Moving and Growing

1. Moving and Growing

2. The human body The endoskeleton SKELETONS INSIDE AND OUT Skeletal systems come in many forms. You have a skeleton inside of your body (endoskeleton) made up of bones.

5. Joints and muscles Our muscles help us move our arms and other parts of our body. Our biceps and triceps help you lower and raise you arms. Your brain sends a signal by your nerves to your muscles. 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. 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. 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.

6. Ball and socket Ball-and-socket joints are a special class of synovial joints that enjoy the highest freedom of motion in the body thanks to their unique structure. The shoulder and hip joints are the only ball-and-socket joints in the human body due to the need for great motion at the end of the body’s limbs and the vast amount of musculature needed to move and support such flexible joints. Two main components make up a ball-and-socket joint: a bone with a spherical head and a bone with a cup-like socket [ In the shoulder joint, the spherical head of the humours (upper arm bone) fits into the glenoid cavity of the scapula (shoulder blade). The glenoid cavity is a small and shallow cavity that permits the shoulder joint the greatest range of motion in the human body. A hyaline cartilage ring called the labrum surrounds the glenoid cavity to provide a flexible reinforcement to the joint, while muscles of the rotator cuff hold the humours in place within the cavity. The hip joint is somewhat less mobile than the shoulder, but is an overall stronger and more stable joint. The added stability of the hip joint is necessary to bear the weight of the body resting on the legs while performing actions such as standing, walking, and running. In the hip joint the rounded, almost spherical head of the femur (thigh bone) fits tightly into the acetabulum, a deep socket in the oscoxa (hip bone). Many tough ligaments and the powerful hip muscles hold the head of the femur in place and resist some of the most powerful strains in the body. The depth of the acetabulum also prevents dislocations of the hip by limiting the movement of the femur within its socket.

7. Hinge A hinge joint is a common class of synovial joint that includes the ankle, elbow, and knee joints. Hinge joints are formed between two or more bones where the bones can only move along one axis to flex or extend. The simplest hinge joints in the body are the inter phalangeal joints found between the phalanges of the fingers and toes. In these hinge joints, the bones are able to flex to decrease the angle between them - like when making a fist or curling the toes - and extend to increase their angle to about 180 degrees when holding the foot or hand flat... [Continued from top] Because very little body weight and mechanical force is exerted on these joints, they are made of very simple synovial joint material with tiny accessory ligaments for reinforcement. Each bone is capped with a thin layer of smooth hyaline cartilage to reduce friction in the joint and to absorb the shock of the joint being compressed. The bones are surrounded by a capsule of tough fibrous connective tissue lined with synovial membrane. The joint capsule at these joints forms the knuckle that is visible through the skin that covers it. Oily synovial fluid produced by the synovial membrane lubricated the joint to reduce friction and ensure the free movement of the hinge joints. The elbow is a more complex hinge joint that forms between the humours of the upper arm and the ulna and radius of the forearm. The elbow is subjected to much stronger forces than the knuckles of the fingers and toes, and thus contains several strong accessory ligaments and unique bone structures that reinforce its structure.

8. Invertebrates About 97 percent of all known animal species are invertebrates. Many of these species are classified in one of eight basic groups (although it should be noted that these basic groups provide a simple overview of invertebrates; there are in fact over 30 phyla of invertebrates). This article explores invertebrate classification in order to better understand the diversity and common characteristics of invertebrates.