SENSES IN ANIMALS AND HUMANS

Transcription

1 SENSES IN ANIMALS AND HUMANS What are the Senses? The senses are organs in the body that both humans and animals use to take in information from the environment. Humans use their senses to see where they are going, to hear a conversation or music, to feel if something is hot or cold, to taste whether food is sour or sweet and to warn us of danger, such as smelling smoke. We Communicate Using Our Senses As humans, we do not have to rely on our senses as much as animals do in order to survive, there are many things that we would not be able to do without them. Our senses help us to enjoy the world around us. The 5 senses are: Sense of Smell The Five Senses Taste we taste with our tongue Touch we feel with our skin Hearing we hear with our ears Smell we smell with our nose Sight we see with our eyes Version 1: December 2013 Copyright My Cyberwall 1

2 Our sense organs respond to certain stimuli in our environment. For example, our eyes respond to light, our ears respond to sound, our tongue and nose responds to chemicals and our skin responds to pressure and heat. Our senses have receptors which can detect light, smell, touch, taste and sound and transmit messages to our brains through our nervous system. Animals have the same senses as we do, but use them in different ways. They rely on their senses to: find food find a mate look after their young avoid danger and protect themselves Mouse Finding Food Finding a Mate Animals Use Senses to Care for their Young Sight Eyes are the organs used to see. Vision or sight is the body s most dominant sense. Sight provides both humans and animals with a huge amount of information about their surroundings. Sight is our Most Dominant Sense Version 1: December 2013 Copyright My Cyberwall 2

3 Our eyes contain millions of light detecting cells which convert light into electrical signals that travel to our brains. In our brains, these signals are changed into coloured, 3D images. The eyelids protect the eye from bright light, dirt and injury. The eyebrows stop sweat from getting into the eyes. The eyelashes keep dirt and dust out of the eye and protect the eye from glare. The pupil lets lights into the eye. A tear duct in the corner of the eye drain tears away from the eye. The iris is the coloured part of the eye. The cornea is the transparent layer that covers the surface of the eye. When we see, what we are actually seeing is beams of light which bounce off an object and into our eyes. The light enters through the cornea of the eye and then passes through the pupil into the lens. The image is then focused through a jelly- like substance called the vitreous humor, onto the back surface of the eyeball called the retina. An Eye Version 1: December 2013 Copyright My Cyberwall 3

4 The retina is filled with 150 million light sensitive cells which send the information to the brain through the optic nerve. This image is sent to the brain upside down and the brain has to then turn the image so that it appears the right way up! Spectacles (glasses) are used by people to correct poor vision. Binoculars and telescopes make far away objects seem closer, while microscopes magnify tiny objects to make them appear bigger. Spectacles Using a Telescope Using a Microscope to Magnify Objects Many animals have a much better sense of sight than humans. For example, a falcon can see a 10 cm object from a distance of 1,5 km. Some fish can see the infra-red wavelength of the electromagnetic spectrum. Version 1: December 2013 Copyright My Cyberwall 4

5 Smell Our nose is the organ that we use for smell. Nose The senses of smell and taste are closely linked because both work by detecting chemicals. However our sense of smell is times more sensitive than our sense of taste, so when you have a cold, often you will not be able to taste your food. Receptors in our Nose Send Messages to our Brain The organ used to smell is the nose. When we smell something the chemicals in the substance that we smell dissolves in the mucous of our nose. Receptors here send messages to our brain. Our sense of smell is connected to our memory, so a certain smell can remind us of certain events and places. Version 1: December 2013 Copyright My Cyberwall 5

6 There are 7 main odours that humans can detect as shown in the table below: Odour Example Picture Camphoric Mothballs Musky Aftershave or perfume Rose Floral Ethereal Dry cleaning fluid Version 1: December 2013 Copyright My Cyberwall 6

7 Odour Example Picture Pungent Vinegar Putrid Rotten eggs Peppermint Chewing gum Although humans can detect between and different smells, a human s sense of smell is much weaker than an animal s sense of smell. Animals have a Strong Sense of Smell Animals use their sense of smell to find food, find each other and to explore their environment. Version 1: December 2013 Copyright My Cyberwall 7

8 Dogs have a very good sense of smell, which is why they are used to find drugs, bombs and missing people. Sharks also have a very good sense of smell and can smell blood from over 4 km away. Sniffer Dog Sharks can Smell Blood from a Distance Taste Taste helps us to detect and enjoy the flavours of food and drinks. It is the weakest of the 5 senses. The Tongue is Used to Taste Our tongue is the organ that we use for taste. It is covered with around taste buds which can detect substances in food and drink. These taste buds have receptors which send the messages to our brain and tell us if the food or drink tastes nice or not. Version 1: December 2013 Copyright My Cyberwall 8

9 The four main tastes that we can detect are: sweet sour Sweet Taste Cupcakes salty Sour Taste - Lemons and Limes bitter Salty Taste Fish Bitter Taste - Black Coffee Version 1: December 2013 Copyright My Cyberwall 9

10 The salty and sweet taste buds are at the front of your mouth, the sour taste buds are at the sides and the bitter taste buds are at the back of the tongue. When we are very young, we have taste buds on the sides and roof of our mouth as well as our tongue, so we are very sensitive to taste. These disappear as we get older and our taste buds become less sensitive, which is why our taste for certain foods can change. Insects have the most highly developed sense of taste. Insects have a Highly Developed Sense of Taste Version 1: December 2013 Copyright My Cyberwall 10

11 Many animals use their tongues to taste. Snakes, some lizards and cats use their tongues to smell. They have a Jacobson s organ on the roof of their mouth, so when they pull back their tongue, the food touches the Jacobson s organ and they taste the food. Snakes Use their Tongues to Smell Fish can taste with their fins and tail, as well as with their mouth. Fish Taste with Mouth, Fins and Tail Some invertebrates, such as butterflies, have sense organs for tasting on their feet and antennae. Butterflies Taste with their Feet and Antennae Version 1: December 2013 Copyright My Cyberwall 11

12 The earthworm s body is covered with taste receptors. Earthworms have Taste Receptors over their Body Touch The sense organs for the other 4 senses are found in a specific place on our bodies, but the sense organ for touch, i.e. the skin, is found all over our bodies. Touching Hands The skin consists of 2 main layers the epidermis on the outside and the dermis inside. The dermis contains sensory receptors and nerves which help us to detect if something is hot or cold, for example. Version 1: December 2013 Copyright My Cyberwall 12

13 There are around 20 different touch receptors which send messages to our brain through the spinal cord. The most common receptors are heat, cold, pain and pressure. Pain receptors are important for safety because they warn your brain if you are getting hurt. We have more pain receptors than any other touch receptors in our bodies. The fingertips, lips, neck, feet and tongue have the most receptors and are therefore the most sensitive to touch. Each fingertip has around 100 touch receptors in it. This is why it hurts a lot when you burn your tongue, as well as why blind people use Braille to read. Braille works by feeling raised patterns of dots. Using Braille to Read Animals use touch in the same way that we do, however, they have special features, like whiskers, which helps them to feel things from further away. Whiskers Help Cats to Feel Some lizards can detect temperature of sand within 1 C, which helps them to know when to lay their eggs. Version 1: December 2013 Copyright My Cyberwall 13

14 Hearing After sight, hearing is the sense that provides humans with the most information. The ears are the organs used for hearing. Hearing allows us to know what is going on around us. Hearing The sensory receptors in our ears are stimulated by the vibration of sound waves coming from a vibrating sound source. Sounds are vibrations. These vibrations are transferred to three tiny ear bones which are the smallest bones in our bodies called ossicles. The sound is then passed into a coiled tube called the cochlea in the inner part of your ear. From here, nerves send a message to the brain so that we can hear the sound. Version 1: December 2013 Copyright My Cyberwall 14

15 The eardrum vibrates in a similar way to the original source of the vibration. This allows us to hear many different sounds. Humans can hear sounds with a frequency between 20 and 20,000 vibrations per second. Each vibration is called a Hertz (Hz) and this is the measurement used for sound frequency. Many hearing-impaired (deaf) people use sign language and can lip read, i.e. work out what other people are saying by the way that their lips move. Hearing aids also help to make sounds louder for people who have difficulty in hearing. Sign Language Hearing Aid Version 1: December 2013 Copyright My Cyberwall 15

16 A doctor uses an instrument called a stethoscope to listen to your heartbeat and breathing when he examines you. Doctor Using a Stethoscope Animals use hearing to communicate as well as to hunt. A bat makes a shrill call that bounces off anything solid. They then listen for the echo to help them find their prey. This is called echolocation. Bats Use Echolocation to Find Prey Animals can detect a wider range of sounds than humans. Many animals can hear sounds that we cannot hear as humans. Animals such as bats, cats, mice, grasshoppers and whales can hear sounds at frequencies much higher than humans can, i.e Hz. Dogs can hear sound as high as Hz and cats have a range of 100 to Hz. Dolphins have the best hearing of any animal and can hear 14 times better than humans. They can hear up to at least Hz. Dogs and Cats have Better Hearing than Humans Version 1: December 2013 Copyright My Cyberwall 16

17 Mice communicate by ultrasound. A baby mouse will use a frequency of around Hz to call its mother and an adult mouse uses sound frequencies up to Hz. A Baby Mouse Communicates by Ultrasound A whale can transmit sounds up to Hz. Dolphins and whales communicate by making clicks and whistles to each other. Like bats, they also use sound to hunt. The sounds they make bounce back from solid objects and make an echo. Dolphins have the Best Hearing and Use Sound to Hunt Other animals can make and hear very low frequency sounds that humans cannot hear, i.e. less than 20 Hz. Animals which are able to do this include the tiger, giraffe, elephant and the rhino. Tigers, Giraffes, Elephants and Rhino use Low Frequency Sounds Version 1: December 2013 Copyright My Cyberwall 17

18 Animals use sound not only to sense danger, but also for other things. A male grasshopper, for example rubs its wings across its legs to make a loud rasping sound in order to attract females. A Grasshopper has Ears on its Stomach and uses Sound to Attract a Mate Not all animals have ears on their heads. For example, a grasshopper s ears are on its stomach and a cricket has ears on its front legs. Frogs' eardrums are found on the outside of its body, behind its eyes. A Cricket has Ears on its Stomach Frogs have External Eardrums Special Animal Senses We have seen that animals often have more highly developed senses than humans, especially their sense of smell, hearing and sight. In addition, they also have unique receptor cells and can sense stimuli that humans cannot. Some species also have the ability to sense the world in a way that we cannot. For example, some fish can sense water pressure and currents. Crabs have hair on their claws and other parts of their bodies which helps them to detect the water current. A Crab Claw has Hairs to Detect Water Current Version 1: December 2013 Copyright My Cyberwall 18

19 Butterflies have hair on their wings to help them detect changes in air pressure. Butterflies can Detect Changes in Air Pressure Bees have a ring of iron oxide on their abdomens which they use to detect magnetic fields. They may also be able to sense any changes in the Earth s magnetic field and use this to navigate. Bees can Detect Magnetic Fields Ants and bees can detect polarised light, which they use to help them to navigate. Several animals, such as fish have the ability to detect very low levels of chemicals. Fish Can Detect Chemicals Version 1: December 2013 Copyright My Cyberwall 19