The Cheeks

• The cheeks (L. buccae) form the lateral wall of the vestibule of the oral cavity.
• They have essentially the same structure as the lips with which they are continuous.

• The principal muscular component of the cheeks is the buccinator muscle.
• Superficial to the fascia covering this muscle is the buccal fatpad that gives cheeks their rounded contour, especially in infants.

• The lips and cheeks act as a functional unit (e.g. during sucking, blowing, eating, etc.).
• They act as an oral sphincter in pushing food from the vestibule to the oral cavity proper.
• The tongue and buccinator muscle keep the food between the molar teeth during chewing.

Sensory Nerves of the Cheeks

• These are branches of the maxillary and mandibular nerves.
• They supply the skin of the cheeks and the mucous membrane lining the cheeks.

•     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 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.

Muscles Around the Nose

The Nasalis Muscle

• This muscle consists of a transverse (compressor naris) and alar (dilator naris) parts.
• It is supplied by the buccal branch of the facial nerve.

The Skeleton of the Nose

• The immovable bridge of the nose, the superior bony part of the nose, consists of the nasal bones, the frontal processes of the maxillae, and the nasal part of the frontal bones.

• The movable cartilaginous part consists of five main cartilages and a few smaller ones.
• The U-shaped alar nasal cartilages are free and movable.
• They dilate and constrict the external nares when the muscles acting on the external nose contract.

The Nasal Cavities

• The nasal cavities are entered through the anterior nares or nostrils.
• They open into the nasopharynx through the choanae.

The Roof and Floor of the Nasal Cavity

• The roof is curved and narrow, except at the posterior end.

• The floor is wider than the roof.
• It is formed from the palatine process of the maxilla and the horizontal plate of the palatine bone.

The Walls of the Nasal Cavity

• The medial wall is formed by the nasal septum; it is usually smooth.

• The lateral wall is uneven owing to the three longitudinal, scroll-shaped elevations, called the conchae (L. shells) or turbinates (L. shaped like a top).
• These elevations are called the superior, middle and inferior conchae according to their position.

• The superior and middle conchae are parts of the ethmoid bone, whereas the inferior conchae are separate bones.

• The inferior and middle conchae project medially and inferiorly, producing air passageways called the inferior and middle meatus (L. passage). Note: the plural of "meatus" is the same as the singular.
• The short superior conchae conceal the superior meatus.
• The space posterosuperior to the superior concha is called the sphenoethmoidal recess.

-> This bone forms much of the base and posterior aspect of the skull.
-> It has a large opening called the foramen magnum, through which the cranial cavity communicates with the vertebral canal.
-> It is also where the spinal cord becomes continuous with the medulla (oblongata) of the brain stem.
-> The occipital bone is saucer-shaped and can be divided into four parts: a squamous part (squama), a basilar part (basioccipital part), and two lateral parts (condylar parts).
-> These four parts develop separately around the foramen magnum and unite at about the age of 6 years to form one bone.
-> On the inferior surfaces of the lateral parts of the occipital bone are occipital condyles, where the skull articulates with C1 vertebra (the atlas) at the atlanto-occipital joints.
-> The internal aspect of the squamous part of the occipital bone is divided into four fossae: the superior two for the occipital poles of the cerebral hemispheres, and the inferior two, called cerebellar fossae, for the cerebellar hemispheres.