Muscles and bones
Muscles
- Muscles are responsible for all types of body movement - they contract in response to a nerve stimulus.
- There are three types of muscles in the human body: skeletal, smooth, and cardiac muscles.
- Skeletal muscles are attached to bones and cause movement by contracting and relaxing in response to voluntary messages from the nervous system.
- Smooth muscles are found in organs such as the stomach and intestines. They work automatically and slowly, controlled by the autonomic nervous system.
- Cardiac muscle is unique to the heart. It contracts involuntarily and continuously to pump blood through the body.
- Muscles are categorised further as flexors or extensors. Flexors close the angle between two bones, while extensors increase the angle.
- Muscle fatigue results from the accumulation of lactic acid and lack of oxygen, which interfere with the ability of muscle fibres to contract.
- Regular exercise leads to muscle hypertrophy, the growth and increase in the size of muscle cells.
- Muscle atrophy is the wasting or loss of muscle tissue due to lack of physical activity or illness.
Bones
- The human skeleton is made up of 206 bones, providing structure and support for the body.
- Bones are classified into four types based on their shape: long, short, flat, and irregular bones.
- Long bones like the femur and humerus, provide strength, structure, and mobility.
- Short bones like the bones in the wrist and ankle, provide support and stability with little to no movement.
- Flat bones like the skull and ribcage, protect internal organs.
- Irregular bones, like the vertebrae and mandible, provide protection and allow for multiple types of movement.
- The joint is the location at which bones connect, allowing for movement and providing mechanical support.
- Synovial joints like the knee and elbow, are the most common type and are freely movable.
- Ligaments connect bones to other bones, while tendons connect muscles to bones.
- The main functions of bones include supporting the body, protecting internal organs, facilitating movement, storing and releasing minerals, and producing blood cells (hematopoiesis).
- Bone density and strength can be maintained or improved through weight-bearing exercises and a balanced diet rich in calcium and vitamin D.