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