Skeletal System Notes

Skeletal System

Overview

  • The skeletal system provides support, protection, and movement for the body.

  • It maintains the body's shape and structure.

  • It protects internal organs.

  • It facilitates movement.

  • It serves as a site for blood cell production and mineral storage.

Skeletal System Complexity

  • The skeletal system varies in complexity and composition across different organisms.

  • Vertebrates (animals with a backbone): possess an internal endoskeleton.

    • Composed of bones, which are rigid structures made of calcium and phosphorus minerals.

    • Bones are connected by joints, allowing movement.

  • Invertebrates (animals without a backbone): skeletal systems vary.

    • Some have an exoskeleton: a hard external structure that covers the body for support and protection. Examples:

      • Shells of mollusks.

      • Exoskeletons of insects and crustaceans.

    • Others have internal structures made of cartilage or other materials.

Functions of the Skeletal System

Support

  • Bones provide a rigid framework supporting the body's soft tissues and organs.

  • Bones maintain the body's shape and structure.

Protection

  • The skeletal system protects vital organs.

    • Skull: protects the brain.

    • Ribcage: protects the heart and lungs.

    • Spinal column: protects the spinal cord.

Movement

  • Bones, muscles, tendons, and ligaments enable movement.

  • Muscles contract and pull on bones, acting as levers.

  • This allows animals to walk, run, jump, and perform other movements.

Blood Cell Production

  • Bone marrow (found inside certain bones) produces blood cells.

    • Red blood cells.

    • White blood cells.

    • Platelets.

Mineral Storage

  • Bones store essential minerals.

    • Calcium.

    • Phosphorus.

  • These minerals are released into the bloodstream when needed to maintain proper levels.

Types of Skeletal Systems

Hydrostatic Skeleton

  • Found in many cold-blooded and soft-bodied organisms.

  • Consists of a fluid-filled cavity (coelom) surrounded by muscles.

  • In some animals, the cavity contains a blood-like substance called haemocoel.

  • Muscles act against the fluid to bring about movement.

  • In segmented bodies, fluid pressure is localized.

  • Occurs in:

    • Flatworms.

    • Roundworms.

    • Earthworms.

    • Starfish.

    • Slugs.

Earthworm Example:

  • Uses its hydrostatic skeleton to crawl.

  • Longitudinal muscles.

  • Circular muscles.

  • Contraction of circular muscles elongates segments, pushing them forward.

  • Bristles anchor segments to prevent backward sliding.

  • Contraction of longitudinal muscles shortens segments, pulling trailing segments forward.

Exoskeleton

  • An external skeleton that supports and protects an animal's body.

  • Non-living, consisting of a cuticle strengthened by chitin (a substance secreted by the epidermis).

  • Crustaceans, like crabs, have exoskeletons further strengthened by calcium carbonate.

  • Confined to animals in the Phylum Arthropoda (jointed-legged and jointed-bodied animals).

    • Insects.

    • Spiders.

    • Scorpions.

    • Crabs.

  • Acts as a hard outer covering made of plates or tubes.

Examples:

  • Chitin exoskeleton:

    • Earwig (insect).

    • Beetle (insect).

    • Spider (arachnid).

  • Calcium carbonate exoskeleton (shell):

    • Snail (mollusk).

    • Scallop (mollusk).

    • Shrimp (crustacean).

Endoskeleton

  • Consists of hard, mineralized structures located within the soft tissue of organisms.

  • Example: spicule of sponges (primitive endoskeletal structure).

  • Vertebrate bones are composed of tissues, while sponges have no true tissues.

  • Provides support for the body.

  • Protects internal organs.

  • Allows for movement through muscle contraction.

  • Positioned internally, unlike exoskeletons.

Examples:

  • Fish

  • Chicken

  • Cow

  • Crocodile

Components of Endoskeleton

Bones

  • Main structural elements.

  • Various shapes and sizes.

  • Provide support and protection.

Joints

  • Points where two or more bones meet.

  • Allow for movement.

  • Classified into different types:

    • Hinge joints (e.g., elbow).

    • Ball-and-socket joints (e.g., hip).

    • Pivot joints (e.g., neck).

Cartilage

  • Flexible connective tissue that covers bone ends at joints.

  • Provides a smooth surface for movement.

  • Acts as a shock absorber.

Ligaments

  • Tough bands of connective tissue that connect bones to other bones.

  • Provide stability to joints.

Tendons

  • Fibrous tissues that connect muscles to bones.

  • Enable the transfer of forces produced by muscle contractions to the bones, resulting in movement.