1. Muscles and Skin

2. The Muscular System One of the organ systems in your body is the muscular system. – The muscular system is composed of all of the muscles in your body. The muscular system enables movement of the body and internal organs.

3. The Muscular System There are about 600 muscles in your body. You are constantly using muscles, no matter how still you try to be. What are some muscles you are always using?

4. Types of Muscles Some muscles in your body are easily controllable. – What are some muscles in your body that you can control? Some muscles in your body are impossible to control completely. – What are some examples of this?

5. Types of Muscles Muscles that you do not consciously control are called involuntary muscles. Involuntary muscles are responsible for functions like breathing and digestion. The muscles that can be controlled are known as voluntary muscles.

6. Types of Muscles Your body has three types of muscle tissue. – Skeletal muscle – Smooth muscle – Cardiac muscle Some of these muscle tissues are involuntary, and some are voluntary.

7. Types of Muscle – Skeletal Skeletal muscles are attached to the bones of your skeleton and provide the force that moves your bones. At each end of a skeletal muscle is a tendon. – A tendon is a strong connective tissue that attaches muscle to bone. Skeletal muscle cells appear banded, or striated. – Skeletal muscles are sometimes called striated muscle.

8. Types of Muscle - Skeletal Skeletal muscles are voluntary. They react very quickly, but tire very easily. Think about running or swimming. The muscles begin to move as soon as the buzzer goes, but feel worn out by the end of the race.

9. Types of Muscle - Smooth Smooth muscles are involuntary. They are found on the insides of many internal organs, such as the stomach and blood vessels. Smooth muscles work automatically to control certain movements inside the body, like digestion.

10. Types of Muscles - Smooth Unlike skeletal muscles, smooth muscles are not striated. They also react more slowly and tire more slowly than skeletal muscles do.

11. Types of Muscles - Cardiac The cardiac muscle tissue is found only in your heart. Like smooth muscle, cardiac muscle is involuntary, but like skeletal muscle, it is striated. Cardiac muscle does not get tired. It contracts repeatedly.

12. How Muscles Work When you flex, the muscles in your arm are contracting, making them shorter and thicker. Muscle cells contract when they receive messages from the brain through the nervous system.

13. How Muscles Work Muscle cells can only contract, not extend. Because of this, muscles have to work in pairs. While one muscle in the pair contracts, the other relaxes to its original shape.

14. How Muscles Work Exercise is necessary to maintain both muscular strength and flexibility. Exercise makes individual muscle cells grow in size. – As a result, the whole muscle becomes thicker. When stretching, muscles gain flexibility.

15. Muscle Injury A muscle strain (pulled muscle) can occur when a muscle has been overworked or overstretched. – Tendons can also be overstretched or torn. After extended exercise, a muscle can cramp. A cramp is when the entire muscle contracts strongly and stays contracted.

16. Skin Skin actually performs many major functions for your body. – Covers and protects the body from injury – Regulates body temperature – Eliminates waste – Gathers information about the environment – Produces vitamin D

17. Skin Protecting the body – The skin protects the body by forming a barrier that keeps disease-causing bacteria and other harmful substances out of the body. – It also keeps important substances inside the body.

18. Skin Maintaining Temperature – Many blood vessels run through the skin. When you are too warm, these blood vessels expand, allowing more blood to flow through. This allows heat to move from inside to outside of the body.

19. Skin Maintaining Temperature – Skin also has many sweat glands. These sweat glands allow perspiration. As this sweat evaporates, it cools your skin. Eliminating Wastes – Perspiration takes with it many waste materials that are dissolved in your sweat. Gathering Information – The nerves in your skin provide information about things like pressure, pain, and temperature.

20. Skin Producing Vitamin D – Some skin cells produce vitamin D when exposed to sunlight. – Vitamin D is important because it helps the cells in your digestive system absorb the calcium in your food. – Your skin needs only a few minutes each day of sunlight to produce all of the vitamin D you need in a day.

21. The Epidermis Skin is organized into two main layers. – The epidermis and the dermis.

22. The Epidermis The epidermis is the outer layer of the skin. The epidermis is thinner than the dermis in most places. The epidermis does not have nerves or blood vessels. – This is why shallow scratches are sometimes not felt and often do not bleed.

23. The Epidermis As skin cells in the lower epidermis die, they form the outer layer of your skin. These dead cells remain on the top layer of the epidermis before they are shed and replaced.

24. The Epidermis Other cells in your epidermis produce melanin. – Melanin is a pigment that gives your skin its color. – The more melanin your skin has, the darker it is. Sunlight stimulates melanin production in your epidermis. Melanin also protects your skin from burning.

25. The Dermis The dermis is the inner layer of your skin. The dermis is located in between the epidermis and a layer of fat. It contains nerves, blood vessels, sweat glands, hairs, and oil glands.

26. The Dermis The sweat glands produce perspiration, which exits the body through openings called pores. Hair grows in the dermis in follicles. Oil produced by oil glands around hair follicles helps waterproof hair and keep skin moist.