# data[].attributes.attachment_link.description
Carlin, Jeremy, and Ameena teach you a lesson about the bones. LYRICS: The bone-a-fied rap is what were gonna do, the bone-a-fied rap will help you learn about you. Wiggle your phalanges up in the air, wiggle your whole body, like you just don't care.

# data[].attributes.attachment_link.description
If you've ever wondered how your brain and nervous system work, this movie about the Nervous System has the answers!

# data[].attributes.attachment_link.readable_text
Listen

Play Stop Volume mp3 Settings Close Player

Larger text size Large text size Regular text size

What Do Muscles Do?

Did you know you have more than 600 muscles in your body? They do everything from pumping blood throughout your body to helping you lift your heavy backpack. You control some of your muscles, while others - like your heart - do their jobs without you thinking about them at all.

Muscles are all made of the same material, a type of elastic tissue (sort of like the material in a rubber band). Thousands, or even tens of thousands, of small fibers make up each muscle.

What Are the Three Types of Muscles?

You have three different types of muscles in your body:

smooth muscle

cardiac (say: KAR-dee-ak) muscle, and

skeletal (say: SKEL-uh-tul) muscle

What Are Smooth Muscles?

Smooth muscles - sometimes also called involuntary muscles - are usually in sheets, or layers, with one layer of muscle behind the other. You can't control this type of muscle. Your brain and body tell these muscles what to do without you even thinking about it. You can't use your smooth muscles to make a muscle in your arm or jump into the air.

But smooth muscles are at work all over your body. In your stomach and digestive system, they contract (tighten up) and relax to allow food to make its journey through the body. Your smooth muscles come in handy if you're sick and you need to throw up. The muscles push the food back out of the stomach so it comes up through the esophagus (say: ih-SAH-fuh-gus) and out of the mouth.

Smooth muscles are also found in your bladder. When they're relaxed, they allow you to hold in urine (pee) until you can get to the bathroom. Then they contract so that you can push the urine out. These muscles are also in a woman's uterus, which is where a baby develops. There they help to push the baby out of the mother's body when it's time to be born.

You'll find smooth muscles at work behind the scenes in your eyes, too. These muscles keep the eyes focused.

What's the Cardiac (Heart) Muscle?

The muscle that makes up the heart is called cardiac muscle. It is also known as the myocardium (say: my-uh-KAR-dee-um). The thick muscles of the heart contract to pump blood out and then relax to let blood back in after it has circulated through the body.

Just like smooth muscle, cardiac muscle works all by itself with no help from you. A special group of cells within the heart are known as the pacemaker of the heart because it controls the heartbeat.

What Are the Skeletal (Striated) Muscles?

Now, let's talk about the kind of muscle you think of when we say "muscle" - the ones that show how strong you are and let you boot a soccer ball into the goal. These are your skeletal muscles - sometimes called striated (say: STRY-ay-tud) muscle because the light and dark parts of the muscle fibers make them look striped (striated is a fancy word meaning striped).

Skeletal muscles are voluntary muscles, which means you can control what they do. Your leg won't bend to kick the soccer ball unless you want it to. These muscles help to make up the musculoskeletal (say: mus-kyuh-low-SKEL-uh-tul) system - the combination of your muscles and your skeleton, or bones.

Together, the skeletal muscles work with your bones to give your body power and strength. In most cases, a skeletal muscle is attached to one end of a bone. It stretches all the way across a joint (the place where two bones meet) and then attaches again to another bone.

What Are Tendons?

Skeletal muscles are held to the bones with the help of tendons (say: TEN-dunz). Tendons are cords made of tough tissue, and they work as special connector pieces between bone and muscle. The tendons are attached so well that when you contract one of your muscles, the tendon and bone move along with it.

What Do Face Muscles Do?

You may not think of it as a muscular body part, but your face has plenty of muscles. You can check them out next time you look in the mirror. Facial muscles don't all attach directly to bone like they do in the rest of the body. Instead, many of them attach under the skin. This allows you to contract your facial muscles just a tiny bit and make dozens of different kinds of faces. Even the smallest movement can turn a smile into a frown. You can raise your eyebrow to look surprised or wiggle your nose.

