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