•     Part of the axial skeleton; strong, flexible rod
      Supports the head
      Gives base to the ribs
      Encloses the spinal cord
      
  o    Vertebrae
      Consists of 34 bones composing the spinal column
  •    Cervical-7 bones
  •    Thoracic-12 bones
  •    Lumbar-5 bones
  •    Sacral- 5 bones.
  •    Coccygeal-4 to 5 bones

      In the adult the vertebrae of the sacral and coccygeal regions are united into two bones, the sacrum and me coccyx
      
  o    Curvatures-from a lateraI view there are four curves, alternately convex and concave ventrally
      Two convex curves are the cervical and lumbar
      Two concave curves are the thoracic and sacral

  o    Vertebra morphology

      Each vertebra differs in size and shape hut has similar components
      Body-central mass of bone
  •    Weight bearing
  •    Fonns anterior part of the vertebra
  •    Encloses the vertebral foramen
      Pedicles of the arch-two thick columns that extend backward from the body to meet with the laminae of the neural arch 

•     Process (7)
  •    One spinous, two transverse, two superior articular, and two inferior articular
  o    Spinous process extends backward from the point of the union of thetwo laminae
  o    Transverse processes project laterally at either side from the junction of the lamina and the pedicle
  o    Articular processes arise near the junction of the pedicle and the lamina- superior processes project upward:inferior processes project downward
  •    Surfaces of the processes are smooth

  o    Inferior articular processes of the vertebra fit into the superior articular processes below
  o    Form true joints, but the contacts established serve to restrict movement

  Distinguishing features

  Cervical region- triangular shape

  •    All have foramina in the transverse process upper six transmit the vertebral artery
  •    Spinous processes are short
      o    C3 to C5 are bifurcated
      o    C7 is long-prominence felt at the back of the neck
  •    Have small bodies (except for C1 vertebra)
  •    C1 vertebra (atlas)
  o    No body
  o    Anterior and posterior arch and two lateral masses
  o    Superiorarticular processes articulate with the condyles of the occipital bone
  •    C2 vertebra (axis)-process on the upper surface of the body (dens) forms a pivot about which the axis rotates

  Thoracic region

  •    Presence of facets for articulation with the ribs (distinguishing feature)
  •    Processes are larger and heavier than those of the cervical region
  •    Spinous process is directed downward at a sharp angle
  •    Circular vertebral foramen

   Lumbar region
   
  •    Large and heavy bodies
  •    Four transverse lines separate the bodies of the vertebrae on the pelvic surface
  •    Triangular shape-fitted between the  halves of the pelvis
  •    Four pairs of dorsal sacral foramina communicate with four pairs of pelvic sacral foramina

  Sacral vertebrae 
  •    Five (sometimes six) vertebrae are fused in the adult to form the sacrum
  •    The sacrum articulates above with L5, laterally with the hip bones, and inferiorly with the coccyx.
  •    It has a roughly triangular appearance with a pelvic and dorsal surface, a lateral mass on each side, and a base and apex.
  •    An anesthetic for the spinal nerves may be injected extradurally through the sacral hiatus (caudal analgesia)
  •    The sacral canal (which contains the dura, cauda equina, and filum terminale) extends from the base to the sacral hiatus. 
  •    The apex of the sacrum may be fused with the coccyx.

  
  Coccygeal vertebrae

  •    Four to five modular pieces fused together
  •    Triangular shape with the base above and the apex below

  F Defects

  •    Lordosis-exaggerated lumbar concavity
  •    Scoliosis-lateral curvature of any region
  •    Kyphosis-exaggerated convexity in the thoracic region

The Lateral Pterygoid Muscle

• This is a short, thick muscle that has two heads or origin.
• It is a conical muscle with its apex pointing posteriorly.

• Origin: superior head—infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone, inferior head—lateral surface of lateral pterygoid plate.
• Insertion: neck of mandible, articular disc, and capsule of temporomandibular joint.
• Innervation: mandibular nerve via lateral pterygoid nerve from anterior trunk, which enters it deep surface.

• Acting together, these muscles protrude the mandible and depress the chin.
• Acting alone and alternately, they produce side-to-side movements of the mandible.

