1. The Special Senses
Chapter 15

2. Unit Objectives
Classify Sense organs as special or general and explain the basic differences between the two groups.
Discuss how a stimulus is converted into a sensation.
Discuss the general sense organs and their functions.
List the major senses.
Describe the structure of the eye and the functions of its components.
Discuss the anatomy of the ear and its sensory function in hearing and equilibrium.
Discuss the chemical receptors and their functions.

3. Classification of Sense Organs
General Sense Organs:
Exist as individual cells or receptor units
Widely distributed throughout the body
Special Sense Organs
Large & Complex
Localized grouping of specialized receptors
Presence or absence of covering
Encapsulated
Unencapsulated

4. General Sense Organs Free Nerve Endings
Location: Skin, Epithelial & mucosa
General Senses: Pain, crude touch, temperature, itch, tickle

5. General Sense Organs Encapsulated Nerve Endings Meissner’s Corpuscles
Location: Skin, fingertips & lips
General Senses: Fine touch and low-frequency vibration
Ruffini’s Corpuscles
Location: Skin & subcutaneous tissue of fingers
Touch & Pressure
Pacinian Corpuscles
Around joints, in mammary glands & external genitals of both sexes
General Senses: pressure & high frequency vibration

6. General Sense Organs Encapsulated Nerve Endings Cont
Krause’s end-bulbs
Location : Skin dermal; mucosa of lips, eyelids, & external genitals
General Sense: Touch & cold
Golgi Tendon Receptors
Location: Near Junction of Tendons & Muscles
General Sense: Muscle tension (proprioception: individual perception)
Muscle spindles
Skeletal muscles
General Sense: Muscle length (proprioception)

7. Special Sense Organs Eye Specific Receptor: Rods & Cones
Type of Receptor: Photoreceptor
Sense: Vision
Ear
Specific Receptor: Organ of Corti & Cristae ampullares
Type of Receptor: Mechanoreceptor
Sense: Hearing & Balance

8. Special Sense Organs Nose Taste Buds
Specific Receptor: Olfactory cells
Type of Receptor: Chemoreceptor
Sense: Smell
Taste Buds
Specific Receptor: Gustatory cells
Sense: Taste

9. Type of Stimuli Defined
Photoreceptors (light)
Chemoreceptors (chemicals)
Pain receptors (injury)
Thermoreceptors (temperature change)
Mechanoreceptors (movement or deforming of capsule)
Proprioceptors (position of body parts or changes in muscle length or tension)

10. Converting Stimulus to Sensation
All sense organs have 3 common functional characteristics:
Can detect a particular stimulus
Stimulus is converted into a nerve impulse
Nerve impulses is perceived as a sensation

11. The Eye
Layers of eyeball
Sclera: tough outer coat; white of eye; cornea is the transparent part of sclera over iris
Choroid: pigmented vascular layer prevents scattering of light; front part of this layer is made of ciliary muscle & 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: inner most layer of the eye; contains rods (receptors for night vision) & cones (reception for day & color vision)

12. The Eye
Conjuctiva: 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

13. Suspensory ligaments 2 1 9 3 10 4 8 11
humor 5 6
humor
Optic Disk 12 7

14. Eye Fluids Aqueous humor: in the anterior chamber in front of the lens
Vitreous humor: in the posterior chamber behind the lens

15. Visual pathway Innermost layer of retina contains rods & cones
Impulse travels from the rods and cones through the layers of the 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

16. The Ear Functions in hearing, equilibrium, & balance
Receptors for hearing & equilibrium: mechanoreceptors

17. Divisions of Ear External Auricle (pinna) External auditory canal
Curves approx. 2.5 cm in length
Contains ceruminous glands (produce a waxy substance)
Ends at tympanic membrane

18. Divisions of Ear Middle Ear Ear ossicles: malleus, incus, & stapes
Ends in the oval window
Eustacian tube connects the middle ear to the throat
Inflammation called otitis media

19. Divisions of Ear Inner Ear Bony labyrinth filled with perilymph
Subdivided into the vestibule, semicircular canals, and cochlea
Membranous labyrinth filled with endolymph
Receptors for balance in the semi-circular canals: cristae ampullairs
Specialized hair cells on the organ of Corti respond when bent by the movement of surrounding endolymph set in motion by sound waves

20. Semi-Circular Canals
Vestibulocochlear nerve
Vestibule
Malleus
Incus
Tympanic Membrane
Cochlea
Oval Window
Pinna
External Auditory Meatus
Eustachian Tube
Stapes

21. Taste Receptors Chemoreceptors called taste buds
Cranial nerves carry gustatory (respond to chemicals dissolved in saliva) impulses
4 primary taste sensations
Sweet
Sour
Bitter
Salty
Gustatory & Olfactory senses work together

22. Smell Receptors
Receptors for fibers of olfactory/cranial nerve 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