The Skeletal System: Support, Protection, and Movement

• The skeletal system provides support, protection, movement, mineral storage (calcium), and blood cell production.
• The skeleton protects soft body parts like the brain (cranium), spinal cord (vertebrae), and heart/lungs (rib cage).
• The skeleton supports the body against gravity, with large lower limb bones bearing the trunk's weight.
• Bones and muscles function together as levers for body movement.
• Bones store calcium, containing more than any other organ.
• Calcium is released from or stored in bones to maintain adequate blood calcium levels.
• Bones produce blood cells in the bone marrow, where red and white blood cells are produced.

Bone Types

• Bones come in various sizes and shapes, classified into long, short, flat, and irregular types.
• Examples of bone types include:
  • Flat bone (frontal)
  • Sutural bone
  • Short bone (carpal)
  • Irregular bone (vertebra)
  • Long bone (femur)
  • Sesamoid bone (patella)

Long Bone Anatomy

• Proximal Epiphysis: The end of the bone closest to the torso
• Distal Epiphysis: The end of the bone farthest from the torso
• Articular Cartilage: covers epiphysis to reduce friction in joints
• Metaphysis: Region between epiphysis and diaphysis
• Spongy Bone: Contains red bone marrow
• Epiphyseal Line: Remnant of the epiphyseal plate (growth plate)
• Diaphysis: The shaft of the bone
• Red Bone Marrow: Produces blood cells
• Medullary Cavity: Hollow space within the diaphysis, contains yellow bone marrow
• Compact Bone: Dense outer layer of the bone
• Endosteum: Lines the medullary cavity
• Yellow Bone Marrow: Stores fat
• Periosteum: Outer covering of the bone
• Nutrient Artery: Provides blood supply to the bone

Axial Skeleton

• Composed of 80 bones, forming the body's vertical axis.
• Includes the skull, vertebral column, ribs, and sternum.
• Protects the brain, spinal cord, heart, and lungs.
• Supports the body and serves as an attachment site for muscles of the head, neck, back, and limbs.

Appendicular Skeleton

• Consists of 126 bones, including the free appendages and their attachments to the axial skeleton.
• Enables movement and manipulation of objects.
• Includes the shoulder girdle, arm, hand, pelvic girdle, leg, and foot.
• Examples of bones in each skeleton are:
  • Axial: skull, ossicles, hyoid bone, thoracic cage, and vertebral column.
  • Appendicular: scapula, clavicle, femur, and patella.
  • Axial: Sternum, Cervical Vertebrae, Thoracic Vertebrae, Lumbar Vertebrae, Sacral Vertebrae (fused), Coccyx (fused)
  • Appendicular: Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges (hand), Ilium, Ischium, Pubis, Tibia, Fibula, Tarsals, Metatarsals, Phalanges (foot)

Anatomical Terminology

• Cervical vertebrae are superior to the thoracic vertebrae.
• Joint: The part of the body where two or more bones meet to allow movement.
  • Fibrous: Immovable
  • Cartilaginous: Slightly movable
  • Synovial: Freely moveable

Joint types

• Fibrous Joints: Bones are very close and separated by a thin connective tissue layer; skull bones are examples of immovable joints.
• Cartilaginous Joints: Bones are connected by hyaline cartilage or fibrocartilage, allowing slight movement; rib connections to the sternum and intervertebral discs are examples.
• Synovial Joints: Opposing bone ends are covered with hyaline (articular) cartilage and separated by a joint cavity, all enclosed in a fibrous capsule with ligaments. A synovial membrane lines the capsule and secretes synovial fluid for lubrication; knee and shoulder joints are freely movable.

Synovial Joints

• Characterized by the presence of a joint cavity.
• The joint cavity is surrounded by an articular capsule.
• The joint cavity contains synovial fluid.
• Hyaline cartilage forms the articular cartilage.

Types of Synovial Joints

• Hinge joints: open and close in one direction (knees and elbows).
• Ball and socket joints: rounded bone end fits into another bone's indentation, allowing rotation and turning (shoulders and hips).
• Condyloid joints: two oval-shaped bones fit together, similar to ball and socket but with limited rotation (wrist and toe joints).
• Pivot joints: rotate in place without moving position (neck).
• Planar joints: flat bones slide over each other without rotating (carpal bones, spinal vertebrae).
• Saddle joints: two curved bones fit together, allowing movement in any direction but not twist or rotate (thumb joint).

Muscular System

• Muscle contraction functions include movement, posture, joint stability, and heat production.
• Skeletal muscles are attached to bones, responsible for skeletal movements, and under voluntary control; the basic unit is the muscle fiber.
• Smooth muscles are in the walls of internal organs, contract slowly and rhythmically, and cannot be consciously controlled.
• Cardiac muscle is in the heart walls, under autonomic nervous system control, striated like skeletal muscle, and involuntary, strong, and rhythmical in contraction.
• Muscle tissue characteristics include contractility (ability to contract and generate force), extensibility (ability to stretch beyond normal length), and elasticity (ability to return to original length after stretching). Muscles can atrophy (shrink) or hypertrophy (grow).

Muscle Structure

• Muscle fibers (cells) are bundled and surrounded by connective tissue layers.
• Epimysium: covers the entire muscle
• Perimysium: surrounds bundles of muscle fibers
• Endomysium: surrounds individual muscle fibers
• Blood vessels supply the muscle.
• Tendons attach the muscle to the bone.
• Muscles to know
  • Anterior: Deltoid, Pectoralis, Iliopsoas, Sartorius, Quadriceps femoris (rectus femoris, vastus intermedialis, vastus medialis, vastus lateralis), Tibialis anterior, Abdominus rectus, External obliques, Biceps brachii
  • Posterior: Trapezius, Triceps brachii, Latissimus dorsi, Gluteus maximus, Hamstrings (biceps femoris, semitendinosus, semimembranosus), Gastrocnemius, Soleus, Erector spinae
• Origin: The more proximal attachment of a muscle to a bone, and stays fixed
• Insertion: the more distal attachment of a muscle to a bone, that is usually the moveable bone.