Dominic Stone
Bones, muscles, and joints form the musculoskeletal system, which enables us to perform daily physical activities. While joints are the areas where two bones meet, muscles are the tissues that cause body parts to move by contracting and then relaxing. Muscles can pull bones but cannot push them back to their original position, so they work in pairs. The brain coordinates and controls the movements of the muscles. The joints, on the other hand, give the skeleton its shape and flexibility.
| Characteristics | Values |
|---|---|
| Definition | Joints are the areas where bones come together. |
| Muscles are tissues that help the body move. | |
| Types of Joints | Synovial joints, cartilaginous joints, hinge joints, ball and socket joints, and saddle joints. |
| Types of Muscles | Cardiac muscle, smooth muscle, and skeletal muscle. |
| Function | Joints give the skeleton its shape and make movement possible. |
| Muscles provide the force and strength to move the body. | |
| Control | Joints are controlled by the brain and nervous system. |
| Skeletal muscles are voluntary muscles that can be consciously controlled. | |
| Cardiac and smooth muscles are involuntary muscles that contract and relax without conscious control. | |
| Age-Related Changes | Joints may break down with age, leading to inflammation, pain, stiffness, and deformity. |
| Muscles may become rigid and lose tone with age, even with regular exercise. |
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What You'll Learn
Joints are where two bones meet
A joint is where two bones meet. They are part of the skeletal system and give the skeleton its shape. Without joints, movement would be impossible. They allow the skeleton to be flexible, enabling the body to move in many ways. For example, some joints open and close like a hinge (such as knees and elbows), while others allow for more complicated movement — a shoulder or hip joint, for instance, allows for backward, forward, sideways, and rotational movement.
Joints come in many shapes, sizes, and types throughout the body. There are three main types of joints: synovial joints, cartilaginous joints, and saddle joints. The most common type is the synovial joint, found in the arms and legs. In a synovial joint, the ends of the bones are covered with cartilage and separated by the joint cavity, which is filled with a thick gel called synovial fluid. This fluid lubricates the cartilage and provides nourishment. Ligaments stretch across the joint, connecting one bone to another and helping to stabilize the joint so it can only move in certain directions.
Cartilaginous joints, found in the spine, pelvis, and between the ribs and sternum, provide more stability but not as much movement. The joints where the ribs meet the sternum (breastbone) and the pubic symphysis joint that joins the left and right pelvic bones are examples of cartilaginous joints.
Saddle joints are formed when two curved bones meet. The joint where the thumb joins the hand is a saddle joint. Saddle joints can move in any direction but cannot twist or rotate.
With age, joints may break down, leading to inflammation, pain, stiffness, and deformity. Conditions such as osteoarthritis, osteoporosis, and rheumatoid arthritis can affect the joints, causing a gradual wearing down of cartilage, loss of bone density, and inflammation. Regular exercise and a healthy diet can help maintain joint health and reduce the risk of these conditions.
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Muscles contract and relax to move body parts
A joint is where two bones meet and is not a muscle. Joints make the skeleton flexible and allow the body to move in many ways. Muscles, on the other hand, are organs that contain cells that can contract and relax, generating force and movement.
The physiological concept of muscle contraction is based on two variables: length and tension. Tension within a muscle can be produced without changes in its length, for example, when holding a dumbbell in the same position. When a muscle contracts, it shortens, pulling one bone towards another across a joint. This movement is coordinated and controlled by the brain and nervous system. 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 motor cortex on the right side of the brain controls the muscles on the left side of the body and vice versa.
Skeletal muscles, which are under voluntary control, work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint. Once the movement is completed, the flexor relaxes and the extensor contracts to extend or straighten the limb at the same joint. For example, the biceps muscle in the front of the upper arm is a flexor, while the triceps muscle at the back is an extensor. When bending at the elbow, the biceps contract, then relax, and the triceps contract to straighten the elbow.
Cardiac muscle, which comprises the walls of the heart, is an involuntary type of muscle. Its rhythmic and powerful contractions force blood out of the heart as it beats. Smooth muscle is another type of involuntary muscle found throughout the blood vessels, gastrointestinal tract, bronchioles, uterus, and bladder. It constricts blood vessels and moves the contents of hollow organs in the body.
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The brain controls muscle movement
The human body is capable of a wide range of movements, from the simple act of winking to the complex motion of performing a dance sequence. All of these movements are made possible by the brain's control of muscle contractions.
