Sensing the Environment (I+II)

Importance of Senses

Vertebrates: active animals living in a variable environment

• The more variable the environment, the greater the advantages of sense organs

(detect heat, light, pressure, other organisms)

• Define & limit the known world

• Sense organs enable vertebrates to:

– Monitor the environment

– Permit evolution of complex behaviors

• Behavior constrained by limits of sensory systems

Types of Sense Organs

1)Chemoreceptors

• Smell

• Taste

2)Mechanoreceptors

• Touch and pain

• Hearing/lateral line

• Equilibrium

3)Electromagnetic

• Light

• Heat

• Electrical / magnetic

Chemoreceptors

smell and taste

• Most ancestral

• Most universal

• Smell more sensitive than taste

• Augments basic tastes detectable by taste buds

Mechanoreceptors

• Touch and pain

• Hearing/lateral line

• Equilibrium

Electromagnetic Receptors

• Light

• Heat

• Electrical / magnetic

Taste

• Taste receptors cells (TRC) located in taste buds

• Taste buds located mainly on tongue (mammals) or also on other areas that contact food (other groups)

• Five basic tastes: sour, salty, bitter, sweet, umami

• Bitter tastes important in warning of toxicity

Smell

• More complex than taste

• Smell receptors located in nasal cavity (in special epithelium w/mucus)

• Although humans not particularly good smellers:

– 20 million olfactory receptors in your nose

– Humans can detect 10,000 odors

• Taste & smell commonly confused

– (easy to realize when you have a cold)

Chemical Scents

• Recognition: species, sex, individuals, predators, prey, etc.

• Emotional states (e.g., fear, readiness to mate)

• Advertisement (e.g., territorial, mating)

• Orientation (e.g., scent tracks)

• Best developed in certain groups (e.g., mammals; some amphibians)

Mechanoreceptors- Touch & Pain

• Receptors located in the skin

• Touch/Pressure distorts sensory receptor (nerve tissue) > local flow of electric current > information sent to CNS

• If touch/pressure is sustained, the receptor adjusts

• Most touch receptors are in the face and limb extremities

• Pain receptors may respond directly or indirectly to injury (important defense of the body)

Lateral Line System

• Found in fish, aquatic amphibians

• Pressure receptor for detecting wave vibrations & currents in water

• Sensory cells (neuromasts) in pits and grooves

• Helps detects nearby movements of prey, predators, mates, or just position of static objects (important in fish schooling)

neuromasts

Collection of hair cells embedded in gelatinous wedge- shaped mass (cupula)

Vibrations o certain frequency is?

Sound

Underwater vs airborne sound? In water____

In water:

– More difficult to initiate (due to density of medium)

– Transmission (speed) more rapid (5x)

– Speed slows down: cold, depth

—Extremities travel best in water (really high clicks or really low bellows)

Frequency

Determines the pitch: high or low

• Cycles/sec (hertz = Hz)

Amplitude

Determines loudness (volume)

Ears (what and path?)

Structure for Detecting Sound

External vibrations > fluid vibrations > membrane

vibrations > move sensory cells > nervous impulses to CNS

Invertebrates live in a __________ world. _________ however do have ears (why?)

Silent

locusts, cicadas, crickets, grasshoppers & moths

—They produce sound

Vertebrate ear originated as a ?

balance organ (labyrinth)

Balance (Equilibrium) what structure? what info do they give? what do they respond to?

Labyrinth

head position and movement

respond to rotational acceleration/otoliths sense linear acceleration (AKA Change in condition!!)

Hearing Mammals 

outer ear, middle ear, inner ear

Outer ear

collects sound waves and take to tympanic

membrane, which starts vibrating

Middle ear

air-filled chamber with 3 bones (malleus, incus,

stapes)

• Vibrations (sound) coming from tympanic membrane is amplified 90 times by ossicles

• Under extremely loud noise, muscles contract, protectingear

Inner ear

• contains the cochlea - organ of hearing

• Filled with liquid that receives vibrations from middle ear

• Hair cells detect movement of the liquid and send info to CNS

cochlea

organ of hearing

Pitch discrimination in mammal ears depends on?

location of hairs stimulated

Loudness in mammal ears

number of hairs stimulated

Hearing Specializations (3)

• Enlarged middle ear

  • Increases amplification

  • Often found in desert animals (many are nocturnal) (ex., kangaroo rat)

• Asymmetrical ears

  • Owls

  • Sound arrives separately to each ear

  • Directional hearing

  • Sound catching facial disk

  • Important for prey location in the dark

• Sonar-Echolation

  • Insectivorous/fisheating bats, Whales, porpoises, Weddell seals

  • High frequency sound (chirp/clicks) emitted and bounced back (prey & objects)

  • Important for dark environments

Electromagnetic receptors – Vision

• Eyes

• Light receptors = photoreceptors (rods and cones)

Eyes are?

