Above t - Orange Board of Education
The Senses – Hearing, Sight, Smell, Taste & TouchThe SensesEverything we learn about the world we learn through our senses. The nervous system receives and processes information about the world around us so that we can react, communicate and keep the body healthy and safe. The majority of this information comes through the sensory organs: the ears, eyes, nose, tongue and skin. Specialized cells within these organs receive the stimuli and translate them into signals the nervous system can use. Nerves relay the signals to the brain which interprets them as the 5 main senses: hearing, sight, smell, taste and touch.HearingMusic, laughter or a honking car horn all reach the ears as sound waves in the air. The outer ear is made up of the pinna and the ear canal. The pinna is the part of the ear you see on the side of your head. It's made of tough cartilage covered by skin. Its main job is to gather sound waves and funnel them to the ear canal, which is the pathway that leads to the middle ear. Glands in the skin lining the ear canal make earwax, which protects the canal by cleaning out dirt and helping to prevent infections.The middle ear is an air-filled cavity that turns sound waves into vibrations and delivers them to the inner ear. The middle ear is separated from the outer ear by the eardrum, or tympanic membrane, a thin piece of tissue stretched tight across the ear canal. Sound vibrations hit the eardrum, making it move. This movement leads to vibrations of three very small bones in the middle ear: the malleus (hammer), which is attached to the eardrum, the incus (anvil), which is attached to the malleus and the stapes (stirrup), which is attached to the incus and is the smallest bone in the body. To hear properly, the pressure on both sides of your eardrum must be equal. When you go up or down in elevation, the air pressure changes and you may feel a popping sensation as your ears adjust. They adjust thanks to a tube that connects the middle ear to the back of the nose and acts as a sort of pressure valve, so the pressure stays balanced on both sides of the eardrum.The vibrations from the middle ear change into nerve signals in the inner ear. The inner ear includes the cochlea and the semicircular canals. The snail-shaped cochlea changes the vibrations from the middle ear into nerve signals. These signals travel to the brain along the auditory nerve. The semicircular canals look like three tiny connected tubes. It's their job to help you balance. The canals are filled with fluid and lined with tiny hairs. When your head moves, the fluid in the canals sloshes around, moving the hairs. The hairs send this information to your brain. The brain interprets this information and sends messages to the muscles that help keep you balanced. When you spin around and around in a circle and stop, the reason you feel dizzy is because the fluid in your semicircular canals continues to slosh around giving your brain the idea that you're still spinning even when you aren't. When the fluid stops moving, the dizziness goes away.Taking good care of your hearing is important. Don’t stick things like cotton swabs or fingernails into them. Doing so can scratch the ear canal, push earwax deeper into the ear or even rupture the eardrum. If earwax bothers you or if you have an earache, you should see a doctor. Protecting your hearing is also important. Turn down the volume on the TV, video games and, especially, earbuds. Being exposed to loud noises over time can lead to hearing damage. So, listen low so your hearing doesn’t go.SightYour eye sight allows you to read the back of a cereal box, see all the colors of a rainbow and see a ball that is heading your way. Your eyes automatically focus on objects far away and up close and allow you to see them clearly. Your eyes are at work from the moment you wake up to the moment you close them to go to sleep. They take in tons of information about the world around you and then send that information to the brain for processing so the brain knows what is going on outside of your body.The eye is about as big as a ping-pong ball and sits in a little hollow area (the eye socket) in the skull. The eyelid protects the front part of the eye. The eyelid helps keep the eye clean and moist by opening and shutting several times a minute. This is called blinking, and it's both a voluntary and involuntary action, meaning you can blink whenever you want to, but it also happens without you even thinking about it. The eyelid also has great reflexes that protect the eye. When you step into bright light, for example, the eyelids squeeze together tightly to protect your eyes until they can adjust to the light. If an object comes too close to your eyes the eyelids shut automatically to protect the eyes from possible danger. The eyelashes also help, they work with the eyelids to keep dirt and other unwanted stuff out of your eyes.The white part of the eyeball is called the sclera. The sclera is made of a tough material and has the important job of covering most of the eyeball. Think of the sclera as your eyeball's outer coat. Look very closely at the white of the eye, and you'll see lines that look like tiny pink threads. These are blood vessels, the tiny tubes that deliver blood, to the sclera. The cornea is a transparent dome that sits in front of the colored part of the eye. The cornea helps the eye focus as light makes its way through. It is a very important part of the eye, but you can hardly see it because it's made of clear tissue. Like clear glass, the cornea gives your eye a clear window to view the world through.Behind the cornea are the iris, the pupil, and the anterior chamber. The iris is the colorful part of the eye. The iris has muscles attached to it that change its shape. This allows the iris to control how much light goes through the pupil. The pupil is the black circle in the center of the iris, which is really an opening in the iris