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Anatomy and Physiology I

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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

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