Biology 30S (11-3) - 2009/2010

Today in class we watched a movie about the Muscular System. Muscles make up 40-50% of a person's body mass. The main functions of muscles are to maintain posture, generate heat, and control voluntary and involuntary movement. Muscles contribute to homeostaiss by helping to maintain a constant body temperature of about 96 degrees. There are three types of muscles: skeletal, cardiac, and smooth.

Skeletal muscles are attached to the bones by tendons. There are two types of skeletal muscles: axial and appendicular. Axial muscles are located in the head, neck and trunk, while appendicular muscles are located in the arms and legs. There are many different types of movements controlled by the skeletal muscles:

• Flexion: brings two bones closer together
• Tension of Extensions: increases the angel betwee two bones
• Abduction: movement of limbs away from the midline of the body
• Aduction: movement of limbs toward the midline of the body
• Rotation: movement in a circular motion (turning the head)
• Circumduction: cone-shaped circular movement of a limb (ball and socket)

The joint between and nerve and a muscle is called a neuromuscular junction. When a nerve impulse is sent by the brain to a muscles, the chemical balance at the neuromuscular junction changes. This causes the muscles to move. We control the movement of skeletal muscles. In other words, it is voluntary movement

Caridac muscle is the muscle that lines the wall of the heart. It contracts and relaxes rapidly in order to keep the heart beating. There are two types of smooth mucles: visceral muscles, which line the walls of hollow organs such as the stomach, and multi-unit muscles, which are located in the iris, sorrounding hair folicles, and line the walls of blood vessels. Both cardiac and smooth muscles expand and contract without nerve impulses. They are involuntary movements.

Muscles have two main energy sources. The most common is oxygen. Endurance building exercise, such as running, requires a lot of oxygen. When muscles run out og oxygen or when muscles cannot take in enought oxygen, they stop contracting. They need a bakc-up energy source so they use sugar or glycolosis. Sugar is a more common energy source from strength building exercise such as lifting weights of sprinting.

The movie also talked a bit about the Integumentary System. This system contains teh skin, hair, nails, and glands. The purpose of it is to protect the body. The skin insulates the body and separates the inside of the body from the outside. As we learned in the Special Senses unit, the skin contains two layers: the dermis and the epidermis. The epidermis is the top layer that contains skin cells. the skin cells are replaced every 35-40 days and are what protect out bodies. Hair also helps protect us from teh sun and also keeps dust adn other particles out of our eyes. Both they hair and nails are made of protein and dead cells. There are two types of glands in the Integumentary system: sebatious and sweat glands. Sebatious glands secrete oil and sweat glands secrete wastes and help regulate body temperature.

Someone had asked about yawning and whether it is voluntary of involuntary. I looked it up and it is involuntary. As you probably know, we yawn when we are bored or tired. During these times, our breathing is shallow and not as much oxygen is reaching the lungs. Yawning is the body`s was of trying to get more oxygen into the lungs. When we yawn, our heart rate increases and the lungs and bloodstream are cleansed of carbon dioxide build-up and are filled with fresh oxygen. This helps us to feel more alert and energized. Even fetuses yawn before they are even born, but scientists do not really understand why yet.