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Chapter 29: The Senses
I. Sensory transduction
A. Cells converts one type of signal (stimulus) into an electrical signal
i. Stimulus: photon of light, molecule of sugar, etc…
Fig. 29.2
Chapter 29: The Senses
I. Sensory transduction
A. Cell converts one type of signal (stimulus) into an electrical signal
i. Stimulus: photon of light, molecule of sugar, etc…
Fig. 29.2
Chapter 29: The Senses
II. Sensory adaptation
A. Tendency of a sensory receptor cell to become less sensitive to repeated stimulus
i. Wear clothes without always being aware of it
ii. “adjust” to a hot showeriii. “adjust” to smell in the room
iv. Etc…
B. Nervous system would become overloaded without it
Chapter 29: The Senses
II. Five categories of stimuli
A. Pain receptorsB. ThermoreceptorsC. Mechanoreceptors
Fig. 29.3A
- touch, stretching, sound, pressure, motion, etc…- bend or stretch PM
Chapter 29: The Senses
II. Five categories of stimuli
C. Mechanoreception by a “hair cell”
Fig. 29.3A
- detect sound waves or movement of water- lateral line system
microvilli- hearing and balance
Chapter 29: The Senses
II. Five categories of stimuli
D. Chemoreceptors
E. Electromagnetic receptors- nose/taste buds/ in arteries
- photoreceptors - in eyes - detect photons
- electric currents in water- detect Earth’s magnetic field
Chapter 29: The Senses
III. Three types of eyes have evolved in invertebrates
1. Eye cup
- simplest- found on planaria- detects only direction and intensity
Fig. 29.4A
Chapter 29: The Senses
III. Three types of eyes have evolved in invertebrates
2. Compound eye
a. focuses light and forms imagesb. Ommatidia
Fig. 29.4B
- tiny light detecting unit- each has own light focusing lens and photoreceptor cells- image formed in brain using combination of signals from all ommatidia
Chapter 29: The Senses
III. Three types of eyes have evolved in invertebrates
3. Single-lens eye
a. Works like a camerab. pupil
Fig. 29.4B
- small opening through which light passes
c. iris- changes diameter of pupil (camera shutter)
Squids, vertebrates - evolved independently
Chapter 29: The Senses
III. The vertebrate single lens eye
1. sclerai. Outer surface
Fig. 29.5
iii. Connective tissue
2. corneai. Fuses to sclera at front of eye
ii. Tough, whitish layer
ii. clear
iii. Lets light in, helps focus
3. choroidi. Pigmented layer below sclera
ii. Forms iris at front of eye
Chapter 29: The Senses
III. The vertebrate single lens eye
4. irisi. Gives eye its color
Fig. 29.5
5. lensi. Held in position by ligaments
ii. Regulate pupil size to adjust amount of light entering eye
ii. Focuses images onto retina
6. Retinai. Layer below the choroid
ii. Contains photoreceptor cells (it’s the film of the camera)
- convert light to electric and send to optic nerve, which goes to brainiii. No photoreceptors where optic nerve attaches (blind spot)
- two eyes, overlapping fields of view, fill in blind spot
Chapter 29: The Senses
III. The vertebrate single lens eye
7. Two chambersi. Vitreous humor
Fig. 29.5
- jellylike
- fills large chamber behind lens
ii. Aqueous humor
iii. Humors help maintain shape
- small chamber in front of lens (b/w cornea and lens)- secreted by capillaries- brings oxygen, nutrients, etc… and removes wastes for cornea, lens, and iris cells.- glaucoma - increased pressure in eye caused by blockage of duct that drains aqueous humor
Chapter 29: The Senses
III. The vertebrate single lens eye
8. Lacrimal glandi. Secrete tears
ii. Lacrimal sac drains tears into nasal cavity
- lubricate and clean the eye
Chapter 29: The Senses
IV. Focusing light
1. mammalsi. change the shape of the lens
i. Change the physical position of the lens
2. Fish and squid- thicker the lens the sharper light bends (muscles contract)
Fig. 29.6
Chapter 29: The Senses
V. Artificial lenses or surgery can correct focusing problems
1. Visual acuityi. 20/20
ii. 20/10
- read the eye chart from 20 feet away
iii. 20/50
- from a distance of 20 feet, you can read the letters designated for 20 feet
- from a distance of 20 feet, you can read the letters that a person with 20/20 can only read from 10 feet
- need to stand 20 feet to read letters that a person with 20/20 can read from 50 feets
Chapter 29: The Senses
V. Artificial lenses or surgery can correct focusing problems
2. Most common visual problemsi. nearsightedness, farsightedness, astigmatism
- all are focusing problems
- corrected with an artificial lens
- named for type of vision that is UNIMPAIRED
Chapter 29: The Senses
V. Artificial lenses or surgery can correct focusing problems
3. Nearsightedness (myopia)i. Eye is longer than normal
- can’t flatten lens enough to see distant objects
Fig. 29.7
Chapter 29: The Senses
V. Artificial lenses or surgery can correct focusing problems
4. Farsighted (hyperopia)i. Eye is too short
- can’t make lens thick enough to bend light onto retina
Fig. 29.7
Chapter 29: The Senses
V. Artificial lenses or surgery can correct focusing problems
5. Astigmatismi. Blurred vision caused by a misshapen lens or cornea
Fig. 29.7
Chapter 29: The Senses
VI. Photoreceptors of the eyes - rods and cones
1. Conesi. Stimulated by bright light (don’t function in night vision)
ii. Distinguish color
iii. 6 million cone cells per retina
2. rodsi. Highly sensitive to light
ii. Enable us to see in dim light (at night)iii. Shades of grey only
iv. 125 million per retina
Fig. 29.8
Chapter 29: The Senses
VI. Photoreceptors of the eyes - rods and cones
3. Foveai retina’s center of focus
ii. Rods mostly on outer edge of retins
iii. Cones mostly in center (fovea)
Fig. 29.8
- easier to see a star at night if you don’t look straight at it
Chapter 29: The Senses
VI. Photoreceptors of the eyes - rods and cones
4. How do rods and cones detect lighti. rhodopsin
- visual pigment in discs of rod cells
ii. photopsins- visual pigments in discs of cone cells
Fig. 29.8
- can absorb dim light
- absorb bright, colored light- There are 3 types of cone cells
- each contains a different type of photopsin
- blue cones, green cones, red cones
- color blindness = deficiency in one or more of these types of cone cells.
