Musculoskeletal System: Bones, Joints, Muscles, and More
Musculoskeletal System
The musculoskeletal system supports the body, facilitates movement, and protects internal organs. It comprises two main systems:
Skeletal System
The skeletal system is the passive part of the locomotor system, forming an internal, mobile frame composed of bones, joints, and ligaments. Its functions include:
- Enabling body movement and providing shape
- Anchoring skeletal muscles
- Storing calcium and phosphorus
- Producing blood cells in the bone marrow
The skeleton is divided into the head, trunk, and extremities.
Muscular System
The muscular system is the active part of the locomotor system, consisting of muscles and tendons. Its functions include:
- Producing movements for vital functions
- Maintaining posture
- Enabling facial expressions
Muscles connect to the nervous system through nerves and join the skeletal system via tendons.
Bones
Bones are living tissues that grow and are nourished. They are composed of calcium, phosphorus, and collagen. The outer layer is made of compact bone tissue, while the inner layer consists of spongy bone tissue.
Bone Types
- Short Bones: Cubic or round shaped (e.g., vertebrae), primarily spongy bone tissue covered by a thin layer of compact bone.
- Flat Bones: Curved or flat plates (e.g., scapula, skull bones) with a protective function, composed of two layers of compact bone tissue surrounding a thin layer of spongy bone.
- Long Bones: Elongated and cylindrical (e.g., femur, humerus) with a supporting and motion function. They consist of a shaft (middle part containing yellow bone marrow) and epiphyses (ends containing red bone marrow where blood cells are produced).
Bones are covered by a thin membrane of connective tissue called the periosteum, responsible for bone growth and tendon/ligament attachment.
Joints
Joints connect adjacent bones, preventing separation. There are three main types:
- Immobile Joints: Cannot move (e.g., sutures in the head).
- Semi-Mobile Joints: Allow limited movement (e.g., vertebrae), connected by cartilage and ligaments.
- Mobile Joints: Allow a wide range of motion (e.g., elbow, knee). These joints have a joint capsule filled with synovial fluid for lubrication.
Muscles
Muscles are formed by elongated cells called muscle fibers, which can contract and relax to produce movement.
Muscle Types
- Smooth Muscles: Slow, involuntary contractions. Found in the walls of internal organs (e.g., digestive tract, blood vessels).
- Cardiac Muscles: Fast, involuntary contractions. Form the heart muscle (myocardium).
- Skeletal Muscles: Fast, voluntary contractions. Responsible for skeletal movement. Each fiber is wrapped in endomysium, bundles of fibers are wrapped in perimysium, and the entire muscle is wrapped in epimysium.
Tendons: Connective tissue that attaches muscles to bones.
Muscle Classification
By Shape: Annular (e.g., anal sphincter), flat, orbicular (semicircular), fusiform (spindle-shaped).
By Function: Flexors/extensors, abductors/adductors, pronators/supinators, elevators/depressors, sphincters/dilators.
Muscle Action on the Skeleton
When a muscle contracts, it shortens and thickens, pulling the bone it’s attached to. When it relaxes, it lengthens, allowing the bone to return to its initial position. Skeletal muscles often work in antagonistic pairs: one contracts while the other relaxes, and vice versa.
Movement involves a fulcrum (pivot point), a point of power (where force is applied), and a point of resistance (where opposing force is applied).
Musculoskeletal Issues
- Fractures: Broken bones. Treatment involves casts, splints, or screws.
- Strains: Affect muscles and tendons due to excessive stretching.
- Sprains: Ligament strains, common in ankles, knees, and wrists.
- Dislocations: Bones move out of their normal position in a joint.
- Muscle Contractures: Involuntary, sustained muscle contractions.
- Scoliosis: S-shaped spinal curvature.
- Lordosis: Increased lumbar curvature.
- Kyphosis: Increased dorsal curvature.
Maintaining Musculoskeletal Health
- Regular exercise
- Balanced diet
- Proper footwear
- Good posture
- Avoid carrying excessive weight
Bone Terminology
True ribs, false ribs, floating ribs, innominate (ilium, pubis, ischium), cranium, frontal, temporal, mandible, clavicle, sternum, scapula, humerus, ulna, radius, carpal, metacarpal, phalanges, femur, patella, fibula, tibia, tarsus, metatarsus, phalanges, parietal, occipital, cervical vertebrae, thoracic vertebrae, lumbar vertebrae, ilium, sacrum, coccyx, frontal sinus, sella turcica, ethmoid sinus, sphenoid sinus, palatal vault, occipital foramen, styloid process.