Cartilage – tough, flexible material found in the nose, outer ear, and joints Cilia – tiny hairs found in the nose and ears Mucus – sticky, slime-like substance found in the nose Nasal passages – curved tubes inside the nose that warm, moisten, and filter air Nostrils – openings in the nose where air enters Olfactory nerve – nerve that sends smells to the brain Receptor cells – nerve cells that react to smells or tastes Saliva – liquid in the mouth Taste buds – receptor cells that react with the chemicals in food so that people can sense whether food is sweet, salty, sour, or bitter Tongue – floppy muscles in the mouth Things to look for: How receptor cells so their jobs The four smells the nose can identify The four tastes the tongue can identify Have you ever… Gagged when smelling some really awful odor? Had a bad cold and found food didn’t taste right? Tasted something and decided you didn’t like the food?
Smell
Smell happens inside your nose. In humans, the sense of smell is about 10,000 times more sensitive or powerful than the sense of taste. But compared to other animals, the sense of smell in humans is very poor.
Physical Structures
The nose is made of bone and flexible cartilage. Air enters the nose through the nasal passages. These passages warm, moisten, and filter the air before it moves into the rest of the respiratory system. The nasal passages are curved so air flows and changes directions. The air is better warmed, moistened, and filtered. The nostrils and nasal passages are lined with a moist, sticky, slime-like substance called mucus. The mucus traps dust and other particles in the air. It also helps to moisten the air as you breather it in. Like your ears, the nose has lots of tiny, curly hairs called cilia inside it. Cilia also help trap particles from the air. Odors are particles floating in the air that are so small they can only be seen using a microscope. Odors are absorbed by mucus in the nasal cavity. There, they come in contact with the receptor cells, or nerve cells, that react to smells. The receptor cells that react to odors are in the upper half of each nostril and within the nasal cavity. The receptor cells change odors into electrical signals which the part of the brain called the cerebrum interprets as smells. Olfactory nerves, like the other sense neurons, or nerve cells, send electrical signals to the brain.
Identifying Scents
Our brain uses the receptor cells to identify four basic smells:
Fragrant (a flower)
Fresh (after a rain shower)
Spicy (chili or Mexican foods)
Putrid (skunk spray)
The brain may respond automatically to some scents. For example, pleasant food odors may cause your mouth to water. Putrid odors may cause you to gag or even vomit. Your sense of smell can warn you of danger, such as smoke, poisonous gases, or even a skunk. When you have a cold, you often lose the sense of smell. Your nose gets blocked with extra mucus, which stops the scent particles from getting to the receptor cells. Much of what you taste is really because of smells. Working together, smell and taste become a system that is sensitive enough to identify thousands of different foods. Because of smells and taste, you enjoy eating food and even develop favorite foods.
Taste
The organ used for taste is the tongue. The surface of the tongue is covered with several thousand receptors called taste buds. To taste something, food must be dissolved by saliva, which is a liquid in the mouth. Taste buds on the tongue respond to chemicals in the dissolved food. Below each taste bud are receptor cells, which send electrical signals to the cerebrum. There, the brain interprets the signals as taste. You have about 9,000 taste buds on your tongue. As you get older, some taste buds die. This is why foods taste different to adults and children. This would also explain why you might hate broccoli as a child but like it as an adult. A smaller number of taste buds can make eating less enjoyable. As a result, some elderly people have poor appetites because nothing tastes good to them any longer.
The Tongue
The tongue doesn’t just help you taste food. This floppy muscle also plays a part in your digestive system by mashing your food and moving it around to be chewed and swallowed. Another important job of the tongue is to help you speak. It shapes the sounds you make, especially the consonants.
Using the description in the chapter about where on the tongue you taste certain flavors, write the correct flavor tasted one each line: Sweet, salty, sour, and bitter. Two of the tastes will be listed twice.
Fill in the missing word.
The _______________________is made of bone and flexible cartilage.
Air enters the nose through the ___________________________.
______________________________ tastes react on the sides of the tongue by your molars.
______________________ is the scientific name for the sticky substance in your nose.
The taste buds for __________________ tastes are on the tip of your tongue.
Burnt coffee tastes __________________.
A skunk makes a _____________________ smell.
Flowers smell ____________________________.
You have two nasal ______________________ in your nose.
There are about 9,000 ____________________ on your tongue.
To taste something, food must first be dissolved in _______________________.
_____________________ in the ears and nose help trap dust and particles.
Chili smells _________________.
The ________________ helps you speak and chew food.
__________________ are found in the nose and ears.
After a rain shower, the air smells _____________________.
The _________________is the main organ for smell.
All sensory nerves send electrical signals to the ________________________.
___________________________ is a sticky slime-like substance in the nose, while ____________________ is a liquid in the mouth.
________________________is a tough, flexible tissue.
Mexican food smells ____________________________.
In the _________________________, air is warmed, moistened, and filtered.
Olfactory _________________________ take electrical signals to the brain.
The tongue is a floppy ___________________ that helps you eat and speak.