Role of Muscles, Ligaments and Tendons in Movement

The skeletal muscles are made up of bundles of muscle fibres. These muscles are attached to the bones of the skeleton to affect movement. Movements of the body are brought about by the contraction of a pair of antagonistic muscles. Energy for this contraction comes from ATP produced in the mitochondria in the muscles. Muscles which contract when receiving impulses from the brain are known as voluntary muscles.
 

Muscles are attached to the bones by tendons. A tendon is a chord of dense connective tissues made up of fibres. These fibres are strong and elastic. At the joints, the bones are held together by ligaments which are flexible, strong and elastic connective tissue. This allows two bones to bones to be held together and permits limited movement but at the same time, ensures that the bones do not become mal-aligned or dislocated.
 

Since muscles can only contract, at least two muscles must be used to move a bone into a position and back again. All skeletal muscles exist in pairs and they act as antagonistic pairs, meaning when one member of a pair of muscles contract, the other must relax. As an example, the movement of the forelimb is brought about by the contraction and relaxation of a pair of antagonistic muscles, namely the biceps and the triceps.
 

When the biceps muscle contracts, the triceps muscle relaxes resulting in the arm being bent. Conversely, to straighten the arm, the triceps muscle contracts while the biceps muscle relaxes. Contraction of the biceps muscle pulls the ulna up thus bending the arm at the elbow joint. Contraction of the triceps muscle pulls the ulna down and the arm is straightened.

Appendicular Skeleton

There are other bones that form the appendicular skeleton which consists of the pectoral girdle, the bones of the limbs and the pelvic girdle.The pectoral girdle provides a connection between the axial skeleton and the forelimbs that is the arm. It is composed of two distinct halves. Each half consists if the scapula and the clavicle. The scapula or shoulder blade is a flat, triangular-shape bone.

The forelimb is made up of the humerus, radius and ulna, carpals, metacarpals and the phalanges. The humerus is the bone of the upper arm. Its upper end is shaped into a rounded head which articulates with the scapula to form a ball-and-socket joint at the shoulder, allowing movement in all directions. The forearm is composed of the ulna and the radius. The ulna is the longer bone and articulates with the humerus whereas the radius is a flattened, slightly curved bone.

The pelvic girdle provides a connection between the axial skeleton and the hind limbs that is the legs. The hind limb consists of several bones, such as the femur, tibia, fibula, tarsals, metatarsals and phalanges. The femur is the largest bone in the human body. Its lower end articulates with the tibia to form a hinge joint at the knee. The fibula is a shorter and smaller bone. Both the tibia and fibula form joints with the tarsus at the ankle.

Happy New Year 2013

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Axial Skeleton

The axial skeleton consists of the skull, vertebral column (made up of vertebrae), ribs and sternum. The human skull looks like a three-dimensional puzzle and is made up of flat bones fused together to form immovable joints. These bones are known as the cranial and facial bones. The lower jaw bone or mandible is movable and allows the mouth to open and close while talking and eating. The eyeballs are located in depressions in the facial bones known as eye sockets.

The vertebral column (backbone or spine) consists of 33 small vertebral bones or vertebrae which are attached together by joints to form a slightly curved, strong and flexible column. The vertebral column supports the head and body and provides a canal for the nerve cord and spaces for the nerves that branch out if the spinal cord. The joints allow limited movement, giving the vertebral column a degree of flexibility. The cartilage disc sandwiched between each pair of vertebrae acts to absorb shock when we move. The vertebral column is divided into five parts based on the location and structure of the vertebrae.
 

There are variations in the size and shape of the vertebrae but a typical vertebra has a solid body or centrum, a neural canal and several bone processes. There are five types of vertebrae based on the five distinct regions where they are found. The cervical vertebrae found in the neck, the thoracic vertebrae found in the thorax or chest region, the lumbar vertebrae found in the abdominal region, the sacrum found in the lower back and the coccyx found right in the end of the vertebral column.
 

Human have seven cervical vertebrae. The cervical vertebrae are easily recognised because they possess a pair of vertebrarterial canals. The function of these canals is to allow the vertebral artery to pass through to the brain. The first cervical vertebra is the atlas while the second cervical vertebra is the axis.
There are 12 thoracic vertebrae. They possess long, backwardly pointing spinous processes and short transverse processes. All the thoracic vertebrae articulate with the ribs except the 11th and 12th thoracic vertebrae. These vertebrae serve to support the ribs.
Scoliosis is a condition caused by the abnormal sideway caused by the abnormal sideway curvature of the spine at the thoracic region, for some unknown reason, it is quite common during childhood, particularly in girls. Scoliosis is treated with body braces or surgery before growth ends. If left untreated, it causes permanent deformity and breathing difficulties.
 

There are five lumbar vertebrae. The lumbar vertebrae are the biggest vertebrae in the vertebral column. They have a short but big centrum because they are subject to the greatest stress. The sacrum consists of five vertebrae fused together to form a broad triangular structure. The coccyx consists of four vertebral bones which are fused together to form a sharp triangular structure. The coccyx is fused to the sacrum and in humans, it is not visible externally. It has no special function.
 

The ribs are flattened, curved bones. There are 12 pairs of ribs and they articulate with the sternum or chest bone ventrally and the thoracic vertebrae dorsally to form a cage known as the rib cage which protects the heart and lungs. Not all ribs articulate with the sternum. The sternum is a flattened, kite-shaped bone.
 