When a person decides to move, the brain's motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract. The motor cortex on the right side of the brain controls the muscles on the left side of the body and vice versa. This area of the brain has long been known to control specific muscle movements, but recent research has revealed a more complex role in planning and coordinating movements.
The motor cortex is a thin band of nerve cells and circuits that extends from the top of the head downward on both sides. It was once thought to have a straightforward role as the command center for voluntary muscle movements. However, studies in non-human primates suggested that the map of body parts in the motor cortex may be divided into concentric zones, with digits like fingers in the middle, surrounded by areas for the wrists, elbows, and then shoulders.
While voluntary muscles are controlled by the motor cortex, involuntary muscles, such as those in the stomach wall, are controlled by other regions of the brain, such as the hypothalamus and the brain stem. These muscles contract without our conscious control and are responsible for essential functions such as digestion and the beating of the heart.
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Joint shape determines its movement
A joint is the point at which two or more bones meet. They make the skeleton flexible and enable movement. Joints are supported by tough connective tissue called ligaments and are cushioned by cartilage. The shape of the joint determines the type of movement it permits.
There are several types of joints, including planar, hinge, pivot, condyloid, saddle, and ball-and-socket joints. Planar joints, also known as gliding joints, are formed by two flat or slightly curved bones of similar size. They allow for gliding movements and are found in the carpal bones in the hand, the tarsal bones of the foot, and between vertebrae. Hinge joints, such as the knee and elbow, allow for angular movement in one direction, like a door opening and closing. Pivot joints consist of the rounded end of one bone fitting into a ring formed by another bone, enabling rotational movement. An example of a pivot joint is the joint between the first and second vertebrae in the neck, which allows the head to move back and forth.
Condyloid joints, also known as ellipsoidal joints, have an oval-shaped end of one bone fitting into a similarly shaped hollow of another bone. This type of joint allows angular movement along two axes, as seen in the wrist and finger joints. Saddle joints are formed by two saddle-shaped bones, concave in one direction and convex in another. This joint type allows movement back and forth and from side to side but does not permit rotation, such as the joint at the base of the thumb. Ball-and-socket joints, like the hip and shoulder joints, allow movement in all directions.
The shape of these joints determines their movement capabilities, with some permitting gliding, angular, or rotational movements, while others allow for more complex, multidirectional motions. The functionality of joints is further influenced by the associated muscles, tendons, and ligaments that facilitate and restrict movements.
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Muscles and joints degenerate with age
A joint is where two bones meet and is cushioned by cartilage, synovial membranes, and lubricating fluid. Bones, muscles, and joints form the musculoskeletal system, which enables us to perform everyday physical activities. Muscles help the body move by contracting and relaxing, and they also help the body perform functions such as chewing food and moving it through the digestive system.
As people age, they experience a reduction in muscle tone and strength, even with regular exercise. Muscles become rigid and lose their ability to contract due to changes in muscle tissue and the nervous system. Bones also become more brittle and break more easily as they lose calcium and other minerals. Height decreases, and the breakdown of joints leads to inflammation, pain, stiffness, and deformity. Joint changes affect almost all older people, ranging from stiffness to severe arthritis.
Exercise is one of the best ways to slow or prevent problems with the muscles, joints, and bones. It can help maintain strength, balance, and flexibility, and it can also slow the rate of bone loss. Older people can increase muscle mass and strength through muscle-strengthening activities. A moderate exercise program can help prevent many age-related changes to muscles, bones, and joints and even reverse these changes.
In addition to exercise, a well-balanced diet with plenty of calcium and vitamin D can help prevent problems associated with ageing in the musculoskeletal system. Women, especially those who have gone through menopause, and men over 70 should be careful to get enough calcium and vitamin D.
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Frequently asked questions
A joint is any place in the body where two bones meet. They are part of the skeletal system and give the body its shape.
Muscles are what allow us to move. They help the body perform tasks such as chewing food, moving food through the digestive system, and smiling and talking. There are more than 600 skeletal muscles in the human body.
Muscles pull on the joints, allowing us to move. They work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint, then the flexor relaxes and the extensor contracts to extend or straighten the limb at the same joint.
Muscles are what allow us to move, but they are attached to bones by tendons. Joints are where two bones meet and allow the body to move in many ways.