And while you're looking at your face, don't pass over your tongue - a muscle that's attached only at one end! Your tongue is actually made of a group of muscles that work together to allow you to talk and help you chew food. Stick out your tongue and wiggle it around to see those muscles at work.

What Are Some Major Skeletal Muscles?

Skeletal muscles come in many different sizes and shapes to allow them to do many types of jobs. Some of the biggest and most powerful muscles are your calf and thigh muscles. They give your body the power it needs to lift and push things. Muscles in your neck and the top part of your back aren't as large, but they are capable of some pretty amazing things: Try rotating your head around, back and forth, and up and down to feel the power of the muscles in your neck. These muscles also hold your head high.

Because there are so many skeletal muscles in your body, we can't list them all here. But here are a few of the major ones:

What's the Deltoid Muscle?

In each of your shoulders is a deltoid (say: DEL-toyd) muscle. Your deltoid muscles help you move your shoulders every which way - from swinging a softball bat to shrugging your shoulders when you're not sure of an answer.

What Are the Pectoralis Muscles (Pecs)?

The pectoralis (say: pek-tuh-RAH-lus) muscles are found on each side of your upper chest. These are usually called pectorals (say: PEK-tuh-rulz), or pecs, for short. When many boys hit puberty, their pectoral muscles become larger. Many athletes and bodybuilders have large pecs, too.

What Are the Rectus Abdominus Muscles (Abs)?

Below these pectorals, down under your ribcage, are your rectus abdominus (say: REK-tus ab-DAHM-uh-nus) muscles, or abdominals (say: ab-DAHM-uh-nulz). They're often called abs for short.

What Is the Biceps Muscle?

When you make a muscle in your arm, you tense your biceps (say: BYE-seps) muscle. When you contract your biceps muscle, you can actually see it push up under your skin.

What Are the Quadriceps (Quads)?

Your quadriceps (say: KWAD-ruh-seps), or quads, are the muscles on the front of your thighs. Many people who run, bike, or play sports develop large, strong quads.

What Is the Gluteus Maximus?

And when it's time for you to take a seat? You'll be sitting on your gluteus maximus (say: GLOOT-ee-us MAK-suh-mus), the muscle that's under the skin and fat in your behind!

Date reviewed: January 2023

# data[].attributes.attachment_link.description
Listen Play Stop Volume mp3 Settings Close Player Larger text size Large text size Regular text size Did you know you have more than 600 muscles in your body? They do everything from pumping blood throughout your body to helping you lift your heavy backpack.

# data[].attributes.attachment_link.description
We couldn’t find the page you were looking for. This is either because:

# data[].attributes.attachment_link.readable_text
Listen

Play Stop Volume mp3 Settings Close Player

Larger text size Large text size Regular text size

Every single person has a skeleton made up of many bones. These bones give your body structure, let you move in many ways, protect your internal organs, and more.

It's time to look at all your bones - the adult human body has 206 of them!

What Are Bones Made Of?

If you've ever seen a real skeleton or fossil in a museum, you might think that all bones are dead. Although bones in museums are dry, hard, or crumbly, the bones in your body are different. The bones that make up your skeleton are all very much alive, growing and changing all the time like other parts of your body.

Almost every bone in your body is made of the same materials:

The outer surface of bone is called the periosteum (say: pare-ee-OSS-tee-um). It's a thin, dense membrane that contains nerves and blood vessels that nourish the bone.

The next layer is made up of compact bone. This part is smooth and very hard. It's the part you see when you look at a skeleton.

Within the compact bone are many layers of cancellous (say: KAN-sell-us) bone, which looks a bit like a sponge. Cancellous bone is not quite as hard as compact bone, but it is still very strong.

In many bones, the cancellous bone protects the innermost part of the bone, the bone marrow (say: MAIR-oh). Bone marrow is sort of like a thick jelly, and its job is to make blood cells.

P

How Do Bones Grow?

When you were a baby, you had tiny hands, tiny feet, and tiny everything! Slowly, as you grew older, everything became a bit bigger, including your bones.

