How do animals detect environmental stimuli? Animal Senses How do animals detect environmental stimuli?

Remember! Sensory stimulation is the starting point of behaviour. Animal’s senses are not necessarily the same as ours.

Photoreceptors In animals light is detected by? The eyes The structure of the eye varies for different organisms.

Structure of Eyes Snails Insects and Crustaceans Have simple eyes which detect light in the same way as we detect heat. Insects and Crustaceans Have compound eyes made up of many separate ommatidia. These give a mosaic vision, very good for detecting movement.

Compound Eyes

Structure of Eyes Vertebrates Have lenses that help to form clear images. If two eyes face forwards they have overlapping fields (Binocular vision) enabling good judgement of distance

Vertebrate Eyes

Vertebrate Eyes

Structure of Eyes Night Vision This involves a structure called the tapetum, this is a layer of silvery crystals that acts as a reflector allowing animals like cats to pick up 50% more light at night than human’s can detect. This is why cat’s eyes glow in the dark.

Night Vision

Vision Animals also use their vision to detect movement, speed of movement, shapes etc.

Colour Vision We, as humans see violet, indigo, blue, green, yellow, orange and red parts of the light spectrum. Bees see ultraviolet light but are less sensitive to red. This is why most red flowers have some blue or a strong scent.

How bees see

Colour Vision cont Goldfish can see far red light. Sea birds are particularly sensitive to red light.

Sea Birds Vision

Thermoreceptors Infra-red light is a form of heat. No animal can “see” infra-red with eyes, but certain animals can detect warm objects as if they can see them. E.g. snakes

Snakes Heat Sensors Snakes have 2 heat sensing pits in front of and slightly below their eyes – these are so accurate the snakes can strike prey in pitch dark.

Thermoreceptors Humans can detect heat with their skin. Other animals e.g. mosquitoes home in on their prey using thermoreceptors.

Mechanoreceptors These sense gravity, touch, pressure, stretch and movement. These let the animal know which way is up. They help recognition of the position of one part of the body in relation to another. This is important for coordinated movement.

Mechanoreceptors Cont Touch, pressure and the texture of objects in the environment, plus the tension in internal organs such as the stomach or bladder, are the functions of these receptors.

Mechanoreceptors cont The skin of humans has tactile receptors. Sometimes animals have hairs with receptors at the base, like whiskers in cats

Cat’s whiskers

Mechanoreceptors cont Some animals have special sense organs called statocysts that serve as gravity receptors.

Mechanoreceptors cont Fish have a lateral line organ that runs the length of the body. This consists of hairs with their tips enclosed in a jelly-like substance. These respond to waves, currents or disturbances in the water.

Lateral Line

Mechanoreceptors cont Proprioreceptors are sense organs that respond to tension in the muscles or joints.

Chemoreceptors Olfaction (smell) this is the detection of chemicals in the air or water that diffuse towards or are swept towards the animal Used for the preliminary examination of things at a distance.

Chemoreceptors Gustation (taste) the detection of chemicals in the liquid or solid state. For the examination of objects that have been touched. Four basic tastes: sweet, sour, salty and bitter

Human Tongue

Gustation Cont These are located in different areas of the tongue.

Chemoreceptors The distinction between smell and taste becomes blurred in simpler animals. Humans use their noses and tongues.

Chemoreceptors Flies have taste hairs on their feet. Many insects smell using antennae.

Chemoreceptors Reptiles have a small opening in the head, this opens into the roof of the mouth. This is called the Jacobson’s organ.

Jacobson’s Organ

Chemoreceptors A snake flicking out its forked tongue is collecting chemical samples and bringing them back to the Jacobson’s organ for analysis.

Pheromones These are chemicals used to communicate between members of the same species. Members of the same species have receptors to pick up these pheromones, other species ignore them.

Auditory Receptors In humans sound waves cause the eardrum to vibrate, these vibrations are transmitted across the middle ear by 3 small bones This sets up vibrations in the fluid-filled cochlea. This initiates impulses in the auditory nerve and we finally hear with our brain.

Human Ear

Auditory Receptors Humans can hear from 20 Hz to 20 000 Hz. Sound above that is ultrasonic. Bats use ultrasonic bleeps as a form of sonar. Dogs and many insects hear in the ultrasonic range.

Auditory Receptors Whales use a complicated communication system involving ultrasonic sounds, echo-location and very low sounds called infrasounds (travel for long distances)

Auditory Receptors Elephants and Hippos use infrasound waves to communicate over long distances.

Detection of Electric Fields. Certain species “stun” their prey with an electric shock e.g. eels Certain fish create an electric field around themselves, allowing them to pick up any disturbances in the field.

Detection of Magnetic Fields. Homing pigeons can detect the magnetic field lines of the earth, they use this to navigate during migration or homing.

Questions Name the colours of light we can see. Which cells see colour and which see black and white? Two eyes facing forward ………. Vision which is good for judging ………… Insects have …….. Eyes made up of many ………. Which give …… vision. Snakes can “see” ……… …….. With small pits set under their ……..

Questions Cont A gravity-detecting organ in invertebrates is called a ………… It consists of a round cavity with small …….., and placed on these is a small, hard, pebble-like object called a …….. In fish the ……... …….. Organ detects disturbances in the water. Name 5 ways that animals use chemicals.

Questions Cont Sounds above those that humans can hear are called …….., and those below are called………. Some fish living in muddy conditions use ……… ………. to test the world around them.