Human Anatomy: Skeletal and Muscular Systems Explained

The Skeletal System: Bones and Structure

Axial Skeleton

Vertebral Column

The vertebral column, or spine, holds the skull, attaches to the ribs, protects the spinal cord, and allows for the insertion of a large number of muscles. It consists of:

• Cervical vertebrae
• Thoracic vertebrae
• Lumbar vertebrae
• Sacrum
• Coccyx

Thoracic Cage

The thoracic cage includes the ribs and sternum.

• Ribs:
  • True ribs (first 7 pairs) join directly to the sternum.
  • False ribs (next 3 pairs) join the sternum indirectly via cartilage.
  • Floating ribs (last 2 pairs) do not join the sternum.
• Sternum: Composed of 3 parts:
  • Manubrium
  • Body
  • Xiphoid process

Appendicular Skeleton

The appendicular skeleton comprises the bones of the limbs and their girdles.

• Upper Extremities:
  • Girdle: Clavicles and scapulae
  • Arm: Humerus
  • Forearm: Ulna and radius
  • Hand: Carpals, metacarpals, phalanges
• Lower Extremities:
  • Pelvic Girdle: Innominate bone (fusion of ilium, ischium, and pubis)
  • Thigh: Femur
  • Leg: Tibia and fibula
  • Foot: Tarsals, metatarsals, phalanges

Articulations (Joints)

Joints are classified according to their degree of movement and structure.

Joints by Degree of Movement

• Synarthrosis: Immovable joints.
• Amphiarthrosis: Slightly movable joints.
• Diarthrosis (Synovial Joints): Freely movable joints.

Synovial joints allow movement along various axes using several key elements:

• Articular cartilage
• Joint capsule
• Ligaments
• Synovial membrane
• Joint cavity
• Meniscus (where present)
• Bursae (where present)

Joints by Structure

• Fibrous Joints: Almost without movement (e.g., sutures of the skull).
• Cartilaginous Joints: Allow slight movement (e.g., intervertebral discs).
• Synovial Joints: The most movable joints, divided into types such as:
  • Plane (Arthrodiac)
  • Hinge (Trochlear)
  • Pivot (Trochoid)
  • Condyloid
  • Saddle (Mutual fit)
  • Ball and Socket

The Muscular System: Muscle Actions

Muscles are responsible for various body movements. Key types of muscle actions include:

• Flexors and Extensors: Muscles that decrease (flexors) or increase (extensors) the angle between bones (e.g., biceps, triceps).
• Abductors and Adductors: Muscles that move a limb away from (abductors) or towards (adductors) the midline of the body (e.g., deltoids).
• Rotators: Muscles that turn a bone around its axis, allowing pronation and supination.
• Invertors and Evertors: Muscles that move the sole of the foot inwards (invertors) or outwards (evertors) (e.g., tibialis anterior).
• Elevators and Depressors: Muscles that raise (elevators) or lower (depressors) a body part (e.g., levator scapulae).
• Sphincters and Dilators: Muscles that close (sphincters) or open (dilators) a body orifice.

Functions of the Skeletal System

The skeletal system performs several vital functions:

• Sustenance: Provides structural support for the body.
• Protection: Protects vital internal organs (e.g., skull protects the brain, ribs protect the heart and lungs).
• Movement: Works with muscles to facilitate locomotion and body movements.
• Hematopoiesis: Bone marrow produces blood cells (red blood cells, white blood cells, platelets).
• Mineral Reservoir: Bones store essential minerals, primarily calcium and phosphorus.

Common Disorders of the Musculoskeletal System

Bone Disorders

Some common conditions affecting bones include:

• Osteoporosis
• Osteosclerosis
• Osteomyelitis
• Osteomalacia
• Paget's disease
• Neoplasms (bone tumors)

Joint Disorders

Common joint conditions and inflammations include:

• Arthritis (general term for joint inflammation)
• Gout
• Rheumatoid arthritis (adult-onset)
• Spondylitis
• Osteoarthritis
• Herniated disc

Joint inflammation can be characterized as acute (sharp, high intensity, short duration) or chronic (moderate intensity, long duration).

Basic Anatomical Definitions

Understanding the body's organization requires defining key terms:

• Apparatus: A set of organs and tissues of various types that collaborate on a common mission (e.g., digestive apparatus).
• System: A set of organs that perform functions of the same order, often more complex than a single organ (e.g., lymphatic system).