Bone and Muscle Structure: Functions and Types
Functions of the Bones
- Maintenance of different positions, the realization of movement and displacement.
- Some participate in protection by forming cavities containing organs.
- Participate in the production of blood cells.
- They are an important reservoir of minerals for the body.
Bone Classification by Structure
Long Bones
These are bones in which length predominates over width and thickness. They participate in the support of the body and allow for its displacement. They are formed by two heads on the ends (epiphyses) and a body called the diaphysis. Inside is the marrow cavity, which houses the bone marrow.
Short Bones
These have a similar size in all three dimensions, like the vertebrae. They can withstand high pressures.
Flat Bones
In these, length and width predominate over thickness, such as the occipital bone. They generally delimit cavities containing organs and contribute to their protection.
Types of Bone Tissue
Bones are made up of bone tissue, consisting of cells called osteocytes and an intercellular substance produced by these cells. There are two types of bone tissue:
Spongy Bone Tissue
Lamellae are arranged irregularly, leaving spaces between them. In these spaces is the red bone marrow, a connective tissue that produces blood cells. Spongy bone tissue is found within the epiphyses and in some sectors of the marrow cavity inside long bones, as well as in short and flat bones. Over the years, red bone marrow loses its blood cell-forming activity and is transformed into yellow bone marrow. This tissue is a source of energy reserves because it is formed by a large number of fat cells.
Compact Bone Tissue
Lamellae are arranged regularly, forming layers with no space between them. This type of tissue is found on the outer surface of all bones and on the surface of the medullary cavity of long bones.
Joint Classification by Mobility
Stationary Joints
These have no mobility between the bones they connect. This results from the close proximity of their surfaces or their connection by bands of fibrous cartilage.
Semi-Mobile Joints
These allow very little mobility between the bones they connect. The articular surface is coated with a layer of cartilage that reduces friction and is composed of a ring-shaped structure of fibrocartilage, which increases the articular surface area. Between the joints is the meniscus, which cushions pressure, and ligaments or fibrous cords that hold the bones together.
Movable Joints
These are the most numerous in the body and allow a wide variety and range of motion between the bones they connect. The articular surfaces of bones are covered with articular cartilage. A mobile joint is formed by structures that expand the joint surface and ligaments that hold the bones together. The associated synovial membrane lines the joint capsule and secretes synovial fluid, which fills the capsule. This fluid reduces friction and facilitates movement.
Function of the Muscular Subsystem
Allows for the movement of the body.
Muscle Classification by Structure
Long Muscles
These are usually found in the extremities and are characterized by allowing the realization of wide movements. Example: biceps.
Short Muscles
These allow limited and sustained movement, located between the vertebrae of the spine. Example: interspinous muscles.
Wide Muscles
These form cavity walls and allow limited and not very sustained movements. Example: abdominal wall muscles.