Special Senses: Vision Text: Chapter 22 - Napa Valley College

Biology 218 – Human Anatomy Clemens

Special Senses: Vision Text: Chapter 22

Eye - functions to receive and focus light
- sensory receptors of the retina transduce light energy into neural signals

A. Accessory Structures of the Eye
eyelid
tarsal plate - supports eyelid
conjunctiva - mucous membrane, covers anterior eyeball and inner eyelid
lacrimal apparatus - lacrimal glands + ducts
extrinsic eye muscles

B. Anatomy of the Eyeball
3 tunics:

1. fibrous tunic
a. cornea - transparent; admits and focuses light
b. sclera - opaque (white); supports and protects eyeball

2. vascular tunic
a. choroid - highly vascular, lines inner surface of sclera
b. ciliary body
ciliary process - secretes aqueous humor
ciliary muscle - attaches via zonular fibers (suspensory ligament) to lens
c. iris - smooth muscle (circular and radial) controls opening = pupil

lens - in anterior cavity of eyeball behind iris
- “fine focuses” image on retina
- change in tension of zonular fibers changes curvature of lens

3. retina (sensory tunic)
a. pigmented layer (epithelium)
b. photoreceptor layer - sensory receptor cells: rods and cones
macula lutea
fovea centralis - concentration of cones → high visual acuity and color vision
c. bipolar cell layer - neurons involved in visual processing
d. ganglion cell layer - primary sensory neurons; axons converge at optic disc,
→ optic nerve (II)

C. Interior of the Eyeball

1. anterior cavity - in front of lens; contains aqueous humor

a. anterior chamber - between cornea and iris

b. posterior chamber - behind iris, bordered by ciliary process
circulation of aqueous humor: ciliary process → posterior chamber → anterior chamber
→ scleral venous sinus

2. vitreous chamber - between lens and retina; contains vitreous humor

Biology 218 – Human Anatomy Clemens

Special Senses: Hearing & Equilibrium Text: Chapter 22 (part)

Functions of the Ear:
hearing - sound reception and transduction
equilibrium - sense of position and acceleration

A. External Ear
auricle (pinna)
external auditory canal
tympanic membrane (eardrum)
ceruminous glands

B. Middle Ear
air-filled cavity
3 auditory ossicles: malleus, incus, stapes
auditory tube (eustacian tube) - connects to pharynx
tensor tympani and stapedius muscles

C. Internal (Inner) Ear

bony labyrinth - internal cavities in temporal bone
- contains perilymph (similar to CSF)

membranous labyrinth - sacs and ducts inside the bony labyrinth
- contains endolymph (high K+ concentration)

hair cells - sensory receptor cells for hearing and equilibrium
- stereocilia on plasma membrane detect motion and vibration

1. Auditory System (Hearing)
a. cochlea [bony labyrinth]
oval window - transmits sound vibrations from stapes to fluid in bony labyrinth
scala vestibuli
scala tympani
round window - releases fluid pressure
cochlear duct (scala media) [membranous labyrinth]
vestibular membrane
basilar membrane
spiral organ (organ or Corti) - contains hair cells
tectorial membrane - rests on hair cells, vibrations bend stereocilia
innervation: cochlear branch of vestibulocochlear nerve (VIII)

2. Vestibular System (Equilibrium)
a. vestibule [bony labyrinth]
saccule and utricle [membranous labyrinth]
–> sense vertical/horizontal position and linear motion
macula - contains hair cells and supporting cells
otoliths - CaCO3 crystals, bend stereocilia of hair cells
b. semicircular canals [bony labyrinth]: anterior, posterior, lateral
semicircular ducts [membranous labyrinth]
–> sense rotational motion in 3 dimensions
ampulla - contains hair cells
cupula - gelatinous “sail”, bends stereocilia of hair cells
innervation: vestibular branch of vestibulocochlear nerve (VIII)

Biology 218 – Human Anatomy Clemens

Study Questions
A. Eye

1. Name the three tunics of the eye and list the major structures found in each tunic.
2. What are the functions of the cornea and the lens?
3. Identify the three main cell layers in the retina.
4. What are the two types of photoreceptor cells of the eye? What specific structure in the
retina contains the most sensory cells (per unit area) and what type of cells are these?
5. What is the optic disk?
6. Which cranial nerve carries visual information from the eye to the brain?
7. What is contained in the anterior cavity of the eye? What is contained in the vitreous
chamber of the eye?

B. Ear

1. Name the three parts of the ear and list their main components. How are these parts
of the ear related to the temporal bone?

2. Name the three ear ossicles from lateral to medial. What structure transmits sound
vibrations from the external ear to the first ear ossicle? Where does the innermost
ossicle transmit vibrations to the inner ear?

3. What are the sensory cells of the inner ear? What are the processes of these cells
that detect vibration or motion?

4. What parts of the inner ear are involved in hearing? What parts of the inner ear
function in the equilibrium (vestibular) system?

5. Which cranial nerve carries sensory information from the inner ear to the brain?

6. What is the bony labyrinth and what are its subdivisions? What fluid is contained in
the bony labyrinth?

7. What is the membranous labyrinth and what are its subdivisions? What fluid is
contained in the membranous labyrinth?

8. What is the sensory function of the saccule and utricle? What is the sensory function
of the semicircular ducts?