that allows light to enter the eye. If you shine a bright light in the eyes, the pupils respond to the brightness and will get smaller when the light shines near them and they'll open wider when the light is gone. The anterior chamber is the space between the cornea and the iris. This space is filled with a special transparent fluid that nourishes the eye and keeps it healthy.Doctors use special microscopes to look at the inner parts of the eye, such as the lens. After light enters the pupil, it hits the lens. The lens sits behind the iris and is clear and colorless. The lens' job is to focus light rays on the back of the eyeball, a part called the retina. The lens focuses the light images so you can see clearly. Your retina is in the very back of the eye. It holds millions of cells that are sensitive to light. The retina takes the light the eye receives and changes it into nerve signals that are sent to the brain so the brain can understand what the eye is seeing. The lens is suspended in the eye by a bunch of fibers. These fibers are attached to a muscle that allow the lens to focus but keep it in place in the eyeball. The biggest part of the eye sits behind the lens and gives the eye its shape because it's filled with a clear, jelly-like material that makes the eyeball slightly squishy. The retina uses special cells that can sense combinations of light waves that enable our eyes to see millions of colors. As a result you are able to see your friend walking down the street that is wearing black shorts and a green shirt carrying an orange basketball instead of everything looking like a black and white photograph.The optic nerve, at the back of the eye, is like a high-speed telephone line that carries messages from the eye to the brain. When you see an image, your eye "telephones" your brain with a report on what you are seeing so the brain can translate that report into an image that it identifies as a cat, an apple, a bicycle or whatever it is you are looking at.Above the outer corner of each eye are glands. These glands make tears. Every time you blink your eye, a tiny bit of tear fluid comes out of your upper eyelid. It helps wash away germs, dust, or other particles that don't belong in your eye. Tears also keep your eye from drying out. Then the fluid drains out of your eye by going into the tear duct. You can see the opening of your tear duct if you very gently pull down the inside corner of your eye. When you see a tiny little hole, you've found the tear duct. Your eyes sometimes make more tear fluid than normal to protect themselves. This happens if you've been poked in the eye, if you've been in a dusty or smoky area, or if you've been near someone who's cutting onions. How about the last time you felt sad, scared, or upset? Your eyes got a message from your brain to make you cry, and these glands made many, many tears.Sometimes someone's eyeball shape makes it difficult for the cornea, lens, and retina to work perfectly as a team. When this happens, some of what the person sees will be out of focus. To correct this fuzzy vision, many people, including many kids, wear glasses or contact lenses. Glasses and contact lenses help the eyes focus images correctly on the retina and allow someone to see clearly. As adults get older, their eyes lose the ability to focus well and they often need glasses to see things up close or far away.It is important to take steps to protect your eyes. Wear protective goggles in situations where debris or chemicals could go flying. Wear eye protection when playing certain sports, like racquetball or hockey, where it is common to get hit in the face with equipment. Wear sunglasses on bright, sunny days. Too much light can, over time, cause damage to your eyes and cause vision problems later in life.SmellBesides being the main gate to the respiratory system, your nose lets you smell and it’s a big part of why you are able to taste things. The nose has two holes called nostrils. The nostrils and the nasal passages are separated by a wall called the septum. The septum is located deep inside your nose, close to your skull, and is made of very thin pieces of bone. Closer to the tip of your nose, the septum is made of cartilage, which is flexible material that's firmer than skin or muscle but not as hard as bone, If you push on the tip of your nose, you can feel how wiggly it is. Behind your nose, in the middle of your face, is a space called the nasal cavity. It connects with the back of the throat. The nasal cavity is separated from the inside of your mouth by the roof of your mouth, which is called the palate.When you inhale air through your nostrils, the air enters the nasal passages and travels into your nasal cavity. The air then passes down the back of your throat into the trachea, or windpipe, on its way to the lungs. Your nose is also a two-way street. When you exhale the old air from your lungs, the nose is the main way for the air to leave your body. But your nose is more than a passageway for air. The nose also warms, moistens, and filters the air before it goes to the lungs. The inside of your nose is lined with a moist, thin layer of tissue called a mucous membrane. This membrane warms up the air and moistens it. The mucous membrane makes mucus, that sticky stuff in your nose you probably know as snot. Mucus captures dust, germs, and other small particles that could irritate your lungs. If you look inside your nose, you will also see hairs that can trap large particles, like dirt or pollen. If something does get trapped in there, you sneeze. Sneezing sends the unwelcome particles speeding out of your nose at 100 mph! Further back in your nose are even smaller hairs called cilia that you can see only with a microscope. The cilia move back and forth to move the mucus out of the sinuses and back of the nose. Cilia can also be found lining the air passages, where they help move mucus out of the lungs.Up on the roof of the nasal cavity are