Special Senses

• Vision


  • Is the sense that has been studied the most
  • All of the receptors in the body, 70% are in the eyes
• Optic tracts


  • carry Information from eyes to the brain are massive bundles and contains over a million nerve fibers
  • the sense that requires the most "learning" and the eye appears to delight in being fooled
  • old expression "you see what you expect to see" is often very true
• Optic nerve


  Is the nerve bundle projecting from the posterior of the eyeball
• Optic chiasm or chiasma


  • Is the part of the brain where the optic nerves cross and is therefore of primary Importance to the visual pathway
  • Located at the base of the brain Inferior to the hypothalamus, and approximately 10mm superior to pituitary gland
• Eye


  • Is a sphere in shape measures 1 inch (2.5cm) in diameter
  • Anterior one sixth of the eye's surface can normally be seen. The rest of it is enclosed and protected by a cushion of FAT and BONY orbit
• Eyelids


  for protection, which meet the medial and lateral corners of the eye (medial and lateral canthus)
• Eyelashes


  projecting from the border of the eyelids.
• Tarsal glands


  modified sebaceous glands associated with the eyelid edges. It produce an oily secretion that lubricates the eye
• Ciliary Glands


  modified sweat glands, lie between the eyelashes
• Conjunctiva


  covers the outer surface of the eyeball. It secretes mucus, which helps to lubricate the eyeball and keep it moist.
• Lacrimal apparatus


  consists of lacrimal gland and a number of ducts that drain the lacrimal secretions into nasal cavity
• Lacrimal glands


  located above the lateral end of each eye. Exocrine tear gland in the superior lateral corner of the orbit.
• Nasolacrimal duct - duct in the Inferior medial corner of the orbit, drains tears from lacrimal canaliculi toward the nasal cavity
• Internal structure of the Eye

  1. Eyeball - eye itself commonly called as? It is also composed of three tunics or coats.
  2. Humors - fluid-filled, help to maintain its shape
  3. Lens - main focusing apparatus of the eye
• What are the three tunics or coats of the eye?

  1. Fibrous tunic
  2. Vascular tunic
  3. Neural/Nervous tunic
• Fibrous tunic


  the outer coat of the eye
• Cornea


  anterior transparent portion of the eye
• Sclera


  is the white fibrous portion
• Vascular tunic


  middle coat of the eye
• Choroid


  posterior portion is thin
• Ciliary 


  (circular body) anterior portion of the eye
• Iris


  attached to anterior edge of ciliary, which has an opening called pupil
• Neural/Nervous tunic


  inner coat of the eye
• Retina


  outer pigmented retina & Inner sensory retina (contains photoreceptor cells called: rods & cones
• Ear is divided into three major areas:

  1. Outer - external hearing
  2. Inner - hearing
  3. Middle - Internal equilibrium
• Outer (External Ear)


  Pinna or Auricle - shell shaped structure surrounding the auditory canal opening
• External Auditory canal or External Acoustic Meatus


  short narrow chamber ( 1 inch long by 1/4 inch wide).
• Ceruminous Glands 


  secrete waxy yellow substance called earwax or cerumen
• Tympanic membrane or Eardrum


  cause to vibrate
• Middle ear


  small, air-filled cavity within the temporal bone.
• Middle ear is composed of 3 bones what are those?

  1. Hammer (malleus)
  2. Anvil (Incus)
  3. Stirrup (Stapes)
• Hammer (malleus)

  when the eardrum moves the malleus moves with it
• Anvil (incus)


  It transfers and vibrates the sound passes to
• Stirrup (stapes)


  presses on the inner ear
• Inner (Internal ear)


  maze of bony chambers called the osseous or bony labyrinth.
• what are the 3 subdivisions of the bony labyrinth?

  1. Cochlea
  2. Vestibule
  3. Semicircular canal
• Taste and Smell

  Chemoreceptors - receptors for taste and olfaction (smell) because they respond to chemical in solution
• Sense of Smell

  Nasal Cavity - thousands of olfactory receptors. Occupy a postage stamp sized area in the roof of each nasal cavity
• Taste

  comes from Latin word "taxare" which means to "to touch, estimate, or judge"
• Taste Buds


  sense of taste, are widely scattered in the oral cavity. 10,000 or so taste buds that we have, located on the tongue.