UNIT 4. BONES AND MUSCLES

Transcription

1 UNIT 4. BONES AND MUSCLES

2 1. Skeletal System 1. Functions of the Skeletal System The cervical vertebrae make up the neck. You have 7 of these and the top one is connected to the base of the skull. They let you bend, tilt and turn your head. The skeletal system has five main functions: It provides shape and support It enables you to move It protects your internal organs It produces blood cells You have 12 thoracic vertebrae. The ribs are attached to these. They don t move much, so that your heart and lungs won`t get squashed. It stores certain materials until your body needs them Your skeleton determines the shape of your body. The backbone, vertebral column or spine, is the center of the skeleton. It consists of 26 small bones called vertebrae (singular vertebra) that provide axial support to the thrunk. Your vertebrae are flexible and able to bend. This fact allow you to bend or twist. If your backbone were just one bone, you would not be able to bend or twist. The backbone also provides protection to the spinal cord, which runs through its central cavity. The backbone has five different sections (look at the picture). You have 5 lumbar vertebrae. They allow twisting and turning. The sacrum is the triangular shaped bone located near the base of the spine. The coccyx. It does nothing now, but it used to be a tail.

3 The intervertebral disks are soft tissues (cartilage) that sit between each vertebrae and act as cushions between vertebrae, and absorb energy while the backbone flexes, extends, and twists. The atlas is the first vertebra. The skull balances on it. The atlas sits on a peg on the second vertebra, the axis. The atlas can rotate on the peg, letting you turn your head.

4 Axial skeleton: consists of bones that forms the axis of the body and support and protect the organs of the head, neck and thrunk. Skull (cranium): it is the bony framework of the head. It protects the brain. Sternum (breastbone): it is a long and flat bone, located in the middle of the chest. With the ribs, the sternum forms the rib cage that protects the heart, lungs, and the major blood vessels from damage. Ribs: they are thin, flat and curved bones that form a protective cage around the organs in the upper body. They are 12 pairs. Floating ribs are the last two ribs and are smaller. Vertebral column: the central axis determining shape of your body. All the bones of your body are in some way connected to your vertebral column. HUMAN BODY SKELETON Appendicular skeleton: it is composed of bones that hold the appendages to the axial skeleton. Upper Extremities Lower Extremities The arm: region between the shoulder and the elbow. It consists of a single long bone: the humerus. The forearm: region between the elbow and the wrist. It is formed by two bones: radius and ulna. The hand: three regions: wrist (carpal bones), palm (metacarpals bones) and fingers (phalanges). The thigh: region between the hip and the knee. It consists of a single long bone: the femur (longest and strongest bone in the body). The leg: region between the knee and the ankle. It is formed by two bones: tibia and fibula. The foot: tarsals (ankle), metatarsals and phalanges. The patella (the kneecap): triangular bone between the femur and the tibia.

5 Appendicular skeleton: Clavicle (collarbone): this bone connects the upper arm to the thrunk of the body. Scapula (shoulder blade): large, triangular, flat bone on the back side of the rib cage. It serves as an attachment point for several muscles. Pelvic girdle (hip girdle / pelvis): it consists of coxal bones and sacrum. HUMAN BODY SKELETON Coxal bones

6 HUMAN BODY SKELETON Bones in the hand Phalanges Metacarpals Carpals Bones in the foot Phalanges Metatarsals Tarsals

7 THE SKULL BONES Cranial bones: they make up the protective frame around the brain. Frontal: it forms the forehead and the upper orbit of the eye and the forward parts of the cranium. Parietal: there are two parietal bones which form the largest portion of the top and sides of the cranium. Temporal: like the parietal bones, there are two distinct temporal bones. They form the lower, central sides of the skull around the external ear. Occipital: it forms the back base of the skull. Many neck muscles attach here. Sphenoid: there are two sphenoid bones and they sit behind the eyes and run back towards the temporal bones. Ethmoid: it forms medial portions of the orbits and the roof of the nasal cavity. Facial bones: they make up the upper and lower jaw and other facial structures. Mandible: it is the lower jaw. It is the only moveable bone in the skull. It articulates with the temporal. Maxilla: there are two maxillae bones. They are the upper jaw and form part of the nose, orbits and the roof of the mouth. Nasal: the nasal bones are a pair of small, slender bones that support the bridge of the nose. They are fused at the top of the frontal bone and to the maxillae at the area that completes the inside orbit of the eye. Lacrimal: there are two small lacrimal bones that sit at the inside corner of each eye. Zygomatic: there are two zygomatic bones and they sit on either side of the skull and comprise the higher area of the cheek. A side view of the skull The bones of the skull are not joined firmly at birth. The sutures gradually accumulate minerals and harden (ossification), firmly joining the skull bones together. In an infant, the spaces where sutures intersect but don t completely touch are called fontanels / fontanelles and they are covered by a fibrous membrane. By the time the child reaches 2 years of age, these fontanels have been gradually covered to bone.

