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 photo-receptor 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
