1. Anatomy and Physiology I
Chapter 16
Sense Organs

2. Sensory Receptors Structure specialized to detect stimulus
Sense organ- structure composed of nervous tissue along w/ other tissue types
Enhance response to stimulus
Fundamental purpose of sensory receptor is transduction- conversion of one form of energy to another
Light, sound
Sensation- subjective awareness of stimulus
Signal must reach brain
Most filtered out in brain stem- keeps from being distracted

3. Sensory Receptors Transmits 4 kinds of information
Modality- type of stimulus or sensation it produces
Vision, hearing, taste (all have same action potential)
Assumes that if signal comes from retina  vision, taste bud  taste, etc
Location- depends on nerve fibers stimulated
Receptive field- skin
touch
Intensity- brain distinguish intensities based on fibers sending signals, how many, how fast fibers firing
Loud/ soft sound, bright/ dim light, soft/ hard touch
Duration- length stimulus lasts
Sensory adaptation- prolonged stimulus, neuron fires more slowly, become less aware of stimulus (hot bath water)

4. Receptor Classification
Stimulus modality
Thermoreceptors- heat and cold
Photoreceptors- light (eyes)
Nociceptors- pain receptors
Chemoreceptors- chemical (taste, odors)
Mechanoreceptors- physical deformation (touch, pressure)
Stimulus origin
Exteroceptors- sense stimuli from external body
Interorecptors- detect stimuli in internal organs
Proprioceptors- sense the position and movements of body parts
Receptor distribution
General senses- widely distributed throughout body (skin, muscles, tendons, viscera)
Touch, pressure, temperature, pain
Special senses- limited to head
Vision, hearing, equilibrium, taste, and smell

5. Taste Anatomy
Gustation- sensation that results from the action of chemicals on the taste buds
Taste buds- lemon shaped (4000)
Taste cells- epithelial cells
Taste hairs- receptor surface for taste molecules
Taste pore- on surface of tongue

6. Taste Physiology Molecules dissolve in saliva and flood taste pore
5 primary taste sensations
1. Salty- vital electrolytes (sodium)
Lateral tongue
2. Sweet- associated w/ carbohydrates
Tip of tongue (triggers licking, salivation)
3. Sour- associated w/ acidic foods
4. Bitter- associated w/ spoiled foods and alkaloids
Trigger rejection response (gagging)
Rear of tongue
5. Umami- “meaty” taste produced by amino acids

7. Taste Physiology
Flavors we perceive are not only due to combination of 5 taste regions, but they are also influenced by
Food texture
Aroma
Temperature
Appearance
State of mind
Many flavors depend on smell

8. Smell Anatomy- Olfaction
Smell receptors form a patch of epithelium on roof of nasal cavity
Olfactory mucosa
Olfactory mucosa consists of million olfactory cells- neurons
Cilia on olfactory cells- olfactory hairs
Binding sites for odor molecules
Directly exposed to external environment
Life span of 60 days
Replaceable

9. Smell Anatomy
Olfactory fibers pass through roof of nose and enter a pair of olfactory bulbs
Beneath frontal lobe
Turn into olfactory tracts
End at inferior surface of temporal lobe

10. Smell Physiology Poorer sense of smell than most mammals
Declined as visual sensation grew
Smell more sensitive than taste
Women more sensitive to odors than men
Distinguish b/t odors, some up to 10,000
350 kinds of olfactory receptors
Olfactory cell has only one receptor type, therefore binds one odorant

11. Smell Physiology
Odorant molecule binds with receptor on one olfactory hair
Triggers action potential of the olfactory cell and the signal is transmitted to the brain

12. Hearing and equilibrium
Hearing- response to vibrating air molecules
Equilibrium- sense of motion, body orientation, balance
Reside in inner ear
Sound- any audible vibration of molecules
Transmitted through water, air, solids

13. Ear Anatomy
3 sections
Outer
Middle
Inner
Outer and middle ear transmit sound to inner ear
Inner ear converts vibrations into nerve signals

