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Part XX: How Organisms Communicate

The Effect of Stimuli on the Behaviour of an organism
The Effect of Chemical Stimuli
The Effect of Sound Stimuli
The Effect of Light Stimuli
The Effect of the Touch on Stimulus
The Effect of Stimuli on Behaviour Summary
(useful for revision)

The Effect of Stimuli on Behaviour : Questions

Chemical Emitters and Receptors
Light Emitters and Receptors
Touch Receptors
Emitters and Receptors Summary (useful for revision)
Emitters and Receptors : Questions

Communication inside the Organism
The Vertebrate Central Nervous System

Topic Chapters Index


More about Sound

Purring is not a noise but a vibration caused by the blood as it passes, inside a large blood vessel, through the diaphragm. Both male and female cats purr. It is not certain why the male purrs but, in the female, purring is a stimulus for the kittens. When kittens are born they are blind, have undeveloped ears and no sense of smell. The purring vibration keeps them in touch with their mother. When the kittens start to suckle, the mother cat stops purring.

Bat, Queensland, Australia  © Shirley Burchill


Ultrasound is the name given to sounds with frequencies too high for most humans to hear. The horseshoe bat is so called because its mouth is shaped like a horseshoe. It sends out a narrow beam of ultrasound waves. The few people who are able to hear these sounds describe them as a series of clicks. Each click sound is 50-60 milliseconds long and the sounds get closer together as the bat gets closer to its prey.


Fact File No.48

The cat has 30 muscles to control its ear movement compared to the 6 muscle which control the human ear.


Elephants communicate using smell, sight, sound and touch. They can make different types of noises including bellows, squeals and growls.


Elephant, African Savannah © Shirley Burchill


The low growl which comes from the larynx can be heard for up to 2 kilometres. The noise serves as a warning for other elephants.


Fact File No.49

The male cricket rubs its wings together 30 times per second.


The snake does not have a voice box or vocal cords. The hissing sound which it produces is made by the fast movement of air through its single lung.


Snake, Bristol Zoo  © Shirley Burchill


The snake has an inner ear but it does not have a membrane. It picks up vibrations from the ground which are then amplified by its long lung and passed to the inner ear. In fact, the snake listens with its chest!


Fact File No.50

The dog has 17 muscles which control its ear movements and it is able to hear sounds which the human ear cannot.



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Noisy sealion, Bristol Zoo, UK © Shirley Burchill


A stimulus is sent from an emitter organ and received by a receptor. A stimulus can also come from the external environment, such as a change in temperature or in the hours of daylight.

There are many different kinds of emitter organs and, as you might expect, a wide variety of different receptors.


Sound: Emitter organs

Drawing of lips © Shirley Burchill

The lips, tongue and teeth are used to produce different sounds. The three drawings above show the positions of the lips, tongue and teeth in the production of three vowel sounds. Can you work out which?


There are various types of emitter organs which produce sound. Mammals have a voice box in their throats, just above the trachea. Inside the voice box there are vocal cords which vibrate as air is passed through them. The sound can vary in pitch if the vocal cords are either tightened or loosened. It is very much the same as adjusting a guitar string. If the string is tightened, the pitch is higher.

It is the shape if the lips which determines the sound which will be produced. The loudness is increased by increasing the speed of the air passing through the vocal cords.


Dolphin drawing © Shirley Burchill

The dolphin makes clicking noises in its throat which are amplified in its forehead. The amplified sound waves then move through the water. If they encounter something solid they are reflected back towards the dolphin. The dolphin detects the reflected sound waves using receptors near the base of its flippers and in its chin.

Male frogs and toads make croaking noises. They both have simple vocal cords; two slits in the floor of the mouth which lead to a vocal pouch. Air from the lungs is forced through the vocal cords and into the vocal pouch. This causes the vocal pouch to inflate and the sound is amplified.


Drawing of song-bird © Shirley Burchill

Bird songs are produced by an organ called the syrinx. The syrinx is found at the point where the trachea splits into the two bronchi and is therefore quite different from the voice box or larynx of mammals. There is a membrane in the syrinx which vibrates and produces sound when air passes over it.

Animals with an exoskeleton, such as insects, make a noise by rubbing together parts of their hard, outer covering. In many cases it is the wings which are rubbed together although animals with long back legs, such as the grasshopper, are able to rub them together to produce sound.

Sound : Receptor Organs


Section through the human ear © Shirley Burchill


The receptor organs which receive sound may look very different and are to be found on different parts of the animals' bodies, but essentially they function in the same way. They all include a membrane which is a thin piece of stretched 'skin'. This membrane vibrates as the sound waves in the air reach it. The vibrations of the membrane are then translated into sound by the body of the animal.

Insects have these membranes on their front pair of legs. Mammals have organs called ears and many have large structures made of skin, called pinnae (sing. pinna) which make up a part of the outer ear. These can collect sound waves and focus the sound towards the membrane and the inner ear.


Lizard, Bristol Zoo, UK © Shirley Burchill


Amphibians, reptiles and birds also have ears with membranes but no pinnae. It is for this reason that a bird needs to move its whole head to find the source of a sound. Fish have a lateral line on each side of the body. The lateral line picks up differences in the pressure of the surrounding water. The lateral line system, however, is thought of as an organ of touch rather than an organ of sound.


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