Unit 20: Special Senses

Question 1

What is the eye?

Answer 1

= a 3 layered sphere filled with liquid

Question 2

What are the 6 structural features of the eye?

Answer 2

Fibrous Tunic, Vascular Tunic, Nervous (Sensory) Tunic = retina, Lens, Anterior Segment, and Posterior Segment.

Question 3

Info about the Fibrous Tunic

Answer 3

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 4

Info about the Vascular Tunic

Answer 4

Parts:
a) choroid (posterior) = highly vascular; contains melanin
b) ciliary body (anterior) = ciliary muscle and ciliary processes - focus the lens
c) iris = coloured part of eye
d) pupil = hole in iris

Question 5

Info about the nervous (sensory) tunic = retina

Answer 5

Parts:
a) outer pigmented layer
b) inner neural layer - 3 layers of neurons:
i. Photoreceptors (2 types = rods [black/white] and cones
[colour])
ii. Bipolar cells
iii. Ganglion Cells = axons from 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 and optic nerve exit eye - no rods or cones

Question 6

Info about the lens

Answer 6

• avascular, transparent

Question 7

Info about the Anterior Segment

Answer 7

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

Question 8

Info about posterior segment

Answer 8

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

Question 9

What are the main structural features of the ear?

Answer 9

External ear, middle ear, inner ear (labyrinth), cochlea, and receptors in inner ear.

Question 10

Info about the external ear

Answer 10

Conducts sound - parts:
a) auricle (pinna) = elastic cartilage, covered w/ skin
b) external auditory canal (meatus)
c) tympanic membrane (eardrum)

Question 11

Info about the middle ear

Answer 11

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

Question 12

Info about the inner ear (labyrinth)

Answer 12

Converts sound vibrations into nerve signals for hearing, also functions in maintaining balance (equilibrium). Parts:
a) bony labyrinth = tunnels in temporal bone (contain
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 duct= inside canals
ii. utricle and saccule = inside vestibule
iii. cochlear duct = inside cochlea

Question 13

Info about the cochlea

Answer 13

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 = btw. cochlear duct and scala
vestibuli
b) basilar membrane = btw. cochlear duct and scala tympani
c) tectorial membrane = covers hair cells (= receptor cells)

Question 14

Info about receptors in inner ear

Answer 14

• called hair cells that synapse w/ neurons - send impulses to
  brain via cranial nerve VIII
• hairs are cilia that extend into endolymph change
  endolymph to cochlear duct if making the changes
  suggested above - tips of cilia embedded in tectorial
  membrane (stability)

Question 15

What are the related medical conditions to the ear?

Answer 15

• Cataracts = clouding of the lens
• Otitis media = inflammation of the middle ear (i.e. ear
  infection)
  
  • common in infants and children b/c their
    pharyngotympanic tubes (Eustachian tubes) are shorter
    and more easily blocked than in adults