Skeletal System Overview Quiz

Skeletal System Overview

• The skeletal system provides support, movement, and protection of internal organs.
• Three main types of skeletons exist: hydrostatic, exoskeleton, and endoskeleton.

Hydrostatic Skeleton

• Composed of fluid held under pressure within a closed body compartment.
• Cushions body parts from shock.
• Provides body shape that can change through muscle contractions.
• Offers support for muscle action.
• Found in earthworms, hydras, and jellies.

Exoskeleton

• A rigid external skeleton (hard or leathery).
• Arthropods have exoskeletons made of chitin.
• Mollusks have exoskeletons of calcium carbonate (shells).

Endoskeleton

• Internal skeleton made of hard or leathery supporting elements among soft tissues.
• Echinoderms (sea urchins, sea stars) have endoskeletons made of hard plates under their skin.
• Vertebrates have endoskeletons made of cartilage or a combination of cartilage and bone.

Vertebrate Endoskeleton - Cartilage

• Cartilage is made up of chondrocytes (cartilage-producing cells).
• Extracellular matrix is abundant, composed of collagen and elastin fibers.
• Jelly-like ground substance with complex sugars.
• Contains 60-80% water, contributing to its resilience.
• Lacks nerves and blood vessels.

Types of Cartilage

• Hyaline cartilage: Flexible and resilient, found in the ends of long bones, trachea, nose, and larynx.
• Elastic cartilage: Highly bendable, with more elastic fibers than collagen, found in the epiglottis and outer ear.
• Fibrocartilage: Resists compression and tension, with thick collagen fibers alternating with chondrocytes, found in intervertebral discs.

Vertebrate Endoskeleton - Bone

• Bones consist of 25% water, 25% protein fibers, and 50% mineral salts.
• Functions: growth, support, protection, movement, mineral storage (calcium and phosphorus), blood cell production (hemopoiesis in red bone marrow), and energy storage (adipose tissue in yellow bone marrow).
• Bone cells: osteoblasts (form new bone), osteocytes (maintain bone structure), osteoclasts (dissolve bone).

Long Bones

• Found in limbs, composed of a diaphysis (shaft), and epiphyses (ends).
• Dense tissue (compact bone) surrounds a hollow central canal filled with yellow marrow (stores fat).
• Spongy bone (at the ends) contains red marrow (produces blood cells).
• Joints are where two bones meet.

Compact Bone

• Osteocytes are in contact with blood vessels in Haversian canals (nutrients/waste).
• Haversian canals and the surrounding bone rings form the Haversian system/Osteon.

Spongy (Cancellous) Bone

• Found at the ends of long bones (epiphysis) and surrounded by compact bone.
• Composed of branching bony plates with spaces filled with red marrow.

Axial Skeleton

• Consists of skull, backbone (vertebrae), and ribs/ribcage
• Supports the trunk of the body.
• Vertebrae (cervical, thoracic, lumbar, sacrum, coccyx). Each vertebrae is part of a curve in the spine, offering support and flexibility.
• Rib cage protects vital organs.

Vertebrae

• 26 vertebrae form the vertebral column, a dorsal backbone that protects the spinal cord.
• Disks between vertebrae act as padding and shock absorbers, allowing for movement.
• The vertebral column serves as the anchor to all other bones.

Ribs and Sternum

• Ribs attach (directly or indirectly) to the thoracic vertebrae in the back and the sternum (breast bone) in front.
• Lower ribs (floating ribs) are not attached to the sternum.
• Ribs are numbered according to their attachment to the vertebral column and sternum.

Appendicular Skeleton

• Consists of bones in the pectoral and pelvic girdles and the limbs attached to them.
• (126 total bones)
• Pectoral girdle (shoulder) with arms and hands are specialized for flexibility.
• Pelvic girdle (hip) with legs and feet specialized for stability.

Pectoral Girdle and Appendages (Arm and Hand)

• Clavicle (collarbone) connects to the sternum.
• Scapula (shoulder blade) in the upper back.
• Humerus (upper arm), Radius and Ulna (forearm), Carpals (wrist), Metacarpals (hand), Phalanges (fingers).
• Parts loosely linked by ligaments (to give flexibility).

Pelvis and Appendages (Leg and Foot)

• Pelvic girdle consists of 2 large hip bones (innominate, ilium, ischium, pubis) and sacrum.
• Appendages: Femur (thigh), Tibia and Fibula (shin bones), Tarsals (ankle), Metatarsals (foot), Phalanges (toes).

Types of Joints

• Fibrous joints: Immovable, such as sutures in the cranium.
• Cartilaginous joints: Slightly movable, such as intervertebral discs and ribs/sternum.
• Synovial joints: Freely movable, such as in the knee and elbow. They contain synovial fluid and articular cartilage to reduce friction.