Topic 20 -Special senses

Question 1

Eye

6 special features

Answer 1

3 layered sphere filled with fluid 
Fibrous tunic 
Vascular tunic 
Nervous (sensory) tunic= retina 
Lens
Anterior segment 
posterior segment

Question 2

Eye: fibrous tunic (3 parts)

Answer 2

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

Vascular tunic parts:

Answer 3

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 - hole in iris

Question 4

Nervous (sensory) tunic

parts:

Answer 4

=retina 
outer pigmented layer
inner neural layer
fovea centralis 
optic disc

Question 5

inner neural layer of nervous (sensory) tunic

Answer 5

• 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)

Question 6

fovea centralis from nervous (sensory) tunic

Answer 6

• where light is focused when looking directly at an object = area of greatest visual acuity
• no rods, just cones

Question 7

optic disc of Nervous (sensory) tunic

Answer 7

• blind spot where blood vessels + optic nerve exit eye

- no rods or cones

Question 8

lens

Answer 8

• avascular, transparent

- cataracts = clouding of lens

Question 9

anterior segment

Answer 9

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

Question 10

Posterior segment

Answer 10

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

Question 11

structural features of the ear

Answer 11

External ear
Middle ear 
Inner ear 
Cochlea 
Receptors in inner ear

Question 12

External ear

Answer 12

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

Question 13

Middle ear

Answer 13

• 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 14

Inner Ear (labyrinth)

Answer 14

• detects sound, involved with equilibrium
  parts:
  bony labyrinth
  membranous labyrinth

Question 15

bony labyrinth

Answer 15

• tunnels in temporal bone
• contains perilymph
• parts:
  i) semicircular canals
• equilibrium
  ii) vestibule
• equilibrium
  iii) cochlea
• hearing

Question 16

membranous labyrinth

Answer 16

• 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 17

Cochlea

3 channels

Answer 17

coiled

a) scala vestibuli
- upper; perilymph
b) scala tympani
- lower; perilymph
c) cochlear duct
- middle; endolymph

Question 18

membranes of cochlea

Answer 18

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 19

Receptors in inner ear

Answer 19

• 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)