Exercise 23 & 24 General Sensation & Vision. Sensory Receptors Structures specialized to respond to...
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Transcript of Exercise 23 & 24 General Sensation & Vision. Sensory Receptors Structures specialized to respond to...
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
Receptor Classification by Stimulus Type
• 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 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 SegmentFigure 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 RefractionFigure 15.18
Astigmatism
Visual PathwaysFigure 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