C.A.B.M. | 2024
1
Introduction to Special Senses
Special senses include five key sensory modalities:
• Smell (Olfaction) – detects airborne chemicals.
• Taste (Gustation) – detects chemicals in food
and liquids.
• Sight (Vision) – perceives light and images.
• Hearing (Audition) – perceives sound waves.
• Equilibrium (Balance) – detects body position
and movement.
These senses involve large, complex sensory
organs or localized clusters of receptors that
process sensory input and send information to the
brain for interpretation.
Part I: The Eye and Vision (Sight)
Overview of Vision
• 70% of all sensory receptors are located in
the eyes.
• Each eye contains over 1 million nerve
fibers, transmitting information to the brain.
1. Anatomy of the Eye
The eye is composed of accessory structures and internal
structures.
A. Accessory Structures
1. Eyelids:
• Protect the eye from debris and light.
• Meet at the medial and lateral commissures
(corners of the eye).
• Contain tarsal glands, which secrete an oily
substance to prevent eyelids from sticking
and lubricate the eye.
2. Eyelashes:
o Contain two types of glands:
▪ Tarsal glands: Produce an oily
secretion to lubricate the eye.
▪ Ciliary glands: Located
between the eyelashes, also
aiding in lubrication.
3. Conjunctiva:
o A thin, transparent membrane that:
▪ Lines the eyelids and covers
the sclera (white of the eye).
▪ Secretes mucus to keep the
eye moist and lubricated.
4. Lacrimal Apparatus:
o Composed of (lacrimal gland +
ducts):
▪ Lacrimal gland (produces
tears) located at the lateral
end of each eye.
▪ Lacrimal canals that drain
tears into the nasolacrimal
duct, which empties into the
nasal cavity.
o Tears contain:
▪ Dilute salt solution.
▪ Mucus.
▪ Antibodies.
▪ Lysozyme: An enzyme that
destroys bacteria, protecting
the eye.
5. Extrinsic Eye Muscles:
o Six muscles that attach to the outer
surface of the eyeball.