Connective Tissue

Functions of Connective tissue:

→ joins together other tissues

→ supporting framework for the body (bone)

→ fat stores energy

→ blood transports substances

Connective tissue is usually characterized by large amounts of extracellular materials that separate cells from each other, whereas epithelial tissue is mostly cells with very little extracellular material. The extracellular substance of connective tissue consists of protein fibers which are embedded in ground substance containing tissue fluid.

Fibers in connective tissue can be divided into three types:

→ Collagen fibers are the most abundant protein fibers in the body.

→ Elastic fibers are made of elastin and have the ability to recoil to original shape.

→ Reticular fibers are very fine collagen fibers that join connective tissues to other tissues.

Connective tissue cells are named according to their functions:

 → Blast cells produce the matrix of connective tissues

→ Cyte cells maintains the matrix of connective tissues

→ Clast cells breaks down the matrix for remodeling (found in bone)

The Articular Capsule

• The capsule of this joint is loose.
• The thin fibrous capsule is attached to the margins of the articular area on the temporal bone and around the neck of the mandible.

The Hard Palate

• The anterior bony part of the palate is formed by the palatine process of the maxillae and the horizontal plates of the palatine bones.

• Anteriorly and laterally, the hard palate is bounded by the alveolar processes and the gingivae.
• Posteriorly, the hard palate is continuous with the soft palate.

• The incisive foramen is the mouth of the incisive canal.
• This foramen is located posterior to the maxillary central incisor teeth.
• This foramen is the common opening for the right and left incisive canals.
• The incisive canal and foramen transmit the nasopalatine nerve and the terminal branches of the sphenopalatine artery.

• Medial to the third molar tooth, the greater palatine foramen pierces the lateral border of the bony palate.
• The greater palatine vessels and nerve emerge from this foramen and run anteriorly into two grooves on the palate.

• The lesser palatine foramen transmits the lesser palatine nerve and vessels.
• This runs to the soft palate and adjacent structures.

The Scalp

• The scalp consists of five layers of soft tissue.
• It extends from the superior nuchal line on the posterior aspect of the skull of the supraorbital margins.
• Laterally, the scalp extends into the temporal fossa to the level of the zygomatic arches.

Layers of the Scalp

• The scalp proper is composed of three fused layers. It is separated from the pericranium by loose connective tissue.
• Because of this potential areolar cleavage plane, the scalp is fairly mobile.
• Each letter of the word "S C A L P" serves as a memory key for one of the layers of the scalp: Skin, Connective Tissue, Aponeurosis Epicranialis, Loose Areolar Tissue and Pericranium.

Layer 1: Skin

• Hair covers the scalp in most people.
• The skin of the scalp is thin, especially in elderly people, except in the occipital region.
• The skin contains many sweat and sebaceous glands and hair follicles.
• The skin of the scalp has an abundant arterial supply and good venous and lymphatic drainage systems.

Layer 2: Connective Tissue

• This is a thick, subcutaneous layer of connective tissue and is richly vascularised and innervated.
• It attaches the skin to the third layer of the scalp.
• Fat is enclosed in lobules between the connective fibres.

Layer 3: Aponeurosis Epicranialis

• This is a strong membranous sheet that covers the superior aspect of the cranium.
• This aponeurosis is the membranous tendon of the fleshy bellies of the epicranius muscle.

• The epicranius muscle consists of four parts: two occipital bellies, occipitalis and two frontal bellies, frontalis that are connected by the epicranial aponeurosis. 

Layer 4: Loose Areolar Tissue

• This is a subaponeurotic layer or areolar or loose connective tissue.
• It is somewhat like a sponge because it contains innumerable potential spaces that are capable of being distended by fluid.
• It is this layer that allows free movement of the scalp proper, composed of layers 1-3.

Layer 5: Pericranium

• This is a dense layer of specialised connective tissue.
• The pericranium is firmly attached to the bones by connective tissue fibres called Sharpey’s fibres, however, they can be fairly easily stripped from the cranial bones of living persons, except where they are continuous with the fibrous tissues of the cranial sutures.