LESSON 13
THE SPECIAL SENSES
Section I. INTRODUCTION
13-1.
GENERAL VERSUS SPECIAL SENSES
a. The human body is continuously bombarded by all kinds of stimuli. Certain
of these stimuli are received by sense organs distributed throughout the entire body.
These are referred to as the general senses.
b. Certain other stimuli (table 13-1) are received by pairs of receptor organs
located in the head. These are the special senses.
SPECIAL SENSE
RECEPTOR ORGAN
STIMULUS
Sight (vision)
bulbus oculi (eye)
light rays
Hearing (audition)
ear (cochlea)
sound waves
ear (membranous labyrinth)
gravity
Smell (olfaction)
olfactory hair cells in nose
airborne molecules
Taste (gustation)
taste buds in mouth
fluid-borne molecules
Table 13-1. The special senses.
c. Since the general senses respond to immediate contact, they are very
short range. In contrast, the special senses are long range.
13-2.
INPUT TO BRAIN
From the special sense organs, information is sent to the brain through specific
cranial nerves. When this information reaches specific areas of the cerebral cortex, the
sensations are perceived at the conscious level.
Section II. THE SPECIAL SENSE OF VISION
13-3.
THE RETINA
Within the bulbus oculi (eyeball) is an inner layer called the retina. See Figure
13-1 for the location of the retina within the bulbus oculi. See Figure 13-2 for the types
of cells found within the retina.
MD0007
13-2