2. Chapter 9
The Senses

3. Classification of the Sense Organs
General sense organs
Often exist as individual cells or receptor units
Widely distributed throughout the body
Special sense organs
Large and complex organs
Localized grouping of specialized receptors
(Cont’d…)

4. Classification of the Sense Organs
(…Cont’d)
Classification by presence or absence of covering capsule
Encapsulated
Unencapsulated (“free” or “naked”)
(Cont’d…)

5. Classification of the Sense Organs
(…Cont’d)
Classification by type of stimuli required to activate receptors
Photoreceptors (light)
Chemoreceptors (chemicals)
Pain receptors (injury)
Thermoreceptors (temperature changes)
Mechanoreceptors (movement or deforming of capsule)
Proprioceptors (position of body parts or changes in muscle length or tension)

6. Converting a Stimulus into a Sensation
All sense organs have common functional characteristics
All are able to detect a particular stimulus
A stimulus is converted into a nerve impulse
A nerve is perceived as a sensation in the CNS

7. General Sense Organs Free nerve endings: pain and crude touch
Meissner’s corpuscles: fine touch and vibration
Ruffini’s corpuscles: pressure and vibration
Krause’s end-bulbs: touch
Golgi tendon receptors: proprioception
Muscle spindles: proprioception

8. General Sense Organs
Distribution is widespread; single-cell receptors are common
Examples
Free nerve endings—pain and crude touch
Meissner’s corpuscles—fine touch and vibration
Ruffini’s corpuscles—pressure and vibration
Krause’s end-bulbs—touch
Golgi tendon receptors—proprioception
Muscle spindles—proprioception

9. Special Sense Organs

10. Special Sense Organs The eyeball Layers of the eyeball
Sclera—tough outer coat; “white” of eye; cornea is transparent part of the sclera over the iris
Choroid—pigmented vascular layer prevents scattering of light; from part of this layer made of ciliary muscle and iris; the colored part of the eye; the pupil is the hole in the center of the iris; contraction of iris muscle dilates or constricts pupil
Retina—innermost layer of the eye; contains rods (receptors for night vision) and cones (receptors for day vision and color vision)
(Cont’d…)

11. Special Sense Organs
(…Cont’d)
Conjunctiva—mucous membrane covering the front surface of the sclera and lining the eyelid
Lens—transparent body behind the pupil; focuses light rays on the retina
Ciliary muscles relaxed let you see far away. Contracted they pull on choroid layer and cause a bulge in the lens
Eye fluids
Aqueous humor—in the anterior chamber in front of the lens
Vitreous humor—in the posterior chamber behind the lens
(Cont’d…)

13. Retinal Receptors Rods- Dim light, black and white vision
Cones- Color vision (3 types) Red, Green, and Blue

14. Vision issues
Glaucoma- pressure in the eye because of aqueous drainage issues
Cataracts- over exposure to UV light clouds the cornea

15. Special Sense Organs Visual pathway
(…Cont’d)
Visual pathway
Innermost layer of retina contains rods and cones
Impulse travel from the rods and cones through the bipolar and ganglionic layers of retina
Nerve impulse leaves the eye through the optic nerve; the point of exit is free of receptors and is therefore called a blind spot
Visual interpretation occurs in the visual cortex of the cerebrum
(Cont’d…)

16. Special Sense Organs The ear
(…Cont’d)
The ear
The ear functions in hearing and in equilibrium and balance
Receptors for hearing and equilibrium are mechanoreceptors
(Cont’d…)

18. Special Sense Organs Divisions of the ear External ear Auricle (pinna)
External auditory canal
Curving canal 2.5 cm (1 inch) in length
Contains ceruminous glands
Ends at the tympanic membrane
(Cont’d…)

19. Special Sense Organs Middle ear
Houses ear ossicles—malleus, incus, and stapes
Ends in the oval window
The auditory (eustachian) tube connects the middle ear to the throat
Inflammation called otitis media
(Cont’d…)

20. Special Sense Organs Inner ear Bony labyrinth filled with perilymph
(…Cont’d)
Inner ear
Bony labyrinth filled with perilymph
Subdivided into the vestibule, semicircular canals, and cochlea
Membranous labyrinth filled with endolymph
The receptors for balance in the semicircular canals are called cristae ampullaris
Specialized hair cells on the organ of Corti respond when bent by the movement of surrounding endolymph set in motion by sound waves
(Cont’d…)

23. Special Sense Organs The taste receptors
(…Cont’d)
The taste receptors
Receptors are chemoreceptors called taste buds
Cranial nerves VII and IX carry gustatory impulses
Six kinds of “primary” taste sensations—sweet, sour, bitter, salty, metallic, and umami
Gustatory and olfactory sense work together
(Cont’d…)

24. Special Sense Organs The smell receptors
(…Cont’d)
The smell receptors
Receptors for fibers of olfactory or cranial nerve I lie in olfactory mucosa of nasal cavity
Olfactory receptors are extremely sensitive but easily fatigued
Odor-causing chemicals initiate a nervous signal that is interpreted as a specific odor by the brain

28. The End