The organ of vision

Light Receptors

Light receptors = photoreceptors (rods and cones)

Structure of the Eye

Eyeball - 3 layers (sclera, choroid, retina)

• Cornea is transparent (bends light)

• Iris regulates light opening (pupil)

• Lens – helps focus

Structure of Retina

Rods and cones

Photosensitive Cells in Retina

Rods

• Achromatic vision

• Lower visual acuity

• Good for vision in dim light

Cones

• Opposite of above

• Color discrimination

The human eye has many

more ____ than ____

rods than cones

How is Light is Detected?

Light (photon) strikes rod » activates rhodopsin» enzymatic activity of opsin » amplifies photon » generates and propagates a nerve impulse » info sent to CNS

(Process similar in cones, but cones have different photopigments that respond mainly to blue, green, or red wavelengths George Wald showed absorption for cones at different wavelengths)

Rods contain the photosensitive pigment?

rhodopsin

Short wavelength (what color?) Long wavelengths (what color?)

Short wavelengths = violet

Long wavelengths = red

Color Vision

• Increases contrasts & discrimination

• Mainly in diurnal animals (many nocturnal species are color blind)

• Good color vision in many fish,

salamanders, frogs, reptiles, most birds and some primates

• Difficult to determine

Evolution of Color Vision

• Color vision in vertebrates evolved ~ 350 MYA

– Found in: fish, salamanders, frogs, reptiles, most birds and some primates

• Full color vision LOST several times (e.g., mammals, snakes): due to loss of a cone type

– Regained in primates

Photosensitivity

• “Median eye” some reptiles &

many fish (light sensitive spot on top of head)

• Most vertebrates: image forming eyes

Visual Field

Area scanned by eyes

Monocular Vision (what type of eyes, pros and cons?)

• Many vertebrates with lateral eyes have monocular vision

• Vision field of left and right eyes do not overlap

• Allows large vision field but poor discrimination of distances

Binocular Vision

• Vertebrates with frontal eyes are capable of binocular vision

• Visual field of left and right eyes with broad overlap

• Allows depth perception (see in 3-D) and accurate location objects

• Somewhat reduced field of view

(both eyes facing same area)

Using both binocular and monocular vision provides? examples?

high acuity (clarity,sharpness)

diurnal avian hunters - soaring hawkspots mouse

Amphibious (birds and fish) Adaptations (Eyes)

• Amphibious fish with highly modified eyes (4-eyed fish)

• Two pupils/eye: aquatic and aerial vision

• Many diving birds with dual focus: for aerial and aquatic vision

Round Eyes (who? and looks like?)

Only nocturnal or diurnal

Vertical Eyes (who? and looks like? Allows for more?)

Nocturnal, sometimes active in day. Allows more complete closure

Vertical pin-holed (why?looks like?)

yield great depth of field despite monocular vision 

Horizontal Eyes (allows for?)

Allows wide-angle scanning

“Third Eyelid”

Nictitating membrane

• Transparent

• Prevents drying and helps cleanse eye

• Found in diverse vertebrate groups

Many deep water fish species capable of ________

+purpose?

bioluminescence

Foraging, predator avoidance, communication

Electromagnetic receptors - Heat

• Some vertebrates sense heat – cold with dermal receptors

• Pit vipers have pair pit organs to detect heat

- Most heat sensitive receptor in animals

Pit vipers have what?for what?

pit organs

Pit vipers use pit organs to hunt small mammals at night

What’s the deal with ground squirrel?

• California ground squirrels generate infrared signal when tail wagging to deter rattlesnake predation (increased bloodflow)

• Rattlesnakes ARE deterred by this (switch from predatory > defensive behavior: tested with robotic squirrel model)

• Squirrels do not display infrared signal to other snake predators that cannot detect signal (e.g., gopher snakes)

Electromagnetic receptors – Electricity

• Some fish can detect electric

signals through a network of

electro-sensitive cells in the

skin: (e.g., sharks can detect flatfish

under sand!)

• Other fish can both emit &

receive these signals

– Some can detect, then stun

prey

– Others use for navigation

and communication

Electromagnetic receptors – Magnetism

• Demonstrated but not well understood

• Some birds (especially migratory) and fish use magnetic fields for orientation and navigation