20 - Special Senses

Question 1

What are the 6 parts of the eye?

Answer 1

Fibrous Tunic
Vascular Tunic
Nervous (Sensory) Tunic
Lens
Anterior Segment
Posterior Segment

Question 2

Describe the Fibrous Tunic

Answer 2

• parts:
  a) sclera (white)
  
  • avascular CT
    b) cornea (transparent)
  • avascular CT
    c) conjunctiva
  • covers anterior sclera
  • vascular mucous membrane
  • when vessels dilate = bloodshot eyes

Question 3

Describe the Vascular Tunic

Answer 3

• parts:
  a) choroid (posterior)
  
  • contains melanin
  • highly vascular
    b) ciliary body (anterior)
  • ciliary muscle + ciliary processes – focus the lens
    c) iris
  • coloured part of eye
    d) pupil
  • opening in iris

Question 4

Describe the Nervous Tunic

Answer 4

• parts:
  a) outer pigmented layer
  b) inner neural layer
  
  • 3 layers of neurons
    i) photoreceptors (2 types)
    ① rods – black +white
    ② cones - colour
    ii) bipolar cells
    iii) ganglion cells
    
    • axons form optic nerve (cranial nerve II)
      c) fovea centralis
  • where light is focused
    = area of greatest visual acuity
  • no rods, just cones
    d) optic disc
  • blind spot where blood vessels + optic nerve exit eye
  • no rods or cones

Question 5

Describe the lens

Answer 5

• avascular, transparent

- cataracts = clouding of lens

Question 6

Describe the anterior segment

Answer 6

• anterior to lens
• contains aqueous humor
  
  • fluid similar to plasma

Question 7

Describe the posterior segment

Answer 7

• posterior to lens
• contains vitreous humor
  
  • gel-like

Question 8

What are the 5 structural parts of the ear?

Answer 8

External Ear
Middle Ear
Inner Ear (Labyrinth)
Cochlea
Receptors in the Inner Ear

Question 9

Describe the External Ear

Answer 9

• conducts sound
• parts:
  a) auricle (pinna)
  
  • elastic cartilage, covered with skin
    b) external auditory (acoustic) canal (meatus)
    c) tympanic membrane (eardrum)

Question 10

Describe the Middle Ear

Answer 10

• conducts sound
• parts:
  a) Eustachian tube
  
  • also called pharyngotympanic tube
    b) ear ossicles
    i) malleus
    
    • secured to tympanic membrane
      ii) incus
      iii) stapes
    • transmits sound to inner ear via oval window

Question 11

Describe the Inner Ear

Answer 11

• detects sound, involved with equilibrium
• parts
  a) bony labyrinth
  
  • tunnels in temporal bone
  • contains perilymph
  • parts:
    i) semicircular canals
    - equilibrium
    ii) vestibule
    - equilibrium
    iii) cochlea
    - hearing
    b) membranous labyrinth
  • surrounded and protected by bony labyrinth
  • contains endolymph
  • parts:
    i) semicircular ducts
    - inside canals
    ii) utricle + saccule
    - inside vestibule
    iii) cochlear duct
    - inside cochlea

Question 12

Describe the choclea

Answer 12

• coiled
• each coil has 3 channels:
  a) scala vestibuli
  
  • upper; perilymph
    b) scala tympani
  • lower; perilymph
    c) cochlear duct
  • middle; endolymph
• membranes
  a) vestibular membrane
  
  • between cochlear duct + scala vestibuli
    b) basilar membrane
  • between cochlear duct + scala tympani
    c) tectorial membrane
  • covers hair cells (= receptor cells)

Question 13

Describe the receptors in the inner ear.

Answer 13

• hair cell that synapses with an associated neuron
• send impulses to brain via cranial nerve VIII
• hairs = cilia that extend into endolymph
• tips of cilia embedded in tectorial membrane (stability)