Histology of Sensory organs in a Nutshell

Histology of Sensory Organs

•  Eye
  • Important parts

1. 1. • Cornea
      • Iris
      • Vitrous body

• • • Retina

1. • 3 wall globe:  outer for support, middle for nutrition, inner for
   • Tunica fibrosa- cornea and sclera.  Outer layer

• • • Cornea- low hydration level
      1. Layers (five)
         1. Outer epithelial
            1. Several cells thick. Straight cells.  Have a germinative layer.  Rapidly generating.  Contacts the outer world.  Connected by tight jxns.  Vast number of unmyelenated nerve fibers to detect pain.
      2. Bowmann’s membrane- protection
         1. Serves as a barrier
      3. Stroma membrane
      4. Endothelial with thicked descanne’s basement layer
         1. 2/3 of focusing power
         2. Aqueous humor gives nutrition to cornea. Does this very selective way (water not allowed in).  An active process needing energy.
      5. Sclera
         1. Mostly connective tissue to keep its shape

1. • Uveal- nutritive layer.  Vascular

• • • Iris
      1. Circumferential that opens at pupil.
         1. Contraction of iris controls light amount
            1. Circular Sphincter papilla
            2. Radially dilator muscles
    • Anterior limiting layer faces anterior chamber
      1. Followed by stroma layer and pigmented epithelium
      2. In stroma are malanocytes that produce light absorbing pigments. Amount determines color of light.
      3. Pigmented layer continues all the the way back to posterior of eye
    • Ciliary body
      1. Regulates shape of lens
      2. Have zonules of zin that suspend the lens with ciliary processes
      3. Contraction of ciliary body allows relaxation of zonules of zin and lens rounds up for near vision
      4. Normally, a natural tension pulls lens flat to accommodate for distal vision
      5. Double layer of cuboidal cells in a head-to head arrangement with a lighter pigment layer on surface and darker layer immediately adjacent (zonules attached to basement membrane
      6. Ciliary body forms the blood/eye barrier to select certain nutrients
      7. Aquous humor released into posterior chamber and goes into anterior chamber. Then it drains into iridiocorneal angle and filtered by microtrabecular meshwork and into the canal of schlemm (drains into venous circulation)
         1. Constant intraocular pressure to maintain shape of eyeball and apply pressure within the eye (glaucoma is involved if pressure is too great. Due to closure of canal of schlemm.)

• Choroid
  • Suprechoroid layer
  • Vessal layer
  • Choriocapillaris layer- source of nutrition of first third of retinal layer (innerportion feed by vessals in retinal artery that enter with optic nerve)
  • Bruch’s (glassy membrane)- serves as a basement membrane. A barrier to prevent access to retina

• Retina-Know the order only 1-10
  • Retinal coat is inserted backwards
  • Light passes 9 layers before hitting first photosensitive layer
    • Retinal pigment epithelium-support cells. Send out processes to cradle outer layers of photoreceptors.  Phagocytic of pieces of photoreceptors.
    • Photoreceptor layer (rods and cones) make up next three layers
      1. Outer segment of rods and cones
      2. Outer nuclear layer- have nuclii of rods and cones. Contact bipolar
    • Plexiform layer
    • Inner nuclear layer- no cell bodies
    • Output cells (ie the ganglion cell layer)
    • Anchoring point of Muller cells (internal limiting layer)
•  Ear
  • Know portions of the ear
  • Bony labyrinth have membranous labyrinth (cochlear duct)
  • Cross section of modiolus

1. 1. • Scali vestibule-has perilymph
      • Scali tympani- has perilymph

• • • Scali media- endolymph. Has vascular layer.  Roof is simple squamous called reissner’s membrane.  Floor is basilar membrane (has hair cells).  Know organ of corti (tunnel of corti, pillar cells, phalangeal cells on bottom.  Outer (exists in 3’s) and inner (exists as 1’s) in relation to bony modiolus

1. • Bending of stereocillia creates the sensation of sound
   • Phalangeal cells create wrappings around hair cells
   • Tectorial membrane normally is flat and have hair cells embedded
   • Vestibular apparatus- two systems for movement and position

1. • 1. Semicircular canals for movement. Expanded ampulla
   • Raised area cristae ampullaris with columnar cells.
   • On raised cristae ampullaris is a gelatinous cuppula.
   • depolarization is sent out of base of hair cells into scarpa’s ganglion to encode change in position. Sloshing of endolymph designed for detection of acceleration
   • In Vestibule: Utricle and saccule to detect static position in space.
     • Macula is a raised bump similar to the cristae ampullaris. Gelatinous membrane on hair cells with the otolithic membrane (with stones called otoliths).  Also detects a constant moving sensation (like the people mover).