A baby's body has about 300 bones at birth. These eventually fuse (grow together) to form the 206 bones that adults have. Some of a baby's bones are made entirely of a special material called cartilage (say: KAR-tel-ij). Other bones in a baby are partly made of cartilage. This cartilage is soft and flexible. During childhood, as you are growing, the cartilage grows and is slowly replaced by bone, with help from calcium.

By the time you are about 25, this process will be complete. After this happens, there can be no more growth - the bones are as big as they will ever be. All of these bones make up a skeleton that is both very strong and very light.

What Does the Spine Do?

Your spine is one part of the skeleton that's easy to check out: Reach around to the center of your back and you'll feel its bumps under your fingers.

The spine lets you twist and bend, and it holds your body upright. It also protects the spinal cord, a large bundle of nerves that sends information from your brain to the rest of your body. The spine is special because it isn't made of one or even two bones: It's made of 33 bones in all! These bones are called vertebrae (say: VER-tuh-bray) and each one is shaped like a ring.

There are different types of vertebrae in the spine and each does a different kind of job:

The first seven vertebrae at the top are called the cervical (say: SIR-vih-kul) vertebrae. These bones are in the back of your neck, just below your brain, and they support your head and neck. Your head is pretty heavy, so it's lucky to have help from the cervical vertebrae!

Below the cervical vertebrae are the thoracic (say: thuh-RAS-ik) vertebrae, and there are 12 in all. These guys anchor your ribs in place. Below the thoracic vertebrae are five lumbar (say: LUM-bar) vertebrae. Beneath the lumbar vertebrae is the sacrum (say: SAY-krum), which is made up of five vertebrae that are fused together to form one single bone.

Finally, all the way at the bottom of the spine is the coccyx (say: COK-siks), which is one bone made of four fused vertebrae. The bottom sections of the spine are important when it comes to bearing weight and giving you a good center of gravity. So when you pick up a heavy backpack, the lumbar vertebrae, sacrum, and coccyx give you the power. When you dance, skip, and even walk, these parts help keep you balanced.

In between each vertebra (the name for just one of the vertebrae) are small disks made of cartilage. These disks keep the vertebrae from rubbing against one another, and they also act as your spine's natural shock absorbers. When you jump in the air, or twist while slamming a dunk, the disks give your vertebrae the cushioning they need.

What Do the Ribs Do?

Your heart, lungs, and liver are all very important, and luckily you've got ribs to keep them safe. Ribs act like a cage of bones around your chest. It's easy to feel the bottom of this cage by running your fingers along the sides and front of your body, a few inches below your heart. If you breathe in deeply, you can easily feel your ribs right in the front of your body, too. Some thin kids can even see a few of their ribs right through their skin.

Your ribs come in pairs, and the left and right sides of each pair are exactly the same. Most people have 12 pairs of ribs, but some people are born with one or more extra ribs, and some people might have one pair less.

All 12 pairs of ribs attach in the back to the spine, where they are held in place by the thoracic vertebrae. The first seven pairs of ribs attach in the front to the sternum (say: STUR-num), a strong bone in the center of your chest that holds those ribs in place. The remaining sets of ribs don't attach to the sternum directly. The next three pairs are held on with cartilage to the ribs above them.

The very last two sets of ribs are called floating ribs because they aren't connected to the sternum or the ribs above them. But don't worry, these ribs can't ever float away. Like the rest of the ribs, they are securely attached to the spine in the back.

What Does the Skull Do?

Your skull protects the most important part of all, the brain. You can feel your skull by pushing on your head, especially in the back a few inches above your neck. The skull is actually made up of different bones. Some of these bones protect your brain, whereas others make up the structure of your face. If you touch beneath your eyes, you can feel the ridge of the bone that forms the hole where your eye sits.

And although you can't see it, the smallest bone in your whole body is in your head, too. The stirrup bone behind your eardrum is only .1 to .13 inches (2.5 to 3.3 millimeters) long! Want to know something else? Your lower jawbone is the only bone in your head you can move. It opens and closes to let you talk and chew food.

Your skull is pretty cool, but it's changed since you were a baby. All babies are born with spaces between the bones in their skulls. This allows the bones to move, close up, and even overlap as the baby goes through the birth canal. As the baby grows, the space between the bones slowly closes up and disappears, and special joints called sutures (say: SOO-churs) connect the bones.

