The Musculoskeletal System Support, Protection, Movement and Locomotion

Skeletal Functions Framework for support Transmits movement Maintains shape Protects internal organs from mechanical injury Contains and protects the red bone marrow, one of the hemopoietic (blood-forming) tissues Mineral reservoir - storage site for excess calcium and phosphorus Storage of fats – yellow marrow

Cytoskeleton Microfilaments Intermediate filaments Microtubules Cilia Maintains cell shape Microfilaments Intermediate filaments Microtubules Protection Enables motion Cilia Pseudopodia Flagella Intracellular transport Cell division

Hydrostatic skeleton Fluid-filled closed chambers Internal pressure generated by muscle contraction e.g. sea anemone and worms

Exoskeleton Shelled molluscs (CaCO3) Arthropods (chitin) Hard segments covering muscles and visceral organs Muscles are attached to the exoskeleton Restricts growth and size of insect  molting

Endoskeleton Endoskeleton Internal, often mineralized, connective tissue Muscles on the outside Cartilage – elasmobranchs Other vertebrates – cartilage replaced by bone as embryo matures and develops

Appendicular and axial skeleton Axial skeleton (80 bones) axis of the body support and protection of main organs Skull Sternum Ribs Vertebral Column + sacrum and coccyx Appendicular skeleton (126 bones) anchors appendages to the axial skeleton Upper Extremities Lower Extremities Pectoral Girdle Pelvic Girdle

Types of bones Long bones Short bones Flat bones Irregular bones Long shaft (diaphysis) Two joint surfaces (epiphyses) Mostly compact bone e.g. femur, tibia, fibula, radius, ulna Short bones Cube-shaped, mostly spongy bone e.g. bones of wrist and ankle, patella Flat bones Thin and curved e.g. skull and sternum Irregular bones Irregular and complicated shapes e.g. spine and hips

Joints or articulations Meeting of two bones Types of joints Immovable Slightly movable Freely movable

Bone Tissue Compact bone series of Haversian canals concentric layers of bone cells (osteocytes) new bone formed by osteocytes Spongy bone ends of long bones less dense contains red or yellow marrow Periosteum outer layer of bone rich in nerve endings, blood, and lymphatic vessels inner portion forms new bone or remodels existing bone

Types of bone cells Osteoblasts immature bone cells manufacture hormones and enzymes that aid in bone mineralization Osteocytes mature osteoblasts in lacunae (spaces) form bone, maintain matrix act for calcium homeostasis Osteoclasts responsible for bone reabsorption and shaping located on bone surfaces

Bone formation Intramembranous ossification  formation of the flat bones of the skull Endochondral ossification  formation of long bones

Bone remodeling Resorption of bone (by osteoclasts) followed by replacement of bones (by osteocytes) Functions to regulate calcium levels, repair damaged bones, and shape and sculpt the skeleton during growth Rate is regulated by parathyroid hormones (PTH) and Vitamin D

Disorders of the skeletal system Osteoporosis Reduced bone density leading to fractures Rickets and osteomalacia Softening of bones leading to deformations and fractures Arthritis Inflammation of joints Bone fractures Scoliosis, kyphosis