Chapter 29: The Senses I. Sensory transduction A. Cells converts one type of signal (stimulus) into an electrical signal i. Stimulus: photon of light,

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


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


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


II. Five categories of stimuli

A. Pain receptorsB. ThermoreceptorsC. Mechanoreceptors

Fig. 29.3A

- touch, stretching, sound, pressure, motion, etc…- bend or stretch PM



C. Mechanoreception by a “hair cell”

Fig. 29.3A

- detect sound waves or movement of water- lateral line system

microvilli- hearing and balance



D. Chemoreceptors

E. Electromagnetic receptors- nose/taste buds/ in arteries

- photoreceptors - in eyes - detect photons

- electric currents in water- detect Earth’s magnetic field


III. Three types of eyes have evolved in invertebrates

1. Eye cup

- simplest- found on planaria- detects only direction and intensity

Fig. 29.4A



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



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


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



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



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



8. Lacrimal glandi. Secrete tears

ii. Lacrimal sac drains tears into nasal cavity

- lubricate and clean the eye


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


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



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



3. Nearsightedness (myopia)i. Eye is longer than normal

- can’t flatten lens enough to see distant objects

Fig. 29.7



4. Farsighted (hyperopia)i. Eye is too short

- can’t make lens thick enough to bend light onto retina

Fig. 29.7



5. Astigmatismi. Blurred vision caused by a misshapen lens or cornea

Fig. 29.7


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



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



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.



4. How do rods and cones detect light

Fig. 29.8


VII., Hearing and balance

1. Human eara. Two separate organs

i. hearingii. balanceiii. Both work by stimulating “hair cells” (microvilli) in fluid filled canals



1. Human earb. Three regions

i. Outer ear- pinna- auditory canal

Fig. 29.9A




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



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




iii. Inner ear- cochlea (latin for snail)

- contains hearing organ (organ of Corti)- three fluid-filled canals

Fig. 29.9B

Fig. 29.9C



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



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



1. Human eard. Volume v. Pitch

i. higher volume = higher amplitude of sound wave

ii. higher pitch = higher frequency of sound wave



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



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



1. Human ear

ii. utricleiii. saccule

ALL filled with fluid

e. Balance (position and movement)

i. Semicircular canals

Fig. 29.10



1. Human ear

- three- detect changes in head rotation and angular 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.



1. Human ear

- detect position of head relative to gravity


i. Utricle and saccule

Fig. 29.10

saccule

utricle


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



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



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

Documents

Chapter 29: The Senses I. Sensory transduction A. Cells converts one type of signal (stimulus) into an electrical signal i. Stimulus: photon of light,