What Do the Bones In the Arm Do?

As you sit and type at the keyboard, while you swing on a swing, even when you pick up your lunch, you're using the bones in your fingers, hand, wrist, and arm.

Each arm is attached to a shoulder blade or scapula (say: SKA-pyuh-luh), a large triangular bone on the upper back corner of each side of the ribcage. The arm is made up of three bones: the humerus (say: HYOO-muh-rus), which is above your elbow, and the radius (say: RAY-dee-us) and ulna (say: UL-nuh), which are below the elbow.

Each of these bones is wider at the ends and skinnier in the middle, to help give it strength where it meets another bone. At the end of the radius and ulna are eight smaller bones that make up your wrist. Although these bones are small, they can really move! Twist your wrist around or wave and you'll see how the wrist can move.

What Do the Bones in the Hand Do?

The center part of your hand is made up of five separate bones. Each finger on your hand has three bones, except for your thumb, which has two. So between your wrists, hands, and all your fingers, you've got a grand total of 54 bones - all ready to help you grasp things, write your name, pick up the phone, or throw a softball!

What Do the Leg Bones Do?

Sure, your arm, wrist, hand, and finger bones are great for picking up the phone, but how are you supposed to run to answer it? Well, with the bones of the legs and feet!

Your legs are attached to a circular group of bones called your pelvis. The pelvis is a bowl-shaped structure that supports the spine. It is made up of the two large hip bones in front, and behind are the sacrum and the coccyx. The pelvis acts as a tough ring of protection around parts of the digestive system, parts of the urinary system, and parts of the reproductive system.

Your leg bones are very large and strong to help support the weight of your body. The bone that goes from your pelvis to your knee is called the femur (say: FEE-mur), and it's the longest bone in your body. At the knee, there's a triangular-shaped bone called the patella (say: puh-TEL-luh), or kneecap, that protects the knee joint. Below the knee are two other leg bones: the tibia (say: TIH-bee-uh) and the fibula (say: FIH-byuh-luh). Just like the three bones in the arm, the three bones in the leg are wider at the ends than in the middle to give them strength.

The ankle is a bit different from the wrist; it is where the lower leg bones connect to a large bone in the foot called the talus (say: TAL-iss). Next to the talus are six other bones. But the main part of the foot is similar to the hand, with five bones. Each toe has three tiny bones, except for your big toe, which has just two. This brings the bone total in both feet and ankles to 52!

Most people don't use their toes and feet for grabbing stuff or writing, but they do use them for two very important things: standing and walking. Without all the bones of the foot working together, it would be impossible to balance properly. The bones in the feet are arranged so the foot is almost flat and a bit wide, to help you stay upright. So the next time you're walking, be sure to look down and thank those toes!

What Do Joints Do?

The place where two bones meet is called a joint. Some joints move and others don't.

Fixed joints are fixed in place and don't move at all. Your skull has some of these joints (called sutures, remember?), which close up the bones of the skull in a young person's head. One of these joints is called the parieto-temporal (say: par-EYE-ih-toh TEM-puh-rul) suture - it's the one that runs along the side of the skull.

Moving joints are the ones that let you ride your bike, eat cereal, and play a video game - the ones that allow you to twist, bend, and move different parts of your body. Some moving joints, like the ones in your spine, move only a little. Other joints move a lot. One of the main types of moving joints is called a hinge joint. Your elbows and knees each have hinge joints, which let you bend and then straighten your arms and legs. These joints are like the hinges on a door. Just as most doors can only open one way, you can only bend your arms and legs in one direction. You also have many smaller hinge joints in your fingers and toes.

Another important type of moving joint is the ball and socket joint. You can find these joints at your shoulders and hips. They are made up of the round end of one bone fitting into a small cup-like area of another bone. Ball and socket joints allow for lots of movement in every direction. Make sure you've got lots of room, and try swinging your arms all over the place.

Have you ever seen someone put oil on a hinge to make it work easier or stop squeaking? Well, your joints come with their own special fluid called synovial fluid (say: SIH-no-vee-ul) that helps them move freely. Bones are held together at the joints by ligaments (say: LIH-guh-mints), which are like very strong rubber bands.

