General Sensation Vision Sensory Receptors Structures specialized to

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General Sensation & Vision

General Sensation & Vision

Sensory Receptors • Structures specialized to respond to stimuli • Activation of sensory receptors

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

• 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 •

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: Unencapsulated Table 13. 1. 1

Simple Receptors: Encapsulated Table 13. 1. 2

Simple Receptors: Encapsulated Table 13. 1. 2

Simple Receptors: Encapsulated Table 13. 1. 3

Simple Receptors: Encapsulated Table 13. 1. 3

Adaptation of Sensory Receptors • Adaptation occurs when sensory receptors are subjected to an

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

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

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. 5 b

Palpebrae (Eyelids) Figure 15. 5 b

Extrinsic Eye Muscles Figure 15. 7 a, b

Extrinsic Eye Muscles Figure 15. 7 a, b

Structure of the Eyeball Figure 15. 8 a

Structure of the Eyeball Figure 15. 8 a

Pupil Dilation and Constriction Figure 15. 9

Pupil Dilation and Constriction Figure 15. 9

Sensory Tunic: Retina Figure 15. 10 a

Sensory Tunic: Retina Figure 15. 10 a

Anterior Segment Figure 15. 12

Anterior Segment Figure 15. 12

Focusing for Distant Vision • Light from a distance needs little adjustment for proper

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. 17 a

Focusing for Close Vision Figure 15. 7 b

Focusing for Close Vision Figure 15. 7 b

Problems of Refraction Figure 15. 18

Problems of Refraction Figure 15. 18

Visual Pathways Figure 15. 23

Visual Pathways Figure 15. 23

Terms • • Accommodation Emmetropia: normal vision Myopia: near-sigthedness Hyperopia: far-sightedness Presbyopia: “old vision”

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

The Retina