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 shower
iii. “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 receptors
B. Thermoreceptors
C. Mechanoreceptors
- touch, stretching, sound,
pressure, motion, etc…
- bend or stretch PM
Fig. 29.3A
Chapter 29: The Senses
II. Five categories of stimuli
C. Mechanoreception by a “hair cell”
microvilli
- detect sound waves or movement of water
- lateral line system
- hearing and balance
Fig. 29.3A
Chapter 29: The Senses
II. Five categories of stimuli
D. Chemoreceptors
- nose/taste buds/ in arteries
E. Electromagnetic receptors
- electric currents in water
- detect Earth’s magnetic field
- photoreceptors - in eyes detect photons
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 images
b. Ommatidia
- tiny light detecting unit
- each has own light focusing
lens and photoreceptor cells
- image formed in brain
using combination of signals
from all ommatidia
Fig. 29.4B
Chapter 29: The Senses
III. Three types of eyes have evolved in invertebrates
3. Single-lens eye
a. Works like a camera
b. pupil
- small opening through which
light passes
c. iris
- changes diameter of pupil
(camera shutter)
Squids, vertebrates - evolved independently
Fig. 29.4B
Chapter 29: The Senses
III. The vertebrate single lens eye
1. sclera
i. Outer surface
ii. Tough, whitish layer
iii. Connective tissue
2. cornea
i. Fuses to sclera at front of eye
ii. clear
iii. Lets light in, helps focus
3. choroid
i. Pigmented layer below sclera
ii. Forms iris at front of eye
Fig. 29.5
Chapter 29: The Senses
III. The vertebrate single lens eye
Fig. 29.5
4. iris
i. Gives eye its color
ii. Regulate pupil size to adjust
amount of light entering eye
5. lens
i. Held in position by ligaments
ii. Focuses images onto retina
6. Retina
i. 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 brain
iii. 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
Fig. 29.5
7. Two chambers
i. Vitreous humor
- fills large chamber behind
lens
- jellylike
ii. Aqueous humor
- 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
iii. Humors help maintain shape
Chapter 29: The Senses
III. The vertebrate single lens eye
8. Lacrimal gland
i. Secrete tears
- lubricate and clean the eye
ii. Lacrimal sac drains tears into nasal
cavity
Chapter 29: The Senses
IV. Focusing light
1. mammals
i. change the shape of the lens
- thicker the lens the sharper light bends (muscles contract)
2. Fish and squid
i. Change the physical position of the lens
Fig. 29.6
Chapter 29: The Senses
V. Artificial lenses or surgery can correct focusing problems
1. Visual acuity - read the eye chart from 20 feet away
i. 20/20 - from a distance of 20 feet, you can read the letters
designated for 20 feet
ii. 20/10
- from a distance of 20 feet, you can read the letters that a
person with 20/20 can only read from 10 feet
iii. 20/50 - 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 problems
i. 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. Astigmatism
i. 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. Cones
i. Stimulated by bright light (don’t function in night vision)
ii. Distinguish color
iii. 6 million cone cells per retina
2. rods
i. 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. Fovea
i retina’s center of focus
ii. Rods mostly on outer edge of retins
iii. Cones mostly in center (fovea)
- easier to see a star at
night if you don’t look
straight at it
Fig. 29.8
Chapter 29: The Senses
VI. Photoreceptors of the eyes - rods and cones
4. How do rods and cones detect light
i. rhodopsin
- visual pigment in discs of rod cells
- can absorb dim light
ii. photopsins
- visual pigments in discs of cone cells
- absorb bright, colored light
- There are 3 types of cone cells
Fig. 29.8
- 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 ear
a. Two separate organs
i. hearing
ii. balance
iii. Both work by stimulating “hair cells” (microvilli)
in fluid filled canals
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
b. Three regions
i. Outer ear
- pinna
- auditory canal
Fig. 29.9A
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
b. 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
- attached to stirrup
- membrane vibrates when stirrup vibrates sending
vibrations into the inner ear
- Eustachian tube
- conducts air b/w middle ear and back of throat
- 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 ear
b. 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 ear
c. Flow of sound
Fig. 29.9B
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. 29.9C
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
c. Flow of sound
Fig. 29.9B
- 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. 29.9C
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
d. 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 ear
d. How does the ear determine volume?
i. volume
- high amplitude wave causes vigorous vibrations of fluid = high
frequency of bending on microvilli
- louder = higher frequency of signals sent to brain
Fig. 29.9C
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
d. How does the ear determine volume?
ii. Pitch
Fig. 29.9B
- basilar membrane is NOT uniform
- varies from narrow and stiff to wide and flexible
- different regions more sensitive to different pitches
- brain determines pitch by which regions are sending
most frequent signals
Fig. 29.9C
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
e. Balance (position and movement)
i. Semicircular canals
ii. utricle
iii. saccule
Fig. 29.10
ALL filled with fluid
Chapter 29: The Senses
VII., Hearing and balance
1. Human ear
e. Balance (position and movement)
i. Semicircular canals
- three
- detect changes in head
Fig. 29.10
rotation and angular movement
- 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
e. Balance (position and movement)
i. Utricle and saccule
- detect position of head relative
to gravity
Fig. 29.10
utricle
saccule
Chapter 29: The Senses
VIII. Odor and taste
1. chemoreceptors
a. One cell responds to a group
of chemically related molecules
(NOT JUST ONE)
Ex. One cell may detect 50 kinds of odors
So how does the brain tell the difference b/w odors.
- specific pattern of signals
Fig. 29.12
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
- Taste receptors in back of throat and taste buds
Fig. 29.12
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
INSECTS: taste with their feet
- chemoreceptors in sensory hairs on their feet