The skeleton acts like a shield for our vital organs, such as our brain and heart. The skull protects the brain, the ribcage protects the lungs and heart, and the backbone wraps all the way around the spinal cord.
Ligaments connect bones to other bones.
Bone density measures how healthy a bone is – it shows how much mineral matter there is in a square centimetre of bone.
Bone marrow is a tissue found inside bones. Bone marrow is part of the lymphatic system, which plays an important role in the immune system – how our body fights diseases.
Bones have three parts:
- The periosteum is a thin membrane on the outer surface – it contains the bone’s nerves and blood vessels.
- Underneath this is cortical bone – also called compact bone – which is smooth and hard.
- Cancellous bone is located in layers within compact bone – it’s sometimes called spongy bone because it has little holes in it.
There are six different kinds of fractures: complete, greenstick, single, comminuted, bowing and open. Doctors use x-rays to help them decide how to set the broken bones so they can join back up with new cells and blood vessels.
Bones need calcium to keep healthy. Calcium can be found in dairy products, dark green leafy vegetables, nuts, orange juice and soy.
Vitamin D helps the body and bones absorb calcium – fish and egg yolks both have vitamin D in them.
There are four main kinds of bones:
There are three kinds of muscles – smooth, cardiac and skeletal.
Smooth muscles and cardiac muscles are also called involuntary muscles, because they move without you telling them to.
Skeletal muscles are also called voluntary muscles, because you can control when you move them.
When muscles feel sore, it can be because of a strain – the muscle fibres have torn a bit and need time to heal. This happens if you’ve picked up something very heavy, or if you’ve been doing a lot of running and jumping.
Another type of muscle injury is a sprain – this happens when a tendon is pulled.
There are four main muscle shapes:
- Spindle-shaped muscles, which are thick in the middle and thinner at the ends, such as your biceps and triceps in your arm
- Flat muscles, such in your forehead
- Triangular muscles, such as the deltoid muscles in your shoulder
- Circular muscles, which are shaped like rings, such as around your mouth
Words to know:
biceps – the muscles in your upper arms
calcium – the mineral that bones need to keep healthy
cancellous bone – a type of bone is located within layers of compact bone, and is sometimes called spongy bone because it has tiny holes in it
compact bone – the smooth, hard part of the bone underneath the periostium, which is what you’ll see when you look at a skeleton
deltoid – the muscles in your shoulders
fracture – the term for a broken bone; there are six different kinds of fractures: complete, greenstick, single, comminuted, bowing and open
involuntary muscles – muscles that you do not control, such as in your heart and stomach
ligaments – strong cords of tissue that connect bones to other bones
osteoporosis – a disease that causes bones to lose density, making them more likely to break
pelvis – the bones at our hips
periostium – the thin membrane covering the outside of the bone, containing nerves and blood vessels
ribcage – a series of connected horizontal bones in your chest that protect the heart and lungs
skeletal muscles – muscles attached to your skeleton with tendons
skull – the bones in our head that protect the brain
sprain – an injury called by pulling a tendon
strain – a muscle injury that can make them feel sore if you’ve picked up something very heavy, or done more running than you’re used to.
tendons – strong cords of tissue that connect muscles to bones
vertebrae – the bones surrounding our spinal cord
vitamin D – helps the body absorb calcium
voluntary muscles – muscles that you can control moving, such as the ones in your arms and legs
What are the main functions of the muscular system?
Muscles play a part in every function of the human body, from circulation to mobility. The muscular system is made up of over 600 muscles. These include three muscle types: smooth, skeletal, and cardiac.
Only skeletal muscles are voluntary, meaning you can control them consciously. Smooth and cardiac muscles act involuntarily.
Each muscle type in the muscular system has a specific purpose. You're able to walk because of your skeletal muscles. You can digest because of your smooth muscles. And your heart beats because of your cardiac muscle.
The different muscle types also work together to make these functions possible. For instance, while you're running (using skeletal muscles), your heart pumps harder (due to the cardiac muscle), which causes you to breathe heavier (using smooth muscles).
Keep reading to learn about some of your muscular system’s main functions.
Mobility is your muscular system's simplest and most crucial function. Your skeletal muscles are largely responsible for the movements and motions you make. Skeletal muscles are attached to your bones. They’re controlled, in part, by the central nervous system. You use your skeletal muscles when you bend, twist, stretch, run, and perform other movements. Fast-twitch skeletal muscles cause short bursts of speed and strength, while slow-twitch muscles function better for longer movement.
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The involuntary cardiac and smooth muscles help your heart beat and blood flow through your body. The cardiac muscle, known as the myocardium, is found in the walls of heart. The cardiac muscle is controlled by the autonomic nervous system, which is responsible for most bodily functions.
This muscle produces electrical impulses, which help pump blood and cause your heart to beat. It’s striated, like skeletal muscles, and has one central nucleus, like a smooth muscle. Your blood vessels are made up of smooth muscles, and are also controlled by the autonomic nervous system.
Digestion is controlled by smooth muscles found in your gastrointestinal tract. This comprises the:
- small and large intestines
The digestive system also includes the liver, pancreas, and gallbladder.
Your smooth muscles contract and relax as food passes through your body during digestion. These muscles also help push food out of your body, whether through defecation or vomiting when you're sick.
Read more: Preventing digestion problems »
Smooth and skeletal muscles make up the urinary system. The urinary system includes your:
- penis or vagina
The dome of your bladder is made of smooth muscles. You’re able to release urine when those muscles tighten up. When they relax, you’re able to hold in your urine. But all of the muscles in your urinary system work together so you can urinate.
6. Child birth
Smooth muscles are also found in the uterus. During pregnancy, these muscles grow and stretch to compensate for the baby's development. When a woman is ready to go into labor, the smooth muscles of the uterus contract and relax to help push the baby through the vagina.
Learn more: Maintaining a healthy pregnancy »
Your eye socket is made up of six skeletal muscles that help you move your eyes. The internal muscles of your eyes, though, are made up of smooth muscles. These muscles work together to help you see the world around you. If these muscles ever become damaged, your vision can become impaired.
The skeletal muscles in your core help with stability and protecting your spine. Your abdominal muscles, back muscles, and pelvic muscles make up your core muscle group. This core muscle group is also known as the trunk. The stronger your core, the better you’re able to stabilize your body. The muscles in your legs also help steady you.
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Your skeletal muscles also control posture, from your head down to your toes. Flexibility and strength are keys to maintaining proper posture. Stiff neck muscles, weak back muscles, and tight hip muscles, among other ailments, can throw off your alignment. Poor posture can affect your shoulders, spine, hips, and knees. This can lead to joint pain and weaker muscles.
The bottom line
The muscular system is an intricate and complex network of muscles that are vital to the human body. Muscles play a part in everything you do, from chewing to dancing to sleeping. They control our heartbeat and breathing, help our digestion, and allow us to move in the world.
Muscles, like the rest of your body, thrive on exercise and healthy eating. But too much exercise can lead to sore muscles from overuse. Muscle pain can also be a sign that something more serious or chronic is affecting your body.
The following conditions can impact the muscular system and its functions:
- myopathy (muscle disease)
- muscular dystrophy
- multiple sclerosis
- Parkinson's disease
It's important to take care of your muscles so they remain healthy and strong. If you have a muscular condition such as muscular dystrophy, speak with your doctor about ways to maintain muscle health and manage your condition.
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