Logan Steele
Joints and muscles are integral parts of the human body. Joints are the areas where two or more bones meet, and they can be classified as immovable, slightly moveable, or freely moveable. On the other hand, muscles are pieces of soft tissue that help the body move, breathe, swallow, and stay alive. There are over 600 muscles in the human body, and they are made of thousands of small fibres that stretch and press together to enable movement. Together, joints and muscles form the musculoskeletal system, allowing humans to perform a wide range of actions and movements.
| Characteristics | Values |
|---|---|
| Definition | Joints are areas where two or more bones meet. Muscles are tissues that move body parts by contracting and relaxing. |
| Composition | Joints consist of cartilage, synovial membrane, ligaments, tendons, and bursas. Muscles are composed of fibres that work in pairs of flexors and extensors. |
| Function | Joints allow bones to move. Muscles generate heat in the body, protect organs, and maintain posture. |
| Types | There are three functional joint types: immovable synarthrosis, slightly moveable amphiarthrosis, and freely moveable diarthrosis. There are also fixed joints that don't move, and mobile joints that allow different types of movements. |
| Injuries and Disorders | Joint injuries include sprains and strains. Muscle injuries include cramps, tendonitis, fibromyalgia, muscular dystrophies, and sarcopenia. |
| Treatment | Arthroplasty is a surgical procedure to replace damaged joints. |
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What You'll Learn
Joint types: fibrous, cartilaginous, synovial
Joints are regions where two bones make contact. They can be classified by the type of tissue present (fibrous, cartilaginous, or synovial) or by the degree of movement permitted (synarthrosis, amphiarthrosis, or diarthrosis).
Fibrous joints are fixed joints (synarthrosis) where collagenous fibrous connective tissue unites two bones. These joints are typically immovable and lack a joint cavity. Bones are bound by a tough, fibrous tissue, and these joints require strength and stability over range of movement. Examples of fibrous joints include sutures, gomphoses, and syndesmoses. Sutures are immobile joints found only in the cranium. Syndesmoses are slightly movable joints (amphiarthrosis) that provide stability during weight-bearing.
Cartilaginous joints are where bones are attached by hyaline or fibrous cartilage. These joints are further classified as primary or secondary cartilaginous joints, depending on the cartilage type involved. A synchondrosis, or primary cartilaginous joint, only contains hyaline cartilage and can be temporary or permanent. A symphysis, or secondary cartilaginous joint, contains thick and strong fibrocartilage. These joints have a remarkable ability to resist pulling and bending forces. Examples of cartilaginous joints include the pubic symphysis and the joints between vertebral bodies.
Synovial joints are freely movable (diarthrosis) and are the most common type of joint in the body. They are defined by the presence of a fluid-filled joint cavity contained within a fibrous capsule. The joint cavity contains synovial fluid, secreted by the synovial membrane (synovium), which lines the articular capsule. The primary purpose of the synovial joint is to prevent friction between the articulating bones of the joint cavity. Synovial joints can be further classified into several types, depending on the shape of their articular surfaces and the movements permitted. Muscles and their tendons are critical in providing additional support for synovial joints.
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Joint functions: structural support, mobility
The human body's musculoskeletal system is made up of bones, muscles, and joints. Joints are the connections between bones that allow them to move. They provide structural support and enable motion. There are three types of joints: immovable synarthrosis, slightly movable amphiarthrosis, and freely movable diarthrosis. Synarthroses are fibrous joints that do not move at all and provide structural support. Amphiarthroses are cartilaginous joints with limited movement, offering a mix of stability and motion. Diarthroses are synovial joints that allow for free movement in most directions.
Synovial joints are the most common type, found in the arms and legs. They have a cavity in one bone that another bone fits into, with slippery hyaline cartilage covering the ends of the bones. A synovial membrane, a fluid-filled sac, lubricates and protects the joint, reducing friction during movement. Synovial joints are crucial for mobility, allowing a wide range of motions.
The stability and mobility of joints are essential for human movement. Stability joints include the foot, knee, lumbar spine, cervical spine, and elbow, while mobility joints include the ankle, hip, thoracic spine, shoulder, and wrist. This alternating pattern of stability and mobility in the kinetic chain creates the ideal platform for dynamic human movement.
Muscles play a critical role in providing additional support for joints, especially synovial joints. They resist forces acting on the joint, and their strength directly correlates with joint stability. Skeletal muscles, which are voluntarily controlled, help with movement and maintaining posture. They work in pairs, with one muscle contracting while the other relaxes, allowing for a range of motions.
Overall, joints provide the structural framework for the body, enabling mobility and stability during everyday activities. They work in conjunction with muscles to facilitate movement and maintain posture, demonstrating the intricate relationship between joint functions and human locomotion.