14. Outer Ear Funnel for conducting vibrations to the tympanic membrane
Pinna- elastic cartilage
Auditory canal- passage leading to tympanic membrane
External acoustic meatis- external opening

15. Middle Ear Located in tympanic cavity of temporal bone
Tympanic membrane (ear drum)- vibrates in response to sound
Auditory tube- filled with air, equalizes air pressure
3 bones of middle ear- Auditory ossicles (smallest bones of the body)
Connect tympanic membrane to inner ear
Malleus- handle and head
Incus- triangular body
Stapes – stirrup shaped

16. Inner Ear Filled with fluid Vestibule- organ of equilibrium
Semicircular ducts- organ of equilibrium
Cochlea- organ of hearing
Round window
Vestibulocochlear nerve Cranial nerve VIII

17. Ear Physiology- Hearing
Sound waves directed toward tympanic membrane by outer ear
Tympanic membrane vibrates in response to sound waves
Vibrations sent through middle ear
Each ossicle vibrates the next
Stapes vibrates cochlear hair cells
Signal sent to brain via cochlear nerve
Brain interprets signal as sound

18. Ear Physiology- Equilibrium
Coordination, balance, orientation in 3-D space
Receptors for equilibrium constitute the vestibular apparatus
3 Semicircular ducts
Rotary movements
Hair cells
Saccule- anterior chamber
Hair cells vertically
Responds to vertical acceleration and deceleration
Utricle- posterior chamber
Hair cells horizontally
Responds linear movements
Detects tilt of head

19. Vision
Perception of objects in the environment by means of the light they emit or reflect

20. Accessory Structures
Eyebrows- enhance facial expressions, protect eyes from glare and sweat
Eyelids- block foreign objects from eye, blink to moisten eye
Medial and lateral commissures
Eyelashes- guard hairs that keep debris from eye
Lacrimal apparatus-
Lacrimal gland- tear gland
Ducts and canals- empty into eye or nose

21. Extrinsic Eye Muscles Superior Rectus- moves eye up
Medial Rectus- moves eye medially
Lateral Rectus- moves eye laterally
Inferior Rectus- move eye down
Superior oblique- rotates eye medially
Inferior oblique- rotates eye laterally

22. Components of the Eye 1. 3 layers that form the wall of the eyeball
Sclera
Choroid
Retina
2. Optical components that admit and focus light
3. Neural components
Optic nerve

23. 3 Layers Outer Layer Middle Layer Inner Layer Sclera- white of eyes
Covers most of the eye surface
Cornea- anterior, transparent region that admits light into the eye
Middle Layer
Choroid- highly vascular, deeply pigmented
Iris- extension of choroid, controls diameter of pupil
Ciliary muscles- found on posterior region of iris
Controls lens, pupil
Pupil- central opening of iris
Inner Layer
Retina
Beginning of optic nerve
3 Layers

24. Optical Components
Transparent elements that admit light rays, refract them, and focus images on retina
Cornea
Aqueous humor- fluid secreted by ciliary body and fills anterior chamber (between cornea and iris)
Lens- suspended behind pupil, composed of transparent cells
Vitreous humor- transparent jelly, fills posterior chamber, supports retina and lens

25. Neural Components Retina- thin, transparent membrane Optic nerve
Attached to eye at optic disc- where optic nerve leaves the eye
Depends on choroid for O2, nutrition, waste removal
Detached retinas cause blurry vision
If detached for too long, leads to blindness
Optic nerve
Optic disc- contains no receptor cells (blind spot)
Visual filling

26. Image Formation Begins w/ light entering eye through pupil
Image formation depends on refraction
Bending of light rays
Focused on retina
Produces tiny, inverted image
Image sent up optic nerve to brain

27. Retina
3 layers
1. Photoreceptors- absorb light, generate chemical and electrical signal
Rods and cones- produce visual images
Rods- responsible for night vision, produce images in shades of gray
Cones- responsible for day vision, function in bright light, produce images in color
2. Bipolar cells- synapse for cones and rods w/ ganglion cells
3. Ganglion cells- receive input from bipolar cells (close to vitreous)
Absorb light, and detect light intensity