Chapter 29: The Senses
VI. Photoreceptors of the eyes - rods and cones
4. How do rods and cones detect light
Fig. 29.8
Chapter 29: The Senses
VII., Hearing and balance
1. Human eara. Two separate organs
i. hearingii. balanceiii. Both work by stimulating “hair cells” (microvilli) in fluid filled canals
Chapter 29: The Senses
VII., Hearing and balance
1. Human earb. Three regions
i. Outer ear- pinna- auditory canal
Fig. 29.9A
Chapter 29: The Senses
VII., Hearing and balance
1. Human earb. Three regions
ii. Middle ear- eardrum
- separates outer ear from middle ear- sound waves vibrate ear drum, which vibrates the three bones
- hammer, anvil and stirrup- oval window
- membrane covered hole in skull
- conducts air b/w middle ear and back of throat
- membrane vibrates when stirrup vibrates sending vibrations into the inner ear
- Eustachian tube
- attached to stirrup
- keeps pressure equal on both sides of ear drum
Fig. 29.9B
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
b. Three regions
iii. Inner ear- fluid filled channels in bones of skull- fluid set in motion by:
1. Sound waves (vibrating oval window)2. Motion of the head
Fig. 29.9B
Chapter 29: The Senses
VII., Hearing and balance
1. Human earb. Three regions
iii. Inner ear- cochlea (latin for snail)
- contains hearing organ (organ of Corti)- three fluid-filled canals
Fig. 29.9B
Fig. 29.9C
Chapter 29: The Senses
VII., Hearing and balance
1. Human earc. Flow of sound
Vibrations in air -> collected by pinna and auditory canal -> vibrates ear drum -> hammer -> anvil ->stirrup -> oval window -> vibration of oval window produces pressure waves in fluid through upper canal to tip of cochlea and back through lower canal dissipating along the way.
Fig. 29.9B
Fig. 29.9C
Chapter 29: The Senses
VII., Hearing and balance
1. Human earc. Flow of sound
- pressure wave through upper canal vibrates basilar membrane
Result: hair cells brush back and forth on overlying membrane, bending microvilli and sending electrical signals
Fig. 29.9B
Fig. 29.9C
Chapter 29: The Senses
VII., Hearing and balance
1. Human eard. Volume v. Pitch
i. higher volume = higher amplitude of sound wave
ii. higher pitch = higher frequency of sound wave
Chapter 29: The Senses
VII., Hearing and balance
1. Human eard. How does the ear determine volume?
i. volume
- louder = higher frequency of signals sent to brain
- high amplitude wave causes vigorous vibrations of fluid = high frequency of bending on microvilli
Fig. 29.9C
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
- basilar membrane is NOT uniform- varies from narrow and stiff to wide and flexible
- different regions more sensitive to different pitches
d. How does the ear determine volume?
ii. Pitch
- brain determines pitch by which regions are sending most frequent signals
Fig. 29.9B
Fig. 29.9C
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
ii. utricleiii. saccule
ALL filled with fluid
e. Balance (position and movement)
i. Semicircular canals
Fig. 29.10
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
- three- detect changes in head rotation and angular movement
e. Balance (position and movement)
i. Semicircular canals
Fig. 29.10
- arranged in three perpendicular planes- detect movement in all directions (X, Y, and Z)
- hair cells located at base of each canal
- microvilli projected into cupula (gelatinous mass)
- as head moves, fluid moves, cupula moves, hair cells bend and signals are sent to brain.
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
- detect position of head relative to gravity
e. Balance (position and movement)
i. Utricle and saccule
Fig. 29.10
saccule
utricle
Chapter 29: The Senses
VIII. Odor and taste
1. chemoreceptorsa. One cell responds to a group of chemically related molecules (NOT JUST ONE) Fig. 29.12
Ex. One cell may detect 50 kinds of odors
So how does the brain tell the difference b/w odors.- specific pattern of signals
Chapter 29: The Senses
VIII. Odor and taste
2. Taste- Taste receptors in back of throat and taste buds on tongue- Types of taste receptors
Sweet, sour, salty, bitter and umami (these detect amino acids)
-Flavor interpreted by brain comes from a combination of signals from taste receptors
Chapter 29: The Senses
VIII. Odor and taste
2. Taste
INSECTS: taste with their feet
- chemoreceptors in sensory hairs on their feet
- Taste receptors in back of throat and taste buds on tongue- Types of taste receptors
Sweet, sour, salty, bitter and umami (these detect amino acids)
-Flavor interpreted by brain comes from a combination of signals from taste receptors
Fig. 29.12
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