How Can I Take Care My Bones?

Your bones help you out every day so make sure you take care of them. Here are some tips:

Protect those skull bones (and your brain inside!) by wearing a helmet for bike riding and other sports. When you use a skateboard, in-line skates, or a scooter, be sure to add wrist supports and elbow and knee pads. Your bones in these places will thank you if you have a fall!

If you play sports like football, soccer, lacrosse, or ice hockey, always wear all the right equipment. And never play on a trampoline. Many kids end up with broken bones from jumping on them. Broken bones can eventually heal, but it takes a long time and isn't much fun while you wait.

Strengthen your skeleton by drinking milk and eating other dairy products (like low-fat cheese or frozen yogurt). They all contain calcium, which helps bones harden and become strong.

Be active! Another way to strengthen your bones is through exercise like running, jumping, dancing, and playing sports.

Take these steps to be good to your bones, and they will treat you right!

Date reviewed: January 2023

# data[].attributes.attachment_link.description
Listen Play Stop Volume mp3 Settings Close Player Larger text size Large text size Regular text size Every single person has a skeleton made up of many bones. These bones give your body structure, let you move in many ways, protect your internal organs, and more.

# data[].attributes.attachment_link.readable_text
What Is the Endocrine System?

The endocrine system is made up of glands that make hormones. Hormones are the body's chemical messengers. They carry information and instructions from one set of cells to another.

The endocrine (pronounced: EN-duh-krin) system influences almost every cell, organ, and function of our bodies.

What Does the Endocrine System Do?

Endocrine glands release hormones into the bloodstream. This lets the hormones travel to cells in other parts of the body.

The endocrine hormones help control mood, growth and development, the way our organs work, metabolism , and reproduction.

The endocrine system regulates how much of each hormone is released. This can depend on levels of hormones already in the blood, or on levels of other substances in the blood, like calcium. Many things affect hormone levels, such as stress, infection, and changes in the balance of fluid and minerals in blood.

Too much or too little of any hormone can harm the body. Medicines can treat many of these problems.

What Are the Parts of the Endocrine System?

While many parts of the body make hormones, the major glands that make up the endocrine system are the:

The pancreas is part of the endocrine system and the digestive system. That's because it secretes hormones into the bloodstream, and makes and secretes enzymes into the digestive tract.

Hypothalamus: The hypothalamus (pronounced: hi-po-THAL-uh-mus) is in the lower central part of the brain. It links the endocrine system and nervous system. Nerve cells in the hypothalamus make chemicals that control the release of hormones secreted from the pituitary gland. The hypothalamus gathers information sensed by the brain (such as the surrounding temperature, light exposure, and feelings) and sends it to the pituitary. This information influences the hormones that the pituitary makes and releases.

Pituitary: The pituitary (pronounced: puh-TOO-uh-ter-ee) gland is at the base of the brain, and is no bigger than a pea. Despite its small size, the pituitary is often called the "master gland." The hormones it makes control many other endocrine glands.

The pituitary gland makes many hormones, such as:

growth hormone, which stimulates the growth of bone and other body tissues and plays a role in the body's handling of nutrients and minerals

prolactin (pronounced: pro-LAK-tin), which activates milk production in women who are breastfeeding

thyrotropin (pronounced: thy-ruh-TRO-pin), which stimulates the thyroid gland to make thyroid hormones

corticotropin (pronounced: kor-tih-ko-TRO-pin), which stimulates the adrenal gland to make certain hormones

antidiuretic (pronounced: an-ty-dy-uh-REH-tik) hormone, which helps control body water balance through its effect on the kidneys

oxytocin (pronounced: ahk-see-TOE-sin), which triggers the contractions of the uterus that happen during labor

The pituitary also secretes endorphins (pronounced: en-DOR-fins), chemicals that act on the nervous system and reduce feelings of pain. The pituitary also secretes hormones that signal the reproductive organs to make sex hormones. The pituitary gland also controls

ovulation and the menstrual cycle in women.