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Muscle types: skeletal, smooth, cardiac
The human body is capable of a wide range of movements, from the involuntary blinking of the eyes to the complex coordination required to run. These movements are made possible by the contraction and relaxation of muscles. There are three types of muscle tissue in the human body: skeletal, smooth, and cardiac.
Skeletal muscle is a voluntary muscle, meaning that its movement can be consciously controlled. Skeletal muscles are attached to the bones and help to facilitate movement. They also help to generate heat in the body, protect organs, and maintain posture. When a person decides to move, the motor cortex in the brain sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract. Skeletal muscles work in pairs, with one muscle contracting and the corresponding muscle lengthening. For example, when the bicep muscle in the front of the upper arm contracts, the tricep muscle in the back of the upper arm lengthens.
Smooth muscle, on the other hand, is involuntary. It is found inside blood vessels and organs like the intestines, liver, pancreas, and stomach. Smooth muscle contracts and relaxes without conscious control, helping to move food through the digestive system, regulate blood pressure, and assist organs in carrying out their functions.
Cardiac muscle is also involuntary and is found exclusively in the heart. It is responsible for the heart's contractions, which cause the heart to beat and pump blood. The contractions of cardiac muscle are controlled by the heart's inbuilt pacemaker, the sinoatrial node.
The different types of muscles work together to enable the body's movements and functions. Muscle strength is essential for joint stability, particularly in synovial joints, which are the most common type of joint found in the arms and legs.
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Muscle function: movement, stability, breathing
The human body is made up of a complex musculoskeletal system that enables us to perform everyday physical activities. This system is composed of bones, muscles, joints, tendons, ligaments, and cartilage. Bones give our bodies shape and support, while muscles help us move, maintain posture, and even breathe.
Movement
Muscles are pieces of soft tissue that contract and relax to move our body parts. They work in pairs of flexors and extensors. For example, when you lift your arm, your brain sends a message to the muscles in your arm, causing them to contract and then relax. When you bend your elbow, the flexor, or bicep muscle, contracts, and the tricep, or extensor, relaxes. Once the movement is complete, the flexor relaxes, and the extensor contracts to straighten the elbow.
Stability
Muscles also play a crucial role in providing stability, especially to synovial joints, which are the most common type of joints found in our arms and legs. Muscle strength directly correlates with joint stability. The muscles and their tendons act as dynamic "ligaments," resisting forces acting on the joint.
Breathing
Breathing involves the use of the diaphragm muscle, which is a dome-shaped muscle located below the lungs. When the diaphragm contracts, it pushes downward, causing the chest cavity to expand, and the lungs to fill with air. When the diaphragm relaxes, it pushes the air out of the lungs. During deep breathing, other muscles, including those in the abdomen, back, and neck, assist the diaphragm. These are called accessory inspiratory muscles and include the sternocleidomastoid, scalenus anterior, pectoralis major, and minor, among others.
In addition to the muscles involved in inhalation, there are also accessory expiratory muscles that aid in exhalation. These include the abdominal muscles, such as the rectus abdominis and internal oblique, and muscles in the thoracolumbar region, such as the lowest fibres of iliocostalis.
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Muscle fibres: contract, relax, move organs/body
Muscle fibres contract, relax and move organs and the body through a complex interplay of the musculoskeletal system, the brain and nervous system. The brain and nervous system coordinate and control the movements of muscles. The brain stem controls involuntary muscles, while the cerebral motor cortex and the cerebellum regulate voluntary muscles. When a person decides to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract.
The process of muscle contraction involves a series of chemical reactions and electrical impulses. When a muscle is stimulated by a motor neuron, it triggers the release of acetylcholine, which binds to receptors on the muscle fibre membrane. This opens membrane channels, allowing an influx of sodium ions into the muscle fibre's cytoplasm. This sodium influx triggers the release of calcium ions, which diffuse into the muscle fibre. The calcium ions play a crucial role in initiating muscle contractions. The interaction between the chains of proteins within the muscle cells changes, leading to the contraction of the muscle fibre.
The sliding filament theory explains that thin filaments are pulled and slide past the thick filaments within the sarcomeres, resulting in muscle fibre contraction. This sliding movement occurs when the myosin-binding sites on the actin filaments are exposed, allowing for cross-bridging between the thin and thick filaments. The contraction stops when the motor neuron signalling ends, leading to the repolarisation of the sarcolemma and T-tubules. Subsequently, the voltage-gated calcium channels close, and the calcium ions are pumped back into the sarcoplasmic reticulum. This results in the reshielding of the actin-binding sites, causing the muscle fibre to lose its tension and relax.
Skeletal muscles, attached to bones, are responsible for body movement and posture maintenance. They work in pairs, with one muscle contracting and the other relaxing to allow for a full range of motion. Smooth muscles, found in organs like the intestines and blood vessels, are involuntary and help move food through the digestive system and regulate blood pressure. Cardiac muscles, on the other hand, comprise the walls of the heart and facilitate blood pumping through the body.
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