Animal Senses
• How do animals
sense stimuli?
• Sensory organs
perceive stimuli (light,
sounds, etc.) with a
receptor cell. The
receptor cell sends
signals to the brain
where they are
processed and
integrated.
Animal Senses
• Each type of animal is equipped with its
own sensory receptors  each animal
perceives its environment differently.
Animal Senses
• Animal senses are more varied and
sharper than human senses.
• Most sensory receptors are found on the
head of an animal—in most cases, the
“head” is the first part of an animal to enter
a new environment
Four Basic Modalities
• Photoreception – response to light
Thermoreception
• Response to heat!
Mechanoreception
• Response to movement.
• This includes hearing, vibration, touch,
balance, etc.
Chemoreception
• Response to chemical energy, including
smell and taste
Insect Senses - Vision
• Compound eyes - made up of 100’s –
1000’s of lenses
• Each individual “eye” is not as accurate as
a vertebrate eye, but the compound eyes
taken together are better at detecting
motion.
• Respond to minute changes in color and
motion—the brain produces 1 detailed
image.
Insect – Chemical Receptors
• For taste and smell
• Found on mouthparts, antennae and legs.
• A fly’s foot can tell whether a liquid
contains sugar or salt.
Sensory Hairs
• Found mostly on head and legs
• Can detect movement in surrounding air or
water, and can detect certain chemicals.
Sensory Hairs detect
Pheremones
• These are odor producing molecules that
act as chemical messages.
• They are synthesized by an individual,
released into the environment and change
the behavior of another individual.
Sensory Hairs detect
Pheremones
• 1000 different insect pheremones known
• Most are produced by females and are
airborne.
• Species specific sex attractants*.
Animal Senses
• Specific examples:
• A homing pigeon senses changes in
altitude as minute as four millimeters.
Pigeons also see ultraviolet light and hear
extremely low-frequency sound.
Animals detect magnetic fields
• Used for navigation by pigeons and other birds,
honeybees, sea turtles, etc.
What happens when an animal
that navigates using magnetic
fields has a magnet glued to its
head?
Pit Vipers – Detect Heat
• Pits are located on head of pit viper
• Pits contain receptor cells that can detect
infrared radiation (heat)
• A pit viper is able to “see” a fuzzy image of
a warm object –a pit viper can strike at a
mouse in complete darkness.
Design an experiment to test if a
“pit” is actually sensing heat.
• Is it possible the snake’s pit is simply
sensing the smell of another animal?
• Hint: Use a light bulb in your experimental
set-up!
Elephants Detect Infrasounds
• Infrasound = sound too low to be heard by
the human ear
• Elephants call to each other with
infrasound and stamp their feet which
create sound waves that travel through
earth.
• Infrasound can travel exceptionally long
distances.
Elephants Detect Infrasounds
• It is hypothesized that this allows
elephants to coordinate movement when
they are miles apart.
• Large elephant ears and feet (vibrations in
ground) are the sense organs*
Animals Detect Ultrasounds
• Ultrasounds = sounds too high to be heard
by humans
• Bats, dolphins, etc.*
Design an experiment to test if
bats actually use ultrasounds for
navigation
• Hint: Use cottonballs as part of your
experimental set-up.
Aquatic Predators detect
Electric Fields
• Sharks (and others) can detect electrical
activity in the muscles of passing prey.
Sharks and Aquarium
• What problem might a
shark have in a large
tank in an aquarium?
Animals detect movement
• An animal’s ear detects sound by the
movement of sound waves through the air
or water.
• Mammals have bones in their middle ear
that transmit the information carried in the
sound waves to the brain.
Animals detect movement
• This includes stimulus detected by the
lateral line system in fish and other
aquatic vertebrates.
• This system detects movements and
pressure changes in the surrounding
water.
Animals and vision
• Some animals can sense parts of the
electromagnetic spectrum that are invisible
to the human eye.
*
Human (and most vertebrate)
Senses
• Vertebrate eyes are camera eyes (vs.
compound eyes of insects). Focuses
incoming light onto a layer of photoreceptor cells on back of retina.
Vertebrate Eyes
• Iris: The colored diaphragm in the anterior
chamber of the eyeball which contracts
and expands to adjust for light intensity.
• Pupil: The opening in the center of the iris
through which light passes.
• Lens: The transparent, dual-convex body
which focuses light rays onto the retina. It
is normally capable of changing shape to
allow the eye to focus on both near and
distant images.
Vertebrate Eye
• Retina – Found on the back of the eye.
Sensory cells contain light absorbing
pigment (a molecule that absorbs only
certain wavelengths of visible light and
reflects or transmits other wavelengths)
– cones = color vision
– rods = light vision
Vertebrate Eye
• The optic nerve attaches to retina and
there are no photo-receptor cells at that
location creating a blind spot.
• Adaptations, such as the eye, (a
characteristic that makes one individual
more fit than another) do not have to be
perfect.
Experiment with YOUR blind spot
Cat’s Eyes
• A reflective layer behind the cat's retina
called the tapetum reflects incoming light
and bounces it back off the cones, making
more use of the existing light.
• The tapetum makes a cat's eyes look like
shiny green orbs at night.
Vertebrates and Taste
• Taste is a chemical sense perceived by
specialized receptor cells that make up taste
buds.
• Flavor is a function of both taste and smell.
Vertebrates and Smell
• Inside the nose is a big area called the
“nasal cavity.”
• On the roof of the nasal cavity are special
sensory smell cells called “olfactory
receptor cells.”
Vertebrates and Smell
• Smells are in the form of a gas that is
breathed in when animals inhale
• The scent molecules in the gas pass by
the olfactory receptor cells on the roof of
the nasal cavity.
• The smell cells send the signal up a nerve
fiber to the brain.
• This allows vertebrates to react quickly to
smells.
Other Senses
• Nociceptors – Sense pain
• Thermoreceptors – Detect changes in
temperature