Thyroid: The thyroid (pronounced: THY-royd) is in the front part of the lower neck. It's shaped like a bow tie or butterfly. It makes the thyroid hormones thyroxine (pronounced: thy-RAHK-sin) and triiodothyronine (pronounced: try-eye-oh-doe-THY-ruh-neen). These hormones control the rate at which cells burn fuels from food to make energy. The more thyroid hormone there is in the bloodstream, the faster chemical reactions happen in the body.

Thyroid hormones are important because they help kids' and teens' bones grow and develop, and they also play a role in the development of the brain and nervous system.

Parathyroids: Attached to the thyroid are four tiny glands that work together called the parathyroids (pronounced: par-uh-THY-roydz). They release parathyroid hormone, which controls the level of calcium in the blood with the help of calcitonin (pronounced: kal-suh-TOE-nin), which the thyroid makes.

Adrenal Glands: These two triangular adrenal (pronounced: uh-DREE-nul) glands sit on top of each kidney. The adrenal glands have two parts, each of which makes a set of hormones and has a different function:

1. The outer part is the adrenal cortex. It makes hormones called corticosteroids (pronounced: kor-tih-ko-STER-oydz) that help control salt and water balance in the body, the body's response to stress, metabolism, theimmune system, and sexual development and function.

2. The inner part is the adrenal medulla (pronounced: muh-DUH-luh). It makes catecholamines (pronounced: kah-tuh-KO-luh-meenz), such as epinephrine (pronounced: eh-puh-NEH-frun). Also called adrenaline, epinephrine increases blood pressure and heart rate when the body is under stress.

Pineal: The pineal (pronounced: pih-NEE-ul) body, also called the pineal gland, is in the middle of the brain. It secretes melatonin (pronounced: meh-luh-TOE-nin), a hormone that may help regulate when you sleep at night and when you wake in the morning.

Reproductive Glands: The gonads are the main source of sex hormones. Most people don't realize it, but both guys and girls have gonads. In guys the male gonads, or testes (pronounced: TES-teez), are in the scrotum. They secrete hormones called androgens (pronounced: AN-druh-junz), the most important of which is

testosterone (pronounced: tess-TOSS-tuh-rone). These hormones tell a guy's body when it's time to make the changes associated with puberty, like penis and height growth, deepening voice, and growth in facial and pubic hair. Working with hormones from the pituitary gland, testosterone also tells a guy's body when it's time to make sperm in the testes.

A girl's gonads, the ovaries (pronounced: OH-vuh-reez), are in her pelvis. They make eggs and secrete the female hormones

estrogen (pronounced: ESS-truh-jen) and progesterone (pronounced: pro-JESS-tuh-rone). Estrogen is involved when a girl starts puberty. During puberty, a girl will have breast growth, start to accumulate body fat around the hips and thighs, and have a growth spurt. Estrogen and progesterone are also involved in the regulation of a girl's menstrual cycle. These hormones also play a role in pregnancy.

Pancreas: The pancreas (pronounced: PAN-kree-us) makes insulin (pronounced: IN-suh-lin) and glucagon (pronounced: GLOO-kuh-gawn), which are hormones that control the level of glucose, or sugar, in the blood. Insulin helps keep the body supplied with stores of energy. The body uses this stored energy for exercise and activity, and it also helps organs work as they should.

How Can I Help Keep My Endocrine System Healthy?

To help keep your endocrine system healthy:

Get plenty of exercise.

Eat a nutritious diet.

Go for regular medical checkups.

Talk to the doctor before taking any supplements or herbal treatments.

Let the doctor know about any family history of endocrine problems, such as diabetes or thyroid problems.

When Should I Call the Doctor?

Let the doctor know if you:

drink a lot of water but are still thirsty

have to pee often

have frequent belly pain or nausea

are very tired or weak

are gaining or losing a lot of weight

have tremors or sweat a lot

are constipated

are not growing or developing as expected

# data[].attributes.attachment_link.description
The endocrine system is made up of glands that make hormones. Hormones are the body's chemical messengers. They carry information and instructions from one set of cells to another. The endocrine (pronounced: EN-duh-krin) system influences almost every cell, organ, and function of our bodies. Endocrine glands release hormones into the bloodstream.