Are bones living or none living? Although the phrase ‘dry as a bone’ is often used, bones are actually made of both living and non-living materials. The living materials are bone cells, blood cells and nerve cells while the non-living materials are calcium and phosphorous. These minerals make the bone hard. In the sixteenth century, Andreas Vesalius of Belgium wrote a book that was the first guide ti the musculoskeletal system. His book was used by Leonardo da Vinci, an Italian artist, inventor and scientist, as a guide to help him make accurate sketches of the human body. 

Support and Locomotion

Necessity for Support and Locomotion in Humans
Have you ever wondered about what supports a building or house? Is it just bricks and cement? You may be surprised to know that beneath the cement and mortar are thousands of steel pieces which are assembled to form the frame of a building. Without this rigid frame, the building would not be able to withstand the forces of nature such as strong winds and rain and would collapse in no time.

Like a building, human also have inner framework which is made of bones. The bones are joined together at the joints to form a framework or skeleton. The skeleton has five major functions. It provides shape and support, enables you to move, protects internal organs, produce blood cells and store certain materials such as calcium and phosphate.

Structure of the Human Skeleton
The parts of the skeleton that form an imaginary line down the back of the body are known as the axial skeleton. The limbs and the bones that connect them to the axial skeleton make up the appendicular skeleton. A newborn baby has about 275 bones whereas an adult has 206 bones. This is because as a person grows, some of the bones are fuse together.

Types of Immunity

Did you have measles or chicken pox when you were young? If you did, most likely you will never get them again as you have acquired immunity against these diseases. Do you know what immunity means?
Immunity refers to the ability of an organism to defend itself against infection by pathogens. Immunity refers to the ability of an organism to defend itself against the infection by pathogens. Immunity depends on the presence of lymphocytes and the production of antibodies which give a specific immune response. The various types of immunity are active immunity (natural and artificial) and passive (natural and artificial).
 

Inherited natural immunity is the immunity which is inherited by an individual through the placenta or mother’s milk. Active natural acquired immunity is acquired after a person recovers from an infection, for example, measles or chickenpox. The body then has the ability to produce more antibodies rapidly against further attack by the same type of invading antigen. Antigens are foreign proteins or polysaccharides usually found in the surface of cells, for example, bacteria and viruses. When they enter the body, they stimulate the lymphocytes to produce antibodies. Antibodies destroy the antigens or neutralise the toxins produced by pathogens.
 

A vaccine contains killed or weakened antigens. When the vaccine is injected into the bloodstream, the lymphocytes in the body produce antibodies against that particular antigen. Vaccination produces active artificial acquired immunity: active because the antibodies are produced by the body itself, artificial because it is obtained through vaccination. This process is known as immunisation. When antibodies are transported from the mother across the placenta to the foetus or through the mother’s milk to the young infant, this gives passive natural immunity for a few months.
 

Passive artificial immunity is obtained by injecting serum containing specific antibodies prepared from the blood of humans or other animals. This is normally used to treat patients who are already seriously ill, for example from rabies, botulism, tetanus or snake bites. The antibodies obtained from other individuals give quick temporary immunity. This type of immunity cannot last for several weeks or months because the foreign antibodies break down in the body and are not replaced.

Body Defence Mechanism

The Three Lines of the Body’s Defence Mechanisms
There are thousands of microbial spores and parasites in the environment. Some organisms are pathogenic and can cause diseases when they enter the human body. These pathogens can be transmitted by air, contaminated food or drinking water, as well as by animal vectors such as mosquitoes and houseflies. Some skin diseases can even be transmitted by contact. The human body have three lines of defense to protect against these pathogens.

First Line of Defence
The skin and mucous membranes act as the first line of defence. The skin acts as a physical barrier. It is made up of a dead keratinised layer which is difficult to penetrate. If there is a cut, the blood clots quickly to seal the wound. Tears secreted by tear glands and acidic sebum secreted by sebaceous glands contains lysozymes which destroy bacteria. Mucus secreted by mucous membranes in the nasal cavity and trachea trap dust particles and bacterial spores. The cilia in the respiratory tract sweep the trapped particles to the pharynx. When microorganisms enter the stomach, they are killed by the hydrochloric acid in the gastric juices.

Second Line of Defence
If pathogens get through the first line of defence, they will meet the second line of defence. Some white blood cells, such as neutrophils act as phagocytes. They are attracted by chemicals produced at the sites of infection. The phagocytes move towards the pathogens, for example, bacteria, and engulf them by phagocytosis. Digestive enzymes are secreted into the phagocytic vacuoles to destroy and digest the bacteria. Useful soluble products are absorbed and assimilated by the phagocytes. Sometimes the phagocytes are destroyed by toxins produced by the pathogens. When there is an infection, the number of white blood cells increases in the body to try to destroy the pathogens.

Third Line of Defence
The third line of defence in the body is the lymphocytes. Lymphocytes are white blood cells found in the lymph nodes and in the blood circulatory system. There are two main types of lymphocytes. The T-lymphocytes attack cells infected by pathogens or produce certain chemicals to coordinate immune response. The B-lymphocytes produce antibodies. An antibody is a protein produced by lymphocytes in response to the presence of an antigen. An antigen is a foreign substance which stimulates the body to produce an immune response. It takes some days to produce an immune response. It takes some days to produce the antibodies. The antibodies are specific in action and promote the destruction of antigens in different ways. After an infection, some lymphocytes remain in the body as memory cells which may last for several months or years. The memory lymphocytes help to defend the body against further infection by the same antigen. The body is then said to be immune against the particular diseases.