mandible and separates the parotid and submandibular salivary glands.

• The sphenomandibular ligament is a long membranous band that lies medial to the joint.
• This ligament runs from the spine of the sphenoid bone to the lingula on the medial aspect of the mandible.