Muscular and Skeletal Systems: Structure and Function

Muscular System

Muscle Characteristics

Involuntary. Located in the heart. Striated fibers are present inside longitudinal filaments called myofibrils. Muscle cells are made of two proteins: actin and myosin. Some form rhabdomyosarcoma.

Types of Muscles

• Long or Fusiform: (spindle-shaped)
• Flat or Planar: (e.g., diaphragm)
• Orbicular: (round body, e.g., orbicularis oculi)

Tendons join muscles to bones. Two muscles are involved in any movement: agonist (contracts) and antagonist (relaxes).

Skeletal System

3.2 - Bones

Functions

• Support the body and give it shape.
• Allow movement of various body parts.
• Protect internal organs (brain, lungs, etc.).
• Serve as the main repository of minerals (calcium, potassium, etc.).
• Some bones act as organs of blood cell production.

Bone Tissue

Bone tissue consists of:

• Organic Matter:
  • Cells: There are three types: osteoblasts (collagen-producing cells), osteocytes (support bone), and osteoclasts (internal bone renewal).
  • Osteoid: Formed by collagen fibers.
• Inorganic Matter: Provides toughness. It contains minerals like calcium, potassium, etc.

Types of Bone

There are three types of bones:

• Long Bones: Elongated and cylindrical shape (e.g., femur, humerus).
• Flat Bones: Thin, wide, and flat (e.g., skull bones, ribs).
• Short Bones: Small, cylindrical, and cuboid (e.g., carpals, tarsals).

Structure of a Long Bone

A long bone has three parts:

• Diaphysis: The central elongated shaft.
• Epiphysis: The end zones.
• Metaphysis: The zone that separates the diaphysis from the epiphysis.

Inside the Bone

The inner zone of the bone is occupied by the marrow cavity, which is divided into two parts:

• Epiphysis: Contains red bone marrow, where red blood cells are formed.
• Diaphysis: Contains yellow bone marrow.

Growth of Bones

• In the embryonic and fetal stages, the skeleton consists of cartilage (the cells are chondrocytes).
• Bone tissue replaces cartilage as the individual grows, a process called ossification.
• Growth in long bones occurs from growth cartilage (growth plates).

Joints

Joints are the unions between bones. There are three types:

• Fixed Joints: Do not allow movement (e.g., skull bones).
• Semi-Mobile Joints: Have limited movement (e.g., vertebrae).
• Mobile Joints: Allow a wide range of movement (e.g., elbow, knee).