8 2. The structure of bones Cross-section of bone In a human body, a living bone is made up of different layers: Periosteum: a thin membrane covering bone surface. It s like the skin of bones. This membrane is full of blood vessels and nerves that supply the cells of the hard compact bone. Compact bone: it is very dense and rigid being packed with calcium and other minerals. Inside the compact bone there is small holes (bone cells) and canals. These canals carry blood vessels (which supply the bone with nutrients and oxygen) and nerves from the bone s surface to the living cells within the bone. Spongy bone: just inside the compact bone is a layer of spongy bone. It is also found at the ends of the bone. It has many small spaces within it. Spongy bone is lightweight but strong. Bone marrow: The spaces in bone contain a soft connective tissue called marrow. There are two types of marrow: red and yellow. Red bone marrow produces the body s blood cells, which fight infection, carry oxygen or stop bleeding. As a child, most of your bones contained red bone marrow. As a teenager, only the ends of your femurs, skull, hip bones and sternum contain red marrow. Your other bones contain yellow marrow, that stores fat and serves as an energy reserve. Spongy bone Compact bone Periosteum Blood vessels Spongy bone Compact bone Yellow marrow Blood vessels Canals Bone cells organized around canals Red marrow Periosteum

9 3. How bones form Bone is formed in a cartilage model. As a child, much of your skeleton was cartilage. Over time, most of the cartilage is replaced with bone. This process of replacement is usually complete by the time you stop growing. Finally, your bones only have cartilage at the end part of them. X-rays of the hands of a 1-year-old (A) and 3-year-old (B) show that the cartilage in the wrist has not yet been replaced by bone. In the X-ray of the 13-year-old s hand (C), the replacement of cartilage by bone is almost complete.

10 4. Joints of the skeleton Body movements are carried out by the interaction of the muscular and skeletal systems. Muscles are connected to bones by tendons. Bones are connected to each other by ligaments. Cartilage forms cushions between bones to stop them rubbing. Where bones meet one another is typically called a joint (the union of two or more bones). Ball-and-socket joint: this type of joint allows the greatest range of motion. In your shoulder, the top of the arm bone fits into the deep, bowl-like socket of the scapula. The joint allows you to swing your arm freely in a circle. Your hips also have this type of joint. Pivot joint: this type of joint allows one bone to rotate around another. The pivot joint in the top of your neck gives you limited ability to turn your head from side to side. Gliding joint: this type of joint allows one bone to slide over another. Wrist and ankles have gliding joints. Hinge joint: this type of joint allows extensive forward and backward motion but not side to side. Knee and elbow have hinge joint Movable joints

11 2. Muscular System 1. Muscle action Muscles make up about 35 40% of the human body weight. There are about 600 muscles in your body. Muscles in your body can be divided into two general groups: Voluntary muscles: they allow us to walk, to smile, to play football. They allow keep your body stable when we are sitting and standing. Our brain sends messages to the muscle when we conciously decide that we want the muscle to contract. Involuntary muscles: their contraction is not under our conscious control. These muscles are normally found in the walls of our internal organs. They are responsible for activities such as breathing and digesting food. 2. Types of muscles There are three types of muscle tissue in your body: Skeletal muscle: they are attached to the bones of your skeleton (by tendons) for voluntary movement. This kind of muscle is commonly called striated muscle because the skeletal muscle cells appear banded or striated. It contains alternating light and dark bands (striations). These striations are caused by the overlapping of the contractile proteins: actin and myosin. This kind of muscle has two important characteristics: they react very quickly and they tire very quickly too. Smooth muscle: This kind of muscle is found in the walls of internal organs like the stomach or blood vessels. Their contraction is not under conscious control so it is an involuntary muscle. They are not striated muscles. Unlike skeletal muscles, they react more slowly and tire more slowly too. Cardiac muscle: this kind of muscle is only found in the heart. Like skeletal muscle cells, cardiac muscle cells contain striations. It is an involuntary muscle. However, unlike skeletal muscles, cardiac muscle does not get tired. It can contract repeatdly. It maintains a consistent heart rate.

12 MAJOR MUSCLES IN YOUR BODY Sternocleidomastoid: long muscle in the neck that rotates the neck and flex the head. Deltoids (shoulder muscles): they move the upper arm. Trapezius: a flat, triangular muscle that covers the back of the neck shoulders and thorax. It elevates and rotates scapula. Pectoral: flexes and adducts arm across chest, pulls shoulders forward. Biceps (brachii): flexes forearm at the elbow. Triceps (brachii): it adducts the arm. Rectus abdominis: a large muscle in the front of the abdomen that assists in the regular breathing movement and supports the muscles of the spine while lifting and keeping abdominal organs such as the intestines in place. Sartorius: it flexes hip and knee. Rectus femoris: it extends knee and flexes hip. Gluteus maximus: powerful extensor of hip. Femoral biceps: it flexes the knee and rotates the leg laterally. Gastrocnemius (calf): the muscle in the back part of the leg that forms the greater part of the calf. It is responsible for the plantar flexion of the foot.

13 MUSCLES OF THE FACE AND HEAD Temporalis: it acts to raise the mandible and close the jaws. Occipital frontal: it raises the eyebrows. Compressor nasi: it constrics the nostrils. Levator labii superioris: it elevates the upper lip.

14 3. Muscles at work Like other skeletal muscles, the muscles in your arm do their work by contracting, or becoming shorter and thicker. Muscle cells contract when they receives messages from the nervous system. Because muscle cells can only contract, not extend, skeletal muscles must work in pairs. While one muscle contracts, the other muscle in the pair returns to its original length. Figure shows the muscle action involved in moving the lower arm. First, the biceps muscle on the front of the upper arm contracts to bend the elbow, lifting the forearm and hand. As the biceps contracts, the triceps on the back of the upper arm returns to its original length. Then to straighten the elbow, the triceps muscle contracts. As the triceps contracts to extend the arm, the biceps returns to its original length. Another example of muscles that work in pairs are those in your thigh that bend and straighten the knee joint.