This document summarizes the structures and functions of the eye and ear. It describes the three layers that make up the eyeball - the sclera, choroid, and retina. It also discusses the role of the eyelids, conjunctiva, lacrimal apparatus and eye muscles. For the ear, it outlines the external, middle and inner sections and describes the auditory canal, eardrum, ossicles, cochlea and semicircular canals. It provides diagrams of both organs and explains the path that light and sound take to stimulate the retina and cochlea's hair cells to initiate vision and hearing.

1. Chapter 13
Special Senses: The Eye and Ear

2. The Eye
Contains the sensory receptor cell for vision
The eyeball is the organ of sight that transmits an
external image by the way of the nervous system- optic
nerve-to the brain.
Other structures that play a role in vision:
eye muscles
eyelids
conjunctiva
lacrimal apparatus
The study of the eye is known as ophthalmology.

3. Eye Figure
The internal structures of the eye.

4. The Eyeball
The eyeball is composed of 3 layers:
sclera: Outer “white” layer; tough protective
coating for the inner structures of the eye.
cornea: anterior, transparent portion of sclera
which allows light to enter; bends/refracts light
rays
choroid: Middle, opaque layer that provides the
blood supply for the eye
iris: colored portion which contains smooth
muscle; muscles change the size of pupil, thereby
controlling how much light enters
pupil:opening in the center of the iris that
allows light rays to enter the interior of the
eyeball
ciliary body: intraocular eye muscles that change
the shape of the lens

5. The Eyeball (cont.)
Retina:The 3rd and innermost layer of the eyeball.
Contains rods and cones
macula lutea (yellow spot)
fovea centralis: depression within macula
lutea which is the point of clearest vision
optic disk: lacks sensory receptors and causes a
blind spot in each eye’s field of vision
aqueous humor: watery-fluid space between cornea
and lens
vitreous humor: semisolid gel large open area
between the lens and the retina

6. Eye Muscles
6 muscles connect the eyeball to the skull
4 rectus-- pull the eye up, down, left and right;
2 oblique muscles--produce diagonal eye movement

7. The Eyelids
A pair of eyelids over each eyeball provides protection
from foreign particles, injury from intense light, and
trauma.
Both upper and lower edges of the eyelids have
eyelashes or cilia that protect the eye from foreign
particles.
Sebaceous glands secrete lubricating oil onto the
eyeball

8. Conjunctiva
The mucous membrane lining that forms a continuous
covering on the underside of each eyelid and across the
anterior surface of each eyeball.
Serves as protection for the eye by sealing of the
eyeball in the socket.

9. Lacrimal Apparatus
The lacrimal gland is located under the outer upper
corner of each eyelid.
Glands produce tears. Tears function of washing and
lubricating the anterior surface of the eyeball.
Lacrimal ducts are located in the inner eye socket and
collect tears and drain them into the nasolacrimal
duct, which ultimately drains tears into the nasal
cavity.

10. The Path of Vision
When light rays strike the eye, the pass:
cornea--> pupil-->aqueous humor--> lens-->vitreous
humor-->retina (rods and cones)
When light rays hit the retina, and upside-down
image is sent nerve impulses to the optic nerve,
which are sent to the brain, where the upside-down
image is translated into the right-side up image we
see.
Vision requires:
coordination of external eye muscles so that both
eyes move together
correct amount of light admitted by the pupil
correct focus of light on the retina by the lens
optic nerve transmitting sensory images to the brain

11. The Ear
Contains the sensory receptors for hearing and
equilibrium (balance)
Hearing and equilibrium sensory information is carried
to the brain by the vestibulocochlear (cranial) nerve.
The ear is subdivided into 3 areas:
external ear
middle ear
inner ear
The study of the ear is referred to as otology, and the
study of hearing disorders is called audiology.

12. Ear Figure
The internal structures of the ear.

13. External Ear
Consist of 3 parts:
auricle: also known as the pinna; referred to as
“the ear” because this is the only visible portion;
earlobe functions like a funnel to capture sound
waves as they pass the outer ear and channel
through the external auditory meatus
auditory canal: canal that leads from exterior
opening of the ear to the eardrum
ear wax or cerumen is produced within the
auditory canal to help protect and lubricate the
ear
tympanic membrane: eardrum; as sound moves along
auditory canal, it strike the membrane causing it
to vibrate; this conducts the sound into the middle
ear

14. Middle Ear
Located in a small cavity in the temporal bone of the
skull
Air-filled cavity that contains 3 tiny bones called
ossicles that are vital for the hearing process:
malleus:also known as the hammer
incus:also known as the anvil
stapes:also known as the stirrup; last of the
ossicles that is attached to a very thin membrane
that covers the opening to the inner ear called the
oval window
The eustachian tube or auditory tube connects the
nasopharynx with the middle ear. Each time one swallows
the tube opens; this connection allows pressure to
equalize between the middle ear cavity and atmospheric
pressure.

15. Inner Ear
Located in a cavity within the temporal bone
Fluid-filled cavity is referred to as the labyrinth
Contains the hearing and equilibrium sensory organs
that contain hair cells (sensory receptors):
cochlea (hearing): hair cells referred to as organs
of Corti
semicircular canals (equilibrium)
utricle (equilibrium)
saccule (equilibrium)

16. The Path of Sound
Sound waves travel down the external auditory canal
strike the eardrum, causing it to vibrate.
The ossicles conduct these vibrations across the middle
ear from the eardrum to the oval window.
Oval window movements initiate vibrations in the fluid
that fills the cochlea.
As fluid vibrations strike a hair cell, they bend the
small hairs and stimulate the nerve ending, which then
sends an electrical impulse to the brain on the
cochlear portion of the vestibulocochlear nerve.