Exercise 23 & 24
General Sensation
&
Vision
Sensory Receptors
• Structures specialized to respond to
stimuli
• Activation of sensory receptors results in
depolarizations that trigger impulses to the
CNS
• The realization of these stimuli, sensation
and perception, occur in the brain
• Mechanoreceptors – respond to touch,
pressure, vibration, stretch, and itch
• Thermoreceptors – sensitive to changes in
temperature
• Photoreceptors – respond to light energy
(e.g., retina)
• Chemoreceptors – respond to chemicals
(e.g., smell, taste, changes in blood
chemistry)
• Nociceptors – sensitive to pain-causing
stimuli
Receptor Classification by Stimulus Type
Receptor Class by Location:
Exteroceptors
• Respond to stimuli arising outside the
body
• Found near the body surface
• Sensitive to touch, pressure, pain, and
temperature
• Include the special sense organs
Simple Receptors:
Unencapsulated
Table 13.1.1
Simple Receptors:
Encapsulated
Table 13.1.2
Simple Receptors:
Encapsulated
Table 13.1.3
Adaptation of Sensory
Receptors
• Adaptation occurs when sensory receptors
are subjected to an unchanging stimulus
– Receptor membranes become less
responsive
– Receptor potentials decline in frequency or
stop
Chemical Senses
• Chemical senses – gustation (taste) and
olfaction (smell)
• Their chemoreceptors respond to
chemicals in aqueous solution
– Taste – to substances dissolved in saliva
– Smell – to substances dissolved in fluids of
the nasal membranes
Eye and Associated Structures
• 70% of all sensory receptors are in the eye
• Most of the eye is protected by a cushion
of fat and the bony orbit
• Accessory structures include eyebrows,
eyelids, conjunctiva, lacrimal apparatus,
and extrinsic eye muscles
Palpebrae
(Eyelids)
Figure 15.5b
Extrinsic Eye Muscles
Figure 15.7a, b
Structure of the Eyeball
Figure 15.8a
Pupil Dilation and Constriction
Figure 15.9
Sensory
Tunic:
Retina
Figure 15.10a
Anterior Segment
Figure 15.12
Focusing for Distant Vision
• Light from a
distance needs
little adjustment
for proper
focusing
• Far point of
vision – the
distance
beyond which
the lens does
not need to
change shape
to focus (20 ft.)
Figure 15.17a
Focusing for Close Vision
Figure 15.7b
Problems of Refraction
Figure 15.18
Astigmatism
Visual Pathways
Figure 15.23
Terms
•
•
•
•
•
•
•
•
Accommodation
Emmetropia: normal vision
Myopia: near-sigthedness
Hyperopia: far-sightedness
Presbyopia: “old vision”
Glaucoma: intraocular pressure imbalance
Cataract: clouding of the lens
Conjunctivitis: inflammation of the
conjunctiva
The Retina
Retina