chapter 20 - special senses

fibrous tunic

outermost portion of the eye that consists of sclera, cornea, and conjunctiva

sclera

white of the eye

cornea

transparent portion of the eye

conjunctiva

vascular mucous membrane that covers the anterior surface of the sclera

vascular tunic

portion of the eye that contains blood vessels and connective tissue, consists of:

1. iris

2. choroid

3. ciliary body

iris

coloured part of the eye

choroid

highly vascular; contains melanin which prevents the reflection and scattering of light

ciliary body

consists of ciliary muscle and ciliary process, which control the shape of the lens and secrete aqueous humour

nervous tunic

the innermost portion of the eye made of nervous tissue, consists of:

1. retina

2. fovea centralis

3. optic disc

cells of the nervous tunic

1. photoreceptor neurons

   • rods = for black and white vision

   • cones = for coloured vision

2. bipolar cells

   • dont have action potential as normal neurons

3. ganglion cells

   • their axons form the optic nerve (cranial nerve II)

   • most neuron like

lens

transparent, avascular layer of the eye that is contracted by ciliary body

cataracts

a condition that occur when the lens become cloudy

anterior chamber

portion of the eye that is located anterior to the lens

• contains aqueous humour

  • very similar to blood plasma

  • replaced every 90 mins

    • drains into a sinus located @ junction between the sclera and cornea

posterior segment

portion of the eye that is located posterior to the lens

• contains gel-like vitreous humour

  • not replaced

external ear

portion of the ear that functions to conduct sound and consists of:

1. auditory canal → meatus

2. tympanic membrane → eardrum

3. auricle → elastic cartilage covered in skin; pinna + helix

middle ear

portion of the ear that functions to conduct sound and consists of:

1. auditory ossicles

   a. malleus → against the tympanic membrane

   b. incus

   c. stapes → against the oval window

2. eustachian (auditory) tube

internal ear

portion of the ear that functions in hearing and equilibrium and consists of:

1. vestibular nerve

2. bony labyrinth

3. membranous labyrinth

bony labyrinth

portion of the inner that is lined with periosteum, filled with perilymph, and consists of:

1. semi-circular canals

2. cochlea

3. vestibule

membranous labyrinth

portion of the inner ear that is filled with endolymph, and consists of:

1. semi-circular ducts — within the canals; connect with the utricle

2. cochlear duct — within the cochlea

3. utricle and saccule — within the vestibule

channels of the cochlea

1. scala vestibuli — located above the cochlear duct

2. scala tympani — located below the cochlear duct

3. scala media — the cochlear duct

   • continuation of the membranous labyrinth — contains endolymph

   • vestibular membrane = separates the cochlear duct from the scala vestibuli

   • basilar membrane = separates the cochlear duct from the scala tympani

   • tectorial membrane = covers hair cells of the spiral organ

hair cells

receptors in the inner ear