olfactory (smell) receptors. There are about 10 million of them, they are very sensitive to odor molecules that travel through the air and they have the ability to sense certain odor molecules. When the smell receptors are stimulated, they send information along the olfactory nerve to the brain and the brain interprets the information as a smell you may recognize. The interaction between these receptors and the brain allow us to recognize about 10,000 different smells. Identifying smells is your brain’s way of telling you about your environment. Your sense of smell also can help you keep safe. For example, it can warn you not to eat something that smells rotten or help you detect smoke before you see a fire.TasteMost people just think of the tongue when they think about taste. But you couldn't taste anything without some help from the nose! The ability to smell and taste go together because odors from foods allow us to taste more fully.Your tongue is made up of many groups of small muscles that run in different directions to carry out all the tongue’s jobs. You need your tongue to chew, swallow, sing, talk and taste. The front part of the tongue is very flexible, can move around a lot. It works with the teeth to create different sounds and also helps to move food around your mouth while you chew. Once the food is ground up and mixed with saliva, the back of the tongue helps to push small bits of food into the esophagus so it can make its way to the stomach.The top of the tongue is rough and bumpy and the underside is very smooth. The bumps on the top are covered with taste buds. People are born with about 10,000 taste buds that helps us taste everything we eat. Taste buds can detect sweet, sour, bitter and salty flavors. Each taste bud is made up of taste cells, which have sensitive, microscopic hairs which send taste messages to the brain. The brain interprets the signals and identifies the taste for you.TouchThe organ for the human sense of touch is the skin. It is the largest sense organ because unlike the others, it is not located at any specific place, but covers the entire body. The skin contains millions of nerve endings that sense the environment around the body. It is composed of several layers. The very top layer is the epidermis and is the layer of skin you can see. It is made mostly of dead skin cells, it is waterproof and serves as a protective wrap for the underlying skin layers and the rest of the body. It contains melanin, which protects against the sun’s harmful rays and also gives skin its color. When you are in the sun, the melanin builds up to increase its protective properties, which also causes the skin to darken. The epidermis also contains very sensitive cells called touch receptors that give the brain a variety of information about the environment the body is in. Our sense of touch uses these receptors to help us to respond to different stimuli such as pain, pressure, tension, temperature, texture, shape, weight, contours and vibrations. It helps us move away when the brain perceives that there is a danger.The second layer of skin is the dermis. The dermis contains hair follicles, sweat glands, oil glands, blood vessels, nerve endings, and a variety of touch receptors. Its primary function is to sustain and support the epidermis by transferring nutrients to it and replacing the dead skin cells that are shed off the upper layer of the epidermis. New cells are formed at the junction between the dermis and epidermis, and they slowly push their way towards the surface of the skin so that they can replace the dead skin cells that are shed. Oil and sweat glands eliminate waste produced at the dermis level of the skin by opening their pores at the surface of the epidermis and releasing the waste.The bottom layer is the subcutaneous tissue which is composed of fat and connective tissue. The layer of fat acts as an insulator and helps regulate body temperature. It also acts as a cushion to protect underlying tissue from damage when you bump into things. The connective tissue keeps the skin attached to the muscles and tendons underneath.Sensory nerve receptors that receive very fine signals (stimuli) are located very close to the surface of the skin such as the epidermis and dermis. A little deeper, other receptors respond to stretching of the skin, vibrations, and pressure. Receptors that respond to heat and cold are known as Thermoreceptors. Nociceptors respond to painful stimuli. Mechanoreceptors are those that respond to mechanical stimuli such as tension, pressure or vibration. Chemoreceptors respond to chemical stimuli such as taste and smell. The entire network of sensory receptors does not only exist in the skin. It is distributed all over the inside of the body such as muscles, bones and joints, heart and blood vessels. A few places without sensory receptors are our hairs and fingernails. This is why we feel no pain when we cut or trim them.Like the other senses, the brain is the master organ that determines the meaning of the signals it receives from each receptor. It decides if an object is cold or hot, rough or smooth, heavy or light, wet or dry, sharp or blunt. The stimuli detected by the receptors would not make any difference if the information could not reach the brain. The receptors receive and transmit messages that are sent to and from the brain. This allows the brain to communicate with the body. When your hand touches an object, the receptors in the skin are activated, and they start a chain of events by signaling to the nearest receptor that they touched something. This message gets passed on from receptor to receptor and on it goes until the message is sent to the brain. Now the brain can process what your hand touched and send messages back to your hand to let the hand know if the brain wants more information about the object it is touching or if the hand should